Geoarchaeology Exploration Enviroment

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Geoarchaeology: exploration, environments, resources



G e o l o g i c a l S o c ie ty S p e c ia l P u b l i c a t i o n s

S e r i e s E d i t o r s

A . J . H A R T L E Y

R . E . H O L D S W O R T H

A . C . M O R T O N

M . S. S T O K E R

It is recomm ended tha t reference to all or part of this book should be made in one o f

the following ways:

POLLARD,A. M. (ed.) 1999.

Geoarchaeology. exploration, environments, resources.

Geological Society, London, Special Publications, 165.

VERNON,R. W ., MCDONNELL, J. G. & SCHMIDT,A. 1999. Medieval iron and lead

smelting works: a geophysical comparison. In: POLLARD,A. M. (ed.) Geoarchaeology:

exploration, environments, resources.

Geological Society, London, Special Publica-

tions, 165, 15-34.



GEOLOGICAL SOCIETY SPECIAL PUBLICATION NO. 165

Geoarchaeology:

exploration, environments, resources

EDITED BY

A . M A R K P O L L A R D

Department of Archaeological Sciences

University of Bradford, UK

1999

Published by

The Geological Society

London



T H E G E O L O G I C A L S O C I E T Y

The Geolog ica l Socie ty o f Lo ndo n was founde d in 1807 and i s the o ldes t geo log ica l soc ie ty in the wor ld .

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Contents

POLLARD,

A. M. Geoarchaeology: an in t roduct ion

Exploration

VERNON,R. W., MCDONNELL, . G. & SCHMIDT,A. Medieval i ron and lead

smelt ing works : a geophysical com par ison 15

MURDIE,R. E., STYLES, P., UPTON,P. EARDLEY,P. & CASSIDY,N. J.

Euler deconvolut ion methods used to determine the depth to

archa eologica l features 35

Cuss, R. J. & STYLES, P. Th e a pplica t ion of micro gravity in industrial

archaeology: an example f rom the Wil l iamson tunnels , Edge Hi ll , L iverpool 41

Environments

LATHAM,A. G. , HERRIES, A. , QUINNEY, P., SINCLAIR,A. & KUYKENDALL,K.

The M ak apa nsg at Aust ralopi thecine s ite f rom a speleological perspective 61

TIPPING, R., LONG, D. , CARTER, S., DAVIDSON,D., TYLER,A. & BOAG,B.

Test ing the potent ial of so i l -s trat igraphic palynology in podsols 79

THORNDYCRAFT, V. R., PIRRIE, D & BR OW n, A. G. Tr ac in g th e r ec ord of

ear ly al luvial t in mining on Da r tmo or , U K 91

Resources

YOUNG, T. P. & THOMAS, G. R. P rov en an cin g iro n o re fro m the

Bristol Ch ann el Orefield: the cargo of the Me dieval M ag or Pill Bo at 103

LAZAR~TH, C. E. & MERCIER, J.-C. C. G eo ch em istry of balla st gr anite s fro m

Brouage and La Rochel le , France: evidence for medieval to post -medieval

t rade wi th Falm outh , Cornwal l , and Donegal , I reland. 123

MILLARD, A. R. Ge oche mistry and the early alum indu stry 139

BUDD, P. D ., LYTHGOE, P., MCG ILL, R. A. R. , POLLARD, A. M . & SCAIFE B.

Zinc i sotope f ract ionat ion in l iquid brass (Cu-Zn) al loy: potent ial

envi ronm ental and archaeological appl icat ions 147

THOMAS,G. R. & YOUNG,T. P. The determinat ion of b loomery furnace

ma ss bala nce an d efficiency 155

ZAYKOV, V. V., BUSHMAKIN,

A. P,

YUMINOV,

A. M.,

ZAYKOVA,

E. V.,

ZDANOVICH,G. B., TAIROV,A. D. & HERRINGTON,R. J.

Geoa rchaeological research in to the h is tor ical rel ics of the South Urals :

problems, resul ts, prospects

Index

165

177



Geoa rchaeology: an introduction

A. M A R K P O L L A R D

Department o f Archaeological Sciences,

University o f Bradford, Bradford BD7 1D P, UK

Of all of the sciences u t il ized in m odern archaeological research, th at of geology has

the longest h is tory o f associat ion wi th archaeology. Surpr is ingly , perhaps, geoarch-

aeology as a recognized sub-discipl ine has taken sl ightly longer to establ ish i tself

than others such as b ioarchaeology. Th ere i s s ti ll some un cer tain ty abo ut w hat exact ly

geoarchaeology encompasses , and some di f ferences of usage of the term between

Europ e and N orth Ame rica. This br ief in t roduct ion explores some of these i ssues,

and at tempts to p lace the o ther cont r ibut ions to th is volume in a s l ight ly broader

context .

Geoarchaeology here is used to describe the applicat ion of the geosciences to solve

research problems in archaeology. Th e in teract ion betw een the sciences of geology and

archaeology has a long and hono urable h is tory , going back to the ear ly 19th century ,

when geology and prehis tor ic archaeology developed substant ial ly in paral lel . Con-

ventionally, i t is usua l to co nsi de r prim ari ly a sub set of the geosciences as included

wi thin the term 'geoarchaeology ' , par t icular ly geomorphology, sedimentology,

pedology and s t rat igraphy. This pr ior i ty perhaps ref lects an observat ion made by

Renfrew in 1976, in h is in t roduct ion to one of the ear l ies t volumes to use the term

geoarchaeology (Davidson & Shackley 1976) , that ' s ince archaeology, or at least

prehistoric archaeology, recovers almost al l i ts basic data by excavation, every

archaeological problem star t s as a problem in geoarchaeology ' (Renfrew 1976) . I t

also reflects the intensi ty of interest durin g the 1980s in the subject of si te form ation

processes, to w hich these techniques have made a considerable con t r ibut ion (e.g .

Schif fer 1987). Chronology , al though cent ral to both archaeology and geology, is

usually considered to be a separate sub-discipl ine.

Opinions d if fer as to whethe r chemical analysis (of raw m ater ial s and ar tefacts) and

geophysics should be included wi th in the term geoarchaeology. The former , par t icu-

larly in the United States, is often termed 'archaeometry ' , and forms a significant

subset of the emerging sub-discipl ine known as 'archaeological chemistry ' (e.g.

Pollard & Heron 1996). The lat ter is often incorporated in the wider f ield of study

known as remote sensing or archaeological prospect ion. We have taken a broad

view of the word geoa rcha eolog y here, and, as signified by the sub-t i t le, have include d

a wider spect rum of geoscience techniques appl ied to problems in archaeology. The

papers presented h ere are a sub-set of those presented at the G eoarch aeology session

of the Geosciences '98 Conference, held at Keele Universi ty on 14-16 Apri l 1998.

Archaeology, geology, geoarchaeology and archaeological geology

The beginnings of scientif ic archaeology in the 19th century are int imately t ied to the

paral lel development of geology. This approach is personified by Sir Charles Lyell

From.


Geoarchaeology: exp loration, environments, resources.

Geol ogical Society, Lond on, Special Public ations, 16 5, 7-14. 1-86239-053-3/99/$15.00

9 The Geological Society of Lond on 1999.



8 A . M . P O L L A R D

(1797-1875) , who no t on ly wro te Principles of Geology (publ ished 1830-1833, and

wide ly regarded as one of the foun dat ion s of m od ern geology), but a lso The Geo-

logical Evidences of the Antiquity of Man (1863) . The in te l lec tua l fe rment dur ing

the 19th century regarding the age of the ear th , the mech anism of evolut ion and

the ant iqui ty o f hu m an kin d is wel l doc um ented (e.g. Tr igger 1989). Increas ing

a t tent ion was pa id dur ing the f i rs t ha l f of the 19th century to the commingl ing of

the bones o f ext inc t animals wi th hand axes as evidence of hu m an ac t iv ity in e i ther

cave depos i ts or the grave l te rraces of major European r ivers . As a resul t of carefu l

s t ra t igraphic obser va t ion of such deposi ts , the wide ly accepted b ib l ical in te rpre ta t ion

tha t these depos i ts re f lec ted the remnants of Noah ' s f lood, and tha t the Ear th

had been c rea ted in 4004 BC - - gradual ly gave way to an ev olut ionary m odel ,

requir ing cons iderably longer t ime per iods . Lyel l ' s work es tabl ished the pr inc ip le

of uni formita r ianism in geology, thereby es tabl ish ing a long chronologica l f rame-

wor k for the evolut ion o f the Ear th , and in 1859 Char les Dar win popu la ted th is

f ram ewo rk wi th h is evolut ionary m odel for the or ig in of the hu m an species wi th

the pub l i ca t ion o f On the Origin of Species. The need to provide a chronologica l

f ramew ork fo r s uch evo lu t iona ry deve lopmen t aga ins t t he backgrou nd o f the advance

and re t rea t of the grea t Ice Ages lead d i rec t ly to the deve lopment of pa laeol i th ic

archaeology as a scientific discipline, intimately associated with geology and

palaeontology.

Towards the l a tt e r ha l f o f the 19 th cen tu ry popu la r imag ina t ion was caugh t by the

s pec tacu la r f inds emerg ing f rom the g rea t excava t ions in Egyp t and Mes opo tamia

(such as Layar d ' s pub l ica t ion o f Ninev eh and Babylo n in 1853). No t only did th is

shi f t a t ten t ion away from the pa laeol i th ic , but i t a lso rekindled the deba te about

the verac i ty of the b ib l ica l account of the Flood. In the longer te rm i t gave r i se to

wh at mig ht be ca l led the Eur ope an v ers ion of the deba te for the ' soul ' of a rchaeology.

Crudely th is might be charac te r ized as the sc ient i f ic approach bui ld ing upon the

geologica l and pa laeontologica l der iva t ion of par t of the subjec t versus a more c las -

s ica l, huma ni t ies -based v iew of a rchaeolog y ar is ing f rom i ts or ig ins in ant iquar ianism

and the growth of c lass ica l a rchaeology a t the end of the 19th century . Such deba te

cont inues today.

The deve lopment of a rchaeology and i t s re la t ionship wi th geology took a d i f fe rent

t ra jec tory in the Uni ted Sta tes, as has been docum ented by Wa ters (1992) and Rap p &

Hil l (1998). The surviva l in to the 20th century of na t ive No rth Am erican cul tures in

many a reas o f the USA and C anad a caus ed the di sc ip l ine s o f a rchaeo logy and an th ro -

pology to deve lop toge ther , to such an extent tha t the major i ty of academic a rchae-

o log i st s in US ins t itu t ions fo rm com ponen t s o f la rge r Depa r tm en t s o f An th ropo logy .

Perhaps surpr is ingly , therefore , the te rm 'geo archaeo logy ' has grea te r currency in the

US A tha n in Europe . This a r ises f rom one of the fundam enta l research ques t ions in

New W or ld Archaeo logy - when , and how, d id huma ns come to co lon ize the Amer-

ican continent (see, for example, Pollard & Heron 1996; chapter 8). Such questions

have been v igoro us ly deba ted for a t leas t a hun dred years , wi th the i s sues polar iz ing

aro und the presence or absence of hum ans before the las t deglac ia t ion and the open-

ing of the so-called ' ice-free corridor ' . Culturally the issue centres on whether the

people known by the i r d is t inc t ive s tone tools (Clovis ) were the f i rs t occupants of

the cont inent , convent iona l ly d a ted a t a ro und 11 000-11 500 unca l ibra ted radio-

carbon years BP (but see, for example, Batt & Pollard (1996) for a discussion of the

importance of radiocarbon ca l ibra t ion on such is sues) .



GEOARCHAEOLOGY: AN INTRODU CTION 9

The eph emer a l na ture of the a rchaeology of c ruc ia l ear ly pa laeo indian s ites has

crea ted the necess i ty for c lose col labora t ion be tween geologis ts and a rchaeologis ts

in order to in te rpre t the evidence . I t i s in th is context in par t icula r tha t the sk i l l s of

geomorphologis ts and sedimentologis ts have been essent ia l to unders tanding the

archaeologica l record . The ear l ies t ev idence for the New World presence of

humans in the Ple is tocene came from the f inding of f lu ted s tone tools wi th the

bones of ext inc t b ison dur ing ex cava t ions in New Mexico in the la te 1920s (Waters

1992) . The s t ra t igraphic s tudies required to prov e the Ple is tocene na ture of these

depos i ts were carr ied o ut by a geologis t (Kirk Bryan) , a nd the resul ts were presented

a t a G eologica l Soc ie ty of Am erica m eet ing in 1929, thus symbol ica l ly es tabl ish ing the

c lose connec t ion be tween geology and a rchaeology in North America . This has con-

t inued to th is day , wi th the bulk of the academic texts in the f ie ld be ing publ ished

there. In one of the most recent of these, Rapp & Hill (1998) discuss extensively

the na ture o f the in te rac t ion be tween geology and a rchaeology, and def ine two

leve ls of in te rac t ion: g eoarcha eology i tse lf , approxim ate ly as defined above , a nd

archa eolog ical geology, which, in their view, is geological research tha t has direc t rele-

vance to a rchaeology. The form er i s par t o f a rchaeology i t sel f. The la t te r i s research

carr ied out for geologica l reasons , but (perhaps inc identa l ly , bu t of ten by des ign) has

impl ica t ions for a rchaeology. As an exam ple , R a p p & Hil l c i te s tudies of coas ta l

l andfo rms and s ea leve l changes a round the Med i t e r ranean , wh ich o f course have

imp or tan t r epe rcus s ions fo r ou r in t e rp re ta t ion o f the deve lopmen t o f s oc iety and

trade in the region.

Ra ther than ge t bogged dow n w i th fur ther c lose ana lys is of the def in i tions of these

highly in te rre la ted ac t iv i t ies , we should perhaps take the lead se t by the journa l

Geoarchaeology,

which, in i ts f irs t editorial , declared that ' i t is

not

t he pu rpos e o f

th is jour na l to define, c ircumscr ibe , or a t te mp t to expla in what g eoarch aeology is

or , s t i l l less , should be ' (Donahue 1986) . Fur thermore , the edi tor ia l poin ts to one

of the fea tures o f in te rd isc ip linary research tha t i s of ten forgot ten: ' an in te rface

involves two-way in te rac t ion , so tha t research making use of a rchaeologic da ta to

expan d geologic in te rpr e ta t ion and u nder s tand ing is jus t as va luable as the reverse ' .

I t i s in th is sp i r i t tha t th is volume has been put toge ther .

Exploration

Of a l l of the scient if ic advances in a rchaeology, und oub tedly one o f the mo s t

s ignif icant has been the deve lopm ent of remote sens ing techniq ues des igned to

loca te and ident ify bur ied fea tures pr io r to (or indeed, wi thou t) excava t ion . Aer ia l

pho tography has fo r many yea rs p rov ided the ma ins tay o f r emote s ens ing app l i ed

to archaeology (Riley & Bewley 1996), but in the past decade or so there has been

increas ing awareness of the potent ia l use of a i rborne and sa te l l i te mul t i spec t ra l

da ta (Shennan & Donoghue 1992) . Mos t remote sens ing , however , i s carr ied out

on the groun d us ing techniques deve loped and m odif ied f rom explo ra t ion geophys ics .

These inc lude res is t iv i ty and magnetometry-based techniques (Clark 1990) , but the

s pec t rum has b roadened cons ide rab ly ove r the pa s t f ew yea rs to inc lude geo rada r

and sha l low seismic work . A new jou rna l

(Archaeological Prospection)

was l aunched

in 1994 specifically to promote this aspect of archaeological research. Mostly these

surveys a re carr ied out in advance of bui ld ing or infras t ruc ture deve lopment in

accordance wi th p lanning guidance , but a recent popular TV ser ies has done



10 A. M. POLLARD

much to publ ic ise the potent ia l for remote sens ing in a wide range of a rchaeologica l

settings!

Two of the b igges t problems in a rchaeologica l remote sens ing a re d iscussed in

papers in th is volume. One is the use of geophys ics in urban a reas . Mos t e lec t r ica l

and magnet ic techniques used convent iona l ly in a rchaeologica l prospec t ion a re of

l i t t le value in urban areas: a sett ing of increasing s ignificance because of the poli t ical

importance a t tached to the re -deve lopment of so-ca l led 'brownfie ld s i tes ' . Cuss &

Styles show how high-resolu t ion microgravi ty measurements can be used to loca te

150 year o ld tunnels benea th inner c i ty Liverpool , thus adding cons iderably to our

knowledge de r ived f rom impe r fec t con tempora ry maps o f the fea tu re s . A s econd

im por tant goa l in a rchaeologica l prospe c t ion is the abi l ity to produc e ver t ica l sec tions

of bur ied fea tures, in order to es t imate the i r depths and s t ra t igraphica l re la t ionships .

Murd ie

et al.

repor t t he us e o f Eu le r deconvo lu t ion on magne t i c g rad iome t ry da ta

from a Roman-Bri t i sh v i l la a t Wroxeter in order to produce such prof i les . These

sec t ions a re compared wi th georadar da ta across the same fea tures . The va lue of

th is work is tha t gradiometry i s re la t ive ly quick and cheap, and can be done by a

number of spec ia l i s t a rchaeologica l contrac tors , whereas georadar i s s t i l l regarded

with in a rchaeology as an expens ive and somet imes d i f f icul t to in te rpre t technique .

Thus i f dep th p ro f il e da ta can be ob ta ined f rom s t anda rd magn e tome t ry da ta se t s,

i t wi l l have an immedia te impact on f ie ld a rchaeology.

In order to i l lus t ra te the va lue of a rchaeologica l geophys ics wi th in an in tegra ted

re s ea rch p rogramme , Ve rnon

et aL

present some da ta taken f rom a re la t ive ly

unpr om is ing (geophys ica l ly speaking!) context the s lag heaps surroun ding

archaeologica l i ron and lead smel t ing s i tes in Yorkshire . Not only do these da ta

help to delineate the extent of these ancient industrial s i tes , but they also serve

to locate areas of smelt ing activity within the s i tes in order to constrain the require-

ments for fur ther excava t ion or schedul ing of such monuments . This s tudy shows

tha t convent iona l ground-based survey techniques can be appl ied in a wider range

of contexts th an h as h i ther to been cons idered , an d have ye t to reach the i r ful l

potential .

Environments

Env ironm enta l recons t ruc t ion f ro m archaeolog ica l evidence has long been one of the

mo s t prod uct ive and in tens ively s tudied o f the in te rfaces be tween the geosc iences and

arch aeo logy (e .g. Butzer 1964, 1982). On e of the mo st pow erful to ols in this respect is

pa lynology. Tipping et ai. e legant ly present a s tudy showing the input of non-na t ive

tree pollen into the soil profi le at a known date as a result of the establishment of

an a rb ore tum abo ut 1840 AD in southern Scot land. The resul ts show rapid mixing

of the pol len in the near-surface hor izons , sugges t ing severe l imi ts on the tempora l

resolu t ions ava i lable f rom such pa laeoecologica l s tudies .

On a completely different t imescale, Latham et aL address the complex issues of

s t ra t igraphy wi th in an important cave s i te in southern Afr ica : tha t of Makapansga t ,

which con tained a num ber of Austra lopithec ine fossils. T he datin g of the cave has

been by magnetos t ra t igraphy, and th is paper sugges ts tha t the cave environment a t

the t ime of depos i t ion was not as s imple as had been previously thought . They hypothe-

sise tha t the bone- rich layer conta ining these fossils was no t the result of flood activity,

but ma y represent a hyena den. They ca l l for a mo re carefu l re -examina t ion of the cave



GEOARCHAEOLOGY: AN INTRODU CTION 11

stratigraphy, in order to obtain a better es t imate for the age of this important fossil

material .

One of the b igges t i s sues in modern day environmenta l sc ience is the impact of

min ing ac t iv i ty on the env i ronmen t . In s ome pa r t s o f the wor ld humans have been

mining for raw mater ia ls for many mil lennia , and have le f t a d is t inc t ive mark on

the landscape . One such a rea i s l ike ly to have been D ar tm oo r in the southwes t o f Eng-

land, wh ich was a ma jo r p roduc e r o f t in and c oppe r du r ing the Med ieva l and l a t er

per iods . I t has been specula ted tha t southwes t England mus t have been one of the

majo r sources of t in dur ing the Eur ope an Bronze Age , s ince t in is re lat ive ly abu nd an t

there and is such a scarce commodity elsewhere (see, e .g. Franklin

et al .

1978). There

is , however , v i r tua l ly no a rchaeologica l evidence for prehis tor ic minin g on Da rtm oo r:

a fac t which is of ten a t t r ib uted to the des t ruc t ion of ear l ie r evidence by la te r

indus t r ia l -sca le mining. ( I t should be noted , however , tha t even in the mos t heavi ly

re-worked mining a reas such as Parys Mounta in , Anglesey , evidence for prehis tor ic

mining does survive : Tim berlake 1990.) Us ing the techniques o f enviro nm enta l

geochemis t ry ,

T h o r n d y c r a f t e t aL

have a t tempted to ident i fy increases in t in concen-

t ra t ions in f luvia l sediments on Dar tm oo r as mark ers o f increased prehis tor ic mining

activity. To date, the earl ies t geochem ical evidence appe ars to be 1280 • 45 AD in the

Erme Val ley , which is cons is tent wi th the documentary evidence , but s t i l l some way

short of so lv ing the problem of the source of the t in used to supply the rapid

demand for bronze near ly 4000 years ago.

R e s o u r c e s

The use of geochemica l ana lys is as an a id to ident i fy ing the prove nance of the source

of a par t icula r raw m ater ia ls has been one of the corners tones of the expans ion of

sc ient i f ic a rchaeology over the pas t 40 years (e .g . Pol la rd & Heron 1996) . Many of

the ear l ie r s tudies a re ana ly tica l ly h ighly sophis t ica ted , bu t u l t imate ly fa l l somew hat

shor t of the i r purpose (a id ing the in te rpre ta t ion of the a rchaeologica l evidence)

because they hes i ta te a t the f ina l s tep in the process - - the in tegra t ion of the ana ly t ica l

evidence wi th a rchaeo logica l models of t rading or c i rcula t ion pa t te rns es tabl ished by

other techniques . In a par t icula r ly incis ive s tudy, Young & Thom as show ho w careful

minera logica l and textura l ana lys is , when combined wi th t race e lement da ta , can

provide an ext remely de ta i led p ic ture of the Medieva l t rade in i ron ore a round the

Bris to l Channel Oref ie ld . The s tudy is par t icula r ly noteworthy because the f indings

appear a t f i rs t s ight to contradic t logic . I t i s sugges ted tha t ore was in fac t be ing

shipped towa rds the ma jor pa r t o f the oref ield when the boa t f r om wh ich the ore

was recovered foundered . E xam ina t io n of the doc um enta ry evidence , however , sug-

ges ts tha t th is migh t be the resul t of changin g pa t te rn s of land o wnership across

the ore f ie ld . This s tudy not only i l lus t ra tes how documentary and mater ia l ev idence

can be in tegra ted to g ive a more comple te p ic ture , but a lso h ighl ights one of the

impor tan t po in t s to be remembered when unde r t ak ing any geoa rchaeo log ica l s tudy

-

not a ll hu m an behav iour i s predica ted on s imple laws of na ture! Lazare th &

M e r c i e r

have a lso used geochemica l knowledge to ident i fy mari t ime t rade l inks dur ing a

s imi la r h is tor ica l per iod . By s tudying the minera logy of la rge boulders carr ied by

ships as ba l las t, and du m pe d a t a por t when loading, they have shown conn ec t ions

be tween Bri t tany, Cornwal l and I re land in a novel and perhaps unexpec ted way.

One o ther aspec t o f th is wo rk wo rth m ent ion ing is tha t they have used the geologica l



12 A. M. POLLARD

age of the granite as a further constraint on the viability of their model. This is some-

thing which is perhaps second nature to a geologist, but is unlikely to occur immedi-

ately to an archaeologist, and could be more widely applied.

The vast majority of geochemical studies in archaeology have undoubtedly focused

on a narrow range of raw materials - - lithics, obsidians, clays, glassmaking sands, and

(more rarely) organic-rich materia ls such as jets and shale. One of the most important

industries throughout antiquity has been that of textile manufacture, and the asso-

ciated chemical process of dyeing. One of the important raw materials for this is

alum, and yet surprisingly little has been done to study the processing and supply of

this raw material. A preliminary study of the 17th and 18th century AD alum industry

in North Yorkshire is provided by Millard. Given the increasing interest in our indus-

trial heritage, and the resulting pressures to extend the scheduling of its monuments, it

is becoming more important to improve our understanding of the chemical processes

involved. Experience has shown that contemporary literary and patent evidence

cannot always be taken as reliable evidence, as has been shown, for example, by our

efforts to understand the development of the post-Medieval European brass industry.

Here it has been shown that the British patent to manufacture brass by direct mixing

of copper and zinc was taken out in 1738, long after the actual introduction of the

process, probably around 1650 (Pollard & Heron 1996; chapter 6).

The paper by Budd e t a L stems directly from the need to use sources of evidence

other than total zinc content in order to predict how a particular piece of brass was

manufactured. It has long been argued that brass made by the original cementation

process introduced by the Romans could not contain more than 28% zinc because

of thermodynamic limitations imposed by the nature of the process. Thus any

metal shown by analysis to contain more than this amount must have been made

by the direct process. Consequently it must date from after the introduction of this

process in Europe (an important consideration when judging the authenticity of

potential ly valuable br ass objects, but note above certain discrepencies in the

actual dates involved). This rather crude test is somewhat unsatisfactory, and Budd

et a l . demonstrate for the first time that anthropogenic processes in brass manufacture

might introduce sufficient differential isotopic fractionation of the zinc to allow the

processing methodology to be distinguished. If verified by higher precision measure-

ments, this observation has not only archaeological significance, but also wider impli-

cations for environmental geochemical monitoring.

Thomas & Young provide a second theoretical paper showing how geochemical

modelling can be used to elucidate the behaviour of particular elements in high tem-

perature processes. They study the chemical interaction between the ores, furnace

lining and fuel ash in the charge of a bloomery iron furnace, and use these predictions

to improve the quality of provenancing information derived from chemical analysis of

the remaining slag. They successfully test their model on data from a Romano-British

iron bloomery near Ross-on-Wye.

The final contribution by Zaykov et a l . is a rare insight into the huge strides made

in understanding the prehistory of parts of the Former Soviet Union during the past

50 years or so. The Southern Urals are important for many reasons, not least of which

is that they may have been an important raw material source for western Europe

during the Bronze Age. This paper discusses the results of recent research into the

exploitation of gold, copper and lead in this region, as well as studying the trade in

lithic raw materials between the Bronze Age settlements in the area.



GEOARCHAEOLOGY: AN INTRODUCTION 13

Summary

The papers presented here exemplify the many and varied ways in which the geo-

sciences and archaeology have come to mutual ly supp ort each other when the subject

of study is one of the most interesting periods in geological history: that in which

mankind has played an ever-increasing role in shaping the Earth's environment.

We can look forward to ever-increasing interaction between archaeology and the

geosciences, in these and o ther areas. The benefits to archaeo logy will be the vast tech-

nical expertise in the geosciences. For geoscientists, the benefit will be the input of a

knowledge of past hu man behaviour, which is of increasing importanc e throu gh the

Quaternary. The future agenda of geosciences undoubtedly requires an improved

understanding of the two-way relationship between humans and the environment.

The editor would like to acknowledge the help of many people in preparing this volume. In

particular, I would like to thank Dr Andrew David, Mr Paul Linford and Dr David Starley

(English Heritage), Dr C. Gaffney and Dr Sue Ovenden (Geophysical Surveys of Bradford),

Dr Armin Schmidt, Dr Arnold Aspinall and Dr Gerry McDonnell (University of Bradford),

Professor Philip Tobias and Professor Tim Partridge (University of Witwatersrand), Professor

Kevin Edwards (University of Sheffield), Dr Keith Bennett (University of Cambridge), Dr Ian

Freestone and Dr Paul Craddock (British Museum), Dr Olwen Williams-Thorpe (Open

University), Dr Barbara Barreiro (NERC Isotope Geosciences Laboratory) and Dr Kate

Brodie (University of Manchester). Thanks also go to Roger Nathan, who helped in the

editorial process. I would also like to thank the staff at the Geological Society for helping to

organize the meeting (especially Amanda Harrison and Judi Lakin), and also the staff in the

Geological Society Publishing House, especially David Ogden and Angharad Hills, for their

forbearance during the production of this volume. I would like to dedicate the outcome to

my mother, who sadly died at the time of the conference.

References

BATT, C. M. & POLLARD, A. M. 1996. Radiocarbon calibration and the peopling of North

America. In: ORNA M. V. (ed) Archaeological Chemistry V, American Chemical Society

Symposium Series 625, Washington D.C., 415-433.

BUTZER, K. W. 1964. Environment and Archaeology: an Ecological Approach to Prehistory.

Aldine Press, Chicago.

1982.

Archaeology as Hum an Ecology: M etho d and Theory for a Con textual Approach.

Cambridge University Press

CLARK, A. J. 1990.

Seeing Beneath the Soil: Techniques in Archaeological Prospecting.

Batsford,

Braintree.

DARWIN, C. 1859. The Origin of Species by means of Natural Selection, or the Preservation of

Favoured Races in the Struggle fo r Life. John Murray, London.

DAVIDSON, D. A. & SHACI<LEY, M. L. 1976.

Geoarchaeology: Earth Science an d the Past.

Duck-

worth, London.

DONAHUE, J. 1986. Editorial.

Geoarchaology, 1, 1.

FRANI<LIN, A. D., OLIN, J. S. & WERTIME, T. A. 1978. The Search fo r A ncient Tin. Smithsonian

Institution, Washington D.C.

LAYARD, A. H. 1853.

Discoveries in the Ruins of Nineveh and Babylon, with Travels in Armenia,

Kurdistan, and the Desert.

John Murray, London.

LYELL, C. 1830-1833. Principles of Geology: being an attemp t to explain the Jbrm er changes of

the earth's surface, by reference to causes now in operation.

John Murray, London (3 vols).

-- 1863.

The Geological Evidences of the Antiquity of M an with remarks on Theories of the

Origin of Species by Variation.

John Murray, London.

POLLARD, A. M. & HERON, C. 1996. Archaeological Chemistry. Royal Society of Chemistry,

Cambridge.

RAPP, G. JR. & HmL, C. L. 1998.

Geoarchaeology.

Yale University Press, New Haven.



14 A. M. POLLA RD

RENFREW,

A. C. 1976. Introduction .

In: DAVIDSON,

D. A. &

SHACKLEY,

M. L. (eds)

Geoarch-

aeology: Earth Science and the Past. Duckwor th , London .

RILEY, D. N. & BEWLEY, R. H. 199 6. Aeria l Archaeology in Britain. Shire Archaeology, Princes

Risborough .

SCHIEFER,M. B. 1987. Formation Processes of the Archaeological Record. Univers i ty o f New

Mexico Press, Albuquerque.

SHENNAN, I. 8Z DONOGHUE, D. N. M . 199 2. Re mo te sen sin g in a rch aeo log ica l researc h. In:

POLLARD,A. M. (ed.) New Developments in Archaeological Science. Proceedings of the

Brit ish Ac adem y 77, Oxford Unive rsi ty Press, 223-232.

TIMBERLAKE,

S. 1990 . Excava t ions a t Parys Mou nta in and N antyre i ra . In:

CREW,

P. t~

CREW,

S.

(eds) Early Mining in the British Isles. Occasional Paper No 1., Plas Tan y Bwlch, 15-21.

TRIGGER, B. G. 19 89 . A History of Archaeological Thought. Camb ridge Univers i ty Press,

Cambr idge .

WATERS,

M. R. 1992.

Principles of Geoarchaeology: a Nor th A merican Perspective.

Univers ity o f

Arizona Press, Tucson.



Medieval iron and lead smelting works:

a geophysical comparison

R O B E R T W . V E R N O N , J. G E R R Y M c D O N N E L L &

ARMIN SCHMIDT

Department o f Archaeological Sciences, University o f

Bradford, Bradford, West Yorkshire BD7 1DP, UK

Abstract:

Geophy sical techniques (fluxgate g radiom etry an d magnetic susceptibil-

ity) have been applied to ten iron an d two lead smelting sites in the Nor th York -

shire Moors National Park and the Pennines, respectively. These geophysical

techniques, particularly mag netom etry, are often regarded as having little applica-

tion on such sites. Larg e quantities of iron slag, for example, can m ask structures

associated with the on-site industrial activity, an d this ma y result in the incomplete

or erroneous interpretation of the geophysical data. Geophysical surveys can,

however, identify the strong magnetic anomalies associated with iron-smelting

furnaces a nd to a lesser extent those associated with lead smelting. To provid e a

valid interpretation of such geophysical data it is important to understand the

processes that have been conducted on iron and lead smelting sites. This paper

compares and contrasts the geophysical responses produced by iron and lead

smelting sites and provides examples o f the structures tha t geophysical techniques

may reveal on smelting sites.

Metal smel t ing s i tes have been geophysical ly surveyed, mainly wi th proton and

f luxgate ma gneto mete rs , s ince the la te 1960s. Some of the ear l ies t surveys in En glan d

were conducted on medieval i ron-working s i tes in West Yorkshi re (Bar t le t t 1971) . In

cont inenta l Europ e, m an y of the ear ly surveys were con duc ted on s lag pi t furnaces ,

m a i n l y i n D e n m a r k a n d G e r m a n y ( S m e k a l o v a et al . 1993). This early work concen-

t ra ted on i ron-smel t ing s ites and was only capable of ident i fying the posit ive ma gnet ic

anom al ies produc ed by furnaces and associa ted s lag deposi t s . This t rend cont inue d

through to t he 1980s wi th magne tomete r su rveys on i ron , l ead and copper work ing

si tes , wi th F luck (1990) and Goldenberg (1990) conduct ing surveys in the Vosges

and Black Fores t , respect ively. Fur ther l imi ted exper iments were being conducted

on smel t ing s ites us ing a var ie ty of geophysical techniques , including ea r th res is tance

and magnet ic suscept ibi l i ty (Hesse

e t a l .

1986; Cre w 1985). The ap plica t ion of these

new techniques pro duce d mixed result s , but provided an assessment of thei r suitabi l-

i ty . The 1990s saw a growing t rend to precise ly re la te and unders tand the nature of

the geophysical responses to bur ied metal -working features . Crew (1989) in Snow-

donia , Nor th Wales was equa t ing magne t i c suscep t ib i l i t y da t a wi th t he spread o f

i ron s lag and more recent ly to the quant i ty of s lag (Crew, pers . comm.) . E lsewhere ,

a mag net ic suscept ibi l ity survey of a smi thy f loor a t Bur ton Dasset t , Wa rwicksh i re

by t he Anc ien t M onument Labora to ry , Engl i sh Her i t age , was p rec i se ly cor r e l a t ed

wi th t he d i s t ri bu t i on by we igh t o f magne t i c ma te r i a l (p r imar i l y hamm ersca l e ) i n

the f loor deposi t s (Mi l l s & McDonnel l 1992) . In Germany, A1-Mussawy (1990)

From: POLLARD, A. M. (ed.) 1999 . Geoarehaeology. explo ration , enviro nmen ts, resources.

Geolo gical Society, Lond on, Special Publica tions, 165, 15-34. 1-86239-053-3/99/$15.00

9 The Geological Society of Lon don 1999.



16 R. W. VERNO N, J. G. MCD ONNE LL & A. SCHMIDT

identi f ied a d i rec t re la t ionship be tween magn et ic anom al ies and the th ickness of i ron

s lag depos i ts and Pani tzki (1994) compared the de ta i led magnet ic charac te r is t ics of

i ron s lag p i t furnaces wi th the var ia t ions of pro ton and f luxgate magn etom eter da ta .

In Bri ta in mos t meta l working s i tes over which geophys ica l surveys have been

conducted a re assoc ia ted wi th i ron . There a re severa l except ions . An inconclus ive

survey was conducted in 1992 over lead s lag depos i ts a t Grin ton , North Yorkshire

( M c D o n n e l l e t a l . 1992). In the same year, f luxgate gradiometer, pulsed induction

(EM) and ear th res is tance techniques were appl ied to a t in process ing s i te a t Cri f t

Farm, Lanl ivery , Cornwal l (McDonnel l 1993) . More recent ly , gamma-ray spec t ro-

scopy techniques have been used to examine a lead-working s i te in I re land (RuffeU

& Wilson 1998).

The current geophy s ica l research projec t in the Dep ar tm ent of Archaeologica l

Sc iences , Univers i ty of Bradford , which a ims to examine the geophys ica l responses

produced by meta l -working s i tes , commenced in 1995. In i t ia l ly three d iverse i ron-

working s i tes were geophys ica l ly surveyed in Bi lsda le and Rievaulx , in the North

Yorkshire Moors Nat iona l Park (Vernon 1995) . This work has cont inued in sub-

sequent years . The surveyed s ites a re representa t ive of a var ie ty of i ron-w orking ac tiv-

i ties , ranging f rom a s imple b loom ery th rou gh to a b las t furnace , wi th a f inery/chafery

complex (Ve rnon e t a l . 1998). In addit ion, the interpretation of one s i te as a bloomery

(Kyloe Cow Beck), geophysically surveyed in 1996, was confirmed by subsequent

excava t ion . Dur ing 1997, a var ie ty of ma gne tom eter surveys were conducted a t

Lock Fa rm, Humbers ide ac ros s a b loomery fu rnace tha t had been rebur i ed in a

magnet ica l ly iner t medium (Schmidt e t a l . 1998). This experimental work was the

first s tep in precisely equ atin g geoph ysical responses with a buried furna ce at different

or ienta t ions .

The research projec t h as now been extended to exa mine geophys ica l ly the responses

produced by lead smelting s i tes . During 1997 surveys on a s i te at Dacre, northwest of

Harroga te , North Yorkshire have enabled severa l fea tures to be ident i f ied which a re

assoc ia ted wi th lead-product ion processes .

The re s ea rch ha s unde rs t andab ly p roduced a l arge amoun t o f geophys ica l da ta

from both i ron an d lead smel t ing s ites , ma king i t possib le to draw some c ompa risons

between responses and to characterize buried features , as will be outl ined below.

Geophysical techniques and methodology

The s t rong pos i t ive magnet ic anomal ies produced by furnace remains and i ron s lags

are genera ted in two ways . Fi rs t ly , induced magnet ism produced by the ear th ' s loca l

magnet ic f ie ld pass ing through the mater ia l ; secondly permanent or remanent mag-

ne t ism is acquired by f i r ing (Clark 1990) . The response f rom the thermoremanent

mag net ism or ig ina tes f rom a comb ina t io n of free i ron oxides (FeO a nd Fe304) and

iron inclusions, becoming fixed when the temperature, on cooling, fal ls within the

range of 600 ~ 4- 100~ The m agni tu de of the pos i tive magnet ic response is therefore

a func t ion of both s lag com pos i t ion and vo lume (V ernon 1995) . The re -or ienta ted

s lag in a tipped depos i t m ay a lso resul t in ran do m m agnet ic re inforcem ent or oppos i -

t ion , contras t ing wi th a furnace , where the thermoremanent magnet ism is coherent

over the whole volume (Vernon 1995).

This work co mp ares the resul ts der ived f rom mag net ic suscept ib i l ity measurem ents

of se lec ted samples and f luxgate gradiometer (magnetometer) surveys . In addi t ion ,



MEDIEVAL IRON AND LEA D SMELTING 17

ear th res i s tance , magnet ic suscept ibi l i ty and pulse induct ion surveys were conducted

over ma ny of the s i tes (Vernon e t a l . 1998) . Al l ma gn eto me ter surveys have been com-

ple ted us ing the Geo scan FM range o f f luxgate gradiom eters . The f luxgate sensors

have a sepa ra ti on o f 0 . 5 m and o n ly record t he ve r ti cal magne t i c com ponent . A l l

f luxgate grad iome ter data is recorded in nanotes las (nT) , the uni t o f mag net ic f lux

densi ty.

The authors adopted the fol lowing approach for surveying smel t ing s i tes : surveys

were usual ly co ndu cted in 20 m, 10 m or 5 m square gr ids , which, a t 400 readings

per grid, gives resolu t ions of 1 m, 0.5 m a nd 0.25 m respect ively. The 20 m grid surveys

were cond ucted for general reconnaissance w ork. O nce the l imit s of the meta l -

work ing s ite were know n, the meta l -w orkin g area w as resurveyed us ing 10 m gr ids.

This provided enough data for the s i te components to be def ined. Furnace features

were then resurveyed us ing 5 m gr ids that enabled the character i s tics of the furnace

to be identified.

The mass specif ic magnet ic suscept ibi l ity ( the degree to which m ater ia l responds to

a magnet ic f ield) of weighed samples o f s lag and furnac e m ater ia l w as meas ured in the

l abora to ry us ing a ba l anced AC br idge .

The surveys

The geophysical surveys have a l l been conducted on s i tes in nor thern England (see

Fig. 1 for si te locat ions) . All the i ron smelt ing si tes are locate d on the we stern side

Fig. 1. Map showing the locations of geophysically surveyed smelting sites.



18 R.W . VERNON, J. G. MCDONNELL & A. SCHMIDT

of t he Nor th Yorksh i r e M oo rs N a t iona l P a rk i n B i lsda le and R ieva lux , t o the nor th -

west of Helmsley. S i tes surveyed up to 1998 range ch ronologica l ly f ro m middle to

la te-medieval bloomer ies as wel l as a pos t -medieval charcoal blas t furnace operat ion

wi th an associa ted f inery/chafery (Vernon

et al .

1998). To supplement this research

programme, exper imenta l work was under t aken a t Lock F arm, Humbers ide t ha t

examined the geophysical responses f rom a rebur ied i ron smel t ing furnace .

The geop hysica l surv eying o f lead sm elt ing si tes at prese nt is confine d to two sites in

the Nor thern Pennine Oref ie ld . The f i r s t i s a t Gr inton, Swaledale , Nor th Yorkshi re

( M c D o n n e l l

et al .

1992) . Curren t wo rk has involved the re-exa mina t ion of f luxgate

gradiometer data and fur ther s lag sampl ing has been car r ied out . A f luxgate gradio-

meter survey has a l so been conducted a t the second s i te a t Dacre , together wi th

examinat ion of s lag samples .

I t i s appropr ia te to br ief ly descr ibe the processes employed to smel t both i ron and

lead in order to apprecia te s i te character iza t ions .

Iron-smelting technology

I ron-smel t ing technology has been subdivided into two dis t inct processes . The

di rec t

p r o c e s s or the bloomery process produces a mal leable i ron (of ten mis takenly

descr ibed as wrought i ron) . In Br i ta in , the bloomery shaf t furnace (see F ig. 2) i s

general ly cylindr ica l , prob ably not m ore than 2.0 m in height and wi th an internal

diam eter in the order of 0 .3 m. A m ixture of charco al and i ron ore i s f ired wi thin

the furnace . The highes t temp eratures (~1 500 ~ occur toward s the base near the

Fig. 2. Simplified section through a shaft (bloomery) furnace showing the main components

and the products at different stages of the process (after McDonnell 1995).



MEDIEVAL IRON AND LEAD SMELTING 19

tuyere , where a i r i s b lown into the furnace . The waste mater ia l f rom the process

ei ther remains wi thin the furnace or i s f requent ly removed via the tap arch. The

i ron does no t m e l t bu t i s r educed t o fo rm a ' b loom ' , a mix ture o f i ron and s l ag

which adheres to the furnace wal l (Crew 1991) . When ext racted the bloom has to

be con t inuous ly r e -hea t ed and hammered t o c l ean i t and p roduce a ma l l eab l e i ron

billet.

The ind i rec t p roces s ut il izes a blas t furnace to produce a cast i ron. I t then u ndergo es

fur ther process ing a t a f inery to produce a mal leable i ron th at i s then conv er ted to bar

i ron a t the chafery. The high bloomery, an intermediate technology between a

bloomery and a blas t furnace , could operate in e i ther mode. An essent ia l requi rement

of t he h igh b loom ery and b l as t fu rnace was wa te r po wer t o ope ra t e be ll ows. These

bloomer ies , h igh bloomer ies and ear ly blas t furnaces were a l l f i red by charcoal .

The furnaces and the s lags f rom al l the processes general ly produce high posi t ive

responses on magnetometer surveys . Bloomery s lags general ly have a higher i ron

conten t t han b l as t fu rnace s lags, an ave rage o f 60% F eO c omp ared t o abou t 5%

FeO, respect ively (Vernon 1995).

The Lock Farm experiment

The Lock F ar m exper iment was conduc t ed i n 1997 as pa r t o f a NER C- fun ded pro j ec t

t o s t udy advanced magne tomet ry (S chmid t et al. 1998). Essential ly an iron-smelt ing

shaf t fu rnace p rev ious ly excava t ed a t Cas t l e shaw, Grea t e r M anches t e r , was r ebur i ed

in a mag net ica l ly iner t envi ron men t . A ser ies of surveys us ing a var ie ty of magn eto-

meters (caes ium, three-component and ver t ica l f luxgate gradiometers) were then

carr ied out across the furnace (Schmidt et al. 1998).

W hen excavated, the c lay furnace had internal an d external diameters of 0 .4 m an d

0.75 m, respect ively. The tap arch was intact. The recovered furnace consis ted of five

large side pieces and abo ut h al f the base , including pa r t o f the tapping channel , a to ta l

of six pieces. A fibreglass mould of the in situ furnace 's in ter ior enabled the pieces to

be or ienta ted accurate ly and f i t t ed together .

The s i t e chosen fo r t he exper iment was Lock F arm, Holme on S pa ld ing M oor ,

Humbers ide . The area i s f la t and composed of sandy soi l under la in by thick deposi t s

of sand. F ig ure 3 deta il s the sect ion and mag net ic suscept ibi l ity of the soi l /sub-soi l

prof ile . The bu lk of the furnace w as bur ied in sand wi th a mean mag net ic susceptibi l-

i ty of 2.5 x 10 -8 kg /m 3, whilst the f i red clay furna ce l ining had a mag neti c susceptibi l-

i ty betw een 1.24 x 10 -6 kg/ m 3 and 1.13 x 10 -5 kg/ m 3.

Only the s ix larger furnace pieces were used for the exper iment . The c i rcular

rebur ied furnace 's diameter was s imi lar to the

in situ

furnace . The rebur ied furnace

was placed so that i ts pos i t ion re la t ive to magne t ic nor th corresp onde d to it s or iginal

or ienta t ion. On rebur ia l , the top of the furnace was 0 .3 m below the sur face. T he

exper iment could not exact ly repl ica te the furnace as found, due to the di f ferent

sur face geology (Namurian sandstone and shales a t Cast leshaw, glacia l sands a t

Loc k F arm ) , s lag spread an d loss of some f rag men ts o f the c lay furnace l ining.

The survey work was car r ied out in f ive s tages as deta i led in F ig. 4 . At each s tage ,

two f l uxga t e g rad iomete r su rveys were conduc t ed a t 0 . 5m and 0 .25m reso lu t i on ,

respect ively.

S tage 1

was the ini t ia l survey of the s i te to es tabl i sh th at the lo cat ion was ma gne-

t ica lly iner t. The var ia t ions of the data had a s tand ard devia t ion of less than 1 nT.



20 R. W. VERN ON, J. G. MCD ONN ELL & A. SCHM IDT

Fig. 3. Lock F arm: soil profile throu gh furnace reburial pit.

Stage 2

was conducted af ter the furnace was rebur ied. F igure 5 shows the f luxgate

gradio mete r read ing recorded over and a rou nd the furnace for 0 .5 m and the 0 .25 m

reso lut ion surveys. The highest posi t ive value record ed (221 nT) is lowe r than th ose

recorded on other surveyed furnaces . At Kyloe Cow Beck (see F ig. 6) , for example ,

th e highest reco rded value at a resolu t ion of 0.25 m was 869 nT. These differences

in fluxgate response m ay be a funct ion of the depth of bur ia l ( the top of the Kyloe

Co w Beck furnace only var ied f rom 0 .15 m to 0 .2 m deep) , type of furnace inf il l

( s lag or soi l) and the com posi t io n of the furnace l ining. I t was no ted dur ing this

s tage of the exper iment that a s l ight bulge on th e southwe st s ide of the posit ive ano m-

aly correspon ded to the posi t ion o f the tappin g arch.

A t

Stage 3,

bags of ran do ml y or ienta ted i ron-s lag were bur ied ag ains t the south-

west edge of the furnace . Despi te being bui l t up to the full height of the furnace ,

t he s l ag a lone d id no t p roduce r ead ings above 20nT . Th i s p robab ly r e su l t s f rom

the tota l ly rand om disposi t ion of the remane nt ly mag net ized s lag pieces .

(In situ

s lag t ips may be less rando m. S lag may s t il l be above i ts Cur ie tem peratu re af ter

t ipping.)

A t

Stage 4,

the s lag was remo ved and the furnace ro ta ted c lockwise throug h 90 ~

This resul ted in a corresp ond ing rota t ion of the negat ive halo on the nor th s ide of

the anomaly , i nd i ca t i ng a p ronounced r emanent magne t i sm. In add i t i on t he re was a

s l ight reduct ion in the negat ive response . This i s a t t r ibuted to the interact ion of

bo th t he r emane nt and i nduced magn e t i za t i on i n the fu rnace . A t

Stage 2

they reinforce

each other, whilst in

Stage 4

they are par t ia l ly ac t ing in opposi t ion.

Stage 5

was the survey of the s i te af ter the furnace had been removed.

S ome s ign if ican t obse rva t i ons cou ld be made f ro m the Loc k F ar m experiment:



M E D I E V A L I R O N A N D L E A D S M E L T I N G 21

Fig. 4. Lock Farm experiment: clipped fluxgate gradiometer plots of surveys recorded at

each stage o f the experiment. D ata clipped to - 1 0 nT (white) to + 10 nT (black).

9 The p osi t ive da ta fo rme d a well def ined c lus ter sur rou nde d by negat ive values . The

pos i t i ve da t a approx imated t he fu rnace ' s l oca t i on .

9 A s l ight bulge on the c i rcumference of the posi tive da ta c orresp ond ed to the l ip of

the tapping channel s t i l l a t tached to the furnace bot tom.

9 The r a ndo m or i en t a t ion o f dum ped s lag g rea t ly r educes i ts ove ra l l r eman ent mag -

netic signal.

9 The mag ne t i c ano ma ly o f the fu rnace i s ma in ly due t o r em anent and on ly to a much

lesser degree induced magnet iza t ion.

North Yorkshire Moors Surveys

A tota l o f ten i ron-sme l t ing s i tes have been surveyed: four in Bi l sdale and s ix in the

v i cin it y o f R ievau lx wi th in t he Nor t h Yorksh i r e M o ors Na t ion a l P a rk . In B i l sda l e,

two s i t e s , Kyloe Cow Beck (b loomery) and T imberho lme (h igh b loomery) , have

been s ingled out for mo re deta i led survey wo rk. See F ig. 1 for locat ions . This was

fol lowed up w i th a par t ia l excavat ion of the bloom ery s ite.



22 R. W. VERNON , J. G. MCD ONN ELL & A. SCHMI DT

Fig. 5. Lock Farm: furnace prior to rotation. Raw fluxgate gradiometer data for a 10m

(0.5 m resolution) and 5 m grid (0.25 m resolution).

Kyloe Cow Beck

The Kyloe Cow Beck si te was discovered in 1996 by f ield walking. The si te is located

in Smiddale ( 'Val ley of the Sm i ths ' in Scandinav ian) on the eas t s ide of Bil sdale . The

si te also l ies near to the outc rop of the Do gg er i rons tone. A 1.0 m reso lut ion f luxgate

gradiometer reconnaissance survey revealed the s i te to conta in an extens ive spread

of s lag. Two areas of high posi tive data , p resum ed to be furnaces , wi th max im um

values o f 321 nT and 469 nT, were noted on the west and eas t s ides of the s lag

spread, respect ively.

The pr inciples der ived f rom the deta i led Lock Farm exper iment survey work were

appl ied to the Kylo e C ow Beck s ite. The area o f slag was resurveyed a t 0 .5 m resolu-

t ion and the eas tern furnace was a l so surveyed a t 0 .25 m resolut ion. The la t ter survey

pro duc ed a higher response (869 nT) tha n the 1 .0 m resolut ion survey. The posi t ions o f

the survey gr ids , together wi th data plots and the actual data for the eas tern furnace ,

are shown on Fig. 6.

Dur ing 1997 the Kyloe Cow Beck eas tern furnace was excavated and the posi t ion

of the furnace was conf i rmed to correspo nd to the large posi t ive ano ma ly that

occurred on a l l three surveys. The external dimen sions of the furnace were 1 .8m

and 1.4m on the nor th/south and eas t /west axis , respect ively. Adjacent areas of

lower readings corre la ted wi th thin (<0 .5 m) spreads of s lag.

S imi l a r t o Lock F arm, da t a f rom Kyloe Cow Beck showed a s l i gh t bu lge on t he

nor thw est s ide of the posi t ive data that cor res pond ed to the excavated ta pping chan-

nel. The group ing of high posi tive values on the n or th s ide of the furnace coincides

wi th the locat ion of the tuyere . This is the f ir s t t ime that th is phe no me no n has been

not ed an d i t is cons idered to be a signif icant discovery. R eferenc e to Fig. 2 indicates



M E D I E V A L I R O N A N D L E A D S M E L T I N G 23

r

+.,0

O

O

O

+,.,o

O

~

O

r , .






T i mber ho l me

A n i n i ti a l f l u x g at e g r a d i o m e t e r s u r v e y o f 2 0 m r e c o n n a i s s a n c e g r id s a t T i m b e r h o l m e

i d e n t i f i e d a w e l l d e f i n e d f u r n a c e a r e a a n d a n a s s o c i a t e d s l a g t i p c o v e r e d b y a p p r o x i -

m a t e l y 0 .3 m o f r i v er a l l u v i u m . T h e v i s i b l e r e m a i n s o f a l ea t t h a t o n c e f e d w a t e r t o a

w a t e r w h e e l t r a v e r s e t h e s it e. T h e r e s u l t s a n d t h e i n t e r p r e t a t i o n o f t h e f l u x g a t e g r a d i -

o m e t e r s u r v e y a re s h o w n i n F i g . 8. S la g a n a l y s e s i n d i c a t e th a t t h e T i m b e r h o l m e

Fig. 8 . Timberholme: a monastic water powered bloomery operation. The si te contains the

remains of a leat and slag t ip . The furnace area is covered by r iver al luvium. The f luxgate

gradiome ter surveys suggest the furnace collapsed across the water leat.



26 R. W. VERN ON, J. G. MCDO NNELL & A. SCHM IDT

furnace p roduced a s lag t ha t r anged i n comp os i t i on f rom a b loom ery t o b l ast fu rnace

type (Vernon 1995; F inney 1997) . F luxgate gradiometer readings var ied between

- 1 9 7 n T to 1391 nT ov er the s lag tip . In the vic inity of the furnace , two areas o f

pos i t i ve r ead ings up t o 2014nT were r ecorded . Compared t o da t a r ecorded a t

other i ron-smel t ing furnaces , e .g . Kyloe Cow Beck, these readings are high. These

high readings , together wi th s lag analyses that are comparable wi th those generated

by b l as t fu rnaces (5% F eO) , suppor t t he hypothes i s t ha t t he T imberho lme fu rnace

was a high bloom ery. The high posi t ive fluxgate gradiom eter readings are except ional.

The only other s i te where s imi lar values have been recorded i s a t the Forge Farm

finery/chafery complex associa ted wi th the Rievaulx Blas t Furnace . The very high

posi t ive values pro bab ly re la te to the presence o f f ree i ron in the s lag. The 0.5 m

and 0.25 m resolut ion surveys (see F ig. 8) over the Timb erho lme Hig h Bloo mery fur -

nace wo uld suggest that i t was pr oba bly a square (up to 5 m 2) s t ructure . Unl ike the

Kyloe Cow Beck surveys , the posi t ive data do not form a dis t inct c i rcular c lus ter

that w ould be a characteri s t ic of the furnace . The reason for thi s may be that af ter

abandonment , t he fu rnace , which would p robab ly have been t a l l e r t han a s imple

shaf t furnace , col lapsed in a souther ly di rect ion across the lea t .

M agne t i c suscep t ib i l i t y measurement s t aken on t he T imberho lme s l ags r ange

betw een 0.7 x 10 -7 kg /m 3 to 4.0 x 10 6 k g/ m 3.

Lead-smelting technology

Very l it tl e i s kn ow n a bou t the ear ly his tory o f lead-smel t ing technology . Unl ike i ron

smel t ing, very few lead smel t ing s i tes have been excavated (Cranstone 1992) . Most

researchers regard medieval lead smelt ing as a two-stage process. Gil l (1992) describes

the var ious methods as fol lows.

The f i r s t s tage involved heat ing the ore in an oxygen-r ich envi ronment . Two bas ic

methods appear to have been used: e i ther the bale (or bole) or the ore-hear th . The

bale was usual ly const ructed on high land to ca tch the wind. I t was essent ia l ly a

wood bonf i re on which the lead ore was placed. The ore-hear th was probably smal ler .

Ai r was int roduc ed by bellows. The lead ore was mixed wi th fuel (coal , wood or peat )

(Gil l 1992). Tem per atu res betw een 600 ~ and 800~ are achieved, giving a recovery of

between 40% to 70% lead. The res idue i s a lead-r ich 'grey ' s lag.

The second s tage involved re-heat ing the 'g rey ' s lag a t h igher tempe ratures (1100 ~

and 1200~ in a s lag hear th . This prod uce d mo l ten lead. The mol ten s lag general ly

f loated on the meta l . Su ch seco ndary s lag i s general ly referred to as 'b lac k ' s lag. This

la t ter phase would have ut i l i zed bel lows, e i ther operated manual ly or by a water

wheel , to provide a i r to ra i se the temperature . Manual ly operated bel lows were

also occas ional ly used a t the bole s tage (Tyson et al . 1995).

Surveyed lead-working sites

G r i n t o n

The first published geophysical survey of a lead-smelt ing si te in England is recorded as

recently as 1992, at Grinto n, N or th Y orks hire (see Fig. 1 for locat ion) ( Mc Do nne ll

et al .

1992). Eigh t 20 m g rids were surveyed w ith a f luxgate gradiom eter . The resul ts from this

survey were inconclusive and i t is unclear whether the survey was conducted over the

si te of a bale or slag furnace. I t was, however, suggested that furnace fragments may




Fig. 9.

Grinton: site plan and clipped fluxgate gradiometer plots (after McDonnell

et al.

1992).

have generated some of the anomalies noted on the survey. A recent (1998) visi t to the

si te for samp ling co nfirms the p resence of two low-lying t ips (see Fig. 9). The w estern t ip

i s predo mina nt ly grey s lag wi th furnace mater ia l whi l s t the eas tern t ip i s comp osed of

black s lag which i s general ly spread abou t the s ite. A re-exam inat ion of the Gr into n

data has yie lded very l i t t l e addi t ional informat ion. I t conf i rms that spreads of lead

s lag have negl igible magnet ic proper t ies . Most of the f luxgate gradiometer data fe l l

between - 4 nT and 4 nT, the range of data produ ced by non-f ired archaeological tar -

gets . Two anomal ies generated d ata between 15 nT and 30 nT. I t was thou ght th at they

could re la te to dis turbed furnaces or hear ths . Ano ther area on the eas tern t ip prod uced

posi tive responses of 100 nT generated by mo dern i ron-r ich debr i s. M easur eme nt of the

magnet ic suscept ibi l ity o f both s lag types conf i rms that the s lag has low magn et ic prop-

erties. Values for the slags varied between 6.5 x 10 -8 kg/m 3 and 3.2 x 10 -7 kg/m 3.

D a c r e

M ore r ecen t su rveys (1997 and 1998) a t Dacre , no r thwes t o f Har roga t e , No r th

Yorkshi re enabled several fea tures to be ident i f ied which could be associa ted wi th



28 R. W. VE RNO N, J. G. MCD ONNE LL & A. SCHM IDT

lead- prod uc t ion . T he s i te i s on low - ly ing g raz ing l and on the w es t s ide o f t he R ive r

N i d d . T h e s it e w a s f i rs t n o t e d d u r i n g a h i s t o r ic a l i n v e s t i g a t io n o f i r o n p r o d u c t i o n

i n N i d d e r d a l e . B l a c k e r et a l . (1996) desc r ibed the s i t e a s l y ing c lose to S m el t Mar i a

B e c k w i t h t h e o u t l in e o f a t w o - r o o m e d b u i l d i n g d e f in e d b y s u m m e r s c o r c h m a r k i n g s .

G re y l ead s lag and s l ag - r i ch sed im ent s a re a l so expose d a bo u t 0 .3 m be low the su r face

in the s ide o f t he ad jace n t beck . T he age o f t he s it e i s no t kn ow n bu t i t ce r t a in ly p re -

da tes the 19 th cen tu ry (B lacke r , pe r s . com m .) .

Fig. 10. Dacre: clipped fluxgate gradiometer data plots and interpretation.



MEDIEVAL IRON AND LEA D SMELTING 29

Pr ior e xam inat ion of the land sur face ena bled the l imi t s of the Dacre s ite to be

def ined. An ini t ia l survey of ten f luxgate gradiom eter 10m gr ids covered m ost o f

the s ite and a l so exam ined the poss ibil i ty of water being condu cted onto the s ite to

wo rk a water wheel . Once the m ain s t ructure was ident if ied a survey of e ighteen

5 m gr ids was co nduc ted over it . The resul ts an d interpre ta t io n of the survey are

shown in F ig . 10. In com mo n w i th t he Gr in ton survey , the r ange o f va lues ( -1 0 nT

to 10 nT) at Da cre w ere general ly low. The p lots sh own in Fig. 10 hav e been cl i :pped

to thi s and lower ranges . I t has been poss ible to ident i fy on the survey a roughly

ci rcular fea ture a bou t 5 m in diameter com pos ed of clus ters o f pos i tive values (see

Fig. 10). This featu re is interp reted as a smelt ing hearth . T he presence of grey lead

slag would suggest that th i s i s a bale- type s t ructure . However , the dimensions of

the hear th are larger than those for previously recorded bales . Rais t r ick (1926/27)

recorded a d i amete r o f 1 .5 m on a ba l e a t Win t e r ings nea r Gu nner s ide , No r th York -

shire . Howev er , as there app ear to be large di fferences in the dimensions and des ign of

these early smelt in g sites (Will ies & Cr an sto ne 1992) it is perfect ly plaus ible to r ega rd

Dac re as a bale s ite. A narro w l inear ano ma ly interpre ted as a channel (up to 1 m

wide) runs eas t f rom the hear th to ward s an i r regular area of pos i t ive data . The

lat ter area l ies close to the exposed slag in the beckside. I t is presumed that , in

common wi th other lead smel t ing hear ths , the l inear fea ture i s a cas t ing channel

terminat ing at a small cast ing f loor.

F igure 11 shows the data associa ted wi th the he ar th on the 10 m gr id survey. Th e

ci rcular hear th fea ture i s def ined by the c lus ters o f pos i t ive values. Th e values va ry

be tween 0 nT and 97 nT wi th t he ma jor i t y o f da t a le ss t han 10nT . Co mp ared wi th

data f rom i ron-working s i tes the values are considerably lower . This a l so appl ies to

magnet ic suscept ibi l i ty resul t s . Dacre grey s lag produced values between 4.3 and

9.1 x 10 8k g /m 3.

Discuss io n

Unl ike i ron-smel t ing technology, lead smel t ing processes and the layout and organi -

zat ion of lead-smel t ing s ites are not ful ly unde rs tood. Top ogr aph ic surveys and

l imi ted archaeological excavat ions of both lead and i ron smel t ing s ites have been

cond ucted s ince the ear ly par t of th is century. F or example , R ais t r ick (1926/27)

descr ibes a lead bale a t Gunners ide , Nor th Yorkshi re and Cowper (1898) excavated

an i ron smel t ing s i te , near Conis ton, Cumbria . Whi le i ron technology can be grouped

into the di rect and indi rect phases , represent ing pre-blas t furnace and blas t

furnace technology, respect ively, th i s i s not ent i re ly t rue for the lead-smel t ing

process . The l imi ted evidence avai lable f rom medieval lead smel t ing s i tes would

suggest tha t bo th te chniq ues and structu res exhibi t so m e re gional v ariat io ns in ~t~his

per iod (see Wil lies & Cran stone 1992). This result s in a chron o- tech nolog ical over lap

making i t d i f f icul t to ass ign speci f ic lead-smel t ing s t ructures to an exact per iod of

time.

Usage o f geophys i cal su rveying meth ods has enab l ed bo th i ron and l ead

sme lt ing sites to be assessed rapidly. H ow eve r, i f the on-si te sme lt ing process es are

not ful ly und ers too d, in terpre ta t ion m ay be di ff icult . Wi th i ron-sme l t ing s i tes a

comb ina t i on o f geophys i cal su rvey ing t echn iques ma y prov ide m ore answers . I t is

even poss ible in some ins tances to ident i fy charcoal s torage areas em ploy ing ear th

res i s tance methods (Vernon et al . 1998) . The shaf t or bloomery technology has



3 0 R . W . V E R N O N , J . G . M C D O N N E L L & A . S C H M I D T

Fig. 11. Dacre: data from part of the 10m by 10m grid survey over the circular feature. The

recorded values are much lowe r than those fo und on iron-wo rking sites. Further, negative

data is found in the central area of the feature. By shading the positive data it is possible to

see the rough ly circular feature. However, this outline is brok en b y areas o f negative dat a.

Com pare the data with the plots o f the circular feature in Fig. 10.

remained vi r tual ly unchanged f rom the la te I ron Age (100 Bc) to the la te-medieval

per iod (c . 1450 go) a l though there are regional and diachronic var ia t ions in furnace

const ruct ion. Major changes in i ron smel t ing furnaces only occurred wi th the

deve lopment o f pseudo-b l as t fu rnace t echnology , r epresen t ed by t he h igh b loomery .

S i tes becam e mor e e laborate wi th the int roduct io n of water pow er , for example , a t

Timb erholm e. I ron -wo rkin g s ites a ll t end to conta in a wide spread o f s lag, somet imes

several met res in thickness . Furna ces can be ident i fied by dis t inctive posi t ive magnet ic

anom al ies that of ten prod uce m agnet ic responses app roach ing 1000 nT. Occas ion-

al ly , s i tes l ike that a t Cast leshaw wi l l conta in mul t iple furnaces somet imes con-

s t ructed on top o f each other (Red head 1993) .

In principle, al l i ron smelt ing si tes are similar . At a basic level they contain a

furnace and s lag dump. However , the geophysical surveys conducted a t h igher reso-

lut ions have shown that i t may a l so be poss ible to ident i fy furnace speci f ic fea tures ,

e .g . t ap arch and tuyere locat ions . In addi t ion, fur ther compar isons between posi t ive

da t a and measu rement s t aken f rom excava tions ma y a l low the fu rnace d i ameter t o be



MEDIEVAL IRO N AND LEA D SMELTING 31

es t ima ted f rom the geophys ica l da ta . Bo th the Lock Fa rm expe r imen t s and the

de ta i led comparisons made a t Kyloe Cow Beck, sugges t tha t th is may be poss ib le .

The adven t o f c as t iron p rodu c t ion p re s en ted g rea te r opp or tun i ty fo r free i ron to

be present in both furnace l inings and s lags, as iron pri l ls . This increases the possi-

bil i ty for clusters o f values, in excess of 2000 nT, to be e nco unt ered on surveys, for

example a t T imbe rho lme .

Co mp ared to i ron , the geophys ical s tudy of lead-smel t ing s ites , and indeed o ther

non-ferrous metal smelt ing s i tes , is s t i l l in i ts infancy. Nevertheless from the l imited

work comple ted , i t has been poss ib le to draw some fundamenta l comparisons . The

Grin ton da ta c lear ly demons tra tes the low responses tha t lead s lag produces . Even

with in the - 1 0 nT to 10 nT range very few fea tures s tand out . In pr inc ip le , the da ta

is com parab le to th a t ob ta ined f rom surveys of non- in dus t r ia l s ites .

In contras t , the Dacre survey is mu ch m ore encou raging. I t shows a poss ib le smel t -

ing hear th , a l tho ugh how i t ac tua l ly func t ioned is not fu l ly und ers tood . There i s a lack

of doc um enta ry records and excava t ion wor k on th is s ite but i t may be medieval , of

mo nas t ic or ig in . Despi te i t s loca t ion next to a beck no evidence , e i ther topog raphic a l

or geophys ica l , has been found for water-power on the s i te . Fur ther , as i t i s not

located on a hil ls ide, the tradit ional s i te for a bale , i t is presumed to be a smelting

or s lag hear th w i th a i r in t rodu ced by han d be l lows . O ther fea tures tenta t ive ly identi -

f ied a t Dacre inc lude a l ike ly tapping channel and cas t ing a rea .

The dominan t f ac to r tha t gove rns the geophys ica l r e s pons es f rom bo th i ron and

lead smel t ing opera t ions i s the presence of i ron an d i ro n oxides. Th e da ta in Fig .

12 demons tra te th is poin t c lear ly by comparing the magnet ic suscept ib i l i ty of the

var ious s lags and furnace mater ia l .

In Fig. 12, sample 2 has th e lowest magn etic susceptibil i ty. This is the value for the

sand in which the Loc k Fa rm exper im ent took p lace . Sample 1, the sandy soil a t Loc k

Farm is h igher , re f lec t ing a h igher i ron content . However , both so i l and sand a re

much lower than the va lue s ob ta ined fo r the Lock Fa rm fu rnace (Sample s 3 , 4 and

5). Most of the Timberholme slags (Samples 6 7 and 8) also fal l within a s imilar

range to the Lock Farm furnace . However , sample 9 has a much lower va lue . This

pa r t i cu la r s ample i s f rom High B loomery t ap s l ag tha t con ta ined 5 .3% FeO

compared to 34 .7% to 74 .8% FeO for samples 6 to 8 . The Kyloe Cow Beck da ta

(samples 10 , 11 and 12) a re genera l ly h igher and probably resul t f rom the h igher

am oun ts of i ron oxides in the s lag , com pare d to d i f fe rent technology th a t op era ted

a t Timberh olme. The da ta f rom the lead smel t ing s ites (Samples 13 to 20) al l exhib i t

lower va lues than those for i ron . M os t of the va lues a re s imi lar to tha t der ived for the

Loc k F arm sand. Sample 20 is an except ion . I t is a mixtu re o f slag f ragm ents and soil

taken f rom the lead s lag r ich layer in the becks ide. I t has a h igher va lue than the la rge

pieces of grey s lag found in the same hor izon and is probably contamina ted wi th

e i ther i ron-r ich so i l or sediment mobi l ized by the beck. I t i s in te res t ing to note

from the da ta presented in Fig . 12 tha t i ron smel t ing opera t ions produce magnet ic

susceptibil i ty values hig her tha n 1.0 x 10 6 kg /m 3, whils t th ose fro m lead sm elting

sites are below this value.

I ron and lead smel t ing si tes therefore a l l produ ce d is t inc t s igna tures on geophys ica l

surveys. A l tho ugh is poss ib le to object ively comp are the da ta so tha t va l id geophysi -

ca l in te rpre ta t ions can be made , i t mus t be s t ressed tha t the in te rpre ta t ion usua l ly

needs s uppor t f rom o the r s ou rce s , fo r example , t opograph ica l mapp ing , excava t ion

and h i s to r i cal d ocumen ta t ion .



32 R. W. VERNON, J. G. MCDONNELL & A. SCHMIDT

Fig. 12. Comparison of the magnetic susceptibility values.

Conclusions

The significance of iron being present when comparing geophysical data from iron

and lead smelting sites is irrefutable. From the limited data available it has been poss-

ible to show that by understanding the geophysical properties and the technological

changes valid interpretations can be drawn for the surveys. Additional surveys of

iron-smelting sites will allow the rudimentary principles that have been outlined to

be honed further so that features that are impo rtan t to the interpretation of iron-

working sites can be determined without excavation and placed within their archae-

ological context.

Lead smelting sites appear to produce a range of magnetic responses that are

weaker but identified on most magnetometer surveys. This is fortunate as it provides

a geophysical distinction between the iron and lead smelting processes. In addition,

lead-smelting techniques and associated structures are not as readily understood as

those associated with iron. Bearing this point in mind, it is anticipated that future

geophysical surveys of lead-smelting sites should make significant contributions in

the furthering of our understanding of how these sites functioned.

We would like to acknowledge the following organizations and individuals. Firstly we would

like to acknowledge the financial support from the Natural Environment Research Council,

the University of Bradford, the British Academy and the North Yorkshire Moors National

Park Authority which enabled the research to proceed. Secondly we would like to thank the

residents and landowners who have given access to sites, particularly in North Yorkshire.

Mr Richardson of Arden Estates, Mr Stoney at Kyloe Cow Beck and Mrs and Mr Dowkes

of Timberholme have shown a continuing interest in our research work. A special thank you




to N. Redhead who provided the Cast leshaw furnace and a lso to Mr. Payne who a l lowed the

Lock Farm experiment to take p lace on h is land. We are a lso indebted to Dr Kamei and Mr

Marukawa for the ir ass is tance a t Lock Farm. Last ly we would a lso l ike to thank P . Halkon,

M. Gil l, G. Blacker , C. Hero n an d M . V ernon w ho ass is ted a t var ious s tages of the research

and the anonymous referees for the ir construct ive comments .

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Mat lock Ba th .



Euler deconvolution methods used to determine

the depth to archaeological features

R U T H E . M U R D I E 1, P E T E R S T Y L E S 2,

P A U L A U P T O N 1, P H I L E A R D L E Y 1 &

N I G E L J . C A S S I D Y 1

1Dep artment o f Earth Sciences, Keele U niversity , Keele,

S ta f fordsh i re ST5 5BG, UK

2Dep artment o f Earth Sciences , Liverpool Univers ity ,

Brownlow S t ree t , P .O. Box 147 , L iverpoo l L69 3BX, UK

Abstract:

Field techniques, instrumentation and data processing for geophysical

location of archaeological remains are now at such a standard that clear maps

of the subsu rface detail are readily obtainable. Mag netic grad iome try and resistiv-

ity plots are widely used to locate diverse features such as walls, ditches and burial

areas. However, information concerning the depth to these features is not often

extracted from such plots and would be useful in planning any following excava-

t ion. H ere we use Euler deconvolution methods, on a reason ably high-resolution

magnetic gradiometer data set , to determine the depth to a buried Romano -Brit ish

villa at the Wroxeter archaeological site. The interpretation of these depth

estimates is compared to GPR sections taken over the same site.

T he Wr oxe te r a rchaeo log ica l s i te i n S hropsh i re has been the sub jec t o f r ecen t

i n t e ns e g e o p h y s i c a l i n v e s t i g a t i o n ( B a r k e r

et al.

1 9 9 7 ; W r o x e t e r H i n t e r l a n d P r o j e c t ,

U n i v e r s i t y o f B i rm i n g h a m ) . A l t h o u g h t h e r e m a i n s o f t h e R o m a n o - B r i t i s h c i t y o f

V i r o c o n i u m C o r n o v i o r u m h a v e b e en t h e f o cu s f o r m u c h a r c h ae o l o g ic a l e x p l o r a t io n

over the l a s t hund red yea r s , a l a rge p ro po r t io n o f the a rea w i th in the s t il l ex t a n t

c i ty r a m p a r t s r e m a i n s u n e x c a v a t e d . S o m e 9 0 % o f t h is l a n d is n o w c o v e r e d b y g r a z i n g

p a s t u r e a n d p a r c h m a r k s e v i d e n t i n d r y s u m m e r s , i n d i c a t e d t h a t e x t e n s i v e w a l l

f o o t i n g s s ur v i v e b e n e a t h m u c h o f t h e a re a . D e t a i l e d m a g n e t o m e t r y a n d r e s i st i v it y

s u r v ey s , c o n d u c t e d a s p a r t o f th e W r o x e t e r H i n t e r l a n d p r o j e c t , h a v e p r o d u c e d a n

e x te n s iv e a n d d e t a i l e d s t re e t p l a n o f t h e w h o l e R o m a n t o w n ( G a f f n e y & L i n f o r d

1997).

T he f i e ld w o rk ca r r i ed ou t fo r t h i s exe rc ise w as co m p le t ed on a U nive r s i ty f ina l yea r

s tuden t f i e ld w eekend over a spec i f i c t a rge t . T he t a sk w as to su rvey an a rea us ing

a G e o s c a n f l u x g a t e g r a d i o m e t e r . T h e s u r v e y w a s c o m p l e t e d i n s i x g r i d s o f

10 m x 10 m wi th a po int spacing of 0 .25 m alo ng each l ine , a l ine spacing of 0 .5 m

a n d a t 0 .1 n T r e s o lu t i o n . D a t a p r o c e s s i n g o n l y i n c l u d e d s p i ke , m e a n a n d t r e n d

rem ova l fo r each g r id . D esp i t e t he inexper i ence o f t he ope ra to r s , t he fina l p lo t o f

th i s 20 m by 30 m a rea c l ea r ly show s the ou t l ine o f a bu i ld ing (F ig . 1a) which i s in ter -

p r e t e d a s s h o w n i n F i g . l b . T h e w a l l s a p p e a r a s n e g a t i v e m a g n e t i c a n o m a l i e s c o m -

p a r e d t o t h e p o s i t iv e a n o m a l i e s o f t h e m o r e m a g n e t i c s o il s as h a s b e e n n o t e d i n

t h i s a r e a o f t h e c i t y b y o t h e r a u t h o r s ( T a b b a g h

et al.

1997) . T hese au thor s have

From. POLLARD,A. M. (ed.) 1999.Geoarchaeology: xploration,environments,resources.

Geological Society, London , Special Publications, 165, 35-40 . 1-86239-053-3/99/$15.00

9 The Geological Society of London 1999.



36 R. E. MUR DIE ET AL.

Fig. 1. (a) Magnetic gradiometer map over the site of a Romano-British Villa at Wroxeter.

(b) Interpretation of the magnetic gradient map (Fig. la) showing the inferred positions of

the walls of the villa. The dashed lines are those profiles selected for deconvolution and the

grey spots are the depths to the features as deduced by Euler deconvolution.

had som e success in us ing spec t r a l ana lys i s m e thods , i nc lud ing the ana ly t i ca l s igna l

t o e n h a n c e t h e d e l i n e a t i o n o f t h e p o s i t i o n o f f e at u r e s, b u t h a v e n o t e x t e n d e d t h e i r

a n a l y s is t o t h e d e t e r m i n a t i o n o f t h ei r d e p th .

T h i s p a r t i c u l a r s i t e w a s a g o o d a r e a t o s t u d y a s t h e u n d e r l y i n g b u i l d i n g h a d b e e n

par t i a l ly excava ted in 1 952-19 53 and the t r enches ha d s ubse quen t ly been f il led in .

F r om K e ny on (1975) , i t i s poss ib l e to co r re l a t e the f ea tu res seen on the t r ench sec t ions

t o th e re s u l ts f o u n d b y th e E u l e r d e c o n v o l u t i o n m e t h o d s a n d G P R ( G r o u n d P e n e t r a t -

ing R adar ) . T he d igs foun d seve ra l ep i sodes o f hab i t a t io n ev iden t i n the l aye rs o f

b u i l d i n g a n d a s s o c i a t e d r u b b l e.



EULER DECONVOLUT ION 37

Euler deeonvolution theory

Euler deco nvo lut ion i s a me tho d fo r locat ing the sources of poten t ia l f ields based o n

both t he ir ampl i t udes and g rad i en ts an d es t ima tes t he p robab le geom et ry o f t he

causat ive body. Previous theoret ica l and actual examples used to tes t Euler deconvo-

lut ion have been on the larger geological scale (Thompson 1982; Reid

et al.

1990) to

look a t t he dep th o f sed imenta ry bas ins and t he ir bound ing f au lt s , dykes and i n t ru -

s ions . Howe ver , i t has been recent ly used for microgra vi ty s tudies of aba nd on ed

stope workings in Gold Mines (S tyles pers . comm.) . The method has been successful

in determ ining the depth to the edges of the fea tures . The theor y i s exact ly the same

for archaeological purposes , except on a sub-met re scale .

Potent ia l f ie lds such as gravi ty , magnet i sm and thei r spat ia l der ivat ives are

so lu ti ons o f Lap l ace ' s equa t ion and a l so sa t is fy Eule r' s equa t ion o f i nhomog ene i ty

OF OF OF

( x - xo)-g-;x + ( y - yo)--g/y + ( z - zo)- z = -n v

The der ivat ives of the cont inu ous f ie ld V sa t is fy the above hom oge neo us equa t ion of

degree n , where n is know n as the s t ructu ra l index. This is an indicator of the fa l l -of f

ra te of the f ie ld wi th dis tance r and d epends on the geom etry o f the suspected b ody

(e .g . l ine , point , sphere or any combinat ion thereof) and the par t icular f ie ld type

(Th om pso n 1982) . Hence, fo r a field which i s me asured a t point (x , y , z) , the gradients

in these di rect ions can be calcula ted. I f one knows or can ob ta in the values of the

der ivatives o f the f ield a t four or m ore locat ions (x , y , z) , and can m ak e an es t imate

for n , one can solve for the locat ion of the causat ive body ,

(xo,Yo,Zo)

by a least-

squared invers ion mat r ix .

In the inves tigated case , we have the ver t ica l gradient of the ver t ica l com po nen t of

the magnet ic f ie ld as our value for V. Usual ly , for magnet ic data , preprocess ing i s

requi red to separate the local f ie ld f rom the regional f ie ld . Howev er , for mag net ic

gradient data , the regional f ie ld i s a l ready removed.

Sof tware developed a t L iverpool Univers i ty was used to solve for the depth to an

anomaly. The hor izonta l der ivat ive was calcula ted f rom the di f ference between adja-

cent values divided by the point separa t ion. We are able to deduce the ver t ica l

der ivat ive f rom the data because the potent ia l f ie ld sa t i s f ies Laplace 's equat ion. I t

i s ca lcula ted via the Four ier domain by mul t iplying each f requency by k, the wave

nu m ber (where k = 27r/A) . I f i t can be assum ed that the bo dy i s 2D in shape i .e . a

wall , then

dZy/dx2= O,

so the second der ivat ive o f the mag net ic grad ient eq uals

zero and hence the 2D vers ion of Laplace 's appl ies (in x and z). The sof tware as

yet only operates in 2D i .e. along a profi le l ine. Profi les were extracted across the

a rea , pe rpend icu l a r t o the ma in f ea tu res and a l so i n E -W and N -S l ines. A

window of 15-20 po in t s ( i.e . 7 . 5 -10 m ) is mo ved ac ross t he da t a , and so lu ti ons fo r

(xo,Yo,Zo)

a re ob t a ined . A window of 15-20 po in t s was chosen as i t gave enough

solut ions to def ine the body. T oo few points give unstab le solut ions an d high leas t -

squares er rors ; too many points give too few solut ions to descr ibe the body. The

exact value i s chosen i tera t ively . The s t ructura l index used assumed that the anomaly

was caused by a vert ical tab ula r bo dy, i .e. n = 1.

On ly those locat io ns of (x0, Y0, z0) whic h are solut ion s fo r several wind ow s are con-

s idered real . F igure 2 shows an E - W prof i le taken across a l ine 98 m no r th runn ing

f rom 30 to 60 m E -W . The c lus te r ing o f c ir cu la r marke r s a rou nd 6m ind ica t es a



38 R.E. MURDIE

E T A L .

Fig.

2. Screen capture of the output from the Euler deconvolution anaylsis program for a

profile 98 m north and 30-60 m East. The figure shows the clustering of solutions a t about

6m along the profile at a depth of about 0.9m. The scattered individual solutions come

from a single window position and are not considered to be valid solutions.

good solution to the equations at that point. Single markers are discounted as these

are only solutions for only one of the windows and therefore unlikely to be real. A

map was then made of the locations and depths indicated by the clusters of markers

(Fig. lb). It can be seen that the clusters lie along the edges of the walls. The depth to

these clusters is fairly consistent, being about 0.65-0.95 m deep. It is interpreted that

the depth indicated by the Euler deconvolution is the depth to the floor of the build-

ing. As seen from the excavated portion of the city, this would have been of bricks or

tiles similar to those found else where on the site which would have a greater magnetic

signature than the sandstone walls of the building.

G P R s e c t i o n

To confirm the depths to the floor of the building, a ground penetrating radar was

taken over a short section of the area (Fig. l a) using a Pulse EKK O 1000 system.

The section produced is given in Fig. 3a. The two-way travel times are converted

into depth using the Sensors and Software program supplied with the radar system

using a uniform velocity of 0.08

x 1 0 9 m s - 1

(the suggested values for a substrate

somewhere between silt and sand). The walls of the building are clearly seen as hyper-

bolic diffraction arcs on the GP R profile at a depth of about 0.6 m at 2 m across and

0.35 m at about 5 m along the section (Fig. 3b). This correlates almos t exactly with the



EULER DECONVOLUT ION 39

Fig . 3. (a) GPR section for a 900 M Hz anten na taken a long the sec t ion mar ked in Fig . l a .

The positions of the walls are clearly seen as diffraction arcs and the intervening floors as

f la t- ly ing ref lectors a t abou t 1 m depth . (b) In terpre ta t ion of the G PR sect ion of F ig . 3a .

e x c a v a t i o n s o f K e n y o n ( 1 9 75 ) . T h e t h i c k n e s s o f t h e w a l l s i s s e e n t o b e a b o u t 1 m w i d e

a l t h o u g h i t s h o u l d b e r e m e m b e r e d t h a t t h e s ec t i o n w a s n o t t a k e n p e r p e n d i c u l a r t o t h e

w a l ls . S t a n d i n g w a l l s m e a s u r e d a t th e s it e r a n g e f r o m a b o u t 0 .5 t o 1 m w i d e . T o e i t h er

s i de o f t h e w a l l s t h e n e x t c l e a r r e f l e c t o r i s s e e n a t d e p t h s o f 1 m o n e i t h e r s i d es o f t h e



40 R. E. MU RD IE ET AL.

tw o w a l l s an d poss ib ly s l igh tly sha l low er a t 0 .7 m be tw ee n them . T h i s r e f l ec to r i s i n t e r -

p r e t e d a s t h e fl a t f l o o r o f t h e b u i l d in g w h i c h w a s m a d e o f m o r t a r a n d l a y a t a b o u t 3 - 4

f e et ( a p p r o x i m a t e l y 0 . 9 - 1 . 2 m ) d e e p ( K e n y o n 1 97 5) . T h e s e v a l ue s t o t h e f lo o r o f t h e

b u i l d i n g c o r r e l a t e w e l l w i t h t h e d e p t h s o b t a i n e d f r o m t h e E u l e r d e c o n v o l u t i o n

m e t h o d s .

T here i s a con t inu ous r e f l ec to r a t ab ou t 0 .5 m dep th t ha t a l so li es a t t he low er lim i t

o f t h e v a lu e s o b t a i n e d b y t h e E u l e r d e c o n v o l u t i o n . T h i s r e f le c to r is d i sr u p t e d b y t h e

w a l ls a n d is in t e r p r e t e d a s a r u b b l e l a y e r t h a t w a s f o u n d t o o v e r l a y t h e r u i n s d u r i n g

excava t ion (K enyon 1975) . I t i s poss ib l e tha t a long the G P R prof i l e , t he d i f f e rence

b e t w e e n t h e m a g n e t i c p r o p e r t i e s o f th e w a l ls a n d t h e s o il h a s g i ve n a g r a d i e n t a n o m a l y

tha t i s su f f ic i en tly l a rge to app ea r a s a so lu t ion to the E u le r de conv o lu t ion .

H ence , w e can es t im a te tha t t he re i s no t m u ch o f the w a l l s l e f t s t and ing as w e in t e r -

p re t t he d i f f e rences in e s t im a ted dep ths to be the d i f f e rence be tw een the top and

b o t t o m o f t h e w a ll s a n d t h e f l oo r s o f t h e b u i ld i n g .

Conclusion

T h e a p p l i c a t i o n o f t h e E u l e r d e c o n v o l u t i o n m e t h o d a p p e a r s t o g i v e g o o d e s t im a t e s o f

d e p t h o f b u r i e d f e a t u r e s i n a n a r c h a e o l o g i c a l s et t in g . D e p t h e s t i m a t e s o b t a i n e d b y

m a g n e t i c g r a d i o m e t r y c a n b e c o r r e l a t e d w i t h f e a t u r e s s e e n o n t h e G P R s e c t i o n

o v e r s a m e t a r g e t . T h e s e m e t h o d s o f o b t a i n i n g d e p t h e s t i m a te s h a s t h e a d v a n t a g e

o v e r G P R i n t h a t i t ut il is e s d a t a t h a t h a s a l r e a d y b e e n c o l l e c te d r a t h e r t h a n e m p l o y i n g

a n o t h e r i n s t r u m e n t . T h i s t y p e o f e s t i m a t i o n c a n b e a p p l ie d t o o t h e r p o t e n t i a l f ie ld

m e thod s such as g rav i ty (C uss & S ty les 1999) and the va r ious c om pon en t s o f t he

magnet ic f ie ld .

We would like to thanks English Heritage for permission to work on the site, the School of

Archaeology, Classic and Oriental Studies, University of Liverpool for the loan of a fluxgate

gradiometer and two anonymous reviewers for their comments on the script.

References

BARKER,

P. A. , WHITE, R. H. , PRETTY, K. B.,

BIRD,

H. &

CORBISHLEY,

M. 1997. The Baths

Basilica Wroxeter: excavations 1966-90. English Heritage, London.

CUSS, R. J. • STYLES, P. 1999. The ap plication o f micro gravity in industrial archaeology: an

example from the Williamson tunnels, Edge Hill, Liverpool.

This Volume.

GAFFNEY,

C. F. &

LINFORD,

P. 1997. The app lication o f geophysical techniques at Wroxeter

Roman City. Proceedings of the 1997 CAA Conference, British Archaeological Reports

International Series 750 (1999), 161.

KENYON,K. M . 1975. Excavations at Viroco nium in Insula 9 1952-3. Transactions of the

Shropshire Archaeological Society, LX, 5-74.

REID, A. B., ALLSOP, J. M ., GARNER, H ., MILLETT, A. J. & SOMERTON, I. W. 1990 . Magn et ic

interpretation in three dimensions using Euler deconvolution. Geophysics, 55, 80-91.

TABBAGH, A., DESVIGNES, G. & DABAS, M. 199 7. Pro ces sing of Z gr ad io me ter ma gne tic da ta

using linear transform s an d analytical signal. Archaeological Prospection, 4, l-13.

THOMPSON,

D. T. 1982. EUL DPH : A new technique for making computer-assisted depth

estimates from magne tic field data.

Geophysics,

47, 31-37.



The application of microgravity in industrial

archaeology: an example from the

Williamson tunnels, Edge Hill, Liverpool

RO B E R T J . CU SS 1 8~; PE T E R ST YL E S 2

1Department o f E arth Sciences, University of Manchester,

Oxford Road, Manchester, M13 9PL, UK

(Present address. British Geological Survey, Keyworth,

Nottingham NG12 5GG, UK)

2Department o f Earth Sciences, University of Liverpool

Brownlow Street, Liverpool L69 3BX , UK

Abstract:

This article presents the results of a high-resolution microgravity survey

which was successful in delineating the 150-year old Williamson tunnels beneath

inner-c i ty Liverpool , England. The tunnels , which date f rom the Napoleonic

Wars , l ie a t depths of c. 5 to 15 metres , and are poorly m appe d because of severa l

phases of la ter development and subsequent dere l ic t ion . The 'brown-f ie ld ' na tu re

of this site create d subs tantial noise signals which required the applic ation of care-

fu l te rra in correc tions and second der ivative and Euler deco nvolut ion m ethods to

isolate and identify the tunnel signatures. Successful delineation was only possible

because of a comprehensive in i t ial desk s tudy a nd p r ior modell ing, w hich assessed

the l ike ly depths an d condit ions of the impassable tunnels an d a l lowed ap propria te

techniques and survey parameters to be determined.

Non-int rusive geophysical metho ds are becoming more co mm only appl ied in archae-

ological and engineering invest igat ions for the detect ion of voids such as burial cham -

bers , l imestone caverns and abandoned his tor ic mine-workings, as an al ternat ive to

tradit ional methods. Geophysical methods, which rely upon differences in resist ivi ty,

condu ctivi ty, densi ty, magn etizat io n, and dielectric perm it t ivi ty betw een rock an d air ,

have increasingly been used in void detect ion through the appl icat ion of res i s t iv i ty

tomog raphy, seismic reflect ion, ground -penet ra t ing radar , ma gnetom etry , a nd micro-

gravimetry . However , a l l geophysical methods have l imi tat ions imposed upon them

by thei r inherent resolut ion thresholds and the noise component of any recorded

signal. The re is subs tantial f ield experience of mic rogra vity for en gineering purpose s,

al though archaeological targets in 'brown-field ' si tes have rarely been surveyed.

After evaluat ing al l the possible geophysical methods, i t was concluded that only

microgravity had the potential to del ineate the 150-year old Will iamson tunnels

which l ie beneath Edge Hil l , Liverpool . Although the survey si te is small , the terrain

is severe with several 5-7 m vert ical drops and the si te was foun d to have b een seriously

affected by redevelopm ent an d de rel iction in several areas, leading to a complex inter-

act ion between surface and sub-surface gravity sources. However, considerat ion of the

development history and geology of the area al lowed the reject ion of many features,

giving increased confidence in the identificat ion of the other features as tunnels.

From. POLLARD,A. M. (ed.) 1999. Geoarchaeology: exploration, environments, resources.

Geological Society, London, Special Publications, 165, 41-5 9. 1-86239-053-3/99/$15.00

9 T he Geological Society of London 1999.



42 R. J. CU SS ~; P. STYLES

M i c r o g r a v i t y h a s n o t y e t b e e n w i d e ly a p p l i e d i n e x t e n s i ve l y r e d e v e lo p e d i n n e r -c i t y

u r b a n a r ea s ; t h is i n v e s t i g a t io n d e m o n s t r a t e s t h e a p p l i c a b i l it y o f th e t e c h n i q u e t o

indus t r i a l a r chaeo log ica l s tud ies w i th in such a reas .

Joseph Williamson and the construction of his tunnels

J o s e p h W i l l i a m s o n ( 1 7 6 9 - 1 8 4 0 ) , a L i v e r p o o l p h i l a n t h r o p i s t k n o w n a s ' T h e K i n g o f

E d g e H i l l ', w a s b o r n i n t o a p o o r W a r r i n g t o n f a m i l y , a n d a t t h e a g e o f e le v en

m o v e d t o L i v e r p o o l t o f i n d e m p l o y m e n t . A f t e r a p p r e n t i c e s h i p w i t h t h e t o b a c c o

m e r c h a n t R i c h a r d T a t e h e m a r r i e d T a t e ' s d a u g h t e r E l i z a b e t h i n 1 8 0 2 a n d r a n t h e

c o m p a n y u n t i l 1 8 1 8 . W i l l i a m s o n t h e n r e t i r e d f r o m t h e c o m p a n y t o h i s M a s o n

S t ree t m ans ions a f t e r am ass ing cons ide rab le w ea l th .

W i l l i a m s o n e m p l o y e d l o c al m e n t o c o n s t r u c t a n u m b e r o f m a n s i o n s o n l a n d h e h a d

p u r c h a s e d a t L o n g B r o o m F i el d , M a s o n S t re e t i n 1 80 6 u n d e r t h e W a s t e L a n d s C o m -

m i s s io n . A f t e r t h e i r c o m p l e t i o n , h e c o n t i n u e d t o e m p l o y t h e m e n t o c o n s t r u c t a t u n n e l

s y s t e m u n d e r h i s la n d w i t h a N o r m a n - a r c h b r i c k - li n e d r o o f g e o m e t r y , p r o b a b l y

in i t i a lly f rom the low w es te rn s ide o f h i s l and . A l tho ug h v au l t ing o f t he tunne l s

w a s u n n e c e s s a r y d u e t o t h e s t r e n g t h o f t h e r o c k , s p e c t a c u l a r b r i c k a r c h e s w e r e p r o -

d u c e d . C o n s t r u c t i o n o c c u r r e d r a n d o m l y , w i t h p i ts , w e ll s a n d b l i n d p a s sa g e s c r e a ti n g

a tunn e l - sys t em m a ny m i l e s long 1 -15 m be low the su r face , 1 -12 m w ide , and up to

15m h igh (H and 1916 , 1927) . T he qua r r i ed rock w as u t i l i zed in the cons t ruc t ion o f

the houses , w a l ls , and o rna te a rch w ays , som e o f w hich a re s ti ll ev iden t .

Wi l l i am son l e ft l i tt l e m o ney as h i s t unne l s had cos t an e s t im a ted s ( the

equ iva len t o f a ro un d s m i l l i on a t t od ay ' s va lue ) and h i s e s t a t e va lued a t s 000

fe ll i n to d i s r epa i r and the loca t ion o f t he tunne l s bec am e lost .

Redevelopment of the site

W i l l i a m s o n ' s l a n d r e m a i n e d u n t o u c h e d u n t i l t h e c o u n c il a s s u m e d c o n t r o l in 1 858 , a n d

t h e a r e a w a s d i v i d e d u p , d e v e lo p e d a n d t h e n r e d e v e l o p e d o v e r t i m e. T h e A r m y u s e d

the m a in u ppe r t e r r ace inc lud ing Wi l l i am son ' s m ans ion houses (F ig . 1 , a r ea 1 ) a s s to re

houses un t i l 1902 w hen m os t o f t he l a rge r bu i ld ings w ere dem o l i shed an d the m a jo r i t y

o f th e t u n n e l s y s t e m b r i c k e d - u p f o r s e c u r it y re a s o n s . T h e a r m y r e t a i n e d c o n t r o l u n t i l

t he 1950s w hen sm al l i ndus t r i a l un i t s w ere cons t ruc ted , one o f w hich in corpora t e s

Wi l l i am son ' s o r ig ina l house f ron tage . T he tunne l s can be accessed f rom th i s now

derelict si te.

The c ounci l kept th e lower ter race of the es ta te (F ig . 1 , area 2) , cons t ruct in g the Ci ty

S tables in 1860 which s t i l l s tand. Complaints of odours in th is area (Anon 1867) were

a t t r ibu ted to the loca l r e s iden t s us ing the tunne l s a s a sew er syst em , and so m a ny tun-

nels were des t royed or covered up, a l though three tunnel ent rances are s t i l l access ible .

T he 1898 O S m ap show s the houses Wi l l i am son bu i l t upon G r indf i e ld H i l l w as t e -

l ands (F ig . 1, a r ea 3 ) t o be st il l s t and in g b u t su r ro un ded by dense ly po pu l a t ed t e r r aces

a long G r indf i e ld S t r ee t and C ongress S t r ee t . S ince then these houses have been

d e m o l i s h e d a n d t h e a r e a h a s b e e n r e s u r f a c e d a n d h a s b e c o m e a w a s t e l a n d .

T he A rm y survey suggest s t ha t Wi l l i am son cons t ruc ted tunne l s ou t s ide o f t he nor th -

e rn b ou nd ary o f h i s land (F ig . 1 , a r ea 4 ) . B y 1898 th i s a rea w as a l so dense ly popu la t ed

w i th t e r r aced hous ing , m os t o f w hich w as dem o l i shed dur ing the deve lop m ent o f t he

A rchb i shop B lanche S choo l i n the 1960s . A l though seve ra l boreho les w ere d r i l l ed

dur ing the cons t ruc t io n o f th i s schoo l, no tunne l d i scover ie s w ere docum e nted .



MICROGRAVITY IN INDUSTRIAL ARCHAEOLOGY 43

Fig. 1. 1847 Ordnance Survey map of Williamson's land soon after his death showing the

location of his houses and gardens.

By 1898, Williamson's houses on the eastern side of Mason Street (Fig. 1, area 5)

were intermingled with terrace developments. Part of this site was developed in the

1930s with the construction of tenement flats to ease the problem of inner-city crowd-

ing: these flats are now derelict. Tunnels were discovered during their construction but

were not fully documented and were probably destroyed. Council houses, which are

still inhabited, replaced the terracing between Helsby Street and Shimmin Street.

Previous investigations of the survey site

A 1903 Arm y survey provides a ma p and cross-section of the system, displaying

what was assumed to be both a typical and a maximal tunnel. The typical tunnel

is a 1.8 x 2.4m Nor man- arc h structure, with the largest feature being the



44 R.J . CUSS & P. STYLES

Fig. 2. Map showing the survey site, with a summary of the tunnel-system as described by

previous surveys, and features noted during site reconnaissance as described in text.

45 x 18 x 12 m Grea t Ha ll a t 4.5 m depth. This survey shows several tunnels within

Williamson's land, and has been incorp orated into Fig. 2 which summarizes previous

surveys.

Techniques for void detection

In engineering terms, the presence of voids within the rock mass lead to restrictions in

development and may result in collapse which can seriously damage building infra-

structure. Prior to re-development the most common method used to identify and

define the spatial extent of cavities has been to drill a detailed borehole grid over

the target area. The zone of sampling of a borehole is extremely small and can

compromise the integrity of the very structure it is meant to sample. There are

many physical properties that are significantly different for rock and air which geo-

physical methods can detect, including conductivity, density, dielectric permittivity,



MICROGR AVITY IN INDUSTRI AL ARCHA EOLO GY 45

magn et iza t ion , and resis tiv ity . Thus , the appl ica t ion of se ismic re f lec tion , gravimetry ,

g round-p rob ing rada r (GPR) , magne tome t ry , and re s i s t iv i ty tomography s u rvey ing

techniques al l offer the potential for void detection (Owen 1983). However, these

me thods have l imi ta t ions impos ed u pon them by the amb ien t and cu l tu ra l no is e com-

pon ent of the recorded s ignal which may be too g rea t for the d i ffe rent techniques

within this area. Seismic reflection was not possible because of the difficult terrain

and h igh ambient noise leve ls present in the a rea . Al though magnetometry can be

ut i l ized in the search for man-made a rchaeologica l fea tures , such as mine workings

(Clark e 1986), i t has rarely been reporte d. In 1959, D r C. D. V. Wilson o f the Univ er-

s i ty of Liverpool conducted an unpubl ished feas ib i l i ty s tudy for the Ci ty Archi tec t ' s

Depar tment in to the poss ib le de tec t ion of the tunne l sys tem us ing geophys ica l

methods . He concluded tha t res is t iv i ty would be adverse ly a ffec ted by noise , and

tha t de tec t ion would be too d i f f icul t by th is technique . His ca lcula t ions showed

tha t the tunne ls could only be de tec ted by magnetometry i f they were f i l led wi th

i ron , whi le gravimetry and se ismic techniques a t tha t t ime were inadequate to

de tec t the expec ted smal l fea tures . Wilson thus conc luded tha t current ly ava i lable

geophysics techniques were unlikely to delineate the system.

While resis t ivity tomography can be effective in detecting voids (Noel & Xu 1991),

the difficult ies of access and the l imited resolution for this depth range made i t inap-

propr ia te for th is s i te . GPR can be very e ffec t ive for cavi ty de tec t ion in mater ia ls of

low conduct iv i ty l ike sands tones (Davis & An na n 1989) and wo uld be an app ropr ia te

technique as par t of a fo l low-up s tudy in ta rge ted a reas ident if ied by microg ravime try .

Microgravimetry

The m icrograv i ty technique in the context of a rchaeology cons is ts of me asur in g

minute var ia t ions in the gravi ta t iona l pul l of the Ear th c rea ted by var ia t ions in den-

s ity and in te rp re t ing the presence of voids and cavi ties, which a re gener ica l ly te rm ed

targe ts , f rom these readings . The mos t common na tura l ta rge ts a re so lu t ion cavi t ies

such as swal low holes and s inkholes in l imes tone , whi ls t man-made cavi t ies inc lude

mine-w orkings , tunne ls and a rchaeologica l tumul i . The va lue of the Ear th ' s gravi ty

is appro ximate ly 9 .81 m s 2 in uni ts of gravi ta t iona l acce le ra t ion but m icrograv i ty

anom alies are q uo ted as microgals (ggal), where 1 gal is 0.01 m s -2. Thus, the E ar th ' s

gravity is abo ut 980 000 000 ggal, whils t varia t ions of s ignificance in cavity detectio n

are genera l ly be tween 5 and 200 gga l . For exam ple , Wil l iam son ' s G rea t H al l would

crea te a 550 gga l gravi ty anom aly , which is ha l f o f the expec ted a nom aly fo r the

26 m deep an d 18 m w ide Lim e Street rai lway tu nnel.

In order to de tec t subsurface voids there needs to be a contras t in dens i ty ( te rmed dp)

be tween the ta rge t and the surrounding bedrock. Air- f i l led cavi t ies offe r the la rges t

anoma ly cond i t ion (dp = - 2 .5 g c m -3 ) because o f the comple te abs ence o f dens e

mater ia l in the ta rge t . Water-f i l led and rubble-f i l led cavi t ies have a lower contras t

(dp = -1 .5 g cm 3 and d p = -1 .0 g cm -3 respec tive ly) , resul ting in gravi ty anomal ies

60% and 40 % respect ively of tha t of an a ir - fi lled fea ture . How ever , as a consequence

of the format ion of a void , f rac tures deve lop which may extend for two or more d ia -

meters away from the cavi ty (Danie ls 1988) . The s ize of a ta rge t i s thus dep enden t no t

only on the s trict volum e of the cavity, but also on this sec onda ry ha lo effect, w hich

increases the apparent target s ize, ensuring that a cavity can be indirectly sensed

(Chamon & Dobere iner 1988; Bishop

et al .

1997, Patterson

e t a l .

1995).



46 R .J . CUSS & P. STYLES

Microg ravi ty surveying has improved considerably over the las t ten years wi th the

development of high-resolut ion equipment, and, al l ied with careful f ield acquisi t ion

techniques and sophis t icated reduct ion and analysis methods, these anomal ies can

be detected and in terpreted . The method i s becoming widely used in engineer ing

invest igat ions, having the advantage of leaving the ground undis turbed. This

al lows not only the determination of the locat ion of features, but also provides infor-

mat ion on thei r depths and geometr ies . Target locat ion depends upon the rat io of

noise to the anomaly of in terest , wi th resolut ion decreasing wi th depth , and upon

the rat io of survey-point spacing to target dimension. Mult iple t raverses with closely

spaced gravity stat ions, or th e collect ion of data on a regu lar grid, resul t in improved

data accuracy that can be used to separate the cavity 's local ized effect , from the

predictable long-wavelength field created by topography, lat i tude and regional geo-

logical variat ions. Although, numerous microgravity case studies exist (see fol lowing

sect ion), microg ravity h as n ot been used extensively in 'brown -field ' si tes; however, i t

represents the only viable f ield-method in this area.

Previous microgravity surveys

The l i terature records some ear ly examples of the a ppl icat ion of microgravi ty tech-

niques to detect cavit ies (Fajklewicz 1956, 1976; Colley 1963; Ne um an n 1967; Arzi

1975; Butler 1984). The success of these studies in del ineat ing and modell ing sub-

surface geometries led to the development of f ield methods and development of

data processing techniques. Fajklewicz (1976) and Butler (1984) both invest igated

the vert ical gravity f ield to enhance feature recognit ion and modell ing. Est imates of

anomalous 'missing-mass ' can be obtained using Gauss ' theorem and proved by

repeat surveying (Arzi 1975).

Ferguson & Styles (1992), Emsley

e t a l .

(1992), Bishop

et al .

(1994, 1997) all

describe the u t i lizat ion of the m icrogravi ty technique using gr idded map s of data in

the detect ion of both kars t ic and man-made cavi t ies . The papers al so descr ibe how

the resul ting data can be enhance d by image-processing to bet ter def ine the anomal ies

associated with the targets. Pat terson

e t a l .

(1995) used the method in detect ion of

dissolut ion subsidence in gypsiferous Permo-Triassic strata in Yorkshire. They calcu-

lated thei r accuracy to be c . 4ggal , and postulated that voids as smal l as 4m in

diam eter mig ht be detected in the r ight circum stances to 12 m depth.

Micrograv i ty has the potent ial to del ineate natura l or m an-m ade void systems in an

effect ive non-dest ruct ive manner , wi th accuracy dependent upon survey-point

spacing and si te coverage. Bishop et al . (1997) concluded that the technique should

be coupled wi th the resul t s of a comprehensive desk s tudy, including knowledge of

the si te geology and topography, and fol lowed up by specifical ly targeted borehole

invest igat ions. Using al l th i s informat ion, anomalous ground condi t ions can be

accurately described, del ineated and where necessary, successful ly t reated.

Survey design

Preceding the acquisi t ion of gravity data, a com prehen sive desk study, modell ing, and

site reconnaissance i s necessary to determine the na ture of the target and to design the

survey specifical ly for this target . Exist ing data were studied to establ ish target size,

al lowing survey point separat ion to be determined, and the locat ion of desi rable




s u r v e y si te s w a s d e t e r m i n e d f r o m m a p s w i t h t h e p o s i t i o n o f s u r v e y a b l e p o i n t s d e t e r -

m ine d by the i r access ib i li t y .

S u r v e y p o i n t s e p a r a t i o n w a s d e t e r m i n e d b y c o n s i d e r a t i o n o f th e d i m e n s i o n s o f t h e

t a r g e ts w h i c h w e r e o b t a i n e d f r o m t h e A r m y s u r v e y a n d f ie ld o b s e r v a t i o n s . A t y p i c a l

s i zed tunne l w as a s sum ed to be a 1 .8 x 2 .4 m N or m an -a r ch f ea tu re , and th i s w as

m a t h e m a t i c a l l y m o d e l l e d o v e r a ra n g e o f d e p t h s w i t h d e n s i t y c o n t r a s t s o f

-2 .0 g cm -3 , -1 g cm -3 , -0 .5 g cm -3 to s im ula t e a i r- f il l ed , w a te r - f i l led , and rubb le -

f il le d tu n n e l s w i t h i n s a n d s t o n e . T h e d e t e c t a b i li t y o f t h e c a l c u la t e d g r a v i t y a n o m a l y

de te r io ra t ed a s po in t - spac ing inc reased w i th in the r ange 0 .5 to 10m , w i th f ea tu re

r e c o g n i t i o n d e p e n d e n t u p o n w h e t h e r a p o i n t w a s t a k e n d i r e c t l y o v e r a t u n n e l f o r

spac ings l a rge r t han 5 m . A 3 m spac ing w as op t im a l fo r t a rge t de t ec t io n and the

num ber o f su rvey li nes r equ i red to cover the su rvey s it e. H ow e ver , i t w as log i s t i ca l ly

im poss ib l e , pa r t ly because o f t e r r a in , bu t a l so because o f r e sources an d t im e ava i l ab le

w i th in the scope o f t h i s i nves t iga t ion , t o cov er the w hole a rea o n a r egu la r 3 m b y 3 m

gr id . I t w as dec ided to have the bes t coverage , a t 3 m by 3 m , in a reas l i ke the sus -

pec ted G r ea t H a l l and to com pro m is e w i th an a long- l ine spac ing o f 3 m w i th p ro f i le s

a t va r i ab le spac ing o r i en ted on the bas i s o f t he s t r ikes and p os i t i on o f suspec ted

fea tu res in the o the r a reas . We apprec ia t e tha t t h i s w i l l necessa r i ly have im pl i ca t ions

fo r t he f r equen cy r e so lu t io n becaus e o f t he ef fec ts o f a l i a s ing a s w e have p rod uce d a

de ta i l ed g r idded m ode l f rom a va r i ab le spac ing da ta se t bu t even w i th th i s spac ing

som e 1200 da ta po in t s w ere co ll ec t ed w hich con s t i t u t e s a ve ry cons id e rab le m ic ro -

g r a v i t y s u r v e y . W e w o u l d a l w a y s r e c o m m e n d a r e g u l a r g ri d a s t h e o p t i m u m c o n fi g -

u r a t i o n f o r m i c r o g r a v i t y s u r v e y s b u t w o u l d p o i n t o u t t h a t t h i s i s a l m o s t n e v e r t h e

case in r econn a i s sance g rav i ty inves t iga t ions w here i r r egu la r ly spaced da t a se t s a re

the ru l e r a the r t han the excep t ion .

D e t e c t i o n b e c o m e s d e p e n d e n t o n g r a v i m e t e r a c c u r a c y a s f e a t u r e s b r o a d e n a n d

dec rease in am pl i tude w i th dep th . T he l a rges t expec ted t a rge t , t he G rea t H a l l , had

d i m e n s i o n s o f 4 5 x 18 x 1 2 m a t a d e p t h o f 4 . 5 m w h i c h s h o u l d c r e a te a 5 5 0 g g a l

ano m aly : t he L im e S t ree t r a i lw ay tunne l , w hich i s 18 m w ide a nd 26 m deep , shou ld

c rea t e a 1000 gga l ano m aly .

T w o t y p e s o f g r a v i m e t e r w e r e a v a i l a b l e f o r u s e d u r i n g s u r v e y i n g ; t h e L a C o s t e -

R o m b e r g G a n d W o r d e n t y p e g r a v i m e t e r s . W h i l e n e i t h e r i s i d e a l f o r t h e h i g h e s t -

r e so lu t ion w ork , t hey can ach ieve good accurac ies w i th ca re fu l f i e ld p rocedure .

R e s u l t s f r o m t h e d i f f e r e n t i n s t r u m e n t s w e r e c o n s i s t e n t , w i t h n o a d j u s t m e n t n e e d e d

and bo th w ere ab le to de l inea te the tunne l sys t em sa t i s f ac to r i ly . Idea l ly a L aC os te -

R o m b e r g D - m e t e r o r a S c in t r e x C G 3 - M s h o u l d b e u s e d fo r m i c r o g r a v i t y s u r v ey s

bu t ca re fu l f i e ld p rocedure i s a s m uch the key to accura t e de l inea t ion o f f ea tu res a s

i n t ri n s ic r e s o l u t i o n o f t h e i n s t r u m e n t .

S evera l o ld m aps w ere acqu i red w hich d i sp layed poss ib l e tunne l l oca t ions , a s

s u m m a r i z e d i n F i g . 2 , w h i c h s h o w s t h e t u n n e l s y s t e m t o b e m a i n l y c e n t r e d a r o u n d

the o r ig ina l m ans ion houses , w i th in Wi l l i am son ' s l and , w i th on ly a f ew tunne l s

e x t e n d i n g o u t s i d e t h e a r e a w h i c h w e r e a s s u m e d t o l e a d t o l o c a l l a n d m a r k s . H a n d

(1927) sugges t s t ha t t unne l s w ere bu i l t t o S t . Mary ' s church and an un iden t i f i ed

P ub l i c H ouse : t he su rvey w as the re fo re ex tended to inves t iga t e th is . T unne l l ing

pro ba b ly be gan f rom the low er s ide o f the s i te i n to the h i ll , t hus i t w as a s sum ed

t h a t t u n n e l s d o n o t e x is t o n t h e l o w g r o u n d w e s t o f S m i t h d o w n L a n e . A s t h e

l a rge r , m o re e l ab ora t e , co ns t ruc t ions a re l ike ly to be close to Wi l l i am son ' s house , su r -

v e y i n g w a s c o n c e n t r a t e d w i t h i n t h is a r ea . T h e t u n n e l s y s t e m m a y h a v e i n t e r c o n n e c t e d



48 R.J. CUSS & P. STYLES

several of Williamson's houses, so original maps were acquired to locate these

properties.

The site reconnaissance identified several features suggestive of the presence of

voids within the field area, as summarized in Fig. 2. Tunnel entrances were found

at locations 1 and 2, with tunnels still accessible. Col lapse features were noted at

locati on 3 with the concrete surface displaying 1-2 m subsidence, while more subtle

subsidence was identified by a curvature in the brickwork of a council house at

location 4. Within the factory units at locations 6 and 7, considerable subsidence

had occurred, and since surveying a major collapse has occurred at location 8. The

uneven-cobbled surface at location 5 showed linear trends possibly caused by the

tunnel system.

Data acquisition

Between June and Dec ember 1994, 1243 data -points were collected during 21 field

days. The base station was located as a secure corner-curb at location BS (Fig. 2)

central to the survey site. This point was repeated at hourly intervals with at least

five gravity readings recorded to remove the effect of drift and Earth tides. Due to

logistic difficulties in achieving base stations at hourly intervals, it was necessary to

establish a series of temporary base stations which were later adjusted to the main

base station.

Survey lines were marked out with a 3 m poin t spacing on all accessible land, with

location identified by clear markers on the OS map. In open-areas, a regular pattern

of survey points was adop ted, with a line spacing o f 12 m (see Fig. 3). At every survey-

point, at least three gravity readings were taken, along with a time reading, and notes

Fig. 3. Bouguer anomaly map of the survey site, showing all survey points.





50 R. J. CUSS & P. STYLES

Fig. 4. 3-D Topographic surface of the Mason Street area, highlighting the severe terrain of

the site.

features are masked by this terrain effect, necessitating the terrain correction. The

circular graticule methods of Hemm er (1939) and Ballina-Lopez (1990) were foun d

to be inapplicable as they are designed for regional scale surveys.

Ketelaar (1976) developed a method for use with regularly sampled terrain surfaces

which are approx ima ted by a 21 21 grid of square prisms with upper surfaces that

slope toward the grid centre. The effect of each prism within the grid is calculated and

summed to give a value of terrain correction of the centre point. Ketelaar showed

that, although for moderate terrain the difference in accuracy between a 5 x 5 and a

17 x 17 grid was insignificant, severe ter rain c reated a significant error. A slope of 7 ~

creates an error of 1%, with a 30 ~ slope creating nearly 25% error. A FO RT RA N

computer program was written and fully tested on simple geometric shapes, giving

results which are consistent with two-dimensional modelling.

Spot heights were added to the height data to avoid edge-effects, and once the

terrain correction had been calculated the border was removed. The terrain correction

method fails in the proximity of the railway tunnel which has a prism slope of

approxima tely 90 ~ This high-frequency error was removed by filtering the terra in

correction which was applied to the raw-Bouguer anomaly results to create a

terrain-corrected Bouguer anomaly map. Some residual features follow the topogra-

phy and may be either due to uncorrected terrain, or geological features controlling

the relief within the area. However, the removal of the terrain effect significantly

improved the data-set.



MICROGR AVITY IN INDUSTRIAL ARCH AEOL OGY 51

Fig. 5. Final Bouguer anomaly map of the Williamson tunnels site after filtered terrain

correction and the removal of the regional surface.

Bouguer anomaly f ie lds a re of ten charac te r ized by long-wavelength regiona l

anomal ies which a re c rea ted by deeper var ia t ions in dens i ty , super imposed upon

which a re h igher wavenumber loca l var ia t ions . By removing the regiona l anomaly

i t i s hoped to only have the res idua l loca l anomaly which is c rea ted by sha l low

features of interest . The regional fie ld can be removed by either surface fi t t ing or

upw ard-c ont in ua t io n of the da ta by a d is tance equa l to the gr id separa t ion . M os t

commonly a low-order polynomia l surface i s removed from the da ta ; in th is case a

th i rd-order polynomia l was removed by f i t t ing the da ta in a leas t -squares sense

(Fig. 5).

The de tec t ion of ta rge t edges can be enhanced by examining the gradients of the

gravi ty f ie ld , as these show marked changes a t boundar ies . The second hor izonta l

der iva t ive i s commonly appl ied for th is purpose as i t can be ca lcula ted very readi ly

for gr idded da ta us ing Fou rie r techniques (Fig . 6) . The m eth od can he lp to de te rmine

the na ture of bur ied geologica l fea tures , and wi th l inear ta rge ts , should de l inea te the

tunnel-sys tem a id ing fea ture recogni t ion . In two dimens ions the second der iva t ive

creates a characteris t ic dis t inct peak feature for a tunnel, which is f lanked by sub-

sidiary negatives .




Fig. 6. Second horiz onta l derivative m ap of the area.

I d en t i f i ca t i o n o f ' n o i s e ' s o u rces

The gravi ty ano ma ly is a com plex supe r imposi t ion of s ignals f rom ma ny sources. The

di ff icul ty of ext ract ion of the ' s ignal ' for the cavi ty f ro m the 'noise ' f ro m al l of these

other ef fects is the ma jor l im i ta t ion of geophysical surveying. To enable conf ident

target ident i f ica t ion a l l o ther anomaly sources need to be ident i f ied. Both natura l

and man-made f ea tu res can c rea t e background 'no i se ' which mask t he t a rge t

anomal ies . The natura l sources der ive f rom geological fea tures including faul t s and

glacia l dr i f t , and tend to be unpredic table unless s igni f icant geological data are

avai lable.

The Perm o-Tr iass ic sediments of the Cheshi re Basin are general ly poor ly-exp osed

due to extens ive Quaternary to recent cover , but have good exposure on Edge Hi l l .

M an y cross-sect ions of the area have been con st ructed us ing the extens ive exposures

created by the Lime St reet ra i lway tunnel (Morton 1863) , and show a faul ted hal f -

graben feature wi thin the Bunter , Muschelkalk, and Keuper fac ies (Evans et al .

1993). Throw s o f up to 200 m are seen wi thin the Sherwood Gr ou p sandstone,

a l though no faul t s seem to cut the survey s i te . Water levels in the area should be

low due to the high aspect o f the s ite, and the proxim i ty of the Lime St reet tunnel

which i s s t i l l pumped and i s deeper than the Wil l iamson tunnels , implying that the

sys tem wi ll be dry. Therefore , the appa rent absence o f both glacia l -dr i f t and faul t ing

predic t s th at the ef fect of geology upo n the resul ts wi l l be s imple , and the d ry-na ture

of the tunnels impl ies that the ma in af fect on the gravi ty ano ma ly s t rength wi ll be the

presence of rubble f i l l .




Man-made noise sources within the survey site are created by the redevelopment of

the land, which as outlined earlier, has been substantial. Developments have modified

the ground-surface with large areas being filled with a variable thickness of low-

density rubble which can create a complex and unpredictable anomaly of up to

40 ggals. The study of development in the area was vital to explain which anomalous

features were due to man-made noise. Grindfield Hill will be the most affected area as

subsequent developments have left the area refinished using a thick and highly vari-

able depth of rubble fill. Lesser thicknesses of rubble are expected at locality 5 (Fig. 2).

Many of the tunnels are suspected to have been modified during development. The

army sealed many of the tunnels close to Williamson's house; it is uncertain whether

any were destroyed. Tunnels would also have been destroyed, filled with debris or

sealed during the construction of the city stables, and the developments on Padding-

ton and Grind field Hill. The filling of debris will reduce the density contrast and hence

the anomaly amplitude but not affect the intrinsic anomaly shape and wavelength.

The 24 m deep open Lime Street tunnel and the deeper enclosed Waterloo tunnel

will create a significant yet predictable noise signal and were modelled from dimen-

sions determined from the OS map. These tunnels will have accompanying smaller

air-shafts that are not documented which creates a possible confusion over the

source of anomalous linear-features in the proximity of the railway tunnels. The

Waterloo tunnel has a number of large air-shafts (locality 10) creating predictable

localized anomalies.

Data interpretation

The Bouguer anomaly map (Fig. 3) shows many high-frequency anomalies super-

imposed upon a complex long-wavelength regional feature which slopes from the

northeast to the southwest. A linear feature trends through the survey site, as high-

lighted in Fig. 3, which coincides with the topographic terracing of the area and may

be explained as either an effect of terrain or by the presence of a geological fault. The

fault would explain the terraced nature of the area but the geological cross sections

show no faults within the site (Morton 1863). The survey points displayed on Fig.

3 shows the dense coverage in some areas, but also identify areas of sparse coverage

within which the interpolation process has created features indicative of tunnels; these

were identified and rejected. Other features were identified as created by terrain,

especially along the topographic terracing and around the periphery of the Lime

Street tunnel. These features complicate target identification as they mask the smaller

features created by the tunnels. No effect was evident from the building infrastruc-

ture, as recognized in Kuwait by Bishop e t a l . (1997). Although the regional and ter-

rain effects are substantial, linear features can be seen around the site of Williamson's

house where coverage is high, with the largest anomaly sub-parallel to Mason Street

representing a previously unidentified feature (Fig. 3 locality a). A large rectangular

anomaly at location b is of similar dimension to the Great Hall, with smaller features

at locations c -f. Many of these features correspond to those of Fig. 2 with an anom-

aly at location g corresponding to the subsidence at location d (Fig. 2) confirming

void collapse.

The removal of the terrain effect and regional trend created the final Bouguer

anomaly map (Fig. 5) and increased the number of identifiable targets, particularly

features h-n which were previously unidentified.




The second der ivat ive m ap shows man y of the expected ' spike- l ike ' lineat ions indi -

cat ive of tunnels as shown in F ig. 6. The m ain feature del ineates the Lime St reet

tunnel (o) and i s an ar tefact of the l imi ta t ions o f the ter ra in correct ion prog ram , as

is the feature at local i ty p. Unexpectedly, the road is clearly del ineated (q) as a

weak anomaly i s created by the di f ference in densi ty between the road-s tone and

surrounding s . Af ter the e l iminat ion of noise fea tures , m any targets were ident i fied

a round Wi l l i amson ' s house , t he school g rounds , and Gr indf i e ld Hi l l , some of

which were previously und eterm ined, locali ti es r - t . The appl ica t ion of the second

der ivat ive method a ided target ident i f ica t ion and represents a valuable method for

the del ineat ion of void features associa ted wi th indust r ia l archaeolog y.

To a id f inal fea ture interpre ta t ion the resul t s were divided into four smal ler maps

cover ing Wil l iamson's house , Gr indf ie ld Hi l l , Archbishop Blanche School , and

Paddington. Using a l l the avai lable informat ion, including the ful l - and smal l -scale

Fig. 7. Ma p of the Williamson tunnels as determined from m icrogravity.



MICROGR AVITY IN INDUSTRI AL ARCH AEOL OGY 55

Bouguer maps , second-der iva t ive map, h is tor ica l documenta t ion , noise survey, f ie ld

evidence , and desk s tudy, the tunne l sys tem was de l inea ted as summarized in Fig . 7 .

All previo usly kn ow n accessible tunnels were located successfully, but no ev idence for

the suspec ted tunnel run ning to St. Mar y ' s ch urch was obta ined. The survey ident i f ied

many known and previous ly unknown tunnels , and was success fu l a t de l inea t ing the

tunnel sys tem. Al though the adverse te rra in and the complex regiona l fea ture , com-

pl ica ted da ta - in te rpre ta t io n , the appl ica t ion of a te rra in correc t ion and the remova l of

the polynomia l surface enhanced fea ture recogni t ion .

Gravity analysis and modelling

The de l inea t ion o f the tunne l sys tem, a l tho ugh success ful , only g ives a two-dimen-

s iona l p lan of ta rge t geometry . Two methods a re ava i lable for the de te rmina t ion of

the depth o f the ta rge ts ; forward gravi ty model l ing o r invers ion me thod s such as

Euler deconvolut ion . Gravi ty model l ing has the potent ia l to de te rmine the depth

and the na ture of the ident i f ied ta rge ts through the cons t ruc t ion of geologica l c ross

sect ions . Seven t ransec ts of in te rest were obta ined f rom the in te rpola ted gravi ty-

g r id and were mode l l ed us ing the G R A V M A G pro gram which calcu la t es the g rav i ty

effec t of geometr ica l bodies o f di f ferent dens i ty wi th in a con s tant dens i ty backg roun d.

The geometry and dens i ty of these bodies a re adjus ted to match the recorded f ie ld-

resul ts . Accura te geologica l c ross sec t ions can be achieved wi th in the l imi ta t ion of

the in t r ins ic non-uniqueness tha t a ffec ts gravi ty model l ing . Models can be con-

s t ra ined us ing addi t iona l informat ion , such as surface l i thology in the model l ing of

regiona l t ransec ts to reduce the ambigui ty .

The nu mer ous surface tunnel express ions he lp to de te rmine the depth o f the fea tures

with respect to land surface, tunnels at locali ty 1 (Fig. 2) were 0.2 -3 m depth, with

previous surveys showing tunnels to a 5 m depth . A ddi t io na l depth es t imates us ing

the ha l f -wid th and g rad ien t -ampl i tude me thods we re ob ta ined f rom the anoma lous

curves , but these showed la rge e rrors due to the sha l low dep th ran ge of the tunnels .

Tunnel loca t ion a long each t ransec t were de te rmined us ing the second-hor izonta l

der iva t ive to ident i fy the ' cent ra l sharp peak and f lanking nega t ive ' s igna ture of a

tunnel.

In order to de te rmine the pos i t ion of the ta rge ts in three d imens ions we have used

the technique of Euler Deco nvolut ion . Euler Decon volu t ion is a me tho d for loca t ing

the sources of potent ia l f ie lds based on bo th the i r am pl i tudes and gradients and an

es t imate of the prob able geom etry of the causa t ive body ( Th om pso n 1982; Reid

et al. 1990) . The technique is very appropr ia te for use in microgravi ty surveys

where high-quali ty, c losely spaced data are available.

Potential f ie lds such as gravity, magnetism and their spatial derivatives satisfy

Eu le r 's eq ua t ion o f homogene i ty :

OV OV OV

( x - xo ) -g - ; x + ( y - yo ) -g - fy + ( z - zo) - z = - n v .

The der iva t ive of the cont inu ous f ie ld V sa tisf ies the abov e hom ogen eou s eq ua t io n of

degree n where n is known as the s tructural index. This is an indicator of the fal l-off

ra te of the f ie ld wi th d is tance r and depends on the geometry of the suspec ted body,

e .g . l ine , poin t , sphere or any combina t ion , and the par t icula r potent ia l f ie ld type .

Hence , f rom a f ie ld which is measured a t poin t

(x ,y , z) ,

the gradients in these




o O

o

r~

~ g

~ ,,,,~

.,.,,a

r.~

~ ,,,,~

~CZ, "" "Z~

r~

==:._,

9 ,.t:Z ~




di rect ions can e i ther be meas ured or ca lcula ted. I f we have the values (x , y , z) and

thei r der ivat ives a t more t han four points , and an es t imate o f n , we can solve for

the loc at ion of the causat ive bod y, (x0, Y0, z0), by a least-square s ma trix inversion.

In this case, we have mic rogra vi ty as our value for V. A wind ow is mo ved across the

data , and solut ions for

(xo,Yo, zo)

are obta ined. Only those locat ions of

(xo,Yo, zo)

which c lus ter as solut ions f rom several window posi t ions are considered real .

The program was used to solve for the posi t ion and depth to an anomaly in 2D, i . e .

a long a prof i le l ine shown on F ig. 8a . F igure 8b shows the Bouguer Gravi ty , and i t s

ver t ica l and hor izonta l der ivat ives and the solut ions for the target pos i t ion der ived

fro m them. The c lus ter ing o f c i rc les aro un d 5 m d epth a t a pos i t ion of 32 m along

the prof i le indicates a good solut ion to the equat ions a t that point . This agrees very

wel l wi th the dep th and posi t ion of the G reat Ha l l which is mod el led as F ig. 8c .

This i s a ful l 3-D gravi ty model implemented us ing Four ier techniques for a void

represen t ing t he Grea t Ha l l and t he anom aly ampl i t ude o f more t han 400 pga l

agrees wel l wi th the observed amp l i tude of the anom aly.

Conclusions

The m ic rograv i ty su rvey success ful ly p roduced a map of the Wi l l i amson tunne ls i n

an accura t e and r e li ab l e manner , dem ons t r a t i ng t he va l id i t y o f app ly ing the me tho d

to indust r ia l archaeology even in 'brown-f ie ld ' s i tes . Wi th careful f ie ld acquis i t ion,

Wo rden and L aCo s t e -R om berg g rav imete rs were shown to be adequa t e , i f no t

ideal , for target lo cat io n fo r air- , water- , or rubble-f i l led cond it ions using a 3 m

point -spacing which was opt imal for these fea tures . The 1243 survey-point readings

gave a high coverage in mo st o f the s ite, especia l ly aro und the locat ion of Wi l l iam-

son's house, but restr ict ions in access resul ted in several sparsely covered areas. We

apprecia te that th i s l imi t s the conf idence which can be placed in the ident i f ica t ion

of fea tures in these sparse ly covered areas an d rec om me nd that wh erever access

and cos t a l low a regular ly spaced gr id a t an appropr ia te spacing i s to be prefer red.

Thi s does no t de t r ac t f rom the conc lus ion t ha t mic rograv i ty has been ex t r emely

useful in the ident i f ica tion of fea tures in thi s area and shou ld be con sidered as a

valuable addi t ional tool in indust r ia l archaeological inves t igat ions .

The Bouguer anomaly map showed many f ea tu res t ha t were cons i s t en t wi th

previous surveys , but a s t rong regional gradient and ter ra in ef fects masked some

of the smal ler tunnel fea tures . Rem ov al of the gradient a l lowed some previously

unrecognized targets to be ident i f ied once noise sources were recognized and

e l iminat ed t h rou gh a comprehens ive desk s tudy of the h i s to ry o f land use . The

second-hor izonta l der ivat ive s igni f icant ly a ided feature recogni t ion by enhancing

smal ler anomal ies and c lear ly del ineated the Lime St reet tunnel and Mason S t reet

as wel l as ident i fying previously unrecognized tunnels . Euler deconvolut ion provided

posi t ions and depths to the anomaly sources . The theoret ica l cross sect ions produced

show that even wi th a di f f icul t data-se t i t i s poss ible to model expected features . The

success of these metho ds highl ighted thei r potent ia l fo r the del ineat ion in three

dimensions of cavit ies associa ted wi th both indust r ia l archaeo logical and geological

features.

A full appraisa l of the sys tem requi red a com prehensive desk s tudy w hich examined

his tor ica l do cum enta t ion and f ie ld evidence. Th e access ibi li ty o f some of the tunnels

conf i rmed ident i f ica t ion, a l lowing many new tunnels to be ident i f ied. Using this




i n f o r m a t i o n a n d a l l a v a il a b le g r a v it y d a t a , m a n y k n o w n a n d u n k n o w n t u nn e ls w e r e

success fu l ly iden t i f i ed .

The authors would l ike to acknowledge the fo l lowing people for the ir invaluable contr ibut ion

during th is survey. J . Harvey and J . Hakes for genera l ass is tance , K. Helps , D. G. Cuss and

P. D. Cuss for ass is tance during level l ing , G. Muies , D. Hart ley (Magnets Showrooms) and

J. M. Venn (Archbishop Blanche School) for a l lowing access to land. We are very gra tefu l

to Sam Toon for h is ass is tance with the computer graphics .

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The Makapansgat Australopithecine site from

a speleological perspective

A L F G . L A T H A M 1, A N D R E W H E R R I E S 1,

P A T R I C K Q U I N N E Y 1, A N T H O N Y S I N C L A I R 1 &

K E V I N K U Y K E N D A L L 2

1Archaeology Department, Liverpool University,

Liverpool , L69 3BX, UK

2Department of Anatom ical Sciences, U niversi ty of

Witwatersrand, Johannesburg, South Africa

Abstract:

R e m a in s o f

Australopithecus africanus

f rom the L imeworks Cave ,

Ma kapa nsga t , South Africa, are believed to belong main ly to a metre-thick,

bone-rich, speleothem layer. The f lowstone is one stratum among a sequence of

speleothems, muds, s i l ts , sands and f ine and coarse breccias, the study of which

has evoked some disagreement. The l imeworkers ' excavations revealed some

strat igraphic relat ionsh ips but they have obscured others. Part ly becau se of this ,

controversy surrounds the supposit ion about whether there are separated deposi-

t ional basins within the overall s ite and, if so, whether s trata can be securely cor-

related. This is important because a reconstruction of an overall s trat igraphic

sequence was used as a basis for a magnetostrat igraphic reversal record and by

which the si te has been ten tat ively dated. There is qualif ication and d isagreemen t

about the o r ig in o f the var ious f lowstones and the ac tua l depos i t iona l env i ronme nt

of the muds and si lts . Evidence is presented which rules out some previous inter-

pretat ions. F rom the point of view of the Australo pithecin e fossils themselves, i t

can be said that the calci te matrix in which they were provenanced was a low-

energy envi ronment and tha t the dense bone accumula t ion of th is layer a lmost

certainly did not arise by the action of f loods, as previously supposed. The m ost

l ikely ma in cause o f the dense ac cum ulation was hy ena d ennin g activity . It is

clear that further work is needed to see how a rel iable overall sequence can be

established and that c loser sampling is required for magnetostrat igraphy.

T h e L i m e w o r k s C a v e i n t h e M a k a p a n s g a t V a l le y , T r a n s v a a l , S o u t h A f r i c a ( F ig . 1 ) i s

w e l l k n o w n f o r i ts r e m a i n s o f Australopithecus africanus f r o m w h i c h t h e r e a r e a b o u t

3 0 s p e c i m e n s , t h e f i rs t f i n d s a p p e a r i n g i n 1 9 47 ( M a s o n 1 9 88 ). D e s p i t e m o r e t h a n 5 0

y e a r s o f re s e a rc h , n e i t h e r t h e f i n d s n o r t h e d e p o s it s f r o m w h i c h t h e y c a m e h a v e

b e e n f i r m l y d a t e d a n d t h e r e i s n o c o m p l e t e c o n s e n s u s o n t h e o r i g i n s o f t h e d e p o s i t s

o r o n w h e t h e r a c o m p l e t e s t r a t i g r a p h i c s e q u e n c e c a n b e r e c o n s t r u c t e d .

B a s e d o n f a u n a l e v i d e n c e , t h e A u s t r a l o p i t h e c i n e d e p o s i t , a k i n d o f b o n e b r e c c i a s et

i n g re y - w h i t e f l o w s t o n e , is t h o u g h t t o b e n o y o u n g e r t h a n 2 .5 M a a n d a s o ld a s 3 M a

( V r b a 1 9 8 2 ) . T h i s g r e y t o w h i t e s p e l e o t h e m i s t o o o l d f o r U - S e r i e s d a t i n g w h i c h , b y

m a s s - s p e c t r o m e t r y , h a s a n u p p e r l i m i t o f a b o u t 5 00 k a . T h e e l e c t ro n s p i n re s o n a n c e

( E S R ) m e t h o d h a s n o t y e t b e e n a p p l i e d t o d a t e t h e e n a m e l o f t ee t h f r o m t h e s it e;

E S R s t u d i e s a t S t e r k f o n t e i n h a v e o n l y b e e n p a r t i a l l y s u c c e s s f u l ( S c h w a r c z

et al.

1 99 4) . R e c e n t ly , U - P b m e t h o d s h a v e b e e n d e v e l o p e d t o d a t e g e o l o g i c a l ly y o u n g

Front. POLLARD,A. M. (ed.) 1999. Geoarchaeology:exploration,environments,resources.

Geolog ical Society, Londo n, Special Publication s, 16 5, 61-77. 1-86239-053-3/99/$15.00




62 A. G. LATHAMT AL.

0

1OKra

~ . ~

, \

Fig. 1. Location map of the Limeworks Cave, Makap ansg at Valley, Transvaal (North ern

Province, South Africa (after Maguire

et al.

1980).

rocks (Getty & DePaolo 1995) and i t has been used successfully to date speleothems,

having h igh uranium content , as young as 250ka (R. Cl i f f , pers . comm. 1998) .

However , a su i te of spe leothem pi lo t samples f rom the Limeworks Cave showed

tha t u ran ium con ten t i s gene ra l ly low (<0 .5ppm) and the common l ead was

comparable to the radiogenic lead (work in progress and de ta i l s to be repor ted

elsewhere).

Perhaps the mos t promis ing method to da te the s i te i s to compare the reversa l

magn e tos t ra t ig raphy o f the va r ious layers w i th the G loba l Mag ne tos t ra t ig raph ic

Timesca le , wh ich was a t t empted by McF add en e t a l . (1979) . The potent ia l a dvantag e

of th is me thod, bear ing in mind the current in te res t in changes in pa laeoc l imate l inked

to changes in pa laeo faun a (Vrba 1996) is tha t i t can potent ia l ly prov ide ages for the

whole sequence. The composite section, from the earl ies t speleothem to the latest

brecc ia , could be p laced somewhere be tween 3 .32Ma and 2 .43Ma. There a re

problems, however, with the ages so est imated. Firs t ly, D. Jones & A. Brock (pers .

com m.) be l ieve tha t the sampl ing dens i ty for pa laeom agnet is m w i th in each subsec t ion

was low, which impl ies tha t reversa l boundar ies might have been misplaced.

Secondly , sampl ing was carr ied out on wide ly separa ted subsec t ions , and as Turner

(1980) , Maguire (1985) and Maguire

et al .

(1985) have noted, i t is not clear that a

comple te compos i te sec t ion was recons t ruc ted re l iably . The la t te r authors be l ieved

tha t there were four depos i t iona l bas ins wi th in the s i te , and pa lynologica l ana lys is

by Cadm an & Rayne r (1989) and Zava da & Cadm an (1993) s howed tha t the depos i-

t ion be tween bas ins was not un i form or synchrono us . Thu s i t is not kn ow n i f there is

an absence of h ia tuses or i f simi la r beds a re a lso t ime-equiva lents , as the com pos i te

recons t ruc t ion for magn etos t r a t igr aph y assumes . Las t ly , the uppe r par t of the

sequence cons is ts of brecc ias . As McFadden

et al .

(1979) recognized, the interpreta-

t ion of the pa laeomagnet ic record of samples taken f rom th is k ind of depos i t has i t s

own spec ia l problems (see la te r) and, because of the inde te rmina te pa laeomagnet ic

di rec tions , the u ppe r p ar t of the brecc ia was essent ia l ly unplaced.



MAKAPANSG AT AUSTRAL OPITHEC INE SITE 63

In ma ny places , the deposi ts sh ow rapid la tera l changes on a scale of tens of

metres or less. A ful l assessment of these changes, showing the effect they wil l have

on an overa l l s t r a t i g raph i c sequence and upon any overa l l magne tos t r a t i g raphy ,

can only be made by surveying and corre la t ing ver t ica l sect ions a t c lose intervals .

The extant survey wo rk has included long cross sections of bro ad s t ra t igraphy , b ut

not ver t ica l sect ions on individual faces . In preparat ion for fur ther sect ional

surveying, palaeomagnet ic and radiometr ic work, and to cont r ibute fur ther to the dis-

cuss ion on s t r a t i g raphy , we presen t a numb er o f obse rva t i ons ab ou t t he mo de of spe -

leothem deposi t ion and ear ly sedimentat ion a t the Limeworks s i te and a l so include

some obse rva t ions abou t spel eogenes is a t M akap ansg a t . I n t he t r ad i t i on o f Bra in

(1958), but di f fering f rom him in a nu mb er of deta il s , our ob servat ions and interpre-

ta t ions are guided by observat ions f rom s tudies o f other caves.

The Limeworks Cave and its broad stratigraphy

The cave , fo rme d in P recam br i an do lomi t e o f the T ransvaa l S upergroup , was

ini t ia l ly worked for i t s th ick speleothem f lowstone by l imeworkers f rom about

1908 to 1936. ( In the l i t era ture , the f lowstone a t Makapansgat i s of ten refer red to

as t raver t ine , meaning cave t raver t ine as opposed to hot -spr ing t raver t ine . ) In

order to get a t the f lowstone, the workers had to blas t and remove consol idated

and unconsol idated breccia ; bones are found in c las t ic sediments , breccias and in

al l but the ear l ies t speleothem. There do not appear to be any extant mining records

which w ould indicate the or iginal extent of the deposi t s but there are s ti ll rem nan ts

of deposi ts in some areas or , in the case of some f lowstones , t races of them left by

negat ive contact sur faces . Broad s t ra t igraphic sequences have been const ructed by

Wel ls & Cooke (1956) , by Brain (1958) and by Par t r idge (1979) and they are in

rough agreement . The pa l aeomagne t i c sampl ing fo l l owed P ar t r i dge ' s (1979) r econ-

s t ructed sequence. Those bone remains conta ining

Australopithecus africanus

were

mos t ly r ecovered f rom the l imeworker ' s dumps , r a the r t han in situ, and were

near ly a l l ass igned to a la ter grey f lowstone cal led Member 3 , in the nota t ion of

Par t r idge (1979). The out l ine plan o f the cave wi th the l imew orkers ' quarr ies and

access cut t ings i s shown in F ig. 2 and the corresponding composi te sect ion i s

shown in F ig . 3 . M ass ive e roded s t a l agmi t i c co lumns above t he Cone mouth , on

the sur face , indicate tha t the or iginal roof of the cavern was tens of met res above

the present sur face .

Be tween the M ain Qua r ry and t he Exit Qua r ry i s a 15-20 m th i ck cemented b recc ia

essent ia l ly separa t ing the two excav ated halves of the s ite. The En t rance Qu arry, to

the west , l eads to the Main Quarry which, on the west s ide , conta ins the Class ic

Sect ion. This , in turn conta ins , una mb iguo usly, deposi t s now refer red to as M em bers

1, 2 and 3. To the south and between the Main Quarry and the East Quarry i s the

Cone, a pi le of breccia that has resul ted f ro m col lapse by underm ining. The co rol lary

of thi s is an inver ted funnel mo uth to dayl ight , conta ining speleothem and ab out 10 m

of breccia and s t ra t if ied red sediment . Aro un d the Cone m out h, the c las tic deposi t s

vary la tera l ly , being f ree of large c las t s adjacent to the back wal l , and there are

non-cemented sect ions to the eas t . Behind the Cone there are shor t cave passages

and a l coves con t a in ing ea r ly phases o f spe l eo them and ano the r en t r ance t o t he sou th-

west . The passages open to the eas t in to the Exi t Quarry and an exi t cut t ing, to the

s ide and under which i s Horse M andib l e Cave . The Exi t Quar ry con t a ins a shor t



64 A. G. LATHA M ET AL.

Fig. 2. The Limeworks quarries and underground workings (after Maguire

et al.

1980).



MAKAPANSGAT AUSTRALOPITHECINE SITE 65

Fig.

3. Composite section of the Limeworks Cave stratigraphy (adapted from Partridge

1979), with subdivision of member 1 into M emb er 1A and Mem ber lB. M emb er 4 includes

former Mem ber 5.

t unne l above which i s a laye r o f cemented sed iment con t a in ing m any roden t bones .

This area i s ca l led 'Rodent Corner ' (F ig. 4) .

Description of Deposits

Member 1 (A and B)

The f i r s t major deposi t ional phase , Member 1 , i s mass ive s ta lagmi te . Wi thin thi s

member there are two qui te dis t inct ive phases , here des ignated A and B.

The s ta lagmi t ic concret ions which coat the f loor , wal l s and roofs are unusual mam-

mil lary forms. These bulbous concret ions p rot rude in var ious di rections , most ly up an d

down, but there are no corresponding s ta lac t i te-s ta lagmi te pai rs as would be the case

for normal subaer ia l , gravi ty-dominated, deposi t ion. Where the miners have smashed

them, they show even deposi t ion over the var ious un dula t ions (F ig. 5). This is me mb er

1A and, in i ts earl iest phase, exposures in recesses inside the Exit Quarry cave show

radiat ing aragonit ic cores with later calci te layering.

In several of the recesses 1A is the end of deposi t ion. There i s no other layer a par t

f rom a thin coat ing of dus t .

At the base o f the Class ic Sect ion, a 7 m long ex posure shows red -brow n s ta ining

wi th in the mam mi l l a ry spe l eo them, which impl ie s an i npu t o f mu dd y wa te r i n to

the local pool (Fig. 6) .



66 A. G. LAT HAM ET AL.

Fig. 4. Looking out from the Exit Quarry to Rodent Corner. The wall to the left consists of

collapsed roof slabs and breccia with flowstone which once rested against massive speleo-

them, leaving a gap. The massive speleothem has been mined out. Behind and above these

slabs is Me mbe r 4 breccia. The tunnel itself was mined th roug h the rhythm ites.

Origins of Member 1A.

I t i s k n o w n t h a t m a m m i l l a r y s p e l e o t h e m s f o r m s u b a q u e o u s l y

(H i ll & F or t i 1986). E v iden t ly , a t t he L im ew orks C ave , t hey fo rm e d und er , and c lose

to , w a te r su r faces f rom w hich C O 2 w as a l low ed to ou tgas to the cave a tm osphere .

T h i s caused the w a te r t o becom e sa tu ra t ed w i th r e spec t t o a ragon i t e and ca l c i t e ,

w hich the reby p rec ip i t a t ed under w a te r on to ava i l ab le so l id su r faces . I t i s ve ry

l ikely tha t , b y th is t im e , t he ac tua l cave fo rm ing s t r eam s w ere no longer ex tan t a nd

t h a t t h e s e p o o l s o w e d t h e i r e x i s t e n c e t o m o r e s a t u r a t e d p e r c o l a t i o n w a t e r f r o m t h e

over ly ing su r face . In a l l l i ke l ihood i t w ou ld have been the sam e w a te r t ha t fo rm ed

t h e m a s s i v e s p e le o t h e m f o r m a t i o n s a n d M e m b e r 1 A a n d 1 B m a y h a v e b e en , in

p a r t , c o n t e m p o r a n e o u s . T h e o u t g a s s i n g o f C O 2 f r o m t h e p o o l s m a y h a v e b e e n a cc e l-

e ra t ed by the p rox im a l deve lo pm en t , t o the nor thw es t , o f su r face co ll apse and regres -

s i o n . A t a n y r a t e , a n e n t r a n c e n e a r t h e M a i n Q u a r r y i s s u g g e s t e d b y t h e r e d - b r o w n

s ta in ing w i th in the m am m i l l a ry fo rm s under the C lass i c S ec t ion . I t m ay w e l l be

tha t , he re , r eg ress ing co l l apse w as c lose enough fo r c l a s t i c sed im ent to en te r t he

u n d e r g r o u n d p o o l s f o r t h e f ir st ti m e.

Member lB.

T h i s c o n s t i t u te s t h e b u l k o f th e m i n e d s p e l e o t h e m f r o m t h e si te a n d

p r o b a b l y r e p r e s e n t e d m o s t o f t h e d e p o s i t i o n w i t h i n t h e i n te r i o r o f t h e c a v er n b e f o r e

i t becam e unroofed . L ayer s o f 1B a re seen to s lope s t eep ly a t f i r s t and then to l i e

s u b h o r i z o n t a l l y i n a n d u n d e r t h e C l a s s i c s e c t i o n e s p e c i a l l y a r o u n d t h e e x c a v a t e d

c a v e r n t o w a r d t h e e n t r a n c e l a b e l l e d t h e ' A n c i e n t O r i g i n a l E n t r a n c e ' . U n d e r c u t s o f

s ta lagm it ic bosses are seen in the roof . 1B is a l ight buff to whi te ca lc i te wi th th ick enin g



MAKA PANSGAT AUSTR ALOPITHEC INE SITE 67

Fig. 5. Mammillary speleothems (Member 1A) from the underground workings, viewed

from below looking upwards. These forms are abou t 200-300 mm in diameter.

intercala ted series of layers of bro wn and red-b row n sediment . Occas io nal ly the ca lc i te

i s coloured by this fine sediment . In the roof , w i thin a few met res of the 'Anc ient

Or iginal Ent rance ' , both precipi ta ted and c las t ic layer ing i s hor izonta l , and there

are several generat ions of negat ives of mu d cracks , w i th varying s izes of m ud crack

polygons (Fig. 7) .

The formation of lB in the Classic Area.

The presence o f mic rogo ur s ( small ~ 10 mm

rimston e pools) , col lapsed layers of ca lci te , and sheet f lows that th icken tow ard the

quar ry , demons t r a t e t ha t 1B was fo rmed subae r i a l l y f rom major f eed sources nea r

the quarry. As in other l imestone caves , these s ta lagmi t ic f lowtones were suppl ied

by carbonate r ich feedwater f rom f i ssures in the former roof . The fact that there

are thickening intercala t ions of layers of f ine c las t ic sedim ent suggests that an

ent rance was a l so opening up in the quarry area a t th i s t ime by progress ive roof

collapse.



68 A. G. LATHAM ET AL.

Fig. 6 . M am mil lary speleothem of 1A, with staining between layers, overlain by 1B, benea th

the Classic Section.

Fig. 7 . Mud-crack polygons in several layers, near the top of Member 1B, in the 'Ancient

Original Entrance ' .



MAKAPANSGAT AUSTRALOPITHECINE SITE 69

A ccord ing to P a r t r idge (1975) a l a rge s t a l agm i t i c boss occup ied the qua r ry a rea ,

be fo re i t w as r em oved by the l im ew orker s , and i t i s t he low er s lop ing 1B f low s o f

t h is w h i c h a r e s ti ll e x t a n t i n t h e q u a r r y a r e a o u t t o t h e ' A n c i e n t O r i g i n a l E n t r a n c e ' .

Member 1A and B in the East Section.

In the eas t sec t ion the re a re tw o 2 .5 -3 m h igh

p i l l a rs o f ca l c it e l ef t by the m ine r s a s sup por t s fo r M em be r 2 . T he base o f t he ou te r

p i l la r s it s o n t h e d o l o m i t e . G r e a t q u a n t i t ie s o f b o t h 1 A a n d 1 B w e r e r e m o v e d f r o m

th i s a rea by the m ine r s . T he sequence i s : 1A , show ing a ragon i t e and ca l c i t e m am m i l -

l a r y f o r m s , u p t o a b o u t l m o r m o r e i n t h ic k n e s s , fo l l o w e d b y u p t o s e v e ra l m e t r e s o f

1 B w h i c h b e c o m e s i n c r e a s in g l y c o n t a m i n a t e d w i t h f in e s e d im e n t . A b o v e t h e s e c o n d

p i l l a r, ano the r c on t r ib u to r t o im pur i t i e s i n the ca l c it e is a 1 m th i ck l aye r o f b lue to

b l u e - w h it e c o l l o p h a n e , m o s t o f i t c r u m b l y . E v i d e n t l y t h is a r e a a c t e d a s a b a t r o o s t

fo r a w hil e (H i ll & F or t i 1986 ; P a r t r id ge 1975). B ack to w a rd the cen t r e o f t he

cavern these 1B depos i t s g ive w ay to the b recc ia o f t he m idd le sec t ion .

The formation o f l B in the East Section. A s in the C lass i c S ec t ion , 1B s t a l agm i te w as

d e p o s i t e d i n t o s o m e k i n d o f b a s i n in s u c h a w a y t h a t w h a t e v e r t h e o r i gi n a l d e p o s i-

t i ona l su r face , t he f ina l su r face w as subhor i zon ta l nea r t he cave rn w a l l s . D epos i t i on

ceased a ro un d the m arg in s o f t he cav i t ie s so these low er r ecesses t end to have on ly 1A

form s .

T he ex tens ive excava t io ns o f t he m ine r s and the nega t ives o f f low s tone l aye r ing , l e f t

a s an im pr in t on the b recc ias , sugges t t ha t m ass ive f low s tone ex i s t ed in a rough ly

h o r s e s h o e - s h a p e d a r c s t r e t c h i n g f r o m t h e E n t r a n c e t o t h e E x i t Q u a r r i e s . I n p l a c e s

th i s m ass ive f low s tone w as in con tac t w i th the w a l l and w as cem ented to i t . T h i s

f o r m e d a b a r r i e r b e y o n d w h i c h s e d i m e n t c o u l d n o t p a s s . O n e n o t a b l e l o c a t i o n i s

u n d e r t h e r o o f o f th e M a i n Q u a r r y a n d i t a c c o u n t s f o r t h e s o u t h e r n l i m it o f t h e C l as s i c

Sect ion.

Member 2

Member 2 in the Classic Section. T h e f in e s e d i m e n t s o f M e m b e r 2 be g i n to d o m i n a t e

o v e r d e p o s i t i o n o f M e m b e r 1 B f l o w s to n e l a y e rs a n d , d e p e n d i n g o n t h e e x a c t lo c a t i o n ,

t h is o c c u r s o v e r t e n s o f c e n ti m e t r e s t o m e t re s . T e n t o t w e n t y m e t r e s f u r t h e r a w a y f r o m

t h e e n t r a n c e, t o w a r d t h e i n te r i o r o f t h e c av e , t h e s e d i m e n t w a s d e p o s i t e d h o r i z o n t a l l y

a g a i n s t M e m b e r 1 B f l o w s to n e w h e r e t h e l a t t e r w a s d e p o s i t e d v e r t ic a l ly . A t t h a t

l o c a li ty , M e m b e r 2 c o n s is t s o f a l m o s t 5 m e t r e s o f t h i n l y d e p o s i t e d l a y e r s o f p u r p l e ,

r e d - b r o w n a n d r e d - y e l lo w c l a y s a n d s il ts w i th o c c a s i o n a l t h i n p a r t i n g s o f c al c it e

( P a r t r id g e 1 97 9) . I t c o n t a i n s f r a g m e n t s o f b o n e a n d b r o k e n s p e l e o th e m s .

Origin of Member 2 in the Classic Section (F ig. 8 ). T he sed im en t is co l luv ium de r ived

f r o m t h e s u r fa c e a n d w a s w a s h e d i n t h r o u g h a n e n t r a n c e t h a t w a s p r o b a b l y c a u s e d b y

c o n t i n u i n g r e t r e a t o f t h e s ur f ac e . R a y n e r et al. ( 1 9 9 3 ) s u p p o s e d t h a t t h e s e d i m e n t s

w e r e l a i d d o w n i n s t a n d i n g w a t e r . I t i s n o t n e c e s s a r y t o i n v o k e a w a t e r - t a b l e o r

s t a n d i n g w a t e r t o e x p l a i n e i t h e r t h e s e d i m e n t s o r t h e i r t e x t u r e s . F r o m t h e p r e s e n c e

o f t he m u d c r a c k p o l y g o n s a n d t h i n c a lc i te p a r t i n g s , t h e s i m p l e r e x p l a n a t i o n i s t h a t

p o o l s c a u s e d b y r a i n e v e n t s s i m p l y d r i e d u p .

Member 2 in the Exit Quarry. I n t h e a r e a o f t h e c o l u m n s , c l a st i c i m p u r i t ie s o c c u r

w i th in the ca l c i te s a t i n t e rva l s o f t ens o f cen t im e t res . T hese a re o ve r l a in in pa r t by



70 A. G. LAT HAM ET AL.

Fig. 8. Member 2 in the Classic Section. The ladder is resting on dolomite bedrock (seen to

the left of the ladder); at the b ase is Mem ber 1A with a vertical remna nt of 1B attache d to

the sediments. The person is at the level of Member 3 and above that is the dolomite cave

roof. The region between the deposits and the camera position is inferred to be mined

speleothem, Member lB.

a b o u t 2 m o f M e m b e r 2 r e d s e d i m e n t s. I n t h e r o o f , t h e c a lc i te s g i ve w a y t o i n d u r a t e d

p i n k i s h c l a s t i c s e d i m e n t s a n d f i n a l l y , t h e b r e c c i a s . T h i s i s a p p r o x i m a t e l y t h e s a m e

s e q u e n ce a s i n t h e C l a ss i c S e c t io n t h o u g h w i t h o u t M e m b e r 3. T h e r o o f is a c t u a l l y

e x c a v a t e d b r e c c ia i n t h e n o r t h w e s t a n d d o l o m i t e i n t h e e as t . B e h i n d a n d b e l o w t h e

c o l u m n s , t h e r e a r e t w o r e c e s s e s ; o n e w i t h n o r e d s e d i m e n t s a n d o n e p a c k e d w i t h

t h e m . E v i d e n t l y t h e s p e l e o t h e m b a r r i e r t o f l o o d - l a i n c l as t ic s w a s i n c o m p l e t e f o r t he

la t te r .

Member 3

F r o m t h e L i m e w o r k s d u m p s , Australopithecus is m a i n l y r e p r e s e n t e d i n M e m b e r 3.

T h i s i s a 1 m t h i c k g r e y to w h i t e f l o w s t o n e w i t h a d e n s e a c c u m u l a t i o n o f b o n e s a n d



MAKAPAN SGAT AUSTRALO PITHECI NE SITE 71

i t l ies directly on top of Member 2 in the Classic Section (Fig. 8). Member 3 is again

visib le in the overhan ging dolomite ro of in ano ther exposure abo ut 10-15 m etres

fur ther in, am on g brok en s ta lac t i tes , and where long bo nes a re v is ib le. I t is traceable

aga ins t the d ippin g dolomite r oo f to abo ut 1 /4 way rou nd the cone to the southwes t .

There i s a 1 m th ick s ta lagmit ic depos i t conta in ing la rge bones on the unders ide of

a bulge a t the back of the Cone but i t appears to l ie s t ra t igraphica l ly be low the

c las t ic sediments . Member 3 i s apparent ly absent f rom the Cone round to the Exi t

Quarry .

In the Class ic Sec t ion , Me mb er 3 was depos i ted outs ide the a rc o f mass ive speleo-

t h e m . A c c o r d i n g t o M c F a d d e n

et al.

(1979), t he Mem ber 2 -M em be r 3 con tac t is

unconfo rmab le , bu t confo rmab le acco rd ing to Magu i re et al. (1985) . Member 3

shows sublayers wh ich a l te rna te wi th ver t ical s ta lagmit ic wal l draper ies, as judg ed

by abutment re la t ionships .

The form er extent of the whole layer in the a rea be tween the Classic Sec t ion to the

Cone , before the l imew orkers underm ined and rem oved i t , i s unk now n, but the exist -

ing remnan t s r ep re s ent an a rea o f ve ry dense bone accumula t ion and concen t ra t ion .

Fro m the d i st inc t ive damage to bone f ragmen t s , Mag u i re et al. (1980) conc luded th a t

the bones der ive large ly f rom hy ena ac t iv ity and, judgin g by the s loping d ispos i t ion of

all the deposits in this area, i t is very l ikely that the bones may have rolled into the

recesses f rom dens nea rby and h igher up . A l te rna tive ly , s ince the layer a lso conta ins

brok en spe leothem s and sand gra ins , flowing water has a lso been invok ed as an agent

to concentra te the bones aga ins t the wal l and roof (Bra in 1958; Par t r idge 1979;

M a g u i r e et al. 1980). This is not easy to reconcile against the observation that the

enc los ing matr ix of the grey brecc ia throughout i s ca lc i t ic , cons is t ing of th in (a few

mm to severa l cm) layers of f lowstone , which is a low-energy water depos i t . In

hand sample , the th in ca lc i te layers a re separa ted by a i r pocke ts showing tha t some

layers formed as th in ra f ts on the tops of smal l gour pools . This k ind of format ion

is common in many caves and is a lways formed by s low f lowing carbonate-r ich

water . Thus , in comparison wi th such fea tures in o ther caves , i t i s more l ike ly tha t

th is a rea was per iodica l ly , perhaps seasonal ly , wet ted , as water seeped down the

wal ls and a lo ng the hor izonta l subs t ra te of M em ber 2 . The p rec ip i ta t ion of ca lci te

would form horizonta l layers wi th in the bones . Toward the ent rance , the uppermos t

layers of M em ber 2 and M em ber 3 abut aga ins t ver tica l s ta lagmit ic f lows and wal l

p i l la rs (ha l f -p i l la rs ) which a re occas iona l ly seen to be cont inu ous wi th the h or izonta l

layering , and severa l genera t ions a re represented . Par t r idge (1979) tended to d iscount

hyena ac t iv ity as an agent for conc entra t ing the bone so c lose ly aga ins t the roof , pre -

fe rr ing ac t iv i ty by f loods . However , near the Cone , the mass ive spe leothem columns

would have p rov ided a rap id change in g rad ien t down which bones migh t have ro l l ed

to l ie finally underneath the roof.

M e m b e r 4

The breccias.

The mine rs ' dum ps s how tha t bone rema ins a l s o came f rom the lower

breccias and

Austra lopi thecus

is represented. The breccias , originally subdivided by

Par t r idge (1979) in to m emb ers 4 and 5 , a re now a l l ass igned to mem ber 4 (Par t ridge ,

pers. comm .) . Th e brecc ias a re coarse p ink to red , conta in ing smal l to la rge c las ts of

dolom ite and de tached f lowstone . On the eas t s ide of the Cone mo uth , the c lasts a re

rounded cobbles whi le , on the wes t s ide and toward the top , the sequence cons is ts of



72 A. G. LAT HA M E T A L .

Fig. 9. The lower west side of the Cone mouth and eroded parts of Member 1B, the under-

side of which has been mined out. M emb er 4 breccia lies above.

b o t h i n d u r a t e d a n d u n c e m e n t e d s t ra t if i e d c l a st - fr e e r e d s e d i m e n ts . T h u s t h e d ep o s i t s

va r y l a t e ra l ly f rom brecc ias to c l a s t - fr ee equ iva len t s . T he c l a s t- f r ee zones im ply

d e p o s i t i o n u n d e r a r o o f. P a r t s o f th e s e la y e r s ar e c e m e n t e d b y c a r b o n a t e w h e r e a s,

a fe w m e t r e s f u r t h e r r o u n d , t h e s e d i m e n t s ar e u n c o n s o l i d a t e d . A r o u n d t h e L i m e w o r k s

s i te , t r ee roo t s have the e f f ect o f deca lc i fy ing indura t ed b recc ia bu t t he e f fec t i s

r e s t r i c t ed to the a rea o f t he roo t s ; t hese a re r e fe rr ed to loca l ly a s 'm eko ndo s ' . I n

t h e C o n e m o u t h , h o w e v e r , t h e u n c o n s o l i d a t e d s t r a t a w e r e p r o b a b l y n e v e r c e m e n t e d .

A s y e t it is n o t k n o w n w h a t t h e di ff e re n c e t h e c e m e n t a t i o n m a k e s t o a p a l a e o m a g n e t i c

r e c or d ; m o s t o f th e s a m p l es o f M c F a d d e n e t a l . (1979) have been t aken f rom cem en-

t ed sed im ent s .

I n t h e C o n e m o u t h , s e p a r a t e d b l o c k s o f m a s s i v e f l o w s to n e i n t h e lo w e r p a r t o f t h e

brecc ia exh ib i t t runca ted g row th l aye r ing , i nd ica t ing tha t t hey w ere pa r t i a l ly d i s -

so lved be fo re be ing enc losed in the b recc ia (F ig . 9 ) . T h i s occur rence w as a l so no ted

b y M a g u i r e

e t a l .

(1985).

T h e w h o l e o f th e a r e a b e t w e e n t h e t w o q u a r r i e s c o n s i st s o f b r ec c ia . I n t h e E n t r a n c e

Q u a r r y , t h e b r e c c i a p r e s e n t s 1 2 m o r m o r e o f a n e g a t i v e i m p r e s s i o n o f t h e f o r m e r

f tow s tones aga ins t w hich i t abu t t ed , and the b recc ia r e s t s on d o lom i te . A sm al l sec t ion

of b recc ia , r e fe r r ed to a s t he P a r t r idge B lock , can a l so be foun d to the w es t o f t he

M a i n Q u a r r y b e t w e e n i t a n d t h e E n t r a n c e Q u a r r y . I n o n e o r t w o p l a c e s s o m e o f

the subver t i ca l f l ow s tone shee t s a re s t i l l v i s ib l e (F ig . 10) . T he g round be tw een the

E n t r a n c e Q u a r r y t o t h e ' A n c i e n t O r i g i n a l E n t r a n c e ' i s a d o l o m i t e ' b r i d g e ' w h i c h ,

on the su r face , s t eps dow n to b recc ia ove r ly ing f low s tones and c l a s ti c s o f Mem ber s

1 and 2 . A p ar t f ro m th i s occur rence , m os t o f t he b recc ia w as depos i t ed ins ide the

a r c o f t h e m a s s i v e s p e l e o t h e m d e p o s it s .



MAKAPANSG AT AUSTRAL OPITHEC INE SITE 73

Fig. 10. The East Quarry wall showing the negative impression of the flowstone on the

breccia, Member 4. The clasts in the breccia can clearly be seen above one extant flowstone

layer. The space between the breccia and the camera posit ion was probably occupied by

massive flowstone.

M e m b e r 4 a t R o d e n t C o r ne r .

P a r t w a y a l o n g t h e Ex i t Q u a r r y , i n a n o p e n a r e a k n o w n a s

R o den t C orn e r , i s a shor t t unne l o f abo u t 2 m in he igh t (F ig . 4 ) w hich has been c rea t ed

by m in ing . P a r t r idge (1979) a sc r ibed i t s cem ent - indura t ed r ed m uds and sands to

M e m b e r 4 a n d , a s su c h , i t w a s s a m p l e d f o r p a l a e o m a g n e t i s m a s a n a i d to c o m p l e t i n g

the m agne to s t r a t ig rap h ic sequence . T he sed im ent s con ta in ing rod en t bone s a re s i t ua t ed

abo ve the rhy thm i te s and a re p rob ab ly w i tness to ow l roos ts . T he rhy thm i te s w ere la t e r

s tud ied by T u rne r (1980) w ho be l ieved tha t t he 2 m of cem ented sands , s i lt s and c l ays

w as an en t i ty sepa ra t e f rom the C lass i c S ec t ion . H e found tha t t he sequence w as m ade

up o f abou t 45 cyc les , each abo u t 30- 40 m m th ick , o f coa r se sands , fi n ing upw ards to

sands w i th m u dcra cke d su r faces . A b ou t tw o- th i rds o f t he w ay up the sequence , t he

rhy thm i tes a re in t e r ru p ted by tw o th in f low s tone l aye r s (he r e fer s to th i s a s ' l im es tone ' ,

bu t t h i s is i ncor rec t) , t he uppe r one c on ta in ing cave pea rl s , and a l aye r o f coa r se sand

w i th g ranu la r cong lom era te . T he d i f f e ren t pa l aeom agne t i c d i r ec t ions o f sequen t i a l



74 A. G. LA TH AM

ET AL.

rhythmi tes suggested, somewhat surpr i s ingly, that they were not annual . From

Turner 's f igures, each cycle appears to represent about a thousand years. The signif i-

cance of this apparen t ly long per iodic i ty i s not known .

The f lowstone layers and owl roosts indicate th at there was s ti ll a roof extant a t th is

t ime. This is a l so born e out by the presence o f cave pear ls as these are kn ow n to form

only by the dr ip-water agi ta t ion of seed-grains (e .g . of sand par t ic les) and by thei r

concentric growth in pools (e.g. Ford & Will iams 1989). I t can be clearly seen, in

the Rodent Corner arch, that the spaces between calc i t ic roof layers and s ta lac t i tes

are f il led with the f ine, red, sand y mud s. Prece ding b ot h of these, appare ntly, is brec-

c ia Me mb er 4 and i t seems l ikely that the rhythmi tes were winnow ed out of the breccia

through the large col lapsed blocks seen a t the edge of M4 in the Exi t Quarry (behind

the person in the f igure) . Thus i f the rhythm i tes are the resul t of winn owing of the

eas tern extent of M4, i t i s uncer ta in how they f i t in the s t ra t igraphy wi th respect to

M4 in the Main Quarry and wi th sediments in the Class ic Sect ion.

The palaeomagnetism of breccias

Unpub l i shed pa l aeomagn e t i c w ork ca r r i ed ou t on borecores f rom the b recc i as a t the

Sterkfonte in Aust ra lopi thecine s i te by V: Schmidt show that sequent ia l ly cored sam-

ples gave near - random or ienta t ions mainly due to the fac t that samples conta ined

rol led det ri ta l t i t anom agne t i te gra ins . They have not yie lded any mean ingful sequence

for magne tos t r a t i g raph i c work . Genera l l y , t he p rob l ems fo r t he pa l aeomagne t i sm of

breccias are that ( i ) most breccias consis t of a var ie ty of randomly or iented par t ic les

and clasts, each one having i ts own magnetic signal , ( i i ) the i ron-rich matrix gives a

signal which may be related to mechanical effects, such as f ine-part icle rol l ing,

ra the r than to the inf luence of the am bient mag net ic f ie ld and ( ii i) i f l a ter , i ron-

r ich, cement i s involved in diagenesis , then there may be a pos t -deposi t ional s ignal

which corres pond s to a time af ter deposi t ion of the breccia. The ques t ion of whether

meaningful s ignals can be recovered f rom breccias , such as those a t the Limeworks

Cave, can only be answered by more ex haust ive s tudies that a im to e l iminate or mini -

mize t he above p rob lems . The wo rk o f M c F ad den e t a l . (1979) and our own pre l imin-

ary work shows that magnet ica l ly c leaned palaeomagnet ic di rect ions can be obta ined

from these deposi t s . As i s usual (Latham e t a l . 1989) , the purer speleothem samples

are magnet ica l ly weaker

Discussion

Massive subaer ia l speleothem is forming in many t ropical caves today. The main fac-

tors are high temp eratu re a nd hum idi ty , an d fas t speleothem deposi t ion i s the no rm

(e.g. Ford & Will iams 1989). Therefore, does the massive speleothem in the Lime-

works Cave bear wi tness to a much wet ter c l imate a t the t ime? Al though the ques t ion

of pa l aeoc l ima te and pa l aeoeco logy has p reoccupied ma ny r esearche rs work ing a t

Ma kap ans gat , we draw at ten t ion to the possibi li ty of infer r ing a mo re hu mid ear l ier

c l imate by the exis tence of such huge quant i t ies of subaer ia l f lowstone.

On the sur face above the cave there i s are areas of dolomi te s t r ipped of vegeta t ion

for research purposes (F ig. 2) . The area shows numerous solut ion holes and hol lows,

up to a few met res deep, occupied e i ther by hardened red breccia or by shrubs an d t rees

wi th soil . Thus , i t i s easy to see how seepage water used this kind of pathwa y to form





76 A.G . LATHAM ET AL.

R o d e n t C o r n e r w e r e p r o b a b l y w i n n o w e d o u t f r o m t h e m . I n t h e M a i n Q u a r r y , d e po s i-

t i o n a l s o o c c u r r e d o n t h e o u t s i d e o f th e a r c b e t w e e n t h e c al c it e f o r m a t i o n s a n d t h e

' A n c i e n t O r i g i n a l E n t r a n c e ' a n d d o l o m i t e w a l ls . L a t e r , w h e n t h e r o o f r e c ed e d f u r t h e r

u p s l o p e t h e c la s ti c s e d i m e n ts w e r e e n t r a i n e d a s a l l u v i u m a n d c o l l u v i u m i n t o t h e C o n e

a r e a . F r o m o n e lo c a l b a s i n t o th e n ex t , t h e r e fo r e , c o n t e m p o r a n e o u s , d i a c h r o n o u s a n d

s e q u e n t ia l d e p o s i t i o n c a n b e e n t e r t a i n e d a s p o s s ib i li t ie s f o r s e d i m e n t a r y m e m b e r s a n d

sub-m em b ers . A re t r ea t ing en t r an ce fo r c l a s t i c i n fi ll fo rces the poss ib i l i t y o f a com plex

s e q u e n ce s t r a t i g r a p h y . T h e g r e y b o n e b r e c c ia i s a s p a t ia l l y l i m i te d d e p o s i t p a r t w a y

t h r o u g h t h e o v e r a l l s e qu e n c e .

C a l c it e p i lo t s a m p l e s f r o m t h e e x it q u a r r y a n d f r o m M e m b e r 3 i n t h e C l a ss ic s e c ti o n

ca r ry a w eak bu t m easurab le , s t ab le , m agne t i c s igna l . T h i s suppor t s t he f ind ings o f

M c F a d d e n

et al.

(1979) tha t m os t o f t he cal c i te s a re access ib l e to pa l aeom agn e t i c

a n a l y s i s f o r r e v e r s a l s t r a t i g r a p h y . O n e c o r e s a m p l e f r o m M e m b e r 3 s h o w s a n i n t e r -

m edia t e d i r ec t ion (D . H es lop , pe r s . com m . 1998) and th i s d i sagrees w i th the con jec -

t ur e o f M c F a d d e n et al. ( 1 9 7 9 ) w h o r e c k o n e d t h a t i t m i g h t b e n o r m a l . T h i s a g a i n

p o i n t s t o t h e n e c e s s it y f o r f u r t h e r p a l a e o m a g n e t i c s a m p l in g . T h e i n t e ri o r E x i t

Q uar ry ca l c i t e sequence cou ld be used to augm ent the r ecord s ince , l i ke C lass i c

S ec t ion Mem be r 1B, i t ove r l ie s 1A w i th ou t a b reak . T he m o s t p rom is ing sec t ion

a p p e a r s t o b e i n th e s o u t h o f t h e C o n e w h e r e , a p a r t f r o m t h e p o s s ib l e a b se n c e o f

M e m b e r 3 , d e p o s i t i o n a p p e a r s t o b e c o m p l e t e f r o m M e m b e r 1 t o t h e t o p o f t h e b r e c -

c ia s . I n t he M a i n Q u a r r y , i t m a y b e p o s s ib l e t o c o n n e c t t h e s a m p l i n g d i r e c t ly fr o m

M e m b e r s 2 a n d 3 t o M e m b e r 4 o f t h e ' P a r t r i d g e B l o c k '. U n f o r t u n a t e l y , t h e o v e r -

hang ing na tu re o f a l l t hese exposures m eans tha t sam pl ing w i l l be d i f f i cu l t .

The Brit ish Academ y a n d the Universi ty of Liverpool supported this work. P. Quinney

acknowledges support from the NERC (UK). R. Cliff , supported by NERC, carried out

U-Pb analyses at Leeds. D. Heslop carried out pilot magnetic studies, at the Liverpool

Geomagnetic Laboratory, on a small set of samples from the Limeworks Cave. We acknowl-

edge permission to sample through the University of Witwatersrand and the Bernard Price

Insti tute, Johannesburg. Collaboration init iated by T. C. Partr idge of the Transvaal

Museum, Pretoria on reversal strat igraphy using samples taken from long cores from the

Limeworks si te is now ongoing and we thank both him and Judy Maguire for al l kinds of

assistance and discussion.

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BIRCHALL,

T. 1989. Secular variation from

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Makapansgat Limeworks Australopithecine si te : some matters aris ing.

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Geological Survey of South Africa, 19, 37-51.

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the Makapansgat Limeworks and Sterkfontein Hominid Sites: a progress report on research

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site of Sterkfontein, South A frica.

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26, 175-181.

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Limeworks. Palaeontologia Africana, 23, 51-58.

VRBA, E. S. 1982. Biostrat igra phy and chronology, ba sed part icularly on Bovidae of southern

hominid-assoc ia ted assemblages : Makap ansga t , S te rkfon tein , Taung , Krom draa i ,

Swar tkrans and a lso E landsfon te in Sa ldanha , Broken Hi l l (Kabwe) and Cave of Hear ths.

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707-752.

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G. H., PARTRIDGE, T. C. & BUCKLE, L. H. (eds) Palaeoclimate and Evolution, with

Emphasis on Human Origins.

Yale U niversi ty Press, Yale, 24-45.

WELLS, L. H . t~r COOKE, H . B. S. 1956 . Foss i l Bovidae f rom the L imeworks Q uarry , M aka-

pansgat , Potgietersrus. Palaeontologia Africana, 4, 1-56.

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Limeworks: an Australopithecine si te . Journal of Human Evolution, 25, 337-350.



Testing the potential of soil-stratigraphic

palynology in podsols

R I C H A R D T I P P I N G 1, D E B O R A H L O N G 1,

S T E P H E N C A R T E R 2, D O N A L D D A V I D S O N l ,

A N D R E W T Y L E R 1 & B R I A N B O A G 3

1Dep artment of Env ironm ental Science, University o f Stirling,

Stirling FK9 4LA, UK

2Headland Archaeology, Albion Business Centre,

78 Albion Road, Edinburgh EH7 5QZ, UK

3 Scott ish Crop Research In stitute, Invergowrie,

Dundee DD2 5DA, UK

Abstract: Pedological, palynological, soil-micromorphological, geochemical and

soil-faunal dat a are presented for a weakly developed free-draining ferric podsol

soil profile in which three securely dated, known-age inputs (non-native tree

pollen, sphe roidal c arbon aceo us particles, 137Cs) have been ad ded to the soil

surface and inco rpor ated over the last c. 150 years, from c. 1840AD. We can

thus observe the mechanisms o f particle incorporatio n over time-spans approp ri-

ate to those ofpedogenic processes, and analyse the rates, depth, extent and signifi-

cance of mixing processes in a soil type tha t has o ften been seen as providin g secure

stratigraphic contexts for subfossil pollen analysis.

Our data indicate that pollen and other particles are thoroughly and comple-

tely mixed within the L/F horizon of podsols. Mixing occurs predominantly by

ingestion and bioturbation by large near-surface feeding invertebrates. Mixing

is also very rapid. Transfer of pollen to lower organic horizons occurs through

the liberation of pollen as large invertebrate excrement is itself ingested by

enchytraeid populations, but bioturbation in these lower horizons is insufficient

to move further the already-mixed pollen assemblages. The absence of earth-

worm populations in these acid soils means that subsequent vertical transfer to

mineral horizons does not occur in any significant way. This ability of organic

horizons in podsols to store pollen, the complete mixing of particles in near-

surface horizons, and the prolonged time-spans over which these mixing pro-

cesses can operate, indicate that resultant pollen stratigraphies are no rmally

probably too coarse in temporal resolution to be of value in palaeoecological

interpretation.

Po l l e n c on t a i ne d w i t h i n so i ls bu r i e d be n e a t h a r c ha e o l og i c a l s it es is w i de l y u se d a s a

sou r c e o f pa l a e oe c o l og i c a l i n f o r ma t i on ( D i m b l e b y 1985) . E f f e c ti ve l y s e a le d f r om

l a t er c o n t a m i n a n t s b y th e c o n s t ru c t i o n o f a r c h a e o l o g ic a l m o n u m e n t s , p o l le n a s s e m -

b l a ge s w i t h i n suc h so i l s a r e a r gue d t o r e t a i n e v i de nc e f o r ve ge t a t i on c ove r a nd l a nd

use s i mme d i a t e l y p r i o r t o bu r i a l ( e . g . Ca spa r i e & Gr oe nma n va n Wa a t e r i nge 1980 ;

Ande r se n 1992 ; T i pp i ng

et al.

1994) . The use of po l len assem blages wi th in so i l s to

r e c ons t r uc t ve ge t a t i on h i s t o r i e s ove r t i me ( D i mb l e by 1957 ; 1961 , 1985 ) , r a t he r t ha n

s i mp l y t he ' s na p sho t ' p r e - bu r i a l a pp r o a c h , ha s be e n mor e c on t r ove r s i a l s inc e m a n y

From.

POLLARD, A. M. (ed.) 1999 .

Geoarchaeology. exploration, environments, resources.

Geo logica l Society, Lon don , Special Publi cation s, 165, 79-90 . 1-86239-053-3/99/$15.00




80 R. TIP PIN G E T A L .

soils are biologically act ive, and the reten t ion of strat igraph ical ly interpreta ble da ta is

thus quest ioned (Godw in 1958; Ha vinga 1967) .

The organic surface (mot) horizons of podsol profi les have long been viewed as

providing the most secure s t rat igraphies f rom which to obtain long- term vegetat ion

his tor ies from soil s (Dimbleby 1962; Hav inga 1968; M un au t

e t a l .

1968; Iversen

1969; Smi th & T aylor 1969; O'Sul l ivan 1973; Stoc km arr 1975; Ande rsen 1979;

Cruick shank & Cruicks hank 1981; Aa by 1990; Di jkst ra & van M ou rik 1995) . The

limited numbers of soi l organisms in these acid soi ls leads to the assumption that

' the fossil m or layer has ac cum ulated l ike peat or g ytt ja ' (Iversen 1969: 39), mo re

conventional sediment-types for pollen analysis, and thus i t retains strat igraphic

integrity.

There are difficul t ies in this assumption, however. Podsols derive from more bio-

logical ly act ive soi ls with mull organic horizons, and the extent to which the mineral

hor izons of podsols retain an imprint of b io logical ly mixed pol len assemblages has

been deba ted (Munau t e t a l . 1968; Iversen 1969; Hav inga 1974) . Mo re important ly ,

mot format ion may not resul t in pol len-s t rat igraphic resolut ions that are any more

than very coarse (e .g . capable of temporal resolut ion at centur ial or poorer resolu-

t ions). Th e deve lopm ent of a ' fossil ' mor (Iversen 1969; Sto ckm arr 1975) is gradual ,

occurr ing over centur ies (Aaby 1990) and passes throu gh s tages in which rates of

biological act ivity are slowly reduce d (Ken drick 1959 ; O'S ull ivan 1973). Early

stages of m ot form ation are charac terized by biological act ivity, part icularly at the

soi l surface where ar thropods d igest l i t t er and mix organic mat ter (Stockmarr

1975) . Deeper and more advanced s tages are character ized by enchyt raeid and

fungal organic matter decomposit ion (Andersen 1979), and i t is here that vert ical

mixing of materials is reduced. A cri t ical issue is, then, to determ ine over wha t dura-

t ion mixing processes in early mor formation occurs.

In 1995 a project comm ence d to establ ish whe ther a range o f curre ntly forming soi l

types, commonly found preserved beneath archaeological monuments , retain

interpretable pollen strat igraphies. One of these soi l types is a podsol . The project

combined the appl icat ion of both f ine-resolut ion palynological and soi l -micromor-

phological techniques (Tipping

e t a l .

1994). In part ic ular, the project was able to

monitor over long t ime-periods ( the last c. 150 years) the deposi t ion, incorporat ion,

processes of movement , degree of mixing and extent of dest ruct ion of known-age

'mar ker ' pol len grains and other dated com ponents in these soils . Othe r publ icat ions

discuss in detai l our f ield site in southe rn S cotland, o ur m ethod olog y and the ways in

which we establ i sh the known age of our 'markers ' (Tipping

e t a l .

1997), the recent

ecological and agrarian history of the f ield si te, cri t ical to pedological change

(Car ter

e t a l .

1997), and discussion of the processes of pollen inco rpora t ion observed

through soi l -micromorphology (Davidson e t a l . 1999). Details of the palynological

techniques are found in Long

e t a l .

(in press). We will discuss elsewhere the rates of

sediment/pollen mixing in al l the soi ls examined and the important processes of

pollen deteriorat ion and destruct ion in podsols and other soi ls.

The f ie ld s i te and methods

The upland rough pasture of Lour l ies in the upper Tweed val ley in southern

Scotland, just south of Peebles (Fig. 1). The treeless grazed gr ass- hea th l ies c. 1 km

downwind of Scot land 's o ldest arboretum at Dawyck (Bown 1992) , which i s the



SOIL STRATIG RAPHIC PALY NOLOG Y IN PODSOLS 81

Fig. 1. (a) The location of Lour in southern Scotland and (b) the site-setting of profile 7 (P7)

outside the agricultural remains mapped by Carter et al. (1997). The location of the Lour

Peat Profile (LP) is also shown.

source fo r mu ch of t he known-age non-na t i ve t ree po l len be ing i ncorpora t ed i n to t he

soil s a t Lo ur (Tipping

et al .

1997). Three dated inputs to the soi ls are examined. N on -

nat ive t ree pollen (Coniferales, F a g u s , P i n u s [not nat ive in southern Scot land] and

U l m u s

[nat ive bu t largely regionally ext inct b efore 18th centur y AD planting];

T ipp ing et al . 1997) was deposi ted on the hi l lside at Lour from c. 1840AD and





SOIL-STRATIGRAPHIC PALYNOLOGY IN PODSOLS

Table 1. Field description of the soil profile at Lour 7

83

LOU R 7: PODSOL

EXC AVA TED 19TH OCT OBE R 1994

FIELD SAMPLED 19/20/25TH OCTOBER 1994

Profile description

0.0-4.0 cm

L/ F

4.0-10 .0cm

H

10.0-16.0 cm

E

16.0-16.5 cm

B(f)

16.5-25.0 cm

B

25.0-41.0 cm

Bs

41.0-45.0 cm +

B(x)

moist fine fibrous poorly, humified peat, clear smooth boundary to

: 5 YR2.5/1 black loamy well-humified fine fibrous peat, increasingly

amorpho us in lower part and leading to organic s taining of upper p art o f

next horizon in basal 2- 3 cm, featuring very weakly developed fine

subangular blocky structure, moist, friable, with man y fine fibrous and few

medium woody

(Calluna)

roots; stoneless, clear wav y (over 2 cm)

boundary to

: 10 YR 4/2 dark greyish brown fine sandy silt loam with very weakly

developed medium angular blocky structure, slightly, moist, friable, with

com mon fine fibrous roots and few small subrou nded Silurian mudstones;

clear wavy (over 4-5 cm) bo undary to

: 7.5 YR 5/6 fine sandy silt loam with very weakly developed m edium

angular blocky structure, slightly moist, friable, with comm on fine fibrous

roots and few small subrounded Silurian mudstones with thin

discontinuous faint to distinct fe-pan or zone of fe-enrichment; broken

boundary to

: 10 YR 5/4 yellowish brown fine sandy, silt loam with weakly developed

fine-medium subang ular b locky structure, slightly moist, friable, with

common fine fibrous roots and common medium subrounded and few

large subrounded Silurian mudstones; gradual wavy (over 2-3 cm)

boundary to

: 10 Y R 6/6 brow nish yellow fine sandy silt loam w ith weakly developed

fine subangular blocky structure, slightly moist, friable, with few fine

fibrous roots and comm on m edium subrounded and few large subrounded

Silurian mudstones; clear wavy (over 2 cm) bou nda ry to

: 10 YR 4/6 dark yellowish brown sandy silt loam with we akly developed

fine-medium platy structure, weakly indurated, with no roots but many

small, many medium and few large subrounded Silurian mudstones.

base not seen

Presentat ion of data and resul t s

The ma ny a nd c ompl e x da t a - s e t s ha ve be e n r e duc e d o r s i mp l i f i e d i n o r de r t o e xa mi ne

t he que s t i on o f s t r a t i g r a ph i c i n t e g r i ty , de g r e e a nd d e p t h o f m i x i ng w i t h i n t he su r f a c e

o r ga n i c ho r i z ons . Ta b l e 1 summ a r i z e s t he fi el d de sc r i p t i on o f the p r of i le . Ta b l e 2

summ a r i z e s t he phys i c a l p r ope r t i e s o f t he soi l: me a n va l ue s o f t he se va r i a b l e s f o r

e a c h ho r i z on a r e p r ese n t e d . F i gu r e 2 p r e se n t s da t a on t he l oc a t i on o f t e t r a d (C a lh m a ,

Erica , Vaccin ium) po l l e n g r a i n s w i t h i n so i l - s t r uc t u r a l c ompone n t s de r i ve d f r om so i l -

mi c r omor pho l og i c a l a na l y s i s ; t he se d i s t i nc t i ve g r a i n s we r e s e e n i n t h i n - s e c t i on u s i ng

a u t o - f l uo r e sc e nc e t e c hn i que s ( Ph i l l i p s 1972 ; Da v i dson et al. 1999) . Thin-sec t ion

de sc r i p t i ons a r e f ound on t he we b - s i t e l i s t e d a bove : t he bounda r i e s be t we e n ho r i z ons

a r e c o m p a r a b l e i n d e p t h a n d c h a r a c t e r b e t w e e n f i e l d a n d s o i l - m i c r o m o r p h o l o g i c a l



84 R . TIP PIN G ET AL.

T ab l e 2 . Physical and soil-faunal data fo r the soil profile at Lo ur 7

Depth pH Organic Di-extractable Mean Part icle Enchytraeids

Horiz on (cm) Con tent (%) Fe Size (gm) per

m 2 *

L/ F 0 -4 2.70 83 0.85 65.10 2500

H 4 -8 2.74 39 1.70 66.93 938

E 8- 19 3.46 10 1.93 54.19 non e recor ded

Bf 19 n.d. n.d. 1.90 n.d. n.d.

Bw 19- 27 3.59 6.5 1.70 57.16 4700

Bw/Bx 27- 31 3.72 5.5 1.87 69.21 none reco rded

Bx 31 + 3.97 2.5 1.28 88.63 non e reco rded

* estimate d from 40 g bulk sa mple an d a ssumin g soil bulk de nsity of 1.25

n.d. not determined

desc r ip t ions excep t t he L /F -H boundary (T ab les 1 , 2 ) . F igure 3 dep ic t s t he f ine -

reso lu t io n s t r a t ig ra ph ic ana lyses o f non -na t iv e po l l en , S C P s and ~ 37Cs con cen t ra t ions

p l o t t e d a g a i n s t d e p t h : s o il h o r i z o n b o u n d a r i e s a r e a l so d e p i c te d . T h e p o l l en d a t a a r e

p r e s e n t e d a s t o t a l c o n c e n t r a t i o n s o f n o n - n a t i v e t re e p o l le n : p e r c e n t a g e v a lu e s o f th e s e

non- na t ive t r ee types a re low because o f t he in f lux o f l oca l he rb po l l en , and th i s

m ea sure i s t he c l ea res t w ay to dep ic t t he dep th o f m ix ing o f t h i s da t ed inpu t . S C P s

3.

4

5

6-

7-

-

E

o 8-

r

~ 9 -

10-

11

12

13

Within mamillate Within undiff.

excrement organic matter

Total no.

On void Between small Within large Within undiff, tetrad

walls ellipsoid excrement ellipsoidal exc rem ent m in er almatter grains

m m

I I

I

I

I

|

BE I

B E

!1

11

m m

88

132

150

37

21

i i ,i , ~ I ~ , i I i i E i

'~0' '4b '2b" '4'0 '6'0' '2'0' '~0' '8'0-~ '2'0' ',~0" 8'0'

% tetrad grains

F i g . 2. T h e l o c a t i o n o f t e t r a d p o l l e n g r a i n s (Ericaceae u n d i f f . ) w i t h i n d i f f e r en t m i c ro -

s t r u c t u r a l e l e m e n t s o f t h e o r g a n i c h o r i z o n s a t L o u r 7 p lo t t e d a g a i n s t d e p t h b e l o w g r o u n d

s u r f ace , i d en t i f i ed f ro m t h i n - s ec t i o n f l u o re s cen ce an a l y s i s .



SOIL-STRATIGRAPHIC PALYNOL OGY IN PODSOLS 85

Fig. 3.

Fine-resolution stratigraphic anal yses of (a) non-native pollen concentrations, (b)

SCP concentrations and (c) 137Cs concentrations plotted against d epth : soil horizon bound-

aries are a lso depicted.

are also depicted as concentrations. 137Csconc entrations are expressed as Becquerels

per kg. Only enchytraeids were identified from faunal samples (Table 2).

pH is throughout the prof i le s t rongly acid, and no evidence for ear thworms was

foun d either from faunal analyses (Table 2) or thin-section identification of excrement

(Lour web-s ite) . L/F and H horizons are highly organic , and from soi l -micromorpho-

logical description (Lour web-site) these comprise organic excrement containing

cellular and amorphous residues. The L/F horizon is s ignificantly richer in recogniz-

able coarse t issue residues (stem, leaf and roo t t issues), an d the H h orizo n h as a mu ch

higher amo rphou s organic compo nent . The crumb /granu lar micro-s t ructure of both

L/ F and H ho rizons is created by invertebrate excrement, principally large ell ipsoids,

wi th consequent high poros i ty. Smal l e l l ipsoid excrement , probably produced by

enchytraeid populat ions , are present in the L/F horizon, but are dominant in the H

and E horizons where they create a micro-aggregate structure. Enchytraeids are

found in faunal analyses throughout the profile (Table 2), al though their rari ty in

Tullgren funnel collections indicates th at est imates o f density per m 2 have large

errors, an d the non -record ing o f enchytraeids in certain horizons has n o significance.

The dis t r ibut ion of te t rad pol len gra ins wi thin s t ructura l components in thin-

sect ion sugges ts that only in the L/F horizon and uppermost par t of the H horizon

is a significant proportion of pollen grains found as free elements on void walls ,

and thus capable of downwashing (Fig. 2) . The high proport ion of such gra ins

above c . 60 mm is probab ly due to the high poros i ty pro duced by faunal excrement.

Nevertheless, the majority of grains are contained within large ell ipsoid excrement,

proba bly from species of Arth rop oda (Stockm arr 1975) . Being conta ined wi thin



8 6 R . T I P P I N G ET AL.

excrement , the pol len gra ins wi th in the t opm ost c. 60 m m are seen to be inges ted by

large inver tebra tes , and a re subjec t to mixing by these animals . These near-surface

la rge inver tebra tes a re , f rom the d is t r ibut ion of la rge e l l ipsoida l excrement , conf ined

to the to pm ost c . 60 m m of the prof ile . Be low 60 mm , w i th in the H hor izon and

minera l hor izons , the proport ions of te t rad gra ins on void wal ls i s very smal l (Fig .

2) . Near ly a l l pol len gra ins a re packed be tween the micro-aggrega tes of enchytrae id

excrement or , in the E hor izon, a re bound wi th in minera l mat te r aggrega tes .

Te t r ad gra ins in th in-sec tion dec l ine in abu ndan ce in to the E hor izo n (Fig . 2). Prop or-

t ions of such gra ins be tween enchy trae id excremen t increase down-prof i le ; re l iable

counts were not poss ib le be low 130 mm .

The da ted inputs show c lose comparabi l i ty in the depths to which they have been

incorporated (Fig. 3). Non-native pollen, deposited on the soil surface after c .

1840 AD, is fou nd only to 50 mm , th rou gh out the L /F hor izon and in to the top o f

the H hor izon. Concentra t ions increase f rom the ground surface wi th in the L/F

hor izon to a peak a t t he L /F-H hor i zon . SCP ' s a re found to 40mm dep th , t he

L/F-H bounda ry , and occur a t un i fo rm concen t ra t ions w i th in the L /F ho r i zon .

137Cs concentra t ions , depos i ted s ince 1963, dec l ine sm oothly f rom 20 m m to

60 mm ; c oncentra t ions a re la rge ly ins ignif icant be low th is depth .

Interpretation

The three da ted inputs to the podsol a re found to appro xima te ly the same depth in the

prof i le . This i s not an a r te fac t of sampl ing because a l l inputs were moni tored a t the

same 10mm sampl ing resolu t ion (Fig . 3) . Smal l and la rge ly ins ignif icant amounts

of 137Cs, pro bab ly in so lu tion , a re fo und a t grea te r depths , but the major i ty of

137Cs, sorbed on to part icles , is locked within the to pm ost 2- 3 cm of the soil. These

inputs a re found to the same depths despi te be ing added as separa te and independent

' injections ' a t different t imes within the last c . 150 years . I t is l ikely that this pattern

represents mixing of these com pone nts w i th in the L/ F hor izon over t ime. The appear-

ance of SCPs a t uni fo rm concen tra t ions to 50 m m sugges ts tha t th is degree of mixing

occurs in much less than a century.

There a re d if fe rences in the degree to which these da ted com pone nts a re d is t r ibuted

through the L/F hor izon. Whi le the o lder components , non-na t ive pol len and SCPs ,

a re more-or- less u ni formly and so comple te ly mixed, 137Cs concentra t ion s dec line

down-horizon, sugges t ing tha t i t takes longer than c . 30 years (1963-1997) for com-

plete mixing to occur.

Non-na t ive pol len gra ins , despi te be ing incorpora ted in to the prof i le s ince c .

1840 AD, have on ly been assim ilated into the to pm ost layer of the H horizon. This sug-

ges ts tha t t rans fer of pol len f rom L/ F to H h or izons i s by no mean s rapid . There i s

thus the potent ia l for pol len to cont inue to accumula te in the L/F hor izons for

very long per iods (d iscussed be low), and tha t fo r th is dura t ion a ll vege ta t ion changes

wil l be conf la ted in to one comple te ly mixed and uniform pol len assemblage .

The depth to which these components a re mixed a t Prof i le 7 i s very la rge ly con-

t ro l led by hor izon-forming pedogenic proper t ies , in par t icula r by the ver t ica l range

of near-surface feeding la rge inver tebra tes . I t i s probable tha t mos t pol len in the

L/F hor izon is t rans ferred in smal l ver t ica l increments through repea ted inges t ion ,

because ~37Cs bo und to par t ic les i s only move d a couple of cent imetres and is not

comple te ly mixed to the base of the L/F hor izon (above) . Over a t ime in te rva l of



SOIL-STRATIGRAPHIC PALYNOLOGY IN PODSOLS 87

less than a century , however , th i s smal l - increment mixing i s thorough . Enchy t raeids

l iberate pol len grains at and below the L /F - H bou nda ry by ingest ing large ell ipsoid

excrement. Enchytraeids are too small to ingest or to move pollen grains. The l ibera-

t ion of pol len grains in th is way does not make pol len grains more suscept ib le to

downwashing because of the densely packed s t ructure of enchyt raeid excrement .

However , any pol len t ransferred f rom L/F to H hor izons and to deeper and more

humified mor horizons in older podsols, wil l remain mixed; pollen assemblages in

lower organic hor izons are no more capable of temporal resolut ion than those in

the surface horizon.

Transfer of pol len does not appear to occur f rom organic to mineral hor izons.

Cruic kshan k & Cruicksha nk (1981) repor t a mar ked increase in pol len conce nt rat ions

at the organic/mineral hor izon b ounda ry , al though th is is not seen at Lo ur 7 ; th is may

again relate to the age of the podsol and the t ime take n for pollen to move d own and

stack against th is boundary . In detai l th i s boundary possib ly exis t s due to micro-

s t ructural changes but in broad terms i s through the absence of ear thworm act iv i ty .

The absence of ear thworms also suggests that up-prof i le t ransfer of pol len (Walch

e t a l . 1970) f rom mineral to organic hor izons does not occur , a l though we cannot

demonst rate th is . The organic hor izons appear , once formed, to be sealed f rom the

addi t ion of o lder pollen f rom subsurface hor izons.

Discussion

Vegetat ion change on a podsol surface wil l be depicted by changing pollen inputs to

the soi l (Di jkst ra & van Mourik 1995) . The mechanisms and rates of incorporat ion

into the surface organic hor izons d iscussed above, however , mea n th at pol len assem-

blages cannot be employed in detai led temporal palaeoecological reconst ruct ions of

such vegetat ion changes. I t i s the length of t ime the L/F hor izon retains a pol len

assemblage and so mixes i t with earl ier assemblages that is cri t ical . O'Sull ivan

(1973) argued that the t ime spent in this mixed zone is short compared to that

within deeper strat i f ied horizons. The debate focuses on whether the 'broad strat i f ica-

t ion' of these mixed assemblages al lows 'meaningful interpretat ion' (O'Sull ivan 1973:

260) . Our data suggest that pol len wi l l remain in the L/F hor izon over very long

periods, and that pollen assemblages wil l not be interpretable.

At Lour we s tat i s t ical ly compared, using DECORANA, the pol len assemblages at

al l soil profiles with the more secure pollen strat ig raph y at the L our P eat (for the lat ter

see Car ter et al . 1997). All soi l profi les fai led to reproduce the pollen strat igraphy

wi thin the peat (Long

et al .

in press) . This suggests that mixing is at least part ly

responsible for a profound reduction in the abil i ty to interpret podsol pollen profi les,

as in al l soi l profi les examined at Lour. Another issue, not discussed in this paper

throug h lack of space, i s the loss of informat ion induced thro ugh pol len dest ruct ion,

and this too is thought to be highly significant (Long et al . unpubl i shed data) .

Our model impl ies that pol len s t rat igraphies f rom deeper mor hor izons wi th in

podsols should be smoothed by this mixing process. This is seen in other studies

(e.g. Ive rsen 1969; Sto ck ma rr 1975). I t is best ana lysed by An der sen (1979), who

il lustrated the vert ical spreading of a known-age ' inject ion' of

C a l l u n a

pollen in

th in immature podsols compared to a master-prof i le (H16) : Andersen refers to th is

master-profi le, with i ts extraordinary 'spiky' pollen record, as a soi l but we interpret

this site as a peat lying within a sm all depression, biological ly inert thro ugh , p erhap s,



88 R. TIPPIN G ET AL.

waterlogging. The majori ty of O'Sull ivan's (1973) eight detai led pollen diagrams are

also smoothed; exceptions (Profi les 1, 7, 8) are abrupt changes that coincide with

pedogenic boundar ies between F and H hor izons, seen as cr i t ical in terms of

storage and transfer of pollen (above).

Our f indings do not quest ion those of other workers in which sequences of 14C

dates are obtained in s t rat igraphic order (O'Sul l ivan 1973; Cruic ksha nk & Cruick-

sha nk 1981; Stoc km arr 1975). How ever, these 14C dates repres ent only the mea n

age of a mixed organic c om pone nt (Scharpenseel 1971; Ma t thews 1993) ; again i t i s

the dura t ion of mixing that i s impor tant . O'Sul l ivan (1973) recognized the problem

of vert ical mixing in the explanation of one erroneous near-surface 14C date (UB-

393), and suggested that organic matter has a prolonged residence t ime in these

shal low hor izons, an observat ion our methodology cannot tes t . Cruickshank &

Cruickshank (1981), with a more intensive dat ing programme, argued that al l 14C

dates l ie in correct strat igraphic order, but this is only so after omit t ing assays (e.g.

UB-2327) argued to be too young, explained through root let penet rat ion (despi te

these being excluded in sample pre- t reatm ent ) bu t perha ps equal ly explicable throug h

organic mat ter mixing. Most relevant to our 'known-age marker ' approach i s the

wo rk of Stoc km arr (1975). 14C dating w as no t used sufficient ly to test interpretat ion s,

but two pollen types of, broadly, known age, Secale cereale and Centaurea cyanus,

were found in samples h igher and younger than expected , and a th i rd , Fagopyrum,

was found deeper and ear l ier than expected . The apparent d isplacement of Secale

and

Centaurea

may be explained by local absence unti l after regional introduction,

but dow n-profi le d isplacement of the Medieval indicator- taxon, Fagopyrum, to pur-

por tedly Roman hor izons, i s harder to explain . These 'marker ' pol len types suggest

tha t vert ical mixing is significant in these profiles, and that pollen of several hun dre d

years age-difference, greater than observed at Lout 7, is possible.

Conclusions

The study has developed techniques able to t race part icle incorporat ion in soi ls over

long t ime-spans of centur ies and longer , durat ions over which s low pedogenic pro-

cesses operate. These techniques confirm earl ier studies in identifying that mixing

of pol len and other par t icles occurs in the uppermost organic hor izon, the L/F

hor izon. Mixing occurs through large near-surface feeding inver tebrates; the taxa

remain unident i f ied al thou gh species of Ar thro pod a are perhaps most l ikely .

Mixing takes p lace through ingest ion of pol len , and subsequent defecat ion, by

these large invertebrates. Physical downwashing through pores is not a significant

process.

What th is s tudy demonst rates i s the completeness of mixing, and the rapidi ty of

mixing. Although the three known-age inputs are separated in t ime by over 100

years, al l three occur to al l depths within the L/F horizon, showing thorough

mixing in, probably, much less than a century. I t has also been shown that there

has been no measurable t ransfer of known-age par t icles f rom organic to mineral

horizons over the last c. 150 years, probably through the absence of earthworms in

th is acid prof i le . We assume that upward movement of o lder pol len f rom mineral

horizon s is also insignificant . Pollen within the orga nic horizons, al tho ugh th orou ghly

mixed, is thus t rapped. This i s d isadvantage ous for palaeoecological reconst ruct ion

from such soi ls because the near-surface organic horizons can potential ly recrui t



SOIL-STRATIGRAPHIC PALYNOLOGY IN PODSOLS 89

a nd t he n mi x po l l e n f o r ve ry l ong pe ri ods ; r e - i n t e r p r e t a t i o ns o f S t o c km a r r ' s ( 1975 )

da t a sugge s t t ha t po l l e n o f ma ny c e n t u r i e s ma y be i n t e g r a t e d i n t o un i f o r m po l l e n

a s se mb l a ge s . Ea r l i e r s t udi e s ha ve sugge s t e d t ha t po l l e n s t r a t i g r a ph i e s i n podso l s a r e

' b r o a d l y ' c a p a b l e o f t e m p o r a l i n t e r p r e ta t i o n . H o w e v e r , a l t h o u g h t h e d e f in i t io n o f

' b r oa d ' i s ope n t o i n t e r p r e t a t i on , ou r da t a sugge s t t ha t t he t e m por a l r e so l u t i on o f

pol len s t ra t ig raph ies in pod sol p rof i les i s so c rude as to be e f fec t ive ly mean ingless .

We would like to thank A. Hipkin for identifying Profile 7 at Lour, and assisting in its

excavation and field description. R. Kynoch produced the pollen samples and undertook

most physical analyses. M. McCleoud manufactured the thin-sections and assisted with

fluorescence techniques. L. Donaldson generated the Fe data, A. Mennim the particle-size

data and S. Bradley the 137Cs counts. The project was funded by a NE RC grant (GR/J73421).

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Tracing the record of early alluvial tin mining

on Dartmoor, UK

V A R Y L R . T H O R N D Y C R A F T 1'2, D U N C A N P I R R I E 1

& A N T H O N Y G . B R O W N 2

1Camborne School o f Mines , Univers i ty o f Exete r , Redruth ,

Cornwal l TR15 3SE, UK

2 We t land Research Centre , Sc hool o f Geography and

Archaeology, Univers i ty o f Exeter , A m or y Bui ld ing,

Rennes Dr ive , Exe ter E X4 4R J , U K

Abstract: Although there has been considerable speculation, there is as yet no

conclusive evidence to confirm D artm oor as a tin producing region in prehistory.

This is in part due to extensive tin mining on the m oor during the Medieval period

destroying evidence of earlier mining activity. This paper presents the p reliminary

results of an integrated mineralogical and geochemical geoarchaeological

approach to identifying the record of early mining activity. Floodplain sedimen-

tary successions, that have no t themselves been mined, and are downstrea m of

known areas o f tin streaming, retain a geochemical record of the mining activities

because the early tin streamin g released large quantities o f min e waste tailings.

Where these successions can be dated, they provide an indirect means of testing

the record of mining activity on Dar tmo or. Geochemical an d mineralogical

analyses of datable fluvial sediments aimed to (a) distinguish between natu ral

and mine contam inated sediments, and (b) to date the onset of sediment aggrada-

tion caused by tin mining activity in the headwaters. Results from the Avon Valley

show negligible Sn concentrations in basal silts that are dated to pre-2845 4- 45 yrs

BP. Ove rlying silts are enriched in S n an d were deposited after 1560 4- 40 AD, sug-

gesting tha t the Sn enrichment corresponds w ith tin streaming in the 16th century.

In the Erm e Valley, significant Sn enrichment post-dates an o rganic-rich silt dated

at 1280 + 45 AD. At both sites there is sediment aggrad ation coupled with a n

enhancement in Sn concentration consistent with mine waste contamination as a

result of Medieval tin streaming.

The m i ne r a l o gy a nd g e oc he m i s t r y o f a l l uvi a l s e d i me n t s r e fl e ct s t he ge o l ogy , l a nd u se

h i s t o r y a nd m i n i ng h i s t o r y w i t h i n a r ive r ' s c a t c hm e n t . Mi n i ng a c t i v i t y , a nd t he r e le a se

o f mi ne wa s t e p r od uc t s c a n ha ve a ma j o r e f fe c t on bo t h t he r a t e o f s e d i m e n t a t i on

wi t h i n c a t c hme n t s , a nd i n a dd i t i on c a n s i gn i f i c a n t l y a f f e c t t he s e d i me n t ge oc he mi s t r y

a nd m i ne r a l ogy . I n r e c e n t ye a r s , ge oc he mi c a l s t ud i e s o f he a vy me t a l c on t a m i na t i on

f r om h i s t o r i c a l m i n i ng ope r a t i ons , ha ve be e n u se d t o da t e a l l uv i a l s e d i me n t s a nd

d e t e r m i n e s e d i m e n t a t i o n r a t e s w i t h r e f e r e n c e t o t h e k n o w n c o n t a m i n a n t p r o d u c t i o n

r e c o r d ( e . g . Ma c k l i n 1985 ; Ma c k l i n et al. 1994, 1997) . In the same way geochemica l

a nd m i ne r a l og i c a l s t ud ie s o f da t a b l e s e d i m e n t a r y sy s t ems c a n be u se d to r e c ogn i z e

t he e nv i r onm e n t a l i mpa c t o f p r e v i ous m i n i ng a c t i v i t y (e .g . P i r r i e et al. 1997). On

D a r t m o o r , t h e r e is a di r ec t d o c u m e n t a r y r e c o r d o f ti n m i n i n g f r o m t h e 1 2 t h c e n t u r y

onwa r d s , a nd t he r e ha s be e n c ons i de r a b l e spe c u l a t i on t ha t t he r e c o r d o f t i n mi n i n g on

From.

POLLARD, A. M. (ed.) 1999.

Geoarchaeology:exploration, environments, resources.

Geological Society , London, Spec ial Publications, 165, 91-102. 1-86239-053-3/99/$15.00




92 v .R . THORNDYCRAFT, D. PIRR IE & A. G. BROWN

D art m oo r m ay d a te back to the Bronze age . However , there i s l it t le d i rec t ev idence to

prove local extraction of t in in the Bronze Age (Penhallurick 1986; Pearce 1979). I t is

poss ib le tha t the f luvia l sys tems dra in ing the moor re ta in tha t evidence .

In th is paper we u t i l ize the contaminant record conta ined wi th in da table f luvia l

sediments in order to ident i fy per iods of pas t t in mining on D artm oo r . In par t icula r ,

we cons ider whether th is appr oach can be used to identi fy prehis tor ic mining ac t iv i ty

on the moor. The firs t t in (Sn) deposits l ikely to have been exploited were al luvial

placer deposits of cassiteri te in valley fi l ls , believed to have been formed under peri-

g lac ia l condi t ions dur ing the Ple is tocene (Hosking & Camm 1982; Camm & Croot

1994). These alluvial t in deposits were extracted using hydraulic mining techniques

( te rmed t in s t reaming) which would have had a s igni f icant e ffec t on the sediment

discharge down s tream from the mining s ite. The des t ruc t ive na ture of t in s t reaming

coupled wi th subsequent la te Medieva l reworking of the Sn-bear ing a l luvium has

probably resul ted in the des t ruc t ion of ear l ie r prehis tor ic and ear ly Medieva l mine

remains , hence the need for th is geoarchaeologica l approach.

Tin min ing o n Da rtmo o r

Do cum en ta ry ev idence f ir st r eco rds t in min ing on Da r tm oor du r ing the 12th cen tu ry

(Greeves 1981; Penhallurick 1986; Harris 1992). Despite theoretical reasons suggest-

ing the l ikelihood o f prehi s toric m ining, there is , as yet , no u neq uivo cal evidence for

earl ier mining on the moor (Pearce 1979; Sharpe 1992). The only physical evidence

that has been cited in the l i terature is the discovery of a cassiteri te pebble and one

fragment of t in s lag f rom an excava ted Bronze Age hut on Dean Moor , in the

River Avo n ca tc hm ent (F ox 1957) . More recent ly , t in ingots (of la te or pos t

Roman age ) have been recove red f rom a wreck in B igbury Bay , nea r the mou th o f

the River Erme (Fox 1995) , but these may have or ig ina ted in Cornwal l where there

is evidence for tin mining as early as 3600 years BP (Miles 1975). The significance

of tin s lag deposi ts a t a poss ib le ear ly Ch ris t ian s i te , a t Week Fo rd in the D art

Valley, is a lso contentious, as i t is only constrained by a s ingle radiocarbon date

(57 0-8 90 AD) (G erra rd 1997).

The docu men ted peak pe r iods o f ti n p roduc t ion on the moor , du r ing the 12 th , 13 th

and 16th centuries (H arris 1992), were associa ted with the t in s treaming o f high grade

a l luvia l t in depos its which typica lly conta ined 0 .45-3 kg (0 .02 2-0 .15 %) cassi ter i te per

cubic metre (Beer & Scr ivener 1982) . The la rges t annual product ion was 252 tons of

processed t in metal in 1524 (Harris 1992). There followed a decline in mining with

production largely ceasing in the late 17th century. A small resurgence, in the 18th

and ear ly 19th centur ies , brought about by increased t in demand, was assoc ia ted

with the reworking of previous ly mined reaches and the ext rac t ion of poor er qua l i ty

lode t in by shaf t and adi t mining (Gerrard 1997) .

The major environmenta l impact of t in s t reaming was an increase in sediment

supply to loca l s t ream sys tems (Knighton 1989) . St reaming involved the removal of

the Holocene overb urden of pea ts and f ine-gra ined a lluvia l sediments to ga in

access to the placer gravels . The dense cassiteri te was separated from the l ighter

gangue minera ls us ing a contro l led f low of r iver water through d iver ted channels

or lea ts (Hi tchens & Drew 1824; Gerrard 1992) . The quar tz domina ted gangue ,

cassiteri te locked within larger s i l icate grains , a long with unrecoverable cassiteri te

in the s i l t and clay grain s ize fractions (Bradley 1990), was washed into the local





94 V. R. THORN DYCRA FT, D. PIRRIE & A. G. BROW N

Fig.

1. Sketch map of Dartm oor showing sample locations and areas of documented mining

activity.

1986) . S ub-sam ples w ere t aken a t i n t e rva l s o f 50m m to p rov ide a su f f i c i en t sam ple

s i ze fo r t he ana ly t i ca l t echn iques used .

Laboratory methods

XRF analysis

T h e s e d i m e n t g e o c h e m i s t r y w a s d e t e r m i n e d b y X - r a y f l u o r e s c e n c e ( X R F ) u s i n g a

P h i l li ps P W 1400 ana lyse r . T he sam ple w as d r i ed ove rn ig h t a t 40~ then r if fl ed to

ob ta in 20 g o f sed im ent . T h i s w as then g r ou nd in a ch ro m e s t ee l t em a m i l l fo r 90

seconds . P ressed d i sks o f t he g round sam ple w ere p repa red us ing a bor i c ac id

j acke t and a b ind ing age n t o f 4% e lvac it e i n ace tone so lu t ion . E ac h sam ple w as ana -

l y s ed fo r S n , A s , C u , P b , Z n a n d W u s i n g i n t e r n a l l y c a l i b r a t e d s t a n d a r d s a n d d a t a a r e

r e p o r t e d a s m g / k g ( e q u i v a l e n t to p p m ) . T h e e r r o r l im i t f o r t h e m e t a l c o n c e n t r a t i o n s

de te rm ined w as 4 -10 m g/k g .



EARLY ALLUVIAL TIN MINING, DARTMOOR 95

Particle size distribution analysis

Particle size distribution analysis was carried out using the procedures outlined by the

British Standards Institu tion (1975, 36). Concentrated (30-40%) hydrogen peroxide

(H202) was added to air-dried samples to remove organic matter. The samples were

left for several days, with occasional gentle warming in order to speed up the oxida-

tion reaction. The remaining sample was sieved at 2 mm and 600 gm, then dried and

weighed. The <600 gm fraction was centrifuged for 30 minutes, washed with methy-

lated spirit, re-centrifuged and dried overnight at 40~ The dried sample was weighed

before addition of 0.4% sodium hexametaphosphate (NaPO3) and sodium carbonate

(NazCO3) dispersant solution. The samples were then stirred in an ultrasonic bath

and analysed using a Malvern Mastersizer MS20 laser particle sizer. The Mastersizer

had a measuring range of 1.2-600 tam.

Sample sieving

Selected samples were prepared for geochemical analysis of the separate particle size

fractions in order to show which sediment fractions were metal-dominated. The grain

size fractions examined were: <63 gm, 63-125 gm, 125-180 gm, 180-250 gm, 250-

500 ~tm, 500-2000 gm, 2- 4mm. In order to obtain 20 g of each size fraction, as

required for X RF analysis, a bulk sample of 0.5-1 kg of sediment was usually

required. Initial screening was carried out by dry sieving the sample on a shaker

for 20-30 minutes followed by wet sieving.

Scanning Electron Microscopy analysis

Scanning Electron Microscopy (SEM) studies were used to determine the mineralogy,

in particular whether cassiterite occurred as liberated grains or in association with

other host minerals and the nature of the heavy mineral assemblage. As the concen-

trations of the heavy metals in the sediments were generally low, density separation

was performed using a shaking-table to obtain a heavy mineral concentrate in

preparation for SEM analysis. SEM analysis was carried out on a polished mount

of the sample using a JEOL 840 with Link (Oxford Instruments) AN10000 energy

dispersive spectrometer (EDS). Digiscan and Digimap software linked to the SEM

allowed grain measurements and chemical classifications to be determined.

Radiocarbon dating

Eleven samples were submitted for radiocarbon dating at the NERC radiocarbon

laboratory at East Kilbride. Nine were conventional dates on bulk samples and the

remaining two were AMS-14C dated due to insufficient carbon content of the samples

for conventional dating.

Resul ts

Natural Sn-bearing sediments: Taw Marsh terrace

For the Taw Marsh terrace sequence the highest Sn concentrations, which range from

93 to 114mg/kg, occur in the basal (placer) gravels (Fig. 2). This is consistent with



96 V. R. THOR NDYC RAFT, D. PIRRIE & A. G. BROWN

Fig. 2. Stratigraphy vs Sn profile for the uncontaminated Taw Marsh terrace. Note the

elevated Sn con centra tion in the basal gravels. Particle siz e vs Sn conc entration for sample

TMG is shown in Fig. 3.

p rev ious sed imento log i ca l s t udi es o f heavy minera l t r anspor t mechan i sms w hich

show the highes t con cent ra t ions of cass iter ite in the gravel bed load (F le tcher &

Loh 1996) . The f ining upwards sedimentary sequence i s associa ted wi th a decreas ing

t rend in Sn concent ra t ion. The par t ic le s ize geochemical di s t r ibut ion f rom the basal

gravels (F ig. 3) c lear ly shows a peak Sn concent ra t ion of 1379mg/kg in the 125-

250 gm grain s ize f rac t ion; th is is coarser than that expected in mine waste co ntami-

nated sediments as the coarser gra ined cass i ter i te can be more eas i ly ext racted by

simple mineral process ing (Bradley 1990) . In addi t ion, the abundance of Sn in thi s

gra in s ize f rac t ion i s comparable to previously descr ibed Cornish placer deposi t s

(Camm & Croot 1994; Camm 1999) . In compar ison to these upland gravel deposi t s ,

the lowla nd f ine gra ined sediments sam pled f r om the up per ter race deposit s , of pre-

mining age f rom the Teign Val ley f loodpla in , conta in negl igible (<5 m g/ kg ) Sn

concent ra t ions .

Con tam inat ed sediments (1). the Teign Valley middle terrace

The Teign Val ley middle ter race shows three dis tinct sedim entary uni t s (F ig. 4), wi th

two phases of con tam inate d sediment deposi t ion se parated by a uni t consis ting of

Fig. 3. Particle size vs Sn conc entratio n for the basal gravels of the Taw Ma rsh terrace

(sample TMG). Note the concentration within the 125-250 gm fraction.




Fig. 4. Diagram showing Sn concentration and percentage silt vs stratigraphy for the Teign

Valley middle terrace. No te th e clear corre lation between percentage silt and Sn concentra-

tion except in the uncontam inated silt-dominated interval 500-900 mm (see text for interpre-

tation). The u ppe r unit contains elevated levels of Pb and Ba, suggesting that it post-d ates

1850.

unco ntam ina ted , overban k, f ine gra ined sediments . Despi te the lack of organic depos-

i ts for radioc arbo n da t ing , the geochemis t ry and m inera logy o f the upper s i l ty-sand

uni t g ives a good indica t ion of the age of the te rrace , and when used in conjunc t ion

with mining h is tory evidence a llows a recons t ruc t ion of the depos i t iona l h is tory o f the

te rrace to be pos tu la ted . This uni t shows increased abunda nce of barytes ( f rom S EM

studies) and enha ncem ent in Pb (up to 372 mg /kg) which sugges ts sediment depos i -

t ion a f te r 1850 AD, the da te of the onse t o f barytes an d ga lena minin g in the m iddle

Teign Valley (Cheshire 1969). I t is l ikely, therefore, that the basal sand deposits

which pre-da te 1850 were depos i ted as a consequence of la te Medieva l t in mining.

The coarse sand gra in s ize of these depos i ts sugges ts tha t they were depos i ted

with in the r iver channel and w ould hav e resul ted in the agg rada t ion of the r iver

bed, as observed in the Ringrooma River th is century (Knighton 1989) . When the

supply of sand to the r iver was reduced fo l lowing the dec line of the t in mining indus-

t ry dur ing the seventeenth century (Harr is 1992) the sand depos i ts would have been

inc ised by the River Te ign, a common occurrence in r iver sys tems recover ing f rom

mine was te contamina t ion (Knighton 1989; James 1991) . As the r iver inc ised i t s

bed sediment depos i t ion on the f loodpla in would only occur dur ing overbank f lood

events resul t ing in the depos i t ion of f ine-gra ined a l luvium and account ing for the

middle s i l t uni t of the te rrace . With the onse t of loca l barytes and ga lena mining in

1850 (Cheshire 1969) and the br ie f resurgence o f the t in indu s t ry in the m id-19th cen-

tury (Harr is 1992) , the supply of mine w as te sediment once aga in increased caus ing

aggr ada t io n o f the r iver bed and a l lowing the depos i t ion of the coarser gra ined

sil ty-sand unit .

In contras t to the negl ig ib le Sn concentra t ions in the na tura l upper te rrace of

the River Te ign f loodpla in (noted in the previous sec t ion) , the va lues in the middle

te rrace a re h igher , reaching 148mg/kg (Fig . 4) . There i s a lso a corre la t ion , wi th in



98 V .R . THORN DYCR AFT, D. PIRRIE & A. G. BROWN

Fig. 5. Particle size vs Sn concentration for the 100 -30 0m m interval from the Teign Valley

midd le terrace. N ote th e significant enrichment of Sn in the < 63 ~tm fraction.

the contaminated uni t s , be tween percentage s i l t and Sn concent ra t ion ( r2= 0.91) ,

suggest ing the enha nce me nt of Sn in the < 63 ~tm f ract ion as found by Bradley

(1990). The enh ancem ent is conf i rmed b y the Sn conc ent ra t ion dis t r ibut ion in the dif -

ferent part icle size fract ions. For both this si te (Fig. 5) and others, including the River

Er me (see Fig. 8), Sn conc entr at io n is highe st in the < 63 p~m fract ion. The increase in

Sn conce nt ra t ion towa rds the top of the prof ile , wi thin both the con tam inated uni t s, is

a consequence of the f ining upw ards sedim entary sequence and the deposi t ion o f

greater quant i t ies of s i l t , onta ining unreco verable cass iteri te.

The m ine was te con t amina t e d sed iment s show a minera logy typ i ca l o f t hose

der ived f rom a grani t ic l i thology. Quar tz i s abundant and the heavy mineral assem-

blage i s dominated by z i rcon, monazi te and var ious Fe-minerals , these being typical

accessory minera ls o f t he Dar tm oo r g ran i te (Edm onds

et al. 1968; Alderton 1992).

Zi rcon and m onaz i te o ccur in a wide range of par t ic le sizes in both the natura l a nd

contaminated sediments . By cont ras t , cass i ter i te gra ins in the mine waste contami-

nated sediments are predominant ly found in the <63 ~m f ract ion and where cass i ter -

i te does occur in the sand grain size fract ion i t is usual ly locked within a quartz host

(Fig. 6) . The mineralogy, therefore, confirms that cassi teri te is concentrated in the

f ines of mine co ntam inate d sediments an d the def ic iency of Sn in the sand f ract ions

is a resul t of efficient recov ery du ring t in strea min g an d pro cessing.

Contamina ted sed iments (2 ) . R iver Erme pa laeochanne l

The River Erm e palaeo chan nel sequence i s show n in F ig. 7. An increase in Sn concen-

t ra t ion f rom 11 to 136 m g/k g occurs in a uni t o f s il ty-sand gra in s ize a t 150 cm below

the sediment sur face and is radio carb on dated as pos t 1280 + 45 AD ( laborato ry code

SRR -6226) b ased on the under lying organ ic r ich si lt . The agg rada t ion of Sn enhan ced

sediment a t app roxim ately 1 .50 m below the sediment sur face is a lso evident in two

nearb y exposures of the ter race . T he par t ic le s ize Sn dis t r ibut ion data f rom these

exposures (Fig. 8) once again shows the highest Sn concentrat ion in the si l t fract ion,

consis tent wi th the mine waste conta min ated sediments of the Teign Val ley.

Con tamin ated sediments (3). River Avo n palaeochannel

The River Av on palaeo chan nel shows negl igible Sn values (< 5 mg /kg) in the lower s i lt

uni t (F ig. 9) , which i s dated to pre-2845 + 45 year BP ( laboratory code SRR-6225)



EARLY ALLUVIAL TIN MINING, DART MO OR 99

Fig. 6. Scann ing electron microscope imag e showing a large cassi teri te grain locked within a

si l icate host (River Erme floodplain, contaminated sediments) .

f r o m a r a d i o c a r b o n d a t e f r o m t h e b a se o f t h e o v e r l y in g p e a t. T h e u p p e r s il t l a y e r

s h o w s S n e n h a n c e m e n t . T h e v a l u e s o f e n h a n c e m e n t a r e l o w ( a r o u n d 2 0 m g / k g ) i n

c o m p a r i s o n t o t h e E r m e a n d T e i g n s i te s , b u t t h i s is a r e f l e c ti o n o f t h e l o w e r e n e r g y

d e p o s i t i o n a l e n v i r o n m e n t o f t h i s si te a t t h e b a c k o f th e f l o o d p l a i n . T h e a g e o f t he

50

100

150

200

250

300

..e.-----

r

350

Sn (rng/kg)

50 100 150

| t

. . . . . . . . .

J . . . . . . . . .

. . . . . . . . . .

| ~ v v v v ~

v v . . . .

| ~ ~ ~ v v v ~

~ v v v ~ v ~

o - o

Q

silty-sand

silt-clay

peat

gravel

1280 +45AD

Fig. 7 . Strat igraphy, Sn concentrat ion and radiocarbon date for the Erme palaeochannel.

Note the prominent increase in Sn concentrat ion post dating the organic si l t horizon dated

at 12 80 -t- 45 AD.



100 V. R. THORNDYCRAFT, D. PIRRIE & A. G. BROWN

Fig. 8. Part icle size vs Sn concentration for the 500 -60 mm interval from the River Erme

floodplain strat igraphy. Note the con centration of Sn in the <63 Bm fraction.

u p p e r b o u n d a r y o f t h e p e a t d e p o s i t is 1 5 6 0 :t: 4 0 AD ( l a b o r a t o r y c o d e S R R - 6 2 2 4 ) t h u s

s u g g e st i n g th e s e s e d i m e n t s w e r e d e p o s i t e d i n r e s p o n s e t o t h e p e a k p e r i o d o f M e d i e v a l

t in s t r eam ing in the 16 th cen tu ry (H ar r i s 1992) .

Conclusions

I t i s poss ib l e to d i s t ingu i sh be tw een h i s to r i ca l m ine w as te con tam ina ted sed im ent s

a n d n a t u r a l s e d i m e n t s u s i n g a c o m b i n a t i o n o f g e o c h e m i s tr y , m i n e r a l o g y a n d p a r t i c le

s ize ana lys i s . Inde ed the skew ed na tu re o f t he pa r t ic l e - s ize S n f r ac t iona t ion d a ta

w o u l d a p p e a r t o d i f f e r e n t i a t e b e t w e e n c o n t a m i n a t e d a n d n a t u r a l s e d i m e n t s . T h e

in i t i a l da t ing sugges t s t ha t aggrada t ion o f S n-enhanced sed im ent seen in the va l l eys

d r a i n i n g D a r t m o o r is o f M e d i e v a l a g e a n d n o e a r l i er t h a n p r e - 1 2 t h c e n t u r y AD.

T h e s i gn a l o f e n h a n c e d m e t a l c o n t a m i n a t i o n b y t h e r e le a s e o f th e f in e se d i m e n t

f r a c t i o n i n t o t h e r i v e r s , a p p e a r s t o c l e a r l y m i r r o r t h e d o c u m e n t a r y e v i d e n c e o f

m i n i n g a c t iv i t y . A g g r a d a t i o n o c c u rs i n t h e R i v e r E r m e v a l l ey in t h e l a t t e r h a l f o f

the 13 th cen tu ry , and cor re l a t e s w i th the f i r s t peak pe r iod o f m in in g iden ti f ied in

Fig. 9. Strat igraphy, Sn concentration and radiocarbon dates for the Avon Valley palaeo-

channel. No te the Sn enrichment post dating the peat dated at 1560

t:

45 AD.




the documentary record (Harris 1992). In the River Avon palaeochannel aggradation

of Sn-enhanced sediment occurred in the 16th century following both the highest Sn

production period and the introduction of pollution legislation (1531 AD) to reduce

the quantity of sediment released into the river systems (Greeves 1981). It must

also be noted, however, that the changes in sedimentation occurring at this time

may also be influenced by climatic change, such as the instability of the late Medieval

climatic deterioration, the Little Ice Age (Brown 1998).

As yet, no prehistoric conta minat ion has been identified on Dartmo or. Any prehis-

toric mining may have been on a very small, local scale, hence would have a minimal

downstream impact. In addition, subsequent reworking by Medieval tin streaming

may have destroyed the earlier record, or may be masking prehistoric sediments

with a lower level of enrichment. However , this paper clearly shows that the combined

mineralogical-geochemical approach adopted has the potential to identify past

mining activity on the moor, even in quite distal sites. The search is now on for critical

sections where the record of prehistoric mining may be retained.

The research was supported by a NERC research studentship (VRT). Radiocarbon dates were

provided through NERC Scientific Services at the NERC Radiocarbon Laboratory, East

Kilbride. Gerard Aalbersberg provided fieldwork assistance. Many archaeologists have

helped with advice and information, including Debbie Griffiths and other staff of the Dartmoor

National Park, and Torn Greeves and members of the Dartmoor Tin Research Group. Thanks

are also due to local landowners for access. The technical support of the analytical laboratories

at the Camborne School of Mines is gratefully acknowledged.

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Provenancing iron ore from the

Bristol Channel Orefield: the cargo of the

Medieva l Magor P i l l Boat

TIMOT HY P . YOUN G 1 & GARY R. THOM AS 2

1GeoArch, 54 Heol-y-Cadno, Thornhill, Car diff CF14 9D Y, U K

2Department o f Earth Sciences, C ard iff University, PO Bo x 914,

Cardiff CF1 3 YE, UK

Abstract" A boat (built c. 1240) foundered with a cargo including iron ore, close to

the settlement of

Abergwaitha,

seaward of the modern Magor Pill (Gwent). Exca-

vation in 1995 recovered 180 kg of mixed powder and lump ores. A source within

the Bristol Channel Orefield may readily be determined from the mineralogy and

texture of the lump ores. Provenancing within the orefield is more problematic.

Various lines of evidence constrain the likely source of the ore as Glamorgan;

including textural evidence that the ore was emplaced within substantial cavernous

porosity, petrological evidence that the ore was within the Carboniferous lime-

stone, and the presence of quartz. This raises the intriguing question of why a

cargo of ore was apparently travelling towards the major ore sources in the

Forest of Dean. An explanation is suggested by the likely date for the cargo of

1250-1280, during the northward expansion of the de Clare Lordship of Glamor-

gan, into Meisgyn (including most orebodies west of the Taft Valley) in 1246, and

Is Caiach (including those east of the TaffValley) in 1267. The de Clares are known

to have undertaken large-scale iron smelting in Trelech (Gwent) in the period

c. 1240-1290. It is possible that ore from the newly secured sources was shipped

to Trelech for smelting during this period of insecurity.

The circumstances of the discovery in 1995 and lifting in 1996 of the Magor Pill boat,

together with a full description of the boat and its cargo, have recently been published

(Nayling 1998). The vessel had foundered close to the settlement of

Abergwaitha,

sea-

ward of the current mouth of Magor Pill (Gwent, South Wales; Fig. 1). On its final

voyage, the boat had been carrying a cargo of iron ore. The ore had been placed

on a hurdle, and comprised a mixture of coarse lump ore and powd er grade material.

Initial expectations that the cargo would have originated within the Forest of Dean

(known to be a major ore producing region in the 13th century) soon proved to be

incompatible with the petrology and mineralogy of the ore recovered. Allen (1996)

argued for a possible origin in the Mendip or Bristol area, but after an extensive sam-

pling of ore outcrops, Young & Thomas (1998) demonstrated the the most likely

source for the cargo was in Glamorgan. Redknap & Young (1998) have described

the place of the Magor boat in the context of 13th century trade and iron-making.

The purpose of this contribution is to illustrate, and to amplify the description of,

the cargo given by Young & Thomas (1998), and to place the cargo within the detailed

context of the Glamorgan orefield, both geologically and with respect to the 13th

century political geography.

From.


Geoarchaeology: exploration, environments, resources.

Geological Society, L ond on, Special Publications, 16 5, 103-121.1-86239-053-3/99/$15.00

9 The Geological Society of Lon don 1999.



104 T. P. YOU NG & G. R. THOM AS

I[ J . Fores, O

~ ' ~ ~ ~ o f Dean : f l ~ 55~ lCJuc es t e r

I ~ 1 7 6 . . . . ~ o ~ I.~ ) |

e• C o . T r e l e c h ~ _ ~ / / ~ ~

I - ' o l r i l ,

~ C) w an se a - , fech

I outcrop of LowerCarboniferous rocks

~ dominantly cave-hosted (quartz

absent)

dominantly cave-hosted (quartz present) 1

" \

dominantly oint/fissure hosted dip ~

~ dominantly hosted by Triassic rocks

50 km

[ ~ dominantly ault-hosted

Fig . 1. The Bris to l Channel oref ie ld , showing the d is t r ibut ion of the main ore body types and

the locat ion of Magor Pi l l

Fig. 2. (a)-(d) Layered facies ore from the Magor Pill boat. (e)-(g) Stalactitic facies ore from the

Magor Pill boat. (f) Botryoidal facies ore. (h) Replacement facies ore. (a) Radial growths of

goethite needles (bright) nucleated on the ghosted outlines of former carbonate crystals and over-

growing euhedral quartz crystals. Scale bar 200~m. Backscattered electron (BSEM) image of

polished block. Sample M48. (b) Quartz (grey) to left overgrowing radial growths of acicular

goethite. Scale bar 200/am. BS EM image of polished block. Sample M 47. (c) Goethite-rich layer,

below, overgrown by botryoidal goethite (above) partially occluding inter-layer void (filled by

grey resin). Margin of goethite rich layer marked by thin layer of haematite, revealing the outline

of carb ona te gra ins replaced by goethite. Scale bar 1 mm. Reflected light photo micr ogra ph of

polished block. Sample M14. (d) Goethite-rich layer bearing an enclosed void (filled incompletely

by resin appearing grey). Haematized surface layer and inner zones of replaced carbonate crystals

reveals the replacive natur e of the goethite. Scale bar 500 ~tm. Reflected light photo mic rogr aph of

polished block. Sample M113. (e) Longitudinal section through stalactites formed of acicular

goethite crystals. Inter-stalactite porosity filled by resin (grey) which has been scratched during

specimen prep ara tion (dar k lines). Scale bar 500 tam. Reflected light photom icrog raph of polished

block. Sample M43. (f) Transverse section through goethite stalactites, which have been over-

grown by botryoidal goethite. Inter-stalactite porosity filled by resin (grey) which has been

scratched dur ing specimen pr epar ation (dar k lines). Scale bar 1 mm . Reflected light photom icro-

graph of polished block. Sample M43. (g) View of central region of a dominantly goethite (grey)

stalactite, showing radial structures of haematite (white) in the core of the denser goethite clusters.

6-fold symmetry of the haematite can be dearly seen (compare Fig. 3). Scale bar 50/am. BSEM

image of polished block. Sam ple M82. (h) Replaced dolomite host rock. Outlines of dolomite

crystals marked by voids. Interior filled largely by fine grained goethite, but also bear geopetal

(gravity controlled) fill of radia l clusters of haem atite crystals. Scale bar 1 mm. Reflected light

image of polished block. Sample M54.



P R O V E N A N C I N G I R O N O R E , B R I S T O L C H A N N E L O R E F I E L D 105



106 T. P. YOU NG & G. R. THOM AS

Description of the ore

The na ture of the ore com pris ing the cargo of the vesse l has been descr ibed br ief ly by

You ng & Thom as (1998). The ca rgo inc luded two com ponen t s , wh ich occur red mixed

toge ther . Th e main com pon ent (129 kg recovered) is a ye llow ochreous pow der , con-

ta in ing smal l f ragments of broke n i ron ore an d hos t do lomit ic l imes tone , whereas the

second com pon ent comprises d iscre te b locks of lump ore ranging up to 4 .3 kg . The

lump ore can be d iv ided in to four fac ies , which occur in in t imate assoc ia t ion .

1. Layered facies (Fig. 2 a-d)

This ore type comprises a l te rna t ing layers (0 .6-6 m m th ick) of h igh-dens i ty goe th i te /

haem at i te ore , wi th low-dens i ty layers (<2 mm ) and open voids (<2 0 ram). The dense

layers a re r icher in haem at i te ( typical ly 10 -20 % ) than the porou s layers (< 10%). The

poros i ty of the low dens i ty layers i s of ten surro und ed by, and smal le r pores may occur

wi th in , the ghos ted out l ines of former carb onat e c rys ta ls (Fig . 2c , d) . The surfaces of

the forme r carb ona te c rys ta ls a re of ten par t icula r ly haemat i te -r ich . This fac ies gener-

a l ly bears smal l q uar tz c rys ta ls (< 200 gm), which a re usua l ly in t imate ly assoc ia ted

with goe th i te needles . Genera t ions of goe th i te a re of ten seen to both pre- and pos t -

da te quar tz prec ip i ta t ion .

2. Stalactitic facies (Fig. 2e-g)

The s ta lac t i tic fac ies comprises th in ( < 3 m m diameter) s ta lac t ites of c rys ta l l ine

goethite . The cores of the s talacti tes may be dense, and these dense areas may bear

radia l groups of haemat i te needles , of ten showing a s ix-fo ld symmetry (each a rm up

to 6 tam long and 0 .5 pm wide) and which a re prob ably twinned (Fig. 2g) . The low-

density areas (Fig. 2e) show crude radial c lumps of goethite needles . The s talacti tes

reach up to at least 180 m m in length. The s talacti t ic facies is a lm ost always ov ergr ow n

by the botry oida l facies (Fig . 2f) , somet imes to the a lmo s t to ta l occ lusion of the in te r-

s talacti te porosity.

3. Botryoidal facies (Fig. 2f)

The botryoida l fac ies occurs as coa t ings (usua l ly <500pm) which overgrow the

s ta lac t it ic and layered fac ies ores. S ome spec imens show overg rowth of the botryoid s

by a layer of goethite crystals u p to 150 lam in length and 5 ~tm in diameter. The

crys ta l l ine overgrowths a re of ten dark in colour , and may have g iven r ise to some

of the ear l ie r repor ts of manganese minera ls be ing present in the ores .

4. Replacement facies (Fig. 2h)

A few spec imens show comple te rep lacement of coarse dolom ite rock by goe th i te and

haemat i te . In the i l lus t ra ted spec imen, the out l ines of the former dolom ite rhom bs a re

marked by poros i ty , and the main goe th i te replacement carr ies geopeta l accumula-

t ions of haemat i te wi th in each former carbonate gra in .

The po wde r ore com pon ent b ears small f ragm ents of the var ious lump ore types, as

well as abun dan t smal l f ragments of a replacement facies l i thology, in which goe th i te



PROVENANCING IRON ORE , BRISTOL CHA NNE L OREFIELD 107

Fig. 3. Powder ores from the Magor Pill boat. (a) Stacked '6-pointed stars' of goethite.

Secondary electron image o f strew mou nte d ochre. Scale bar 1 gm. Sam ple M 117. (b) Lattice

of '6-po inted sta rs' of goethite, together with oth er goethite grains. Secondary electron image

of strew m oun ted ochre. Scale bar 5 gm. Sample M 115.

i s of ten subordinate to f ine-gra ined quar tz . The quar tz dis t r ibut ion i s var iable on a

lam ina scale, imp ar t ing a crude f i ss il ity to the dis t inct ive yel low rock. M uc h of the

sand-grade com pon ent o f t he powder o re is fo rmed of degraded s t a lac t it ic f ac ies

mate r i a l . The d om inan t f i ne -gra ined com pone nt o f the pow der o re is o f c l ay g rade ,

and i s typi fied by s ix-pointed goethi te ' s tars ' (<5 m m diam eter ) . These ' s tars ' m ay

be l inked together axial ly (Fig. 3a) or lateral ly to form a lat t ice-l ike structure (Fig.

3b) . Impur i t ies in the powder ore include quar tz and c lay minerals , together wi th

some bar i te and re l ic t carbonate gra ins . These features indicate that the powder

ore i s l argely re l ic t mater ia l dep osi ted af ter di ssolut ion of hos t dolom i t ic l imestone,

freeing microscopic goethi te part icles, pieces of si l icif ied host and larger blocks of

adher ing goethi t ic ore .

The ores are a l l of high grade, wi th the lum p ores hav ing a goethi te + haema t i te

conten t of 97 -9 9% (Table 1). The po wd er i s of s light ly lower grade, bu t s t il l has a

bulk goethi te content of arou nd 83% . Trace e lemen t contents (Tables 2 and 3) of

t h e l u m p o r e s a r e e x t r e m e l y l o w ( E R E E < 1 6 p p m a n d u s u a l l y < 1 0 p p m , U a v e r a g e

2 .0 ppm , P t yp i ca l ly <0 .025% ) .

The cargo a ppea rs to have been der ived f ro m a s ingle deposi t , indeed the fea tures of

the ore and the dem ons t rably c lose re la t ionship between the var ious fac ies , me ans th at

t he ca rgo was p robab ly de r ived f rom min ing o f a si ngl e kar s t ic cham ber . The vo lume

of mater ia l i s smal l, so the cham ber mig ht have b een l i tt le more th an a met re across ,

but equal ly the mater ia l could have been der ived f rom par t of a larger cavi ty .



108 T. P. YOU NG & G. R. TH OMA S

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P R O V E N A N C I N G I R O N O R E , B R I ST O L C H A N N E L O R E F I E L D 109

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PROVE NANCI NG IRON ORE, BRISTOL CHANNE L OREFI ELD 111

Provenance of the iron ores

The arguments for an origin of the iron ores in Glamorgan have been presented

in detail by Young & Thomas (1998). The evidence included the REE contents,

the U content, the quartz-bearing mineralogy, the ore textures and the associated

host-rock fragments. Since preparation of the specialist report for the Magor

boat monograph, the authors have had the opportunity for further investigation

of the Glamorgan ores and the discussion of a more precise provenance is now

appropriate.

Geology of the Glamorgan orefield

The Glamorgan iron orefield comprises a series of areas v th mineralization in caver-

nous porosity. Most of the significant deposits lie within the Lower Carboniferous

limestones of the South Crop of the South Wales coalfield (Fig. 4), but other lesser

deposits are known from elsewhere in the Vale of Glamorgan. The major ore occur-

rences of the South Crop (Llanharry, Miskin, Lesser Garth and Fforest Fawr) lie

within pre-existing karstic voids. These caves have been interpreted to be of mid-

Triassic (Norian) age (Simms 1990). In the western part of the Glamorgan orefield,

at Llanharry and Miskin, the caves lie in the uppermost Dinantian limestones (the

Oxwich Head Limestone at Llanharry and the Hunts Bay Oolite Group at

Miskin), immediately below the seal provided by the unconformably overlying

impermeable Namurian mudrocks. To the east, at Lesser Garth and Fforest Fawr,

the major orebodies lie lower in the succession (within the Gully Oolite), and are

capped by the dolomitized High Tor Limestone.

Study of the Glamorgan iron ores is hampered by the lack of extant exposure. Llan-

harry Mine closed over twenty years ago; Trecastell, Bute, Mwyndy and Lesser Garth

Mines closed over a century ago. The Bute Mine opencast pit is backfilled, the

Mwyndy opencast pit is flooded, the Lesser Garth Mine is worked out at the

depths to which it is currently accessible (the lower parts are flooded) and the Fforest

Fawr workings are also flooded. Iron ore is visible at a few localities, but these are

Fig. 4. Simplified geological sketch map of the area northwest of Cardiff, showing the princi-

pal localities mentioned in the text.



112 T. P. YO UN G & G. R. THOM AS

proba b ly unrepresen ta t i ve o f t he ma jo r deposi ts . O n Lesse r Ga r th p oor examples o f

ores can be seen, both in the underground workings and in the adjacent TaWs Wel l

Quarry. Perhaps the bes t cur rent exposures are in Blaengwynlais Quarry where re la-

t ively smal l -scale mineral iza t ion can be seen wi thin what i s pro bab ly the Gul ly Ool i te .

There i s a limi ted l i t era ture on the Gla m org an i ron ores . Some accoun ts o f the ores

were publ i shed when the mining was in i t s heyday dur ing the las t century (Vivian

1885, 1872, 1876, 1877; Watson 1859), and these subsequently formed the basis for

later accou nts (Sibly 1919; Sibly & Llo yd 1927; Stra cha n 1899, 1909; Stra cha n &

Ca ntri l l 1902, 1904, 1912). Mor e recent wor k includes studies of the Llan ha rry

deposi t by Gayer & Cr iddle (1970) , Rankin & Cr iddle (1985) and Wil l iams (1958) .

Recent ly revised geological sheet memoirs (Waters & Lawrence 1987; Wi lson et al.

1990) con ta in l it tl e mo de rn addi t ion to the descr ipt ion of the orefie ld beyo nd c lar if i-

ca t ion of the s t ra t igraph y of the host s t ra ta .

S tudies of the i ron ores of other sectors o f the Br is tol Chan nel Oref ie ld are equal ly

sparse . The 'Specia l repor t s on the Mine ral Reso urces o f Gr eat Br i ta in ' , publ i shed as

M em oi r s o f t he Geolog i ca l S urvey , p rov ide an overv i ew o f t he F ores t o f Dea n (Sib ly

1919; Sibly & Lloy d 1927). Similarly Can tri l l et al. (1919) p rov ided a sum ma ry o f t he

deposi t s o f the Br is tol and Somerset area .

Detailed provenance of the Magor Pil l cargo

G e o l o g i c a l e v i d e n c e

Clearly , ma ny of the p rob l ems sur rounding t he i n te rpre t a t ion o f con t ext , owner sh ip

and des t inat ion of the cargo m ight becom e clearer i f a mo re precise or igin of the cargo

could be determined. The features of the cargo descr ibed abo ve s t rongly suggest that

o re was mined f rom wi th in an open cave sys tem, con t a in ing in situ ores on the walls

and cei ling of the cave and a cave-fi ll com pris ing the ochreous mater ia l w i th reworke d

lump ore c las t s . Minor ore accumulat ions a t Blaengwynlais Quarry have these

features on a smal l scale , and resemble the Magor mater ia l in having a low quar tz

con ten t , and a l ack o f ma jo r subsequen t c a rbona t e p rec ip it a ti on . Higher qua r t z con-

tents in the larger ore accum ulat ions , and s ignif icant amo unt s o f la ter carbo nate

minerals in open voids , seem to be more character i s t ic of the G lam org an ore field . S ig-

n i f ican t accumula t i ons o f ochre were r ecorded dur ing m in ing a t M wyn dy , and some

quar tz-poor layered ores can be found in the surviving spoi l dumps.

The sma l l am ou nt of mate r ia l in the cargo, com pat ible w i th der ivat ion f rom a smal l

cavi ty , mean s that i t is imposs ible to ascer ta in how representa t ive this mater ia l is of i ts

paren t sys tem. The Blaengw ynlais Q uar ry orebodies include smal l cavi ties (< 1 m dia-

meter ) wi th very var iable f i l l : some are dominated by haemat i te , some by goethi te ;

some show s igni f icant pos t -ore ca lc i te precipi ta t ion, whi le others conta in no carbo-

nate phases . This inhom ogen ei ty o f the ore deposi t ham pers p roven ancing s tudies.

A spec t rum of ore types has been recovered f rom the area of the forme r Bute Mine,

nea r M isk in . Un publ i shed excava t ion o f an ea r ly , p robab ly Rom an, sme l ti ng sit e

100 m so uth of the s ite of the Bute Mine has yie lded a substant ia l q uant i ty of ore

(Table 4) , as have n earby la ter smel t ing si tes . Provis ional in terpre ta t ion of s lag chem-

is t ry (autho rs ' unpu bl i shed data) suggest that th is ear ly s ite smel ted ores of up to 20%

SiO2, whereas pro bab le 16th century bloomer ies in the same area app ear to have been

smel t ing ore wi th less than 10% SiO2. A smal l group of recent analyses of ores f rom



P R O V EN A N C I N G I R O N O R E, BR I S TO L C H A N N E L O R EF I ELD 11 3

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116 T. P. YO UN G & G. R. THOMA S

Fig. 6. Log Ba (in ppm) v. log Pb (in ppm) for lump ores from the Magor cargo, and from

comparative locaities in Glamorgan.

earlier suspicions that the REE profiles are closely correlated with ore facies. Extreme

LREE depletion is seen in botryoidal facies examples from Llanharry and the Wor-

cester Graben faults. Layered and replacement facies ores plot much closer to a

normal upper crust profile, suggesting that their REE contents may be determined

by their sedimentary precursors. The stalactitic facies from Magor plots with a

moderate LREE depletion, probably reflecting the large proportion of botryoidal

facies overgrowth present in these rocks. A similar range of values is suggested by

the data from Llanharry and Miskin.

The U content of the ores varies considerably across the orefield, and may in due

course prove a valuable provenancing tool. At present the rather sparse data from

Glamorgan show high U values in most samples from the Taft Gorge area (Lesser

Garth, Fforest Fawr, Blaengwynlais), but the low-quartz goethite void fill at Blaeng-

wynlais was also low U. The Llanharry data are mostly low U, as are those from

Miskin, and resemble the values from the Magor cargo.

The South Crop of the South Wales coalfield hosts small-scale lead/zinc/barium

mineralization both near Miskin and to the east near Rudry. The Pb and Ba contents

of the Glamorgan ores are correspondingly variable (Fig. 6). The Magor cargo

analyses are strikingly low in both these elements, and contrast strongly with most

of the Miskin and Taft Gorge area samples, but are close to the Llanharry specimens.

The geochemical evidence is thus ambiguous. The major problem appears to be the

high degree of local variation within the orefield. There are relatively few analyses

from ores from the eastern part of the Glamorgan sector (Blaengwynlais, Fforest

Fawr, Lesser Garth), but these appear slightly different from the Magor material.

The existence at Blaengwynlais of the small goethite orebody with a mineralogy

and geochemistry close to that of the Magor material warns against dismissal of

this area as a possible source. In general the Magor material more closely resembles

the western areas of Llanharry and Miskin, but the Pb/Ba data argue against

Miskin. The possible existence of orebodies in the Miskin area without high Pb

and Ba cannot be ruled out, and none of the analysed material comes from the

area east of Mwyndy (Llwynsaer - Brofiskin), at a greater distance from the known

Pb mineralization.



PROVE NANCI NG IRON ORE, BRISTOL CHANNE L OREFI ELD 117

Exploitation evidence

There i s cons iderable doubt tha t the ores of the wes te rn end of the oref ie ld a round

Llan harry wou ld have been exploi ted a t th is ear ly per iod . T he la te onse t of 19th cen-

tu ry min ing a t L lanha r ry (apa r t f rom nea r Pa tch Co t t ages ) wou ld a rgue tha t the re

was l i t t le i f any ear ly exploi ta t ion in th is a rea . Accounts of the geology of the main

Llan harry and Trecas tel l mine s i tes ma ke i t c lear tha t the so l id geology was over la in

by cons iderable depths of Quaternary grave ls . I t i s l ike ly therefore tha t the main

orebodies were not exploi ted ear ly on, a l tho ugh e xploi ta t ion o f min or occurrences

to the south of the main be l t cann ot be ru led out .

To the east of the River Ely the ores d id c rop out . There i s documen tary evidence tha t

the Bute Mine cut through earl ier workings, and there is ample evidence for early

(Ro ma n and Medieva l ) i ron-ma king a rou nd the la te r open p i ts of the Bute and

Mwyndy mines . To the wes t smal le r orebodies may have c ropped out on Cefn-yr-

hendy, a l tho ugh mo s t of the v is ib le workings here a re probably la te 19th century . T he

s i ting of the pro bable ear ly pos t -medieva l b loom ery a t Hen dy-isaf may have been influ-

enced by proxim ity to these occurrences. S ixteenth century m ining in this general area is

described by contemporary sources (John Leland, 1506?-1552: Smith 1906). The Cefn-

yr-hendy area toge ther w i th the la te r Bute Mine lay wi th in the bound s of the M edieva l

deer park o f Clun or Gelynog, wi th in which the 16th century mining was recorded, as

did the He ndy -isaf si te . Early m ining outs ide the dee rpar k is less easy to demo nstrate .

There i s no f ie ld or docu men tary evidence for early mines on the M wynd y/Llwy nsaer

mining a rea , but the majo r ear ly b loomery a t Mw yndy, apparent ly ous ide the deerpark ,

toge ther wi th another poss ib le b loomery a t Rhiwsaeson, a re s t rongly sugges t ive of

activity in this area. The (tria l?) workings north of Brofiscin are probably younger.

Three km EN E of Brof isk in lie the next ore workings , a t Pe n-y-garn (P entyrch) , but

these a re min or . T he next major ore occurrences a re a fur ther 2 km E N E on Lesser

Ga rth Hi ll . As wi th Mwy ndy, the l ike ly a reas of early exploi ta t ion a re la rge ly

masked by la te r mining, but the s i t ing of 16th century i ronworks ( in exis tence by

1565, Riden 1992) at the foot of this hil l , implies exploitat ion by this date .

On the oppos i t e s ide o f the Ta f t Gorge , the re a re numerous work ings in F fo re s t

Faw r, of which the Sl ide Pi t is the la rges t. Trackw ays , w i th abu nd ant ore f ragments ,

lead downs lope f rom the Sl ide Pi t towards Tongwynla is , where another ext remely

early blast furnace was s i tuated (in exis tence by 1564, and therefore one of the

ear liest b las t furnaces in Wales ; Riden 1992) . One km n orthe as t of Ffor es t F aw r

l ies Blaengwynla is Quarry , wi th i t s outc rops of orebodies , but wi th no evidence ye t

for exploi ta t ion . Evidence for subs tant ia l minera l iza t ion is genera l ly lacking eas t of

Blaegwynla is , but minor ores were encountered when the Caerphi l ly Rai lway

tunnel , 3 km E N E of Blaengwynla is , was cut , and a fur ther 3 km EN E a smal l

mine was opera ted near Maenl lwyd, Rudry in the 19th century .

Thus there a re three a reas in which medieva l exploi ta t ion of i ron is l ike ly to have

occurred: f i rs t ly in the Cefn-yr-hendy to Llwynsaer t rac t , near Miskin , secondly on

Lesser Garth Hi l l and th i rd ly in Ffores t Fawr. The ava i lable geologica l da ta do not

permit d is t inc t ion of the ores f rom these a reas .

Genes i s o f the o re

Somewhat i ronica l ly , the Magor cargo represents the mos t in tens ive ly s tudied and

analysed ore depos i t f rom the Bris to l Channel oref ie ld . Despi te the fac t tha t the



118 T .P . YOU NG & G. R. THOMAS

mater ia l i s obvious ly not in situ, the cargo does offer evidence for the nature of ore

genesis . The textural evidence indicates a paragenetic sequence from layered to s talac-

t i tic to bot ryoid a l ore fac ies . The layered facies shows carb onate c rys ta l te rmina t ion s

in to open voids, inc luding subs tant ia l c racks . Such c racks , wi th l inings of ca lc i te and

dolom ite c rys ta ls, a re typica l of the box wo rk s t ruc ture assoc ia ted wi th the Crease

Limes tone in the Fores t of Dean, and a re par t icula r ly wel l deve loped where the

hos t i s not par t icula r ly minera l ized . They a re therefore in te rpre ted as having deve l -

oped as par t of the process of cavernous poros i ty genera t ion . The genera t ion of the

large-scale porosity is probably not a s ingle event (Lowe 1993), but s tarted with

pa laeokars t assoc ia ted wi th the pa laeosols in the roof of some orebodies (see

above) , reworked wi th major f lu id f low dur ing Variscan orogenes is , having a

ma jor phase of kars t i f ica t ion dur ing the Tr iass ic (Simm s 1990), and cont inuing

with kars t i f ica t ion fo l lowing upl i f t in the Ter ia ry to Recent . The emplacement of

i ron and s i l ica may have occurred more or less s imul taneous ly wi th the major void

genera t ion , but they pos t -da te dolomit iza t ion and th is , in par t a t leas t , i s i t se l f

spatial ly associated with the voids (Sibly 1919). The generation of the s talacti t ic

and botryoida l fac ies may represent reworking of th is i ron under d i f fe rent ground-

water condi t ions .

H i s t o r i c a l c o n t e x t

Ident i f ica tion of the source of the M ag or Pi ll ca rgo as the Gla mo rga n oref ield imme-

dia te ly ra ises im por tant ques t ions abo ut the pol it ical context of the boa t . The majo r

orebodies a t outc rop wi th in the oref ie ld wes t of the Taff fa l l in to the commote of

Meisgyn an d those eas t of the Taf t wi th in the com mo te of Is Caiach (par t of the

cantre f of Senghenydd; Fig . 7) . These two commotes lay immedia te ly to the nor th

o f the lands he ld by Ea r l G i lber t , Lord o f G lamo rgan 1218-1230 . Ea r l R icha rd

Fig. 7. Map showing the territorial acquisitions of the de Clare Lordship of Glamorgan

during the 13th century, in relation to the iron ore deposits of the Glam organ pa rt of the

Bristol Channel orefield.



PROVE NANCI NG IRON ORE, BRISTOL CHAN NEL OREFIEL D 119

was a min or a t the t ime of Gi lber t ' s dea th , but he ld the Lor dship 1243-1262. He soo n

expanded h is te rr i tory , f i rs t d ispossess ing the Lord of Meisgyn and Glynrhondda in

1246 and th a t of Afan the fo l lowing year. H e is be l ieved to have es tabl ished o r

en la rged Llan t r i s an t Cas tl e ( ju st 2 km nor th o f the M wynd y o rebodie s) in a roun d

1250. His son , Ear l Gi lber t the Red con t inued the dynas t ic expans ion of the de

Clares , a t leas t in par t as a response to the Trea ty of Montgomery (1267) in which

Henry I I I appea red to g ive con t ro l o f the up land co mm otes to L lywe lyn ap Gru f fudd ,

ruler of Gwynedd. Gilbert seized Is Caiach in a series of actions, including the build-

ing of Cas te l l Goch (1266) , the imprisonment of the Lord of Senghenydd, Gruffudd

ap Rhys in 1267 and bu i ld ing of Caerphi l ly Cas t le in 1268 -1271. T hus d ur ing the

per iod 1246-1266 the de Clares took contro l of the a reas conta in ing a l l the major

Glamorgan i ron o rebod ie s .

A major indus t r ia l cent re assoc ia ted wi th the de Clares has been ident i f ied a t

Trelech, Gw en t (Ho well 1989, 1995a,b). The earl ies t reco rd of a castle at Trelech,

dates from 1231, but by 1288 i t had 378 burgages, making i t the second largest

town in Wales a t the t ime. Tre lech appears to have dec l ined dur ing the ear ly 14th

century . The borough therefore had a re la t ive ly shor t - l ived importance , co inc id ing

wi th the pe r iod o f the de C la re Lords h ip o f G la mo rgan (1218-1314) . Excava t ions

a t Trelech have dem ons t ra t ed the enormous s ca le o f i ron -m ak ing in and a ro und

the town, par t icula r ly concentra ted in the per iod 1240-1290. Tre lech is ment ioned

spec if ica lly in 'The Boo k of Dennis ' the 'M iners Lawes a nd P r iv i ledges ' as a

loca t ion ( toge the r w i th Monmouth , Cae r l eon , Newpor t and Be rke ley ) a t wh ich

iron-making was under taken by smiths wi th par t icula r suppl ie rs wi th in the Fores t

of Dean. The ear lies t pr in ted vers ion of the book da tes f rom 1678 (reprod uced by

Nichol ls 1866) , a l though there a re extant manuscr ip t copies da t ing f rom as ear ly

as 1610. These versions of the book are generally believed to be based on a

th i r teenth cen tury code , an d ident ica l s ta temen ts o f par t o f the laws a re to be

found in a ' regard ' da ted to 1282. I t seems reasonable to in te rpre t the foundat ion

of such a major i ron making borough in a somewhat ' a r t i f ic ia l ' loca t ion , as an

a t tempt by the de Clares to u t i l ize the Fores t of Dean ore by bui ld ing wi th in

the i r domains , but as close to the F ores t as poss ib le . Ind eed, Tre lech is only 6 km

far ther f rom the ore sources of the wes te rn Fo res t o f De an than the th i r teenth

century Roy al forge and a rsena l a t St Briave ls (a lbe it on the oppos i te s ide of the

Wye Valley).

The da te of the founder ing of the Magor Pi l l vesse l i s d i f f icul t to de te rmine , but

an es t imate for i ts age as 10 -40 years seems mos t l ike ly (M. R edk nap , pers. comm .) .

This would p lace the like ly da te of found er ing in the per iod 1250-1280, b ut the

vessel is unlikely to have been more than 50 years old, so the date almost certainly

l ies wi th in 1240-1290; the peak per iod of i ron ma kin g a t Tre lech . This same per iod

saw the de Clares subsume the ore-producing a reas in Glamorgan wi th in the i r

hold ings , so a l ike ly scenar io would be tha t ore f rom those a reas would be sh ipped

to the de Clare indus t r ia l base a t Tre lech for smel t ing . The route for such a

shipment would mos t l ike ly have been over land to Cardi f f , and then by boa t up

the channel, up the Wye as close as possible to Trelech; a route passing

Abergwaitha.

I t i s poss ib le tha t the Glamorgan oref ie lds found o ther cus tomers dur ing th is

per iod , but i t may be s igni f icant tha t the mines on the la te r Bute Mine s i te , a t

leas t , were on demesne land, and would therefore have been subjec t to d i rec t

se igneur ia l contro l . I t i s worth not ing tha t the Tewkesbury Annals for 1262





PROVENANCING IRON ORE, BRISTOL CHANNEL OREFIELD 121

SmLu T. F. 1919. Special reports on the mineral resources of Great Britain. Vol. X - - Iron ores

(contd.) - - The haematites of the Forest of Dean and South Wales. Memoirs of the

Geological Survey. HMSO, London.

- - & LLOYD, W. 1927.

Special reports on the mineral resources of Great Britain. Vol. X - - Iron

ores (contd.) - - The haematites of the Forest of Dean and South Wales. 2nd Edition.

Memoirs of the Geological Survey. HMSO, London.

SIMMS, M. J. 1990. Triass ic Paleokarst in Brita in, Cave Science, 17, 93-101.

SMITH, L. T. 1906. The Itinerary in Wales of John Leland in or about the years 1536-1539

extracted from his MS S. George Bell, London.

STRACHAN, A. 1899. The Geology of the South Wales Coalfield. Part L The country around

Newport . Memoir of the Geological Survey. HMSO, London.

-- 1909. The Geology of the South Wales Coalfield. Part I. T he country around Newp ort (2nd

edition). Memoir of the Geological Survey. HMSO, London.

- - • CANTRILL,

T. C. 1902. The geology of the South Wales Coalfield. Part IlL The country

around Cardiff. Memoir o f the Geological Survey of Great Britain. HMSO, London.

- - & - - 1904. The geology of the South Wales Coalfield. Part VI. The country around

Bridgend.

Memoir o f the Geological Survey of Great Britain. HMSO, London.

-- & -- 1912. The geology of the South Wales Coalfield. Part IlL The country around

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crust: rare earth element evidence from sedimentary rocks. Philosophical Transactions of

the Royal Society, A301, 381-399.

THOMAS, G. R. & YOUNG, T. P. 1999. The determinat ion ofbl oomery furnace mass balance and

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VIVIAN, S. 1885 . The haemati te deposits o f the southern outc rop of the C arbon iferous

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164 [discussion p. 211]

- - 1872. The Mwyndy Mines. Transactions of the C ardiff Naturalists ' Society, 3, 79.

1876. Note on paragenetic formation of carbonate of lime and oxide of iron, at the

Mwyndy Mines, Glamorgnashire. With note on the specimens by J. H. Collins. Transac-

tions of the Cardiff Naturalists' Society, 4, 70.

- -

1877. Furthe r notes on the oxides of iron, enclosed in quartz, at Mwynydy, Glamorg an-

shire. Transactions of the Cardiff Naturalists Society, 4, 117.

WATERS,

R. A. &

LAWRENCE,

D. J. D. 1987. The geology of the South Wales Coalfield. Par t IlL

The country around Cardiff. M em oir fo r 1:50,000 geological sheet 263 (En gland and Wales)

(Thir d edition). Britsh Geological Survey. HMSO, London.

WATSON, J. J. W. 1859. The haematit e deposits of Glamorganshire. Geologist, 2, 241-256.

WILLIAMS,

M. 1958. Geology and mineralisation of the Llanha rry hema tite deposits, South Wales.

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WILSON, D., DAVIES, J. R., FLETCHER, C. J. N. & SMITH, M. 1990. The geology of the South

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YOUNG, T. P. & THOMAS, G. R. 1998. The cargo: iron ore analysis . In. NAYLING, N. The Magor

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105-111.



Geochemistry of ballast granites from Brouage and

La Rochelle, France: evidence for medieval to

post-medieval trade with Falmouth, Cornwall,

and Donegal, Ireland

C L A I R E E . L A Z A R E T H 1 &

J E A N - C L A U D E C . M E R C I E R

Univers i t~ de La Roche l le , C LD G, UF R Sc iences ,

A ven u e M a r i l l a c F - 1 7 0 4 2 L a R o ch e l l e c ed ex 1 , F r a n ce

1presen t address. A N C H - V U B , P le in laan 2 ,

B -1050 Brusse l s , Be lg ium

Abstract: Determina t ion of the geographica l o r ig in o f exo t ic ba l las t bou lders

found in var ious a rchaeo log ica l ly da ted cons t ruc tions o f medieva l and pos t -med-

ieval age along E urop ean shores provides evidence for early comm ercial sea l inks.

However, ballast often consists of com mo n granites. Some are identif ied here by

com binin g multip le geochemical tools which sup port a f irs t-degree classif ication

into two groups, muscovite-bearing (with or without bioti te) or muscovite-free

(with bioti te as the only mica), each one showing a remarkably very narrow and

dist inct range in mineral composit ions. This suggests a s ingle locali ty for the

origin of each type of granites. Ind ist inguis hable musco vite-bearing facies are

found in La Rochelle and Brouage, with one representative sample geologically

dated at 274 + 6 Ma. In agreeme nt with the evidence from b ulk-rock and p hase

chemistry which are similar to those of the Carnm enell is intrusion, Co rnwall ,

this geological age strongly supports early comme rcial sea l inks with nearby Fal-

mou th, a t least from the end of the 14th to the middle of the 16th century. For the

muscovite-free granites fou nd in Brouage in a different s ite dated c . 1650, s imilar

inves tigation s and a 393 -4- 9 M a geological age, s trong ly sugg est bal last lo adi ng

nor th o f Ros Eo ghain Poin t , I re land , and d i rec t t rade wi th nearby Donega l .

E u r o p e a n - s c al e m a r i t i m e t r ad e w a s i m p o r t a n t i n th e M i d d l e A g e s a n d e a r l y m o d e r n

t im e s , t h o u g h w r i t t e n r e c o rd s a r e n o l o n g e r a v a i l a b l e t o r e c o n s t r u c t r o u t e s a n d m o d e s

o f tr a d e w i t h m u c h c o n f i d e n ce . B a l l a s t b o u l d e r s s u c h a s t h os e f o u n d a l o n g a 3 0 0 k m

s t re t c h o f th e F r e n c h A t l a n t i c c o a s t o n e i t h e r s id e o f L a R o c h e l l e m a y n o w p r o v i d e

u s e f u l c o n s t r a i n t s o n s u c h o l d s e a l i n k s .

F l a t - h u l l m e r c h a n t s h ip s s a i l in g o ff s h o re o n b a l l a s t u s u a l l y c a rr i e d b o u l d e r s

c o l le c t ed o n b a r s o r m o r a i n e s n e a r t h e p o r ts o f d e p a r t u r e . W h e n t h e y a r r iv e d c l o se

t o t h e m e r c h a n d i s e l o a d i n g p l a ce , b o u l d e r s w e r e o f t e n t h r o w n o v e r b o a r d t o r ed u c e

t h e d r a u g h t a n d m a k e s p a c e f o r t h e g o o d s s u c h a s s a l t o r w i n e . C h a r t s s h o w t h a t

u n l o a d i n g b a l l a s t a t s pe c i fi c p l a c e s w a s s t r i c t l y e n f o r c e d , w h i c h p r o d u c e d o v e r t h e

c e n t u r i e s a m i x t u r e o f r o c k s f r o m v a r i o u s o r i g i n s . T h e s e d e p o s i t s a r e u s u a l l y s e e n

a s t h e s o u r c e o f th e b a l l a s t b o u l d e r s u s e d a s b u i l d i n g m a t e r i a l i n c it ie s a n d v i l l a g e s

a l o n g t h e s e a s h o r e .

From. POLLARD,A. M. (ed.) 1999. Geoarchaeology:exploration, environments,resources.

Geolo gical Society, Londo n, Special Publications, 1 65, 123-137. 1-86239-053-3/99/$15.00




12 4 C . E . L A Z A R E T H & J .- C. C . M E R C I E R

This i s however not supported by observa t ions a t severa l a rchaeologica l ly da ted

sites we s tudied, which co nsis t of wall found atio ns, walls in elevation, or oth er s truc-

tures made of ba l las t boulders . In none of these s i tes d id we f ind mixed exot ic rock

types. Specifically, in Brouage, the same types/facies are found at a scale of several

metres (up to decametres ) , though d i f fe rent ones a re observed a t the sca le of a

whole wall or in walls buil t a t different t imes.

To have such a d is t ribut ion pa t te rn ( fur ther docum ented be low), the rocks had to be

or ig ina l ly p icked up in a na tura l geologica l environment , presumably near the home

port , they were not dumped and re loaded a t es tabl ished unloading s i tes but ra ther

brought directly to final destination and they were ult imately discharged directly on

the docks to be used very shortly afterwards as building material . If any one of these

condit ions had not been fulfi l led, a mixing of rock types should have occurred.

Carry ing ba l las t in such a way may have been except iona l and should not be

opposed to t radi t iona l v iews on ba l las t dumping. However , i t provides a unique

opp ortu ni ty to recons t ruc t fo rmer co mm erc ia l routes a t spec if ic da tes . Indeed, miner-

a logica l and geoch emica l da ta for boulders m ay be used to cons t ra in the i r geographi-

ca l orig in which , in th is case , corresponds to the hom e p or t (or main por t of ca ll ) of

indiv idua l sh ips s ince the rocks were brou ght d i rec t ly . On the o ther ha nd, the i r t ime of

unloading is g iven by a rchaeologica l ly da t ing the s t ruc ture , which y ie lds e i ther the

same age i f the boulders were used immedia te ly as bui ld ing mater ia l , or an u pper age .

The major-e lement phase-chemis t ry da ta d iscussed here were obta ined on a

CAMEBAX mic roprobe (Campar i s ana ly t i c a l c en te r , Un ive rs i ty Pa r i s -VI ) unde r a

15 kV acce le ra t ion vol tage , a 9 .2 nA current and wi th a count ing t ime o f 10 s . In our

s tudy, d iagrams appeared to be more d iscr imina t ing when cons ider ing the e lementa l

f rac t ion for each c rys ta l lographic s i te (Lazare th 1998) . Hence , the compos i t iona l

da ta for micas a re reca lcula ted in a tom num bers for 22 pos i tive charges, subsequent ly

abb rev iated as 'a t . per 22 + f .u. '. T his con ven tion also mak es i t easier to identify com-

pos i t iona l corre la t ions tha t a re mere a r te fac ts due to s to ichiometry and/or charge

com pensa t ion . The s ignif icant corre la t ions o bserved be tween ca t ions and the repl ica te

analyses yield a nalytical uncertain ties s ignificantly less than 0.01 per 22 + f .u. for al l

analysed elements , w ith the ex ception of fluorine (+0 .05 per 22 + f .u.) .

The sample se lec tion for whole-rock ana lyses of each type of grani te was based on

the degree of a l te ra t ion , the rock hom ogenei ty , and the f resh-core volume ava i lable .

Fis t -s ized f ragments of the se lec ted samples were ana lysed through induct ive ly

coup led p la s ma-a tomic emis s ion s pec t rome t ry ( ICP-AES) a t t he Cen t re R6g iona l

de Mesures Phys iques , Univers i ty of Cler mo nt-F erran d. Analyt ica l condi t ions and

standards are given in Cantagrel & Pin (1994). Selected samples were geologically

da ted on s epa rate mine ra l s by the K/A r me tho d , w i th po ta s sium con ten t s meas u red

by a tomic abs o rp t ion s pec t rome t ry and a rgon on a mod i f ied T HN 205 E mas s

spec t rometer , both a t the Centre de Recherche P6trographique e t G6ochimique ,

C N R S - N a n c y .

Sample environments

L a R oche l l e

This c ity, 170 km nor th of Bordeaux on the wes t coas t of France , grew out o f a smal l

medieva l v i l lage and h arb ou r a f te r 1146, wi th the se t tl ing of he i rs of the mighty feuda l



GEOCHEMI STRY OF BALLAST GRANITES, FRAN CE 125

lord of Chatelai llon expelled in 1130 from his chgtteau, 12 km to the south. Mean-

while, the English founded an important garrison fort beside it, the so-called Vauclair

castle. Built in 1162 under Henri II Plantagen6t, Vauclair had full control of harbour

activities which included trade with Southampton, Portsmouth and Dublin, as early

as 1185 (Delafosse et al. 1991). This fortified place was taken and levelled to the

ground in 1372 by the inhabitants of La Rochelle by authorization of the king of

France. At this time, La Rochelle already had the privilege of making metal money

and, soon after the dismantling of the garrison, the manufacture was moved to the

former garrison grounds, in 1394.

The place where this new 'H6tel de la Monnaie' used to stand was excavated in

1995. Among various structures illustrating all the steps of processing the metal,

from ore to coins, there was also found the basal part of an importan t ore treatment

complex made of local Jurassic limestone except for the internal faces of a furnace

(Fig. l a) entirely built of rounded granitic boulders (except for rare gneisses and

for a few bricks used in repairs). These granites (0.2-0.8m long, >0.1 m thick) are

unknown regionally in natural geological environments and hence they are inter-

preted as ballast boulders used here for their (relative) refractory properties, as is

also the case in back-chimney stews found in a medieval tower of La Rochelle.

As this structure was to be dug out, all the granites used as internal facing stones

were numbered and collected (159 samples) and, in the absence of any spatial hetero-

geneity in petrological types, our further studies were arbitrarily limited to the 36

boulders of the eastern wall. Archaeological stratigraphic data (Bocquet & Mille

1995) suggest the very first years of the 15th century for the date of construction of

the furnace and, considering the manufacture was moved in 1394, the intermediate

date of c. 1400 will be used.

B r o u a g e

Brouage, a still fully fortified city about 30 km south of La Rochelle, was founded

around 1550 (La Popelini~re 1581) at the mouth of the main channel used to drain

the furthest inland marshes and, at rising tides, to feed the lower salt marshes sur-

rounding the area. Extraction of salt in these marshes began as early as the second

century Be, but production increased tremendously between the end of the 8th and

the early 9th centuries (Gl6nisson 1981). Soon after 1550, Brouage became the fore-

most port in Europe for salt exportation.

In Brouage, abundant exotic rounded ballast boulders (about 0.3 m in size, some up

to 0.5 m) were sampled in three structures:

9 a remnant of the oldest-dated city wall built by Italians in 1570 and which consists

of the lower part of the internal facing of the northern wall named 'Courtine

Royale'

9 the foundat ion garnish (rock/l ime filling between elements of a wood structure built

on the marsh to support a wall) of the external doubling built under Richelieu in

1631 against the western city wall named 'Courtine de la Mer' (from here on,

referred to as CM; Fig. lb)

9 a discontinuous sandy layer directly underneath an earth-made internal terrace

built under Vauban in 1689 against the city wall named 'Cour tine Richelieu'

(henceforth referred to as CR)



126 C .E . LAZ ARE TH & J.-C. C. ME RCIE R

(a)

Ib)

Fig . 1 . Two o f t he s t ruc tu re s p rov id ing a rchaeo log i ca l l y da t ed b a l l a s t bou lde rs: (a ) o re

furnace ( lower hal f) of the co in manufacture in La Rochel le (c . 1400); (b) wood s t ructure

used fo r bu i ld ing o n t he m arsh , wes t e rn wa l l, Bro uage (1631) .



GEOCHEMISTRY OF BALLAST GRAN ITES, FRAN CE 127

Rock type distribution as evidence for direct travel

In Brouage, the samples collected virtually al l belong to a s ingle rock-type or series at

each s i te (Table 1) and are different from one s i te to another. The Ital ian wall is char-

ac te rized by a par t icula r type o f syenites kn ow n to or ig ina te only in Norw ay where i t

i s loca l ly ca l led la rv ik i tes , whereas mos t of the CM samples a re muscovi te -bear ing

grani tes (85%) and the CR ones , muscovi te -f ree grani tes (90%). Moreover , a carefu l

inspec t ion of a l l ba l las t -made h is tor ic wal ls of Brouage fa iled to provide any evidence

of mixing for the l i thologica l types which co uld be ident if ied

in s i tu ,

such as larvikites ,

but a lso f resh o l iv ine basa l ts and amphibol i t ized coarse gabbros , each one of these

being s trict ly restricted to a very well defined part of a wall .

As for L a R ochel le , the in te rna l fac ing s tones of the ore furnace were v i r tua l ly a ll

muscovi te -bear ing grani tes (96%) and the few gne isses descr ibed ac tua l ly a re the

main par ts of igneous na tura l polymic t samples par t ly made of s imi la r grani tes ,

hence poin t in g to a com mo n geog raphica l or ig in . This contras ts wi th the la rge var ie ty

of me tam orp hic rocks observed in the walls and towers of La Rochel le , inc luding the

medieva l back-chimney s tews in Tour de la Chaine .

As s ta ted ear l ie r , th is non-mixin g of sample types a t one s i te is a s t rong a rg um ent

for d i rec t t rave l f rom the geologica l source regions o f the boulders , ra ther than

cabotage , a t leas t for the sh ips sa i l ing on ba l las t which t raded wi th Brouage and

La Rochel le . Cabotage , tha t i s t rading wi th numerous por t s tops en rou te , w o u l d

have indeed needed unloading and re loading of ba l las t a t spec i f ic s i tes , wi th mixing

of the rocks f rom var ious sh ips . Simi la r ly , ba l las t p icked up for cons t ruc t ion a t

nearby ear l ie r unloading s i tes would have a lso been mixed, according to the la rge

var ie ty of rock types o bserved in the var ious w alls . This sugges ts tha t ba l las t was

used immedia te ly upon unloading, i .e . tha t i t was taken to a dock (as would have

been commerc ia l goods) as bui ld ing mater ia l for works in progress .

The above pre l iminary conc lus ion is fur ther supported by the phase chemis t ry for

the grani tes (Lazare th 1998) . For ins tance , the muscovi te -f ree and the muscovi te -

bear ing facies mu s t indeed be cons idered as two dis t inc t popu la t ions . As an exam ple ,

plott in g the s i licon (Si; al l te trah edra l) versus oc tahe dra l alu mi niu m (VIA1) con tents of

bioti tes (Fig. 2) yields two g roup s with a comp osit ion al ga p in between. Eve n if A1-

sa tura ted b io t i tes of musco vi te -bear ing grani tes a re l ike ly to be r icher in A1 (formal ly ,

th is would ho ld only under s imi la r phys ica l condi t ions of crys ta ll iza tion) , a con t inu-

ous change in l iquid compo s i t ion as expec ted f rom frac t iona l c rys ta l l iza t ion could n ot

result in such a gap. Thus , w e a re dea ling wi th two gene t ica l ly unre la ted p opu la t ion s

which we sha l l d iscuss independent ly . The res t r ic ted compos i t iona l domain for each

group compared to var ious European grani tes wi l l provide fur ther evidence for the

absence of mixing an d therefore aga ins t the prac t ice of cabotage .

The muscovite-bearing granites

Mu scovi te-beati ng granites have been found b oth in La Rochelle (furnace; c . 1400) and

in Brouage (s i te CM, precisely dated 1631). They are described together s ince no

significant difference has been found between them at any point during the s tudy. A

geologica l da te could not be obta ined for the samples f rom La Rochel le because of

their long exposure to the very high temperatures reached in the furnace, whils t the

da te o f furnace cons t ruc t ion rest r ic ts the ir geographica l or ig in to Eur opean shores .



1 28 C . E . L A Z A R E T H & J .- C . C . M E R C I E R

r

0

. 0

Z

c~

0

0

0

c~

0

.~..~

~ o ~

~ , . . .~ g~l~ ~'~

o

Z

a =

o , - ~

,.._r

o

o u . ,

o

4.o 0~



GEOCHEMISTRY OF BALLAST GRANITES, FRANCE 129

Fig. 2. Concentrations in Si and VIA1for the biotites of all the granites from La Rochelle and

Brouage (CM and CR sites). A significant gap exists between the biotites of the muscovite-

bearing and muscovite-free granites, but overlaps between samples do not support further

identification of subg roups.

Petrography

The muscovi te-bear ing grani tes are most ly two-mica grani tes that can be ascr ibed to

di f ferent fac ies according to thei r mineralogy. In addi t ion to quar tz , p lagioclase and

potass ic fe ldspars ( the three bas ic com pon ents of a grani te) and, of course , to biot i te

and muscovi te , the mineral assemblage may a lso include garnet , green tourmal ine and

blue tourmal ine , the la t ter two never being found together . Biot i te- f ree grani tes are

always associa ted wi th the two-mica grani tes in our di f ferent s i tes and they share

some common charac t e r i s t i c s ( same compos i t i ons o r same compos i t i ona l t r ends

depending on the parameters) . Accordingly, they wi l l be descr ibed together under

the gener ic nam e o f musc ovi te-be ar ing grani tes .

Acco rding to the textures observed in thin sections , the two micas may h ave crys ta l-

l ized s imul taneously or not . In the f i rs t case , b iot i te and musc ovi te are sys temat ical ly

associa ted (F ig. 3a) ; in the second, muscovi tes can be subdivided into two popula-

t ions : ear ly muscovi tes included in fe ldspars (F ig. 3b) and la ter ones occurr ing as

i sola ted table t s in the 3D-m ineral mat r ix (associa t ion of the two micas i s then excep-

t ional ) . Ga rnet s are a lways smal l isola ted crys ta ls (0 .25 to 0 .80 mm ), xen om orph ic in

most grani tes , somet imes subidiomorphic in the biot i te- f ree grani tes . Green tourma-

l ine occurs ei ther as small isolated crystals or part ly included in biot i tes (Fig. 3c) . This

cont ras t s w i th the behav iour of blue tourm al ine that i s e i ther inters t i ti a l between crys-

ta l s (F ig. 3d) or in termingled wi th fe ldspar , apparent ly f i l l ing hydraul ic f rac tures in

crys ta l s of the la t ter phase . U nl ike green tourm al ine , blue ones are thus c lear ly

la te-crys ta l l iza t ion phases and correspond to the las t l iquids .

A magmatic series

The abo ve character i s t ics can be used to def ine a large nu mb er of mineralogical types

and sub types of grani tes am on g the samples . In theory, th i s may resul t f rom the

mixing of musc ovi te-be ar ing grani tes of di f ferent geograph ical or igins . However ,

phase chemis t ry (composi t ions , Fe par t i t ioning, e tc . ) ra ther suggests a cont inuous

ser ies resul t ing f rom magma di f ferent ia t ion.







132 C. E. LAZARETH & J.-C. C. MERCIER

Fig. 5. Ti/Mn trend for the muscovites in granite boulders according to differentiation

inferred from the mineral assemblages (arrow). All symbols include garnet-bearing and

garnet-free granites as presence of this phase has no apparent effect on the chemical param-

eters used here. B and Tb stand for biotite and blue tourmaline, respectively.

I n a d d i t i o n , t h e n a r r o w r a n g e s i n p h a s e c o m p o s i t i o n s ( b o t h s a m p l i n g s i t e s c o m -

b i n e d ) c o m p a r e d t o t h o s e f o r E u r o p e a n m u s c o v i t e - b e a r i n g g r a n i t e s ( S c a n d i n a v i a ,

S co t l and , C ornw al l and B r i t t any ; r e fe rences in F ig . 6 ) i s s t r ik ing , and im ply a

c o m m o n s pe ci fi c r a n g e o f p h y s i c a l c o n d i t i o n s f o r a ll th e m u s c o v i t e - b e a r i n g g r a n i t e s

fou nd as bou lde r s . F o r the l a t t e r , t he V IA 1 va lues fo r b io t i t e s l ie be tw een 0 .25 and

0 .70 a t . pe r 22 + f .u . (m ax im um range) , w i th m o s t sam ples be tw een 0 .30 and 0 .55 , i n

con t ras t t o the 0 .05 to 0 .93 r ange r ecorded in the l i t e r a tu re . F ur the rm ore , t he ove ra l l

sca t t e r fo r t he b ou lde r s i s even l e ss t han tha t fo r any o f the loca l i t ie s desc r ibed in the

l i t e ra tu re , w hen d i sca rd ing the l im i t ed da tase t fo r B r i t t any . I t is t hus h igh ly p ro bab le

t h a t a l l t h e m u s c o v i t e - b e a r i n g g r a n i t e s f r o m b o t h L a R o c h e l l e a n d B r o u a g e h a v e t h e

same or igin , a t leas t a t a regional level .

Fig. 6. Con centration s in Si and VIA1 for biotites o f the muscovite-bearing granites from

Brouage and La Rochelle (ballast: solid circles and patterns, the darker one including 95%

of the samples) and fro m E uro pean localities: Scandinavia (L azareth 1998), Scotland (Tindle

& W ebb 1990; Harrison 1990), Cornwall (Tindle & Webb 1990; Stone et a l . 1988) and Brit-

tan y (Na chit 1986). Biotite com positions fro m the literature have been recalculated on 22 +

charges for consistency.



GEOCHEMISTRY OF BALLAST GRAN ITES, FRAN CE 133

Geographical origin

We may f i rs t compare the pe t rochemica l charac te r is t ics of our boulders to those of

va r ious European mus cov i t e -bea r ing g ran i t e s l i ke ly to have p rov ided ma te r i a l fo r

shore bars and mora ines . Scandinavian muscovi te -bear ing grani tes can be exc luded

as a potent ia l source as the i r b io t i tes mainly have to ta l ly d is t inc t compos i t ions

(Fig . 6) . Though bio t i tes f rom Scot land and Cornwal l grani tes not only show a

la rge sca t te r , but a lso a compos i t iona l d is t r ibut ion somewhat offse t , such sources

cann ot be exc luded because the sparse da ta in the l i te ra ture m ay n ot be volumetr ica l ly

representa tive . Th e Bri t tany grani tes would h owever ap pear as be t te r candida tes , s t i ll

confo rmin g to the b io t i te comp os i t ions . O ther minera ls such as accessory phases a lso

provide some cons t ra in ts . For ins tance , the tourmal ines in Scandinavian grani tes

have much higher Mg co ntents an d ab out three times mo re X-s i te vacanc ies per s t ruc-

tura l formula than those f rom any ba l las t grani te (Lazare th 1998) , aga in exc luding

such a poss ib le Scandinavian or ig in .

In addi t io n to phase-chem is t ry c r i te r ia, whole-rock co mpo s i t ions m ay a lso be used .

No ne of the b inary p lo ts (e .g . CaO v SiO2, B av Sr , e tc . ; (Lazare th 1998)) appear to be

suff ic ient ly d iscr imina t ing to indica te whether the grani te boulders come from e i ther

Bri t tany o r Cor nwal l (or even Scot land) by c learly exc luding one (or two) o f these

regions . However , the grani tes f rom Cornwal l have ra re -ear th e lement pa t te rns

qui te s imi la r to those for the ba l las t boulders , one o f which , tha t for the Carnm enel l i s

in t rus ion , near Fa lmouth , i s v i r tua l ly ident ica l (Fig . 7) .

I t is thus c lear tha t geochem ica l da ta , e i ther for mine ra l phases or bu lk rocks , may

provide def in i te c r i te r ia to exc lude some grani tes , but tha t the va l id i ty of the source

ident i f ica t ion depends on the qua l i ty of a European -sca le d a taba se w hich is st il l

very f ragmentary . The geographica l or ig in of the ba l las t grani tes can however be

ul t imate ly cons t ra ined by geochronolog ica l da ta , i . e. geologica l ages of form at ion .

Grani tes in shore bars and coas ta l mora ines may be re la ted to three major tec tonic

and age units : the Bal t ic -Fen noscan dian sh ield (Precam brian , c . 3300 -550 Ma) , the

No rth- At la nt ic C aledonides (Caledon ian , c . 500 -400 M a) and the Varisc ides (Her-

cyn ian , c. 400-24 0 Ma) . As the age o f fo rma t ion ob ta ined th rough K/ Ar da t ing on

mus cov i t e fo r one rep re s en ta t ive mus cov i t e -bea r ing g ran i t e f rom Brouage (BR.G5)

Fig. 7. Ranges and means o f normalised rare-earth element concentrations for blue-tourma-

line-free muscovite-bearing granites occurring as ballast boulders (Brouage, La Rochelle)

and from the Carnmenellis intrusion, Cornwall (Jefferies 1985).



134 C. E. LA ZAR ET H & J.-C. C. ME RC IE R

is 274 + 6 M a, t ha t is of Herc yni an age, the source locali ty should b e looked fo r exclu-

s ive ly only a long the coas t of Bri t tany, Cornw al l , P or tug a l or Gal ic ia . T he la t te r two

can be read i ly d i s ca rded a s be ing too o ld (>310Ma) and /o r ho rnb lende -bea r ing

(Julivert

et al.

1980) . As the grani tes of Bri t tany a re a lways o lder than 300Ma

(Car ron

et al.

1994) , the young er ones in Cornw al l (268 to 290 Ma ; L ond on & Man -

ning 1995) appear to be the only poss ib le source for the muscovi te -bear ing grani te

ba l las t . The exac t provenance can even be p inpointed as be ing the Carnmenel l i s

in t rus ion , w i th an age rang ing f rom 269 + 2M a to 290 + 2M a (Darbys h ire &

Shepherd 1985, 1987) which encom passes the BR .G5 age of 274 M a 4-6 Ma. Al l the

other intrusio ns are you nge r (268 + 2 M a) or older (from 280 to 287 -+- 4 M a) granite

(Lo ndo n & Ma nn ing 1995) . Thus , cons ider ing a l l the charac te ris t ics of the muscovi te -

bear ing grani te boulders (minera l chemis t ry , rock compos i t ions and geologica l age) ,

the only p lace f rom where they could have been p icked up is a long the Channel shore

to the south of the Carnm enel l i s in t rus ion , by sh ips f rom the home por t of Fa lm outh .

The muscovite-free granites

Muscovi te -f ree grani tes a re the only p lu tonic type (except for one tona l i te sample)

found in the d iscont inuous sandy layer benea th the eas te rn wal l ear thwork bui l t by

Vauban in 1689 (s i te CR). Previous occupat ion and apparent sand removal before

building the earth terrace justifies an earl ier date for the ballast deposit , es t imated

to be c. 1650. Hence, a Ne w W orld im po rt w ould be his torically possible if i t were

not tha t such grani tes a re not ident i f ied a t nearby por ts then potent ia l ly t rading

with Brouage . Archaeo logica l s ites not ye t sampled (e.g. the wal ls of the former

hospi ta l ) , however , show volcanic /p lu tonic rocks tha t could have a New World

origin (Antil les , Canada).

P e t r o g r a p h y

The minera logica l assemblage of the muscovi te -f ree grani tes i s very homogeneous ,

wi th the four rock-forming phases : quar tz , p lagioc lase , K-spar and b io t i te . A few

rare samples a lso have some sca t te red amphibole , the only accessory phase found

in th is type o f grani te . Co mp are d to the muscovi te -bear ing grani tes , the s implic ity

of the assemblages, the lack of specific textural relat ionships and the l ikeness of the

samples (Lazare th 1998) do no t jus t ify fur ther pe t rogr aphic descr ip t ions here in .

Geograph i ca l o r i g i n

In te rms of Si v WA1, the b io t i te com pos i t ions of the S candinav ian m uscovi te -f ree

grani tes a re mainly not cons is tent wi th the boulder b io t i te compos i t ions (Fig . 8) .

The muscovi te -f ree grani tes f rom England and Bri t tany show a la rge sca t te r , wi th

only two analyses for Brit tany plott ing over the main field for the ballast granites .

As for amphiboles , those f rom boulders p lo t somewhat to the lower s ide of a gross

M g/( M g + Fe) v Na § K nega t ive corre la t ion foun d for Eu rop ean muscovi te -free

grani tes (Lazare th 1998) , which does not support a source loca l i ty in England and

vir tua l ly exc ludes an or ig in in Bri t tany (muc h lower N a § K) . This conc lus ion is

in agreement wi th hand-spec imen observa t ions , the muscovi te -f ree grani tes f rom

Bri t tany having a typica l p ink hue never observed for any boulder .



G E O C H E M I S T R Y O F B A L L A S T G R A N I T E S , F R A N C E 135

Fig. 8. Concentrations in Si and VIA1 for biotites of muscovite-free granites from Brouage

and La Rochelle (symbols as in Fig. 6) and from European localities : Scandinavia (Brigatti

et al.

1991; Lazareth 1998), England (Shap granite; C aunt 1986) and Brittany (Nac hit

1986).

In te rms of whole-rock compos i t ions , the Si content , potent ia l ly s igni f icant as a

di f fe rentia t ion index, a lso does not su ppo rt a source loca l i ty in Englan d for the ba l las t

muscovi te -f ree granites . Such an or ig in can be def in ite ly d iscarded according to o ther

param eters such as the Ba/Sr ra t io , 1 .6 for grani tes f rom E nglan d com pare d to 4 .5 for

the ba l las t samples (Lazare th 1998) . Hence , the geochemica l da ta s t rongly sugges t

tha t the boulders were loaded in I re land inasmuch as amphibole-bear ing fac ies a re

also known in this region.

As muscovi te -f ree grani tes a re Hercynian (c . 400-240 Ma) in Bri t tany, Caledonian

(c. 500-400 M a) in I re land and P recam brian (c. 3300-550 M a) in Scandinavia , the

age of format ion of the boulder grani tes aga in i s a f ina l and c r i t ica l a rgument for

es tabl ish ing the ir geographic or ig in . Meas urem ent o f K/ A r iso topes on separa te

bio t i tes f rom a representa t ive muscovi te -f ree sample f rom Brouage (BR.C10) y ie lds

an age of 393 + 9 Ma , which u nam bigu ous ly denotes i t as a C aledo nian grani te.

Englan d a nd Scandin avia can thus be def in i te ly exc luded as potent ia l source regions ,

as was a l ready sugges ted above . The muscovi te -f ree grani tes mus t , then , have been

picked up in the Bri t i sh Caledonides and, even more prec ise ly , a long the shore of

nor thwes te rn I re land. Indeed, only the Donegal ba thol i th , which is loca ted a long

this shore , has whole-rock compos i t ions s imi la r to those of the ba l las t muscovi te -

f ree grani tes . Fur th erm ore , the ages of form at ion for th is grani te range f rom 357 to

400 Ma . M or e specifically s t il l, the oldest age of 392 + 8 M a is indis t inguish able

from tha t of the ba l las t sample . I t i s found to the nor th of Ros Eoghain Point ,

which ships coming from the c ity of Do nega l (Dd n N a G al l ) had to pass on the i r

way to the I r i sh Sea and to France (Fique t & Leblanc 1997) .

C on c lu s ion s

Two granite series are identified within the samples , the presence or absence of

muscovi te be ing the s imples t d isc r iminant c r i te r ion . Muscovi te -bear ing grani tes

and muscovi te -f ree grani tes a re to ta l ly unre la ted pe t rogenet ica l ly as shown by the i r

phase chemistry (e .g. bioti tes), their whole-rock chemistry (e .g. rare-earth elements)

and geologica l ages de te rmined for two representa t ive samples (Hercynian v



136 C. E. LAZAR ETH & J.-C. C. MERC IER

Fig. 9. The ea rly commercial sea links reconstru cted from the gran ite ballast study:

Falmouth - La Rochelle, Falmouth - Brouage and Donegal - Brouage.

C a l e d o n i a n ) . T h a t t h e y a r e f o u n d i n s e p a r a t e s i t e s w i t h n o m i x i n g w i t h e a c h o t h e r

o r w i th o the r l oca l ba l l a s t rock types ( l a rv ik i t e s , basa l t s , gabbros rocks ) , show s the

b a l l a s t s tu d i e d w a s c a r r i e d d i re c t ly f r o m n e a r t h e h o m e p o r t s t o B r o u a g e o r L a

R oche l l e , w i th ou t cabo tage . T h i s is a l so i ll us t r a t ed b y the d i s t r ibu t io n o f speci fi c

l i t ho log ica l t ypes am ong the sea l ed a rchaeo log ica l s i t e s and p rov ides m ul t ip l e

e v i d en c e f o r a m o d e o f t r a d e p r e v i o u s l y a s s u m e d t o h a v e b e e n m i n o r r e la t iv e t o

c a b o t a g e .

T h e p e t r o c h e m i c a l s t u d y o f a r c h a e o l o g i c a ll y s e al e d g r a n i te b a l l a s t f r o m B r o u a g e

and L a R oche l l e has a l so p roved e f f ec t ive fo r r econs t ruc t ing ea r ly com m erc ia l sea

l inks (F ig . 9 ) desp i t e t he l im i t ed chem ica l da t a base ava i l ab le in the l i t e r a tu re . T he

m u s c o v i t e - b e a r i n g g r a n i t e b a l l a s t c o r r e s p o n d s t o d i r e c t c o m m e r c i a l t r a d e b e t w e e n

F a l m o u t h , C o r n w a l l , a n d L a R o c h e l le ( c. 1 4 00 ) a n d B r o u a g e ( 16 3 1) , p r e s u m a b l y

re l a t ed to w ine and sa l t t r ade , r e spec t ive ly . A s fo r t he m uscov i t e - f r ee g ran i t e ba l l a s t ,

i t d o c u m e n t s d i r e c t c o m m e r c i a l s e a -l in k s b e t w e e n B r o u a g e a n d I r e l a n d a t a l a te r

period (e. 1650).

T h o u g h t h e p r e s e n t r e s ul t s fi t i n w i t h t h e g e n e r a l p a t t e r n a c k n o w l e d g e d f o r o l d

t r ade , he re , fo r t he f i rs t t im e , t he hom e p or t fo r t h ree d i f f e ren t se ri e s o f ba l l a s t s am ples

in the B r i t i sh I s l ands , tw ice fo r F a l m o uth and once fo r D oneg a l , a r e p rec i se ly iden t i -

f i ed a t da t e s a rchaeo log ica l ly e s t ab l i shed . S uch exo t i c ba l l a s t bou lde r s hence becom e

a s v a lu a b l e a s a r t e f a c ts a n d t h e i r g e o c h e m i c a l s t u d y m a y n o w b e c o n s i d e r ed a s a n e w

t o o l f o r a r c h a e o l o g y .

The Conseil R+gional du Poitou -Chare ntes prov ided a 3-year stipend to C. E. Lazareth and the

Conseil G6n6ral de la Charente-Marit ime (Syndicat Mixte de Brouage) and Comm unaut6 de

Ville de La Rochelle, the financial support for field work and analyses. Thanks are extended

personally to N. Fiquet, T. Eliasson and A. Sylvester.



GEOCHEMISTRY OF BALLAST GRANITES, FRA NCE 137

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Geochemistry and the early alum industry

A N D R E W R. M I L L A R D

Department of Archaeology, University of Durham,

South Road, Durham DH1 3LE, UK

Abstract: One of the earliest chemical industries in Britain was the alum produc-

tion industry. The early alum industry relied on a complex series of extractions

from suitable shale deposits, until the rise of alternative methods in the 19th

century, based on industrially produced sulphuric acid. Relatively little is known

about the actual processes involved. This paper discusses the evidence that can

be gleaned for the chemical processes involved and reports investigations on

residues recovered from waste tips at the 17th- 18th century alum works at Carlton

Bank, North Yorkshire. For the first time it can be said that the sulphur content of

the alum shale would have limited yields from the alum production process. Wide

variability in the sulphur content of unworked shale implies variable yields in the

alum production process, which may have contributed to the historically recorded

boom and bust of individual alum works. Analyses of waste calcined shale were

shown to be of limited value without experimental reconstruction of shale proces-

sing. Future investigations need to concentrate on waste residues recovered from

alum works during excavations, and on reconstructions of the process.

This paper i s an a t tem pt to d raw the a t tent io n of archaeolog ical sc ienti s ts an d geo-

chemists to some interesting problems relating to the archaeological investigation

of early industrial chemistry.

An alum is a hydrated double sulphate of formula XAl(SO4)z.12H20, where X is

commonly K, N H 4 or Na. Alum was widely used in the past as a mor dan t to bind

dyes to cloth. In the post-medieval period its large-scale production gave rise to the

first chemical industry . In Englan d from c. 1600 the alu m ind ust ry developed based

mainly on extraction from the Jurassic alum shales of North Yorkshire. There are

thus a large number of former alum works in North Yorkshire and Cleveland that

survive from the 17th to 19th centuries. There is some documentary evidence of

these works, as well as excavated evidence from a few of them. The economic aspects

of the industry have been fairly well studied, but the industrial process of converting

shale to pure alum is known only in outline and not in detail (Marshall 1995). This

is due in part to the complexity of the processes involved, a lack of study of the

processes, and the fact that the historical accounts are often deliberately vague in

order to prevent rivals from picking up in any local improvement to the process.

The alum industry in the 16th to 19th centuries

Prior to the 15th century alum was imported into Europe from a number of sources,

mostly in the Byzantine Empire. After the fall of Byzantium to the Turks in 1453, a

shortage developed and European sources were sought. Vast deposits of alunite

(KA13(SO4)2(OH)6) were discovered at Tolfa, Italy, and became Europe's chief

From.



Geological Society, London, Special Publications, 165, 139-146. 1-86239-053-3/99/$15.00




140 A. R. MILLARD

source of a lum. Tolfa lay wi th in the Papa l Terr i tor ies and so the a lum supply of

Europe became vi r tua l ly a Papa l monopoly (Taylor & Singer 1956) .

Afte r the Engl ish Reformat ion th is Papa l contro l became a problem for suppl ies to

the Engl ish c lo th dye ing indus t ry a nd He nry V III in i t ia ted prospe c t ion for indigenous

a lum sources . Afte r a se ries of unsuccessfu l a t tem pts to es tabl ish an Engl ish a lum

indus t ry in the second ha l f of the 16th century , success fu l exploi ta t ion of the North

York shire a lu m sha les began c. 1600. Unt i l 1679, the r ight to produ ce a lum rem ained

a Crow n mo nop oly tha t was fa rm ed ou t to a smal l grou p o f l icensees . This early Eng-

l ish produc t ion was pro babl y a lso l imi ted by the d i f f iculty of perfec t ing the ext rac t ion

process for th is new source . Product ion appears to have f i rs t sa t i s f ied the home

dem and of abo ut 1800 tons per ann um by c. 1635, and by the 18th century produ ct ion

reached 4000-5000 tons per annum (Marsha l l 1995, Turton 1938) . Al though other

areas of Bri ta in deve loped a lum works in the la te 18th century , the North Yorkshire

works cont inued to domina te the indus t ry unt i l 1850, when Pe ter Spence in t roduced

a new product ion method based on sulphuric ac id d iges t ion of coa l measure sha les .

One Spence p roces s works cou ld p roduce a lum more rap id ly than the en t i r e Nor th

York shire indu s t ry a t i ts peak, a nd so by 1871 a ll the Nor th Y orkshire works had

closed (Marshall 1995).

The alum production process

The N or th York shire pro duc t ion process involved quarry ing of the sha le, ca lc in ing to

oxidize su lphides to su lpha tes , ex t rac t ion of a luminium sulpha te , pur i f ica t ion , con-

vers ion to a lum by addi t ion of an a lka l i , and fur ther pur i f ica t ion of the a lum.

Turton (1938) gives the best descriptions of the processes involved for the calcining,

and Young (1817) and Marsha l l (1995) for the ext rac t ion and pur i f ica t ion . The

fol lowing ana lys is of the chemis t ry involved is based on these accounts . The Im peria l

uni ts of the or ig ina l accounts a re g iven here , toge ther wi th ap prox imate metr ic

equiva lents . Figu re 1 g ives a d iagra mm at ic su mm ary of the process.

The sha le was quarr ied a f te r removal of the overburden and bui l t in to a c lamp

(ca lc in ing heap) composed of a l te rna t ing layers of brushwood and sha le . The la rges t

c lamps were as muc h as 200 fee t (61 m) square and 80- 90 fee t (24-27 m) in he ight,

though more typica l d imens ions may have been 90fee t (27m) square . A c lamp

would be l i t when i t reached 4 fee t (1 .2m) h igh and layers would cont inue to be

added . The p rocess o f c a lc in ing wou ld t ake 9 -12 mon ths to comple te . Fo r op t im um

product ion the tempera ture had to be h igh enough to conver t fe rr ic su lpha te ( formed

from oxida t ion of the fe rrous d isu lphide of the shale ) to su lph ur t r ioxide, but not h igh

enou gh to decom pose the a lumin ium su lpha te tha t was formed by the reac t ion of the

SO3 wi th the a luminos i l ica te c lays. This i s achieved a t 450 -55 0~ (230-290~ In

order to regula te the tempera ture , s low the combus t ion and re ta in gaseous SO3,

the s ides of the clamp were plastered with wet earth, c lay or shale , part icularly on

the windward s ide . Addi t iona l ly , a 'mel lowing per iod ' of s low cool ing was a l lowed

af te r ca lc in ing to a id the recombina t ion of any decomposed a luminium sulpha te .

Once the c lam p had cooled i t was opened and the br ight red ca lc ined sha le was dug

out . Extrac t ing the a luminium sulpha te and conver t ing i t to a lum would have been

re la t ive ly easy but for the fac t tha t the product had to be of h igh pur i ty . I ron sa l t s

co-extrac t f rom the ca lc ined sha le impart an orange or brown colour to the a lum.

If such a lum is used to mordant dyes , i t has the undes i rable e ffec t of darkening



GEOCHEMISTRY AND THE EARLY ALUM INDUSTRY 141

Shale

[FeS2]

[alum inosi l icates]

I

h e a t

Calcined shale

[AI2(S O4)3]

[Fe203]

steep

raw l iquor

i

evaporate

l iquor

1

sett le

c leared l iquor

t

!

boil + add atkali

,1,

alum l iquor

i

cool

c r u d e

alum t

crystals

I

wash in mother

l i q u o r (

w a s h e d crystals

i

dissolve in hot

water

,1,

hot concentrated

l iquor

co o l

l

waste calcined

shale

slam

liquor

mother l iquor

impure alum

Fig. 1. Schematic representation of the alum extraction process.

their colour. The refor e the extraction pro cess involv ed a series of puri ficat ion steps in

order to obtain colourless alum.

The calcined shale was steeped in water to extract the soluble alumi niu m sulphate

as a 'raw alum liquor'. This was transported through a series of troughs to the alum

house where it was heated to evaporate the water and concentrate the solution. Mu ch

of the iron imp uri ty was removed at this stage as a yellow iron silicate crust kno wn as

'slam'. After solid impurities had settled out, the 'cleared liquor' was moved on to a

further set of evaporating p ans where it was boiled to concentrate it, and an alkali was

added. The main sources of alkali were urine for ammonia and potash (or muriate

(chloride) of potash) for potassium. Upon cooling, crude alum crystals formed.



142 A .R . MILLARD

The crys ta l s were col lec ted and the solut ion recycled to the previous s tage to be

fur ther concent ra ted. The crys ta l s were then washed wi th 'mother l iquor ' , a sa tura ted

solut ion of a lum generated in the f inal s tage , ' roached ' ( recrys ta l l ized) by dissolving

them in hot water (or , in some la ter works , us ing s team) and then crys ta l l ized in

barre l s . The cask would be opened and a hole dr i l led to remove the 'mother l iquor '

f rom the cent re of the mass of a lum crys ta l s . At the base of the cask would be

impure a lum , bu t t he upper p a r t s con t a ined t he puri fi ed p roduc t . Any of t he a lum

not of sui table pu r i ty (as judg ed by it s colour) w ould be roached again.

The scale of the indust ry , handl ing vas t tonnages of shale and large volumes of

' l i quor ' means t ha t t he re a r e numerous bu i ld ings and o the r r emains a t a lum works

s i tes , but few have been excavated and interpre t ing them in terms of the product ion

process i s di f f icul t as the di f ferent evaporat ion or cool ing operat ions produce s imi lar

remains . Th ere are a l so large waste t ip deposi ts of red calc ined shale , and occas ional

excavated deposi t s o f s lam.

Whilst the above outl ine can be constructed from the historical sources, i t is a com-

posi te account and, as such, cannot reflect variat ions in the process between different

works and through t ime. There remain ques t ions such as whether the opt imum calc in-

ing tempera tures were at tained, and whe ther there were several steps within a stage, e.g.

repeated eva pora t ion of raw l iquo r and rem ova l of slam. The eff iciency of the extrac-

t ion, both overal l and in individual s tages i s a l so ent i re ly unknown, a l though Young

(1817; 814) states tha t between 50 and 130 tons of shale were required to produce 1

ton of a lum, depending on the qual i ty o f both the shale and the calc ining process.

Ge oc h e m ic a l s tu d ie s a t Car l ton Ban k s Alu m Wor k s

Car l t on Banks Alum Works , Car l t on , Nor th Yorksh i r e , (Na t iona l Gr id Refe rence

N Z 520 027) was in opera t ion c . 1680-1774 (Yo ung 1817; 811) , but l i t tl e doc um enta ry

evidence survives . The s i te consis ts o f the aba nd one d quar ry a nd waste t ips on the

hi l l s ide below i t s mouth. The f i r s t edi t ion Ordnance Survey map indicates that

there was an 'a lum h ouse ' a t the mo uth of the quarry above the waste tips, which

was pres um ably the locat ion of a lum process ing. No deta i led mo de rn archaeological

o r h i s to r i ca l s t udy had been under t aken un t i l r ecen t ly when the Nor th Yorksh i r e

Na t iona l P a rk commiss ioned a s t udy f rom the Lancas t e r Unive r s i t y Archaeo log i ca l

Uni t ah ead of rec lamat ion and lan dscapin g w orks . Th e waste tips of ca lcined shale

were to be regrade d to make them safer and, as par t of mi t igat ion works , samples

were taken f rom an exposed sect ion in an eros ion gul ly .

The geo chemical resul t s presented here ar i se f rom an explo ra tory analys is of these

samples and samples o f f re sh sha le ob t a ined f rom the abandon ed quar ry . The a im of

the prog ram me was to explore the potent ia l fo r geochemical analys is of shale deposi ts

to address ques t ions re la t ing to the indust r ia l process of a lum prod uct ion. How ever

the excavated sam ples proved l imi ted and ques t ions re la ting to tempera ture of f ir ing,

and changes in the process thro ug h t ime could not be tackled. The calc ining of shale

turns i t br ight red due to the oxidat ion o f the i ron com pou nds present and thus wi ll

resul t a very large increase in ma gne tic suscep tibi li ty. This al lows sam ples of al tered

calc ined shale to be dis t inguished f rom samples conta ining orange-red c lays , which

wi l l not be so oxidized. This method for ident i fying deposi t s conta ining calc ined

shale was successful, an d the chemical com posi t io n of f resh and calcined shales

al lows an ini t ial evalu at ion of the eff iciency of the extract io n process.



G E O C H E M I S T R Y A N D T H E E A R L Y A L U M I N D U S T R Y 143

Dupl ica te sam ples were taken f ro m s t ra ta w i th in the was te t ip and f resh sha le f rom

three s i tes a round the quarry . Elementa l ana lys is by X-ray f luorescence was under-

taken to examine extraction efficiencies; magnetic susceptibil i ty was used to identify

burn ing v ia i ron mine ra l t r ans fo rma t ion .

Methods

Magnetic susceptibility

Samples were a i r dr ied and grou nd in a m ort a r to less than 2 m m par tic les . L ow-

frequency magnet ic suscept ib i l i ty and f requency dependence were de te rmined as

descr ibed by Clark (1996; 103-104) on samples of approximate ly 10g us ing a

Bart ington MS2 magnet ic suscept ib i l i ty meter .

Energy dispersive X-ray fluorescence (EDX RF )

Ana lysi s fo r ma jo r and m inor ino rgan ic compone n t s was un de r t aken by ene rgy di s-

pers ive X-ra y f luorescence (E D XR F) on 0 .5 g of dr ied , grou nd and pe l le t ized sample .

Quan t i ta t ive ana lys is was und er tak en for the e lements Na , Mg , A1, Si, P , S, K, Ca , Ti ,

M n, Fe and Sr , the results be ing ca l ibra ted us ing the Uni ted Sta tes Geologica l Survey

Sco-1 shale s tandard.

Results and discussion

Magnetic susceptibility

High magnet ic suscept ib i l i ty va lues wi th h igh-frequency dependence a re to be

expec ted in ca lc ined sha le , due to the format ion of maghaemite (~/Fe203) of smal l

grain s ize during the calcination process , whils t the fresh shale is expected to show

low values. This is borne out in the results (Table 1) where the fresh shale shows

low va lues and the samples wi th a la rge prop ort i on of v is ible red sha le (CB97 3-A,

J -A and J -B) show e leva ted va lues . Samples f rom layer K wi th less red sha le show

sl ight ly e leva ted va lues . Other samples where burnt sha le was not noted v isua l ly

are shown to conta in burnt mater ia l , or so i l , by the i r magnet ic suscept ib i l i ty va lues

(contexts 4 , 5 and 13) , some of which a re e leva ted and show frequency dependence .

EDXRF

In the e lementa l ana lyses , Si , Ca , Na , Mn and Sr were e i ther not de tec ted or showed

very l i t t le var ia t ion: they a re not repor ted or d iscussed here . Context 13 s tands out

from all the other samples in i ts composit ion, this is not surpris ing given i ts interpre-

tat ion on-site as a buried soil rather than a shale deposit . The fresh shale samples

show uniformity in the i r A1 contents , but wide var ia t ion in the i r S contents . The

was te t ip samples over lap in the i r ranges of concentra t ion wi th the f resh samples .

Contexts 2 and K s tand out as lower in Mg and A1 and context 5 as lower in K

and higher in Ti than the f resh sha les . A reduc t ion in Mg, A1 and K and increase

in Ti would be consis tent with a leaching process , e i ther natural or art if ic ial . The

wide var ia t ion in f resh sha le compos i t ion prec ludes def in i te s ta tements on the

na ture of th is leaching, or whether o ther samples have been leached.



1 44 A . R . M I L L A R D

, .4

. - t . - . o . o . o . - t . o . o . ~ " o "-n. . . . . - t . ~ . ~ . ~ .

._ . .=

~ o ~ ~ ~

~ ~

~ ~

~ ~ o ~ ~ c ~ c ~ ~.~

I l l I I l l l l ~ 1 1 1 1

o0



GEOCHEMISTRY AND THE EAR LY ALU M INDUSTRY 145

The e lemen t of mo st in teres t, sulphur , shows mo re var ia t ion in the f resh shale than

the waste shale , which me ans that def ini te conclus ions on the ef f ic iency of the process

canno t be d rawn. H owever , some use fu l deduc t ions can s t il l be made . The ma xim um

sulphur con tent of the shale is 1 .7% SO3, which impl ies a m ax im um yie ld of

potass ium alu m o f 2 .7% of the weight of shale used. This yield wo uld reduce the

alum ina c onten t of the shale by only 1 .1%, wh ich wi l l be di ff icul t to detect given

an observed n atura l var ia t ion of 0 .9% . The wel l ca lc ined shale f rom context J ,

which has presu ma bly been processed, has a SO3 content o f a t leas t 0 .48% , suggest ing

that a high yie ld ma y have only been 2.0% alum:shale . This matc hes c losely the 1 ton

of a lum for 50 tons of ca lc ined shale repor ted as a goo d yie ld by Yo un g (1817;

814).

The low sulph ur co ntent of some shale here , a t 0 .34% SO3, wo uld give a yie ld of

only 0 .56% alum:shale . Such low yie lds ma y have mea nt th at as cer ta in par t s of a

quar ry were work ed p roduc t iv i t y would have dec l i ned and t he un it cos t o f p roduc t ion

r i sen to a point where a works could become economical ly unviable . The pr ice of

a lum i s r ecorded as hav ing f l uc tua t ed wi th p roduc t ion and va r ious works went i n

and out o f bus iness as i t d id so (Yo ung 1817; 816-81 7, Ma rsha l l 1995) . Perhaps

par t of the f luctuat ion a t individual wo rks was due to var ia t ion in the qual i ty of

the a lum shale .

I t is a l so ins t ruct ive to co mp are these analyses wi th those o f Ga d et al. (1969) on the

coasta l exposures of the a lum shales . They rep or t 1 .55 -2.55 % S ( i. e. 3 .9 to 6 .4% SO3)

which i s much h igher t han a t Car l t on . Thus y i e lds f rom the coas t a l works may we l l

have been higher than a t Car l ton, hence the larger scale and more successful works

on the coas t .

Conclusions

This work has sh own th at magn et ic suscept ibi l ity can be a useful me tho d of detect ing

bur nt shale wi thin a deposi t , due to the high ma gha em i te co ntent of ca lc ined shale .

How ever , e lem ental analys is of waste shale i s not a par t icular ly prod uct ive exerc ise ,

because there i s unl ikely ever to be a specif ic com posi t io n of f resh shale wi th wh ich to

comp are i t. F ur the r under s t and in g o f t he a lum prod uc t ion p rocess wi ll r equ i re r econ-

s t ruct ions of the var ious s tages of prod uct io n in order to generate reference mater ia l s

aga ins t which excava t ed ma te r i a l can be compared . Excava t ed samples o f was t e

calc ined shale ma y be useful in inves t igat ion of the ca lc ining process , bu t no t for

inves t igat ion o f product ivi ty . S lam an d other im pur i t ies , especial ly i f recovered

from ident i f iable par t s of the prod uct io n process , are more l ikely to yie ld informat io n.

Samples col lec ted f rom excavat ions target ted wi th the chemis t ry in mind wi l l be the

bes t way to gain greater ins ight in to the m etho ds of the Br i ta in 's f i rs t l arge-scale

chemical indust ry .

I would like to thank Phil Clogg for conducting the EDXRF measurements, and Lancaster

University Archaeological Unit who commissioned the analyses as part an archaeological

evaluation of the Carlton Banks site funded by the North Yorkshire Moo rs N ational Park.

References

CLARK, A. 19 96 .

Seeing Beneath the Soil: Prospecting Methods in Archaeology.

Batsford,

London.



146 A. R. MIL LA RD

GAD, M. A.,

CATT,

J. A. & L~ RICHE, H. H . 1969. Geoche mistr y o f the Wh itbia n (Up per Lias)

sediments of the Yorkshire Coast .

Proceedings of the Yorkshire Geological Society,

37,

105-139.

MARSHALL,

G. 1995. Redress ing the balance - an archaeological evaluat ion of No rth York -

shire 's coasta l a lum industry . Industrial Archaeology Review, 18, 39-62.

TAYLOR,

F. S. •

SINGER,

C. 1956. Pre-scientific industrial chemistry. In: Singer, C. , Holm yard ,

E. J. , Hall, A. R. & Williams, T. (eds) A History of Technology. II . The Mediterranean

Civilizations and the Middle Ages c. 700 BC to c. AD 1500.

Oxford Univers i ty Press ,

Oxford , 347-374.

TURTON, R. B. 1938.

The Alum Farm.

H o r n e & S o n , Wh i t b y .

YOUNG, G. 1817. A History of Whitby and Streoneshalh Abbey; with a statistical survey of the

vicinity to the distance of tw enty five miles. Cla rk and Medd , Whi tby .



Zinc isotope fractionation in liquid brass

(Cu-Zn) alloy: potential environmental and

archaeological applications

P A U L B U D D 1 , P A U L L Y T H G O E 2, R O N A A . R . M C G I L L 1,

A . M A R K P O L L A R D 1 & B R E T T S C A I F E 1'3

1Department o f Archaeological Sciences,

University of Bradford, Bradfo rd BD 7 1D P, U K

2Department o f Earth Sciences, The University of Manchester,

Oxford Road, Manchester M13 9PL, UK

3present address: Sub- Unit fo r M edical Sta tistics,

Nuffield Institute, University o f Leeds, Leeds LS 2 9L N, UK

Abstract:

A prelimina ry study o f zinc isotope fractionation in brass m elting sug-

gests that the process can be modelled by simple Rayleigh fractionation. Brass

melting experiments at l l00~ followed by quad rupole ICP- MS isotope ratio

measurements of the resulting alloys suggest that the model is appropriate and

that a useful approxim ation of the fractionation factor (c0 is 1.0064. The d ata

indicate that the change in isotope ratio of the residual liquid alloy would be mea-

surable for zinc losses by evaporation of more than about 30wt.%. It is unlikely

that measu rements at the precision of the curren t study (~0.55%o am u -1) would

be sufficient to distinguish between the two principa l historical brass -ma king

processes, altho ugh more precise measure ment using a multi-collector ICP-M S

prob ably w ould be. The experimental data also suggest that zinc vapo ur evolving

during the evaporation of the first few per cent of the metal will be significantly

fractionated (~l.5% oam u -1) with respect to the liquid. This might provide a

basis to distinguish between e nvironmen tal zinc from high-tempe rature indu strial

processes and that derived from natural and manufactured product sources.

The cur r en t s t udy was under t aken i n o rde r t o examine t he hypothes i s t ha t measurab l e

i sotopic f rac t ionat ion wou ld take place dur ing the evap orat ion of z inc f rom l iquid

brass (C u-Z n) a l loys at e leva ted t empera tu res . I f t he mag ni tude o f f r ac t i ona t i on

was suf f ic ient to m easu rably a l ter the i sotopic com posi t io n of the res idual l iquid, i t

could a l so be poss ible to use z inc i sotope ra t io measurements to dis t inguish the

prod ucts of the two pr incipal brass-m aking processes used in ant iqui ty . Add i t ional ly ,

i f es tabl ished, such f ract ionat ion mig ht provide a bas is for di scr iminat ing between

envi ronmenta l z inc emi t t ed by evapora t i on dur ing va r ious h igh- t empera tu re p ro-

cesses and t ha t o r ig ina t i ng f rom manufac tu red z inc p roduc t s o r na tu ra l mine ra l

sources.

As the boi ling point of z inc i s only 906~ the me ta l canno t be prod uced s imply by

di rect reduct ion wi th out d i s t il l a tion. The f i r s t app earan ce of brass , however , in the

Ana to l i an and M edi t e r r anean I ron Age , r e sul ts no t f rom the deve lopment o f z inc

dis t i l l a t ion, but f rom the discovery that copper-z inc a l loys could be produced by

From.



Geolo gical Society, Lon don , Special Publications, 165, 147- 153. 1-86239-053-3/99/$15.00

9 T he Geological Society of Lon don 1999.



148 P. BU DD

ET AL.

' cementa t ion ' (Pol la rd & Heron 1996, 201) . The cementa t ion process involves the

prep ara t io n of Zn O which is p laced in a sea led vesse l wi th charcoa l and g ranu lar

copp er and hea ted to ~1000~ At th is tempe ra ture , and in the h ighly reduc ing

condi t ions p rodu ced by the burning charcoa l , z inc vap ou r i s prod uced which d i ffuses

in to the so l id copper to form the brass a l loy .

The cemen ta t ion p rocess is t hough t to have dom ina ted E urope an b ra s s p roduc t ion

unt i l the e ighteenth century when z inc d is t i lla t ion was in txoduced. This a l lowed brass

to be made by the 'd i rec t ' p rocess , in which meta l l ic z inc i s added to l iquid copper .

The maximum z inc content of brass a l loys produced by cementa t ion is k ine t ica l ly

cons t ra ined to ~31-33wt .% (Werne r 1970 ; Haedecke 1973) . Howeve r , t he h igh

z inc content of some la te r medieva l brasses sugges ts tha t z inc d is t i l la t ion and d i rec t

a l loying may have a cons iderably longer h is tory in Europe than previous ly thought

(Pol la rd & Heron 1996, 205-232) . As mos t medieva l brasses have z inc contents of

less than 31 wt .% , an inde pende nt m eth od wi th which to assess the i r product io n

process would be a useful a id in char t in g the in t r oduc t ion of zinc d ist i l la t ion and

poss ib ly a lso in the authe nt ica t ion of early brass a r te fac ts .

I f i so topic f rac t iona t ion dur ing eva pora t ion were to prove s igni f icant, and grea te r

than any na tura l var ia t ion be tween ore sources , i t might be poss ib le to use z inc

iso tope measurements to d is t inguish be tween the two brass making processes .

Cementation is a gas-solid reaction in a sealed vessel a l lowing l i t t le scope for zinc

evapora t ion and e s cape o f the vapour . By con tra s t , d i rec t p roduc t ion me thods ,

especially the addit ion of volati le metall ic zinc to l iquid copper, are processes l ikely

to resul t in cons iderable z inc evapora t ion wi th scope for a consequent enr ichment

of the heavier zinc isotopes in the residual l iquid.

The paper se ts out a theore t ica l model for z inc f rac t iona t ion dur ing evapora t ion .

This i s compared wi th exper imenta l da ta to der ive a f rac t iona t ion fac tor for the

par t icula r process und er cons idera t ion: brass mel t ing a t 1100~ Al tho ugh empir ica l

and semi-quant i ta t ive , the resul t ing es t imate of f rac t iona t ion may be used to com-

ment on the potent ia l for z inc i so tope measurement to be used in pol lu t ion source

t rac ing and process recons t ruc t ion .

Modelling zinc isotope fraetionation during evaporation

The frac t iona t ion of zinc as a resul t of i ts evapor a t ion f rom l iquid meta l a t e leva ted

temperature arises from the s l ight difference in vapour pressure between i ts isotopes.

This ensures tha t , in equi l ibr ium, the vapo ur wi ll be margina l ly enr iched in the l ighte r

isotopes with respect to the l iquid. In various industrial and metallurgical processes

involving the manip ula t io n o f z inc at h igh tempera ture , v apo ur m ay be lost f rom

the l iquid to condense elsewhere. If vapour is progressively lost in this way there

wil l be a sys temat ic change in the i so topic compos i t ion of the res idua l l iquid and,

correspondingly , of the evolving vapour .

The z inc iso tope com pos i t ion of the remaining l iquid a f te r a propo rt io n of i t has

evapo ra ted can be model led on the bas is of the k ine t ic theory o f 'Rayle igh f rac t iona-

t ion' . T his will be familiar to geoch emists in the contex t of meteor ologi cal oxy gen iso-

tope f rac t iona t ion (Faure 1986, 430-436) but has a lso recent ly been appl ied to the

evap ora t io n o f meta ls such as lead (Budd et al . 1995a, Macfarlane in press) and t in

(Budd

et al .

1995b, Begemann

e t a l .

in press ) . According to th is model , the change

in z inc i so tope ra t io in a l iquid f rom which the meta l i s be ing los t as vapour can be



Z IN C ISO T O PE FR A C T IO N A T IO N IN L IQ U ID B R A SS 149

es t imated as:

R I f = R l o f [ ( 1 / , ~ )

1] 1)

wh ere Rlf is the 68Zn/64Zn ra tio of the resid ual liq uid, R10 is the 68Zn/64Zn r atio of the

in i t ia l l iqu id , f i s the pro po rt io n of l iquid remain ing and a i s the f rac t iona t io n fac tor .

A re la ted express ion g ives the i so topic compos i t ion of the vapour evapora t ing a t the

same stage (Rvf):

R l o f [ ( 1 / o , ) - 1]

Rvf = (2)

OL

Although the model i s essent ia l ly very s imple there a re a number of compl ica t ing

fac tors . Mos t important ly , the f rac t iona t ion fac tor (a ) for z inc in re la t ion to par t icu-

la r processes cannot eas i ly be de te rmined. A

m a x i m u m

value for the f rac t iona t ion

fac tor can be der ived f rom kine t ic theory as the square root of the ra t io of the

masses of the i so topes ofha te res t , so tha t :

O~ < (M 2 /M 1 ) 1/2 (3 )

Fo r 68Zn/64Zn this gives a value of c~ < 1.0308, bu t i t is prob abl y mo re realis tic to

cons ider the evapoxat ion of ZnO ra ther than Zn, m akin g c~ < 1 .0247.

In practice, for th e process u nd er con sider ation here, the valu e o f o~ is l ikely to be

s ignif icant ly lower than th is . The theory assumes ins tantaneo us equi l ibr ium, com ple te

mixing wi th in the l iquid and ent i re ly e ff ic ient separa t ion of the vapour . In prac t ice ,

equ i l ib r ium i s no t in s t an taneous . Incomple te mix ing wi th in the l iqu id , vapour -gas

molecular col l i s ions and re -condensa t ion of the vapour can a l l reduce the e ff ic iency

of f rac t iona t ion . Fu r the rm ore , t he theo ry dea ls w i th evapora t ion f rom a pu re e l emen t

ra the r than an a l loy . A l though coppe r ha s a ve ry much lower vapour p re s s u re than

z inc , the presence of copper molecules in both l iquid and v apo ur wou ld be expec ted

to reduce the f rac t iona t ion fac tor .

Th e value of o~ is therefor e proce ss-dep ende nt, relat ing to fac tors such as temp era-

ture , pressure and the e ff ic iency of vap our rem oval an d hence can only be accura te ly

de te rmined empir ica l ly . An exper iment was therefore under taken to measure the

ma gni tu de of i so topic f rac t ion a t ion dur ing brass mel t ing a t 1100~ This has been

used to m ak e a n estim ate o f c~ which, i t is suggested, may be a useful firs t-order

approximat ion for a number of s imi la r processes .

Experimental methodology

The expe r imen t invo lved zinc evapora t ion f rom b ra s s in the man ne r expected du r ing

the direct process of brass making and subsequent hand.l i t~g of the l iquid alloy at high

tempera tu re . A s ma l l quan t ity o f a hom ogenou s pu re b ra s s s t anda rd (BN F C30 .05 ;

29.99% Zn) was hea ted to l l00~ in a muffle furnace , unde r excess charcoa l for

var iable per iods be tween 5 to 30 minutes (Table 1) . Zinc evapora t ion f rom the

l iquid a l loy was moni tored by weight loss on cool ing . This was found to g ive a

us e fu l appro x ima t ion fo r the lo ss o f z inc a s vapo ur a s the vap our p re s su re o f coppe r

is ins ignif icant a t th is tem pera ture . Eight samples wi th z inc weight losses of be tween

approximate ly 20 and 80% were se lec ted for z inc i so tope ana lys is by ICP-MS.



150

P . B U D D

ET AL

Table 1. Change in zinc isotope composition o f the residual brass or various losses of zinc by

evaporation at llO0~

Sample Heating time Zn los s Measured ~568Zn Error a

(mins) wt.% 6SZn/64Zn %0 amu 1 (2 SE)

Standard 0 0.00 0.4114 0 0.55

1100-19 5 19.38 0.4117 0.18 0.61 1.0034

1100-20 10 20.03 0.4117 0.19 0.58 1.0033

1100-33.6 10 33.60 0.4116 0.15 0.34 1.0012

1100-38.1 12 38.15 0.4120 0.35 0.86 1.0030

1100-51 15 50.95 0.4131 1.03 0.44 1.0058

1100-61.6 18 61.60 0.4137 1.39 0.92 1.0059

1100-69.7 23 69.77 0.4151 2.18 0.60 1.0075

1100-76.5 30 76.52 0.4153 2.36 0.40 1.0066

M e a s u r e d

68Zn/64Zn ratios are tabulated together with the fractionation presented

as ~568Zn

(in units

%o amu -~ ). Errors (2 SE) are calculated from the six replicate analyses for each sample (12 for the standard).

The table also shows calculated values of the fractionation factor (a) for each of the samples.

S a m p l e p r e p a r a t i o n

Samples of each alloy and the brass standard were collected to give a total Zn content

of ~2 mg. The samples were dissolved in dilute aqua regia (all Romil Ultrapure acids),

dried down and then re-eluted with 2M HC1 to form a 2 mg (Zn) ml 1 Cu-Z n solu-

tion. The samples were then treated to separate the zinc from the copper in order to

eliminate potential isobaric interferences from 63Cu and 65Cu. Separation of the two

metals was carried out by ion exchange chromatography. Poly-Prep 2 ml columns

were filled with 2 g of Bio-Rad AG1-X8 ion exchange resin (chloride form, 200-400

mesh). The resin was then washed with alternate column volumes of water and 2M

HC1. The sample solution (1 ml) was then loaded on each co lumn. Coppe r was

eluted from the column by 15 column volumes of 2M HC1. Zinc is most strongly

adsorbed on the resin with this concentration of acid, but copper (and ma ny other

divalent transition metals e.g. Ni and Fe) are not (Kraus & Moore 1953; Friel et al.

1996). Zinc was then eluted by 10 column volumes of 0.05M HC1. Final solutions

conta ined approximate ly 0.1 mg m1-1 of zinc (100 ppm) with no significant copper.

Column performance was monitored by ICP-AES.

I C P - M S z i n c i s o to p e a n a l y s e s

Sample solutions were diluted to 50 ppb zinc in 2% HNO3, minimizing C12 isobaric

interference from use of HC1, and bringing sample concentration into the optimum

range for isotope ratio ICP-MS. All stable isotopes of zinc were measured, but results

are given as the 68Zn/64Zn rat io maximizing mass difference and minimizing analytic al

error. 65Cu was monitored in case of isobaric interference. Measurements were made

using a VG Elemental PQ 2+ ICP-MS at the Depa rtmen t of Earth Sciences, University

of Manchester. The instrument was operated in rapid peak jumping mode (dwell time

10.24ms, and 3 points per peak), sample uptake time was 115 seconds (acquisition

time 60 seconds) with a 120 seconds wash of 2% HNO3

(Primar)

between samples.

Six replicate measurements were made for each sample. No mass discrimination

correction was applied and measured ratios were not normalized as no accepted

value 68Zn/64Zn standards were available. Measured ratios were used directly in the



ZINC ISOTOPE FRAC TION ATIO N IN LIQUID BRASS 151

c a l c u l a t i o n o f ~6 8Z n. I n s t r u m e n t d r i f t wa s mo n i t o r e d b y si x r e p l i ca t e me a s u r e m e n t s o f

t h e s t a n d a r d a t t h e e n d o f t h e a n a l y t i c a l ru n . N o d r i f t wa s o b s e r v e d .

E x p er i m en ta l r e s u l t s

T h e r e s u lt s o f th e z in c i s o t o p e a n a l y s e s a r e g i ve n in T a b l e 1. F r a c t i o n a t i o n , e x p r e s s e d

as 66SZn, in the res idu al l iqu id bras s m ay be ca lcu la te d ( in uni ts %0 a in u 1) as :

1 (R ,f - R10)

~6 S Z n - (68 64) x x 103. (4)

- Rl0

The re la t ion sh ip be tw een ~68Zn and z inc we igh t lo ss is p lo t t ed in F ig . 1. The m easur e -

me n t s s h o we d v a r i a t i o n s b e t we e n 0 .1 8 a n d 2 . 3 6 %o a mu -1 wi t h r e s p e c t t o t h e b r a s s

s t a n d a r d

R 1 0 ) .

T h e v a r i a t i o n a p p e a r s s y s t e ma t i c , b u t i s c l e a r ly c lo s e t o t h e r e s o l u t i o n

o f t h e q u a d r u p o l e i n s t r u me n t . T h e e r r o r s ( al l r e p o r t e d h e r e a s 2 SE ) a r e r e la t i v e l y

l a rg e , r a n g i n g f r o m 0 . 34 t o 0 . 92 a i n u - 1 . On l y t h e f in a l two s a mp l e s ( 1 1 0 0 - 6 9 . 8 -

Z n a n d 1 1 0 0 - 7 6 . 5 - Z n ) wi t h v a l u e s o f 2 . 1 8 4- 0 . 6 0 %o a mu -1 a n d 2 . 36 d : 0. 4 0%o

a m u -1 a p p e a r t o b e s i g n i fi c a n tl y f r a c t i o n a t e d f r o m t h e b r a s s s t a n d a r d ( i ts e l f

me a s u r e d wi t h a p r e c i s i o n o f +0 .5 5 %0 a mu - 1 ) .

E s t i m a te o f the f ra c t i o n a t i o n fa c to r i n b ra s s m e l t i n g

E x p e r i me n t a l v a l u e s f or t h e i s o t o p i c c o mp o s i t i o n o f t h e r e s id u a l l i q u id ma y b e u s e d to

c a l c u l a t e th e f r a c t i o n a t i o n f a c t o r ( ~) . R e a r r a n g i n g e q u a t i o n 1 g iv es :

O

2 . 5

1 . 5

1

e -

N

0.5

0

- 0 . 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - . . . . . . . . . . . . . . . . . . . .

- 1 1 . , , , , ~ ' , ~ ~ , ~ - ~ " ~ ~ . r . .

- 1 . 5 V a p o u r

-2 l , , , , , ,

0 10 20 30 40 50 60 70 80

Zn loss (wt.%)

Fig. l . The variation in zinc isotope fractionation (expressed

a s

668Zn) with respect to the

brass standard with zinc loss by evapo ration from brass at l l00~ Experim ental brass

samples are plotted with 2 SE measurement errors (n -- 6). Short dashed lines represent the 2

SE measur ement errors on the brass standa rd (n = 12). The solid black line represents the

theoretical fractionation within the residual l iquid according to the Rayleigh model with

c~ = 1.0064. Similarly, the dashed line represents the theore tical fra ction ation of the evolving

vapour .



152 P. BU DD ET AL.

Values of c~ for each of the exper im enta l samples a re g iven in Table 1. Al t hou gh a ll of

the calculated values o f c~ are est imates applicab le to the brass m elt ing process , the

accuracy of those relat ing to relat ively small z inc losses , where expected variat ions

are l ikely to be lower than the measurement errors , are the least rel iable. This is

re flected in the da ta . The ca lcula ted va lues of ~ for those samples wi th in measur eme nt

error of the s tan dard a re cons iderably more var iable than those re la t ing to z inc losses

over ~ 50 % . The me an of ca lcula ted va lues of c~ for the fo ur sam ples wi th z inc losses

over 50% is 1.0064 (or = 0.0008) and this is considere d the best es t im ate fo r the

frac t iona t ion fac tor re la t ing to brass mel t ing a t 1100~

Usin g equa tion (1) i t is possible to calculate (568Zn for the ~ d u a l l iquid using this

es t imate of the f rac t iona t io n fac tor to g ive an app rox ima t ion of the i so topic f rac tion-

a t ion for any pr opo rt io n of zinc loss (Fig . 1). This curve in te rsec ts the 2 SE error on

the meas u rem en t o f the b ra s s s t anda rd a t ~ 30 % Zn loss , p rov id ing a rough e s tima te

of the evapora t ion required to produce a measurable sh i f t in the i so tope ra t io of the

res idua l l iquid us ing the quad rupo le IC P-M S me thod. Simi la r ly , equ a t ion (2) may be

used to es t imate the i so topic comp os i t ion of the vap ou r (Fig . 1). This sugges ts tha t the

init ia l vapo ur emitt ed will be fract iona ted by ap pro xim ately -1.5%o am u -1 (~568Zn)

with respec t to the l iquid , approximate ly three t imes the 2 SE error on the measure-

men t o f the b ra s s s t anda rd .

Discuss io n

The data suggest that z inc has a large enough relat ive mass difference between i ts

s table isotopes (68Zn and 64Zn) and is sufficiently volati le to un der go isotopic fractio-

na t ion dur ing eva pora t ion , even f rom a z inc-bear ing copper a l loy . I t i s sugges ted tha t

the process can be useful ly model led by s imple Rayle igh f rac t iona t ion equa t ions .

Brass mel t ing exper iments , ca rr ied out under contro l led condi t ions a t 1100~ have

produced a series of samples for zinc isotope ratio analysis to tes t this hypothesis

and to es t imate the appro xim ate va lue o f the f rac t io na t ion fac tor (c~) . The resul ts

sugges t tha t the Rayle igh model i s appropr ia te and tha t a useful , a l though only

app rox im ate, es t imate of c~ is 1.0064. It ap pear s l ikely that s imilar values o f c~ ma y

apply to a wider range of indus t r ia l processes involving z inc evapora t ion f rom the

liquid metal , or i ts a l loys, a t e levated temperatures .

The p rec is ion o f the i so tope ra tio meas u remen t t e chn ique (quad rupo le ICP-M S)

used in this prelim inary s tudy is relat ively poor (~0.55%o am u -1, 2 SE). Ho wev er,

the da ta sugges t tha t the change in i so tope ra t io of the res idua l l iquid a l loy would

be meas u rab le fo r z inc lo ss es by evapora t ion o f more than abou t 30wt .% . Z inc

losses in modern d i rec t process brass making a re only ~5% (Alexander & Stree t

1976, 61) , but were pro bably very mu ch h igher in ant iqui ty - for example , Chinese

17th Century texts doc um ent losses of 25% (Pol la rd & Hero n 1996, 204). I t seems

unl ike ly tha t measurements a t the prec is ion of the current s tudy would be suff ic ient

to d is t inguish be tween cementa t ion and d i rec t ly produced brass g iven the range of

losses (5-25%) tha t might be expec ted in the la t te r . However , h igher prec is ion

s table i so tope ra t io me asurem ent i s poss ible us ing the m agnet ic sec tor , mul t i -collec tor

technique . I t seems l ike ly tha t mul t i -col lec tor measurement could be used for th is

application.

Perhap s the mo s t s ignif icant predic t ion to a r ise f rom the inves t iga t ion is the sugges-

t ion tha t the z inc vapour evolving dur ing the evapora t ion of the f i rs t few percent of





The determination of bloomery furnace

mass balance and efficiency

G A R Y R . T H O M A S & T I M O T H Y P . Y O U N G 1

De partm ent o f Earth Sciences, Card i f f Univers i ty ,

P O B o x 9 1 4, C a r d i f f C F 1 3 Y E , UK

1Current address. Geo Arch, 54 He ol-y-C adn o, Thornhill ,

Card i f f CF14 9D Y , UK

Abstract: A techniqu e for the graph ical solution o f the ore:furnace lining:fuel ash

mixture in the melt and the yield of the reaction d uring bloom ery iron smelt ing is

presented. The tech nique focuses on the so-called immobile elements, partic ularly

the rare earth elements, but em ploys a wide range o f elements. Previous attem pts

to determine ore sources from iron slag chemistry have generally examined the

majo r and min or elements of the slags, but are comp licated both by the significant,

but variable, concentrations of some of these elements in charcoal and by the

mobili ty of some major elements during weathering. The new approach has

been developed to aid the provenancing of slags from the smelting of iron-ores

from the Bristol Channel Orefield, which is characterized by high purity

goethite/haematite ores with extremely low trace element concentrations. It is

thus part icularly important to understand the involvement of furnace l ining in

the melt, for this materia l will have the do min ant co ntribu tion to the trace elemen t

chemistry. The mass balance a ppr oac h is illustrated using smelting slags, furnace

lining and roasted ore fragments from the Rom an iron making town o f

Ariconium

(near Ross-on-Wye, Herefordshire) and a good degree of compatibility of these

materials is demonstrated.

M o d e r n a n a l y t ic a l t e c h n iq u e s s u c h a s t h e r m a l i o n i z a t io n m a s s s p e c t r o m e t r y ( T I M S )

and induc t ive ly coup led p l a s m a-m ass spec t rom e t ry ( IC P -MS ) o f fe r no t on ly the ab il i t y

to ana lyse r ap id ly fo r a l a rge r r ange o f e l em ent s (Y oung et al. 1997), but also to a

g rea t e r degree o f p rec i s ion than p rev ious ly . H ow ever , w orke r s inves t iga t ing the com po-

nen t s o f anc ien t i ron sm e l t ing s ti ll p l ace g rea t r e l i ance up on a sm a l l num ber o f e l em ents ,

and m os t a t t em pt s to so lve fu rnace m ass -ba lance equa t ions ( e .g . S e rnee l s 1993) have

em p loyed the sm a l l e s t num ber o f s im ul t ane ous eq ua t ions poss ib l e fo r a so lu t ion .

T y leco te (1986) no ted tha t t he s i l ica con ten t o f a s lag can be e l eva ted by the a s s im -

i l a t ion o f fu rnace l i n ing . L ikew ise F u l fo r d & A l l en (1993) sugges t ed tha t m u ch o f t he

n o n - f e r r o u s m a t e r i a l p r e s e n t in R o m a n s la g s f r o m t h e s m e l ti n g o f F o r e s t o f D e a n o r e s

a t W o o l a s t o n ( in th e n o r t h e a s t o f t h e B r i s to l C h a n n e l O r e fi e ld ) w o u l d h a v e o r i g i n a t e d

f rom the fu rnace l i n ing and no t f rom the o re . S e rnee l s (1993) has , am ongs t o the r s ,

d i scussed t echn ique s o f a ssess ing the con t r ibu t ion o f the fu rnace l i n ing to the s l ag

a n d d e s c r ib e d s u c h a c o n t r i b u t i o n a s ' c o n t a m i n a t i o n ' . H o w e v e r , i t i s c l e a r f r o m t h e

w o r k o f F u l f o r d & A l le n ( 19 9 3) a s w e ll as t h e a u t h o r s ' u n p u b l i s h e d d a t a , t h a t t h e

con t r ibu t ion f rom the l i n ing in the B r i s to l C hanne l O re f i e ld s l ags i s ex t r em ely h igh .

T h e a p p r o a c h a d o p t e d i n t h i s s t u d y i s t o e x a m i n e t h e o r e : f u r n a c e l i n i n g m i x i n g

us ing as m any e l em ent s a s poss ib l e . A g raph ica l t echn ique a l low s easy inspec t ion

From:POLLARD,

A. M. (ed.) 1999.

Geoarchaeology:exploration, environments, resources.

Geological Society , London, Special Publications, 165 , 155-164 . 1-86239-053-3/99/$15.00




156 G. R. TH OM AS & T. P. YO UN G

for 'goodn ess of f i t' o f any par t icula r o re- l in i ng -fu e l ash system. This technique can

be employed, as i t is here, to assess whether ore samples are compatible with the s lags

genera ted f ro m a furnace mad e of a par t icu la r mater ia l , or to model the ore compos i-

t ion capable of genera t ing a par t icula r s lag in a furnace bu i l t of a g iven mater ia l. T he

bas ic idea o f the g raph ica l app roach was in t roduced by Thomas & Young ( fo r th -

coming) , in which we cons idered a s imple ore- l in ing mixture wi thout inf luence

from charcoa l ash . One co mp one nt of th is contr ibut io n is to jus t i fy th is s impl if ica tion

for the smel t ing of the h igh pur i ty Bris to l Channel ores. Ho wever , i t should be emp ha-

s ized tha t the smel t ing of o ther ores , or the u t i l iza t ion of o ther furnace types , may

involve a mu ch grea te r degree of inco rpor a t ion of the fue l ash than observed here .

The provenance of ore f ragments loca ted a t a rchaeologica l s i tes wi th in the UK

tends to rely heavily upon a proximity to a local ore source, (e .g. Ruddock 1961)

as , unl ike copper , the widespread ava i labi l i ty of i ron ore was tho ugh t to ma ke long

distance t ran spo rt u nlikely (Salter 1987). There exis ts a great variabil i ty in the

major e lement chemis t ry of i ron ore bodies (Sa l te r 1987) . However , the grea tes t

obs tac le to provenan cing ore mater ia l i s the lack of goo d geologica l and geochemica l

da ta on U K i ron sources, par t icula r ly the bog ores , because of the i r current econo mic

un impor tance .

Slags a re readily abu nd an t a t smel t ing si tes, and a l thou gh the remains of furnaces

are ra re , smal l quant i t ies of l in ing can f requent ly be found a t tached to s lag samples.

Cha rcoa l s ample s , if no t fo r thcoming f rom excava t ions , c an be p roduced f rom wood

samples col lec ted f rom the mo dern -day s ite, as the bulky na tu re of charcoa l sugges ts

tha t t ra nsp orta t ion would be l imi ted . Frag me nts o f i ron ore f rom sm el t ing s ites a re

rare and when they do occur they should not automat ica l ly be assumed to represent

the mater ia l ac tua l ly smel ted , as these could equa l ly represent mater ia l d iscarded as

unsui table for smel t ing .

In th is s tudy 21 s lag samples cons is t ing of both tap and furnace s lags ( to ta l weight

5 kg) a long w i th 3 l in ing samples (0 .4 kg) an d 2 ore f ragme nts (52 g) were obta ined

f rom 220 kg o f ma te r i a l excavated by the He re fo rd and Worces te r C oun ty Counc i l

Archaeology Service dur ing the i r 1993 excava t ion a t the major Roman i ron working

site of Ariconium. These were subjected to geochemical analysis using X-ray fluores-

cence of fused beads (major e lements ) and powdered pe l le ts (minor and t race

e lemen t s) a long wi th Induct ively Coup led P la s m a-M as s Spec t rome t ry o f s o lu t ions

(minor and t race e lements ) .

Geological background

The i ron ores of the Bris to l Channel Oref ie ld genera l ly occur wi th in cavernous por-

os i ty in the Carbonife rous Limes tone , c lose to the pos t -Variscan unconformity .

Tow ards the south o f the region, in the Bris to l and M endip a reas, the ores a re

found wi th in the Tr iass ic 'Dolomit ic Conglomera te ' . The la rges t orebodies occur in

the Fore s t o f Dean and G lamorg an , and a re hosted by ka rst i c fea ture s o f p robab le

Triass ic age (Simms 1990) . The age of the minera l iza t ion is poor ly cons t ra ined, but

is probably Tr iass ic to ear ly Jurass ic , a l though i t i s poss ib le tha t some of the

quar tz -r ich i ron minera l iza t ion in the Vale of Glamorgan may be s l ight ly o lder .

The o re s a re domina ted by the anhydrous i ron ox ide , haema t i t e and the hydra ted

oxide, goethite , these being characterized by their high levels of purity (goethite +

haem at i te typica l ly in excess of 97%). I t i s the low de t r i ta l content of the ores f rom



B L O O M E R Y F U R N A C E M A S S B A L A N C E A N D E F F I C I E N C Y 157

the Bristol Channel region that results in them possessing a relatively low total REE

(EREE) value, typically <40 ppm.

There has been a long tradition of iron mining within the Bristol Channel Orefield

from the pre-Roman Iron Age to relatively recently; the last mine in Glamorgan, at

Llanharry, closed in 1978. The Forest of Dean was, in particular, a major centre for

iron production in Roman and Medieval times, with a reduced importance during the

industrial period.

Ma ss balance of smelting components

It is possible to construct a mass balance description of the reaction in the bloomery

furnace. For each element the input to the reaction must be equal to the output. Some

of these values will be relatively easy to measure (e.g. elemental composition of the

ore, furnace lining and charcoal), others may be more difficult (e.g. elemental compo-

sition of the gas and ash particles lost through the top of the furnace to the atmos-

phere). If, however a few basic criteria are met, then the mass balance equations

become manageable:

9 For all elements involved in the analysis, the system must be closed (i.e. there must

be no additional sources or losses). This means that the elements must not be lost

from the system via routes such a volatilization, or incorporation in the metallic

iron phase of the bloom.

9

Incorporation of fuel ash and lining is assumed to be complete; no partial melting of

these phases to generate the slag may occur.

9 The slag composition in the calculation is the overall composition of the entire

slag production of the smelt. Slags produced in smelting may be extremely heteroge-

neous. Only when a process is producing relatively large volumes of slag (and there-

fore usually with that slag being tapped) will individual slag samples be likely to

approach the mean composition of slag for the smelt. Alternatively, the slag

values used can be averaged from the range of slag types generated at the furnace.

A graphical technique can be used to solve simultaneously the mass balance equations

for each element. The concentration of species N in phase P is expressed as c~, and in

our calculations is measured by weight% for major element oxides and ppm element

for traces. All components are recalculated to be an anhydrous composition with all

iron expressed as FeO. As iron is removed from the system the remaining elements

respectively increase in concentration, thus the degree of enrichment (E) for any ele-

ment N, other than iron, brought about by the removal of iron to produce the con-

centration observed in the slag can be calculated as:

s l a g . r , o re , , i n i n g . , ~ ( c ~ e l a s h z ) ]

E = c N /[ [ , c N x) - -J- (c N .v / +

where x, y and z are the proportions of ore, lining and fuel ash by weight incorporated

into the melt and where x + y + z = 1.

The iron concentration in the slag is related to the components by the following

equation:

Total concentration of FeO in the system (F):

F ore / lining x / fuel ash x

= (CveoX) + ~.CFe Y) + (CFeO Z).



1 58 G . R . T H O M A S & T . P . Y O U N G

P rop or t i on o f sys t em removed fo r b loom format ion ( expressed as F eO)

= B

E = 1/(1 - B)

B = 1 - ( l / E ) .

The i ron concent ra t ion in the s lag wi l l be :

slag __--E (F - B)

CFe

s l a g = E l F - ( 1 - l / E ) ]

CFe

slag

= v E = ~ C F e - 1 ) / ( F - I )

, l in ing , ( c ~e l a s h z ) .

eslag 1)l[(c re x) + eFo + - 1]

= ~ E = t Fe - -

Values o f E are ca lcula ted a t 0 .02 intervals for the ore : lin ing mixture ranging f r om 0

(l ining + fuel ash only) to 1 - z (ore + fuel ash on ly) for part icu lar values o f the fuel

ash com pon ent , z . The resul ts of th i s are then plot ted so that each e lem ent is repre-

sented by a l ine of ore- l ining-fuel ash/enr ichm ent fac tor solut ions . I f a per fect

match between ore , charcoal , furnace l ining and s lag occurs then the respect ive

l ines wi l l show a common intersect ion. Such a case wi l l represent the s i tuat ion

where a l l e lements in a s lag can be produced a t the appropr ia te concent ra t ions

f rom a s ingle mel t com bina t ion of ore , ash and l ining by the s ingle degree of enr ich-

ment (E) . For such a solut ion to be poss ible a l l the var ious cr i ter ia expressed above

mus t have been met .

In practice the graphical solut ion i s rare ly per fect , and a com bina t ion of the above

cr i ter ia may not have been met . However , the greates t problem is the inhomogenei ty

of natu ra l mater ia l s and the unl ikel ihoo d that i t wi ll be poss ible to sam ple ore , s lag

and l ining that were actual ly involved in a par t icular smel t , ra ther than jus t being

typ ica l o f the ma te r i a l s pass ing t h roug h the b loomery .

I f the e lemental l ines dem ons t ra te a c lose groupin g of intersect ions , then a 'bes t - f i t'

solut ion to the smel t ing mass balance can be placed by eye. The mix and enr ichment

values obta ined f rom the diagram can then be used to inves t igate the yie ld and

efficiency o f the process.

The p rop or t io n of the mel t that wi ll be remov ed as a bloo m (B) wi ll be represented

by:

B = (1 - 1/E)

Thu s 1 kg of reduced anh ydro us ore wi ll requi re y/x kg o f furnace l ining (L) and

z/x kg o f fuel ash (A) to give a yield (bloom ), expressed as kg Fe O (I) , of:

( I + L + A ) M

equivalent to metal l ic i ron yield, in kg, of:

I x (Atomic we igh t F e /M olecu l a r we igh t F eO) = I x 56 /72

and produce

1 + L + A - I k g of slag (S) .



BLOOMERY FUR NAC E MASS BALANCE AND EFFICIENC Y 159

The concen t r a t i on o f i ron i n t he b loom can t hen be compare d t o t ha t o f t he o re to

give an overal l indicat ion of the eff iciency of the smelt ing process.

Eff ic iency = weight o f i ron in bloom /weig ht of i ron in ore .

S ince the oxidat ion and hyd rat io n s ta te of the ore feed is rare ly know n, thi s can be

s tandar ized to:

E f f i c i e nc y '= I x (56 /72) /F eore

where Feore i s the weight of i ron in a qu ant i ty of ore , which w ould be equivalent to

1 kg o f anhyd rou s mater ia l in which a l l i ron i s present as FeII ( i .e . core FeO , see

p. 157).

For the Br is tol Channel Oref ie ld goethi te ores being smel ted a t Ar iconium, as an

example , 1 kg o f anh ydr ous reduced ore is equivalent to 1 .25k g o f goethi te or

1.1 kg o f haemat i te . Therefore , the express ion:

Efficiency' ore

I ( 5 6 / 7 2 ) / C F e 0

wil l overes t imate the t rue ef f ic iency by abo ut 20% i f the mate r ia l fed to the furnac e

was goethi te and by abo ut 10% i f the feed was haemat i te . In pract ice the precise

oxidat ion and hyd rat ion s ta te o f the ore entering the furnace i s unl ikely to be able

to be determ ined wi th a high degree of cer ta inty , unless pos i t ive evidence for ore

roas t ing i s found.

The cons i s tency o f t he mode l ga ined f ro m the mass ba l ance appro ach wi th r e spec t

t o any pa r t i cu l a r component can be i nves t i ga t ed by compar ing t he va lues genera t ed

wi th those observed in the ac tual specimens . Thus , one might check that the model i s

sa t i s factor i ly c lose in predic t ing the concen t ra t ion of key comp one nts ( such as FeO

and 2R EE ) , and has n ot been too biased tow ards e lements of a lesser signif icance.

Example:

r i c o n i um

Recen t excava t ions a t t he Romano-Br i t i sh i ron work ing s i t e o f

A r i c o n i u m

have

yie lded a large qu ant i ty of s lag, but a l so samples of furnace l ining and two ore f rag-

ment s : th r ee o f t he four compone nt s r equ i red fo r a mass ba l ance ap proac h t o fu rnace

opera t ion . The fo ur th com ponen t , cha rcoa l a sh , has been de r ived by p roduc ing cha r -

coa l i n t he l abora to ry fu rnace f rom wood t aken a t va r ious po in t s wi th in t he s t udy

area. M ajor e l ement chemica l da t a fo r each o f the smel t ing comp onent s a r e p resen t ed

in Table 1.

The bes t - fi t solut ion to the mass-b alance graph s has been judged by eye. The pro -

por t io n of fuel ash involved i s very smal l , and i ts value i s largely dr iven by the need to

balance the calc ium a nd m agn esiu m l ines. The f i t of these l ines is poo r , as are those o f

some of the o the r 'm a jor ' e l ement s . The ca l c ium and m agnes ium l ines ar e s trong ly

inf luenced by the fuel ash composi t ion, which has been found to be ra ther var iable .

At t emp t s t o p roduce mass ba l ance so lu t ions fo r va ry ing fue l a sh p ropor t i ons demo n-

s t ra te that only a smal l range of values a l low a reasonab ly c lose appro ach to a

common in t e r sec t i on be tween ca l c ium, magnes ium and the o the r ma jor e l ement s .

A fuel ash contribution of 1.8% (Fig. 1) , produces the closest f i t for these l ines, so

that value has been used for the graphs on which the f i t for E and for the ore con-

t r i bu t ion has been based . P hosphorus and manganese so lu t i ons a r e poor ; i n bo th

cases the l ines are lower than the expected f i t pos i t ion, indicat ing that the e lements

are too r ich in the mixture to a l low for the observed s lag composi t ion. The l ikely



1 60 G . R . T H O M A S & T . P . Y O U N G

.~

9

9

.,..~

9

9

c-q

c~

Z

9

9

9

L~

era,

9

<

9

o~

c~

0 0 0 0

c~

< < < <



BLOOMERY FURNACE MASS BALANCE AND EFFICIENCY 161

Fig. 1. Required concen tration factor (E) against propo rtion of contribution from the ore

(x) for mass b alance calculation for major elements o f material from Ariconum. Ore, sample

A26; lining, sample A13; slag, average of tap slags from site; fuel ash, sample A29 (charcoal

produced from oak wood growing near site) . Model assumes fuel ash concentration o f 0.018

(i.e. 1.8% of total mix).

so lu t ion to th i s is t ha t bo th a re p resen t i n the m e ta l l i c i ron phase , a nd n o t j us t t he s lag .

The l ikely f i t po si t i on l ies betw een E = 1 .3 (80% ore co nt r ib ut ion and E ---- 2 .2 (90%

o r e c o n t r i b u t i o n ) .

T h e t r a c e e l e m e n t g r a p h ( F ig . 2 ) s h o w s a w i d e s p r e a d o f s o lu t i o n s , m o s t l y i n c o m -

p a t i b l e w i t h a s e n s i b l e s o l u t i o n . T h e e l e m e n t s a p p e a r i n g t o o l o w o n t h e d i a g r a m

i n c lu d e P b , C u , M o a n d C r . T h e P b a n d C u a r e l i k el y t o h a v e b e e n l o st t h r o u g h v o l a -

t i l iza t ion , w hi l s t Mo and C r m ay be in the m e ta l l i c iron . T h e e l em en t s w i th li nes w hic h

a r e t o o h i g h ( i. e. in d i c a t i n g t h e y a r e m o r e a b u n d a n t i n th e s l ag t h a n t h e r a w m a t e r i a l s

shou ld pe rm i t ) i nc lude B e , Z n , B a , V , Z r . T he fue l a sh com pos i t ion m ay be a s t rong

i n fl u en c e o n t h e B a c o n t e n t , a n d m a y b e s t r o n g l y l o c a l ly v a r i a b le . T h e c a u s e o f

v a r i a t i o n i n t h e o t h e r e l e m e n t s i s n o t k n o w n , b u t i t s h o u l d b e n o t e d t h a t V w a s

be low de tec t io n in the o re sam ple . T he r em ain in g e l em en t s g ive a ve ry c lose zone

o f i n t e r s ec t i o n b e t w e e n E = 1.6 ( 8 0 % o r e c o n t r i b u t i o n ) a n d E - - - 2 . 2 ( 8 7 % o r e

c o n t r i b u t i o n ) .

T he in t e r sec t ion o f t he R E E l ines (F ig . 3 ) sugges t s an E va lue o f be tw een 1 .25 (67%

o r e c o n t r i b u t i o n ) a n d 1 . 8 ( 8 2 % o r e c o n t r i b u t i o n ) .

S e v e r a l c o m p o n e n t s a r e p a r t i c u l a r l y u s e f u l i n e s t i m a t i n g t h e f i t p o s i t i o n . T h e s e

inc lude i ron (because i t dom ina te s the sys t em ) , u r an ium (because i t i s t he on ly e l em ent

o t h e r t h a n i r o n c o m m o n l y m o r e a b u n d a n t i n t h e o r e t h a n i n t h e f u r n a c e l i n i n g ) ,

t h o r i u m a n d t h e s u m o f t h e R E E ( b o t h i m m o b i l e , a n d t y p i c a l l y i n v e r y l o w c o n c e n -

t r a t ions in the o re ) . S o lu t ions fo r t hese t aken a lone g ive poss ib l e so lu t ions be tw een

E = 1 .6 5 ( f o r a n o r e c o n t r i b u t i o n o f 8 2 % ) a n d E = 2 .2 ( o r e c o n t r i b u t i o n 8 8 % )

(Fig. 4).



162 G. R. THOM AS & T. P. YO UN G

Fig. 2 . E against x for min or a nd trace elements. Mod el and sample detai ls as Fig. 1.

I t is r e a d i l y a p p a r e n t t h a t t h e r e is c o n s i d e r a b l e ' n o i s e ' i n t h e d a t a ; t h e r e a re v a r i o u s

p r o b l e m s i n h e r e n t i n t h is e x a m p l e . M o s t o b v i o u s i s t h e p o o r c o n t r o l o n f u e l a s h

c o m p o s i t i o n , b u t a l so i m p o r t a n t is t h e f a ct t h a t t h e m a t e r i a l s a n a l y s e d w e re n o t

t h o s e i n v o l v e d i n a s i ng l e s m e lt , a n d t h a t t h e s l a g a n a l y s i s is n o t t h a t o f t h e t o t a l

s l a g f r o m a s i n g le s m e lt , b u t i s b a s e d o n l y o n t h e a v e r a g e t a p s l a g c o m p o s i t i o n . I t

i s p o s s i b l e h o w e v e r , t o t a k e a v a l u e ( E = 1 .8 a n d o r e c o n t r i b u t i o n = 8 3 % ) w h i c h i s

a ' b e s t f i t ' t o t h e so lu t io n s d i s c u s se d a b o v e .

Fig. 3 . E against x for rare earth elements. Mode l and sample detai ls as Fig. 1 .



BL OOME RY FURN ACE MASS BAL ANCE AND E FFICIE NCY 163

F ig . 4 . E aga ins t x fo r ' key ' componen ts . Model and sample de ta i l s as F ig . 1 .

Because this is a 'best f i t ' there ar e result ing errors; the overall mo del s lag com posi-

t ion would have the concentra t io n o f FeO = 64.1% (observed average tap s lag has

67 .1%) and ~R E E = 69 .0 ppm (obs erved ave rage tap s lag ha s 72 .6 ppm) . A d jus t ing

the model to remove these discrepancies (i .e . taking a solution solely at the inter-

sec t ion of the Fe and 2 R E E l ines) would necessar i ly in t roduc e grea te r e rrors wi th

other elements .

Putt ing this 'best f i t ' solution into the yield equations discussed above gives the

follow ing results :

1 kg o f anhydrous ore

would reac t wi th

0.18 kg o f reduced anhydrous

lining

and

O.02 kg of ue l a sh,

and wi l l produce

0.42 kg of metallic iron

a n d

0.67 kg of

slag.

The

efficiency'

(we igh t o f i ron in b loom/we igh t o f i ron in reduced anhydrous

ore) =

56%.

I t is wo rth n ot ing th a t 0 .02 kg of fue l ash would co rrespo nd to app roxim ate ly 0 .4 kg

of charcoa l (based on a typica l ash content of charcoa l of 5%). Fue l usage is repor te d

by Crew (1991; Experiment 27 has fuel to ore rat io of 3.5), Tylecote

et al.

(1971;

average fue l :ore ra t io for la te r exper iments 2 .3) and in our own unpubl ished exper i -

men ts ( fuel to ore ra t io 3-3 .5) . This impl ies tha t only a smal l f rac t ion (a pproxim ate ly

12% in this case) of fue l ash becom es inco rpor a ted in to the s lag phase.

Conclusion

Mas s ba lance ca lcu la t ions o f the s me l t ing componen t s r ecove red f rom

Ariconium

prod uce a reasonably t ight ly group ed se t of in te rsect ions . This indica tes tha t the

ore samples recovered by the excava tors a re compat ib le wi th the compos i t ion of

the ma terial smelted at this s ite in antiquity. The impr ecis ion of the solu tion reflects

the na ture of the mater ia ls on which the mass ba lance has been based, wh ich do not

cons t i tu te components and products f rom a s ingle smel t . There a re addi t iona l prob-

lems assoc ia ted wi th poor cons t ra in t on the compos i t ion of the charcoa l ash .



164 G .R . THOMAS & T. P. YOU NG

T h e c o m p o s i t i o n o f sl a gs f o r m e d f r o m t h e s m e l t i n g o f th e h i g h p u r i t y ( l ow N R E E )

o r es f o u n d i n th i s re g i o n a r e s u b j e c t to a n o v e r - r i d i n g d o m i n a n c e b y t h e a s s i m i l a t i o n

o f s m a l l q u a n t i t i e s o f f u r n a c e l i n i n g . I n a s s e s s i n g t h e c o m p a t i b i l i t y o f s l a gs a n d o r e

f r a g m e n t s r e c o v e r e d f r o m a n c i e n t i r o n w o r k i n g s i te s i n th i s a r e a , i t i s t h u s a l s o es s e n -

t i a l t o s t u d y t h e c h e m i s t r y o f t h e f u r n a c e l i n i n g .

The au thors would l ike to thank the Hereford and Worces te r County Counci l Archaeology

Service for providing the mate rials used in this s tudy.

References

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Metallurgy Society,

25, 21-36.

FULFORD, M. G. & ALL~N, J. R. L. 199 3. Iron ma kin g at the C hesters villa, Woo lasto n,

Gloucestershire: Survey and excavation 1987-1991.

Britannia,

23, 159-215.

RUDDOCK, F. A . 1961. Me talwor king at Bage ndon and f inds of clay, metal , s tone, f l int and

glass. In: CLIFFORD, E. M . Bagendon: A Belgic Oppidum. Heifer , Cambridge.

SALTER, C. J. 1987. The relevan ce of chem ical prove nan ce studies to C eltic ironw ork in Britain.

Bulletin of the Institute of Archaeology University of London,

19, 73-81.

SIMMS, M. J. 1990. Triassic pa laeo kar st in Britain. Cave Science, 17, 93-101.

SERNEELS, V. 1993. Arc h6om etrie des scories de fer. R eche rche s su r la sid~rurgie a ncienn e en

Suisse occidentale. Cahiers d'arch~ologie Romande, No. 61, Lausanne .

THOMAS, G. R. & YOUNG, T. P. (forthco ming ). T he in fluenc e of f urnac e lini ng on the com-

pos i t ion of i ron m aking s lags in Roman -Br i t i sh smel t ing of h igh pur i ty i ron ores (Br is tol

Chan ne l Orefie ld , UK) . In: YOUNG, S. M . M ., BUDD, P. D., IXER, R. A. &

POLLARD,

A. M.

(eds)

Metals in Antiquity.

Archaeopress, Oxford.

TYLECOTE, R. F. 19 86 . The Prehistory of Metallurgy in the British Isles. The Insti tute of Metals ,

London .

- - , AUSTEN, J. N. &

WRAITH,

A. E. 1971. The me cha nism of the bloome ry process in shaft

furnaces. Journal of the Iron & Steel Institute, 209, 342-363.

YOUNG, S. M. M ., BUDD, P., HAGGERTY, R. • POLLARD, A. M . 1997 . Ind uc tiv ely cou ple d

plasm a-ma ss spectrometry for the ana lysis of ancient metals . Archaeometry, 39, 379-392.



Geoarchaeological research into the

historical relics of the South Urals:

problems, results, prospects

V . V. Z A Y K O V 1, A . P . B U S H M A K I N 1, A . M . Y U M I N O V l,

E. V . ZA YK OV A 1, G. B . ZD AN OV IC H 2, A . D . TA IRO V 2 &

R I C H A R D

J.

H E R R I N G T O N 3

l Institute of Mineralogy, Urals Branch o f Russian Acad emy of

Sciences, 456301 Ilmen Nature Reserve,

Chelyabinsk District, Russia

2Chelyabinsk State University, 454136 Chelyabinsk,

Bratr Kashiriny street, 129, Russia

3Natural History M useum , Cromwell Road,

London SW7 5BD, UK

Abstract : A description is given here of the major geoarchaeological research

under taken in the Southern Ura ls reg ion be tween 1991 and 1998. Genera l pe t ro-

graphic characteris t ics of the stone material used for the manufacture of tools in

the set t lements of Ark aim an d Al ands koe are discussed, together with their possi-

ble raw material sources. Research has indicated that Bronze Age sett lements in

the region used at least nine types of copper ore. One of these, the ancient mine

'Vorovskaya Yama ' , i s descr ibed . Chemica l ana lys is o f meta l ob jec ts f rom the

se t t lements o f Arka im, S in tash ta and Kuisak show tha t th ree types o f copper

(pure, arsenical and argentiferous) and three kinds of bronze (arsenical , s tanni-

ferous, and nickeliferous) are used for the artefacts . Buried objects show evidence

of cor rosion wi th fo rmat ion of the minera ls a tacamite , para tacamite , nan tok i te ,

malachite , cupri te , and tenori te . The process of corrosion in the presence of

organ ic mater ia l has been s tud ied and malach i te , azur i te and sample i te have

been shown to form. Microprobe analysis of gold objects from eight burial

mounds shows that , in the Bronze Age, pure native gold was used to make

jewellery. The use of bin ary art if ic ial a l loys of gold and si lver is characteris t ic of

the Early Iron Age; in the Early Middle Ages ternary art if ic ial a l loys of gold,

si lver and copper were used. The composit ion of lead wire found in the Kuisak

sett lement has also been determined.

R e c e n t l y t h e s c ie n ti f ic d i r e c ti o n o f th e I n s t i t u t e o f M i n e r a l o g y h a s b e e n f o c u s e d o n t h e

g e o l o g ic a l a n d m i n e r a l o g i c a l s t u d y o f a r c h a e o l o g i c a l r e l ic s i n th e S o u t h U r a l s ( Y u s h -

k i n 1 99 0) . T h e r e s e a r c h w a s p r o m p t e d b y t h e c r e a t io n i n 1 991 o f th e A r k a i m C u l t u r a l

R e s e r v e , w h i c h h i g h l i g h t e d t h e n e e d t o s t u d y t h e t e r r i t o r y a n d t h e h i s t o r i c a l r e l i c s

l o c a t e d o n i t. T h e o b j e c t s a r e e v i d e n c e o f t h e m a t e r i a l d e v e l o p m e n t o f t h e P a l a e o l i t h i c ,

N e o l i t h i c , B r o n z e a n d E a r l y I r o n A g e c u l t u r e s ( F i g . 1 ). T h e m a i n a r e a s o f s t u d y a r e

p r o t o - t o w n s o r s e t tl e m e n t s o f 1 8 t h - 1 5 t h c e n t u r ie s BC, g r o u p e d b y G . B . Z d a n o v i c h

a n d I. M . B a t a n i n a i n t o t h e s o - ca l le d ' C o u n t r y o f t o w n s ' ( Z d a n o v i c h 1 99 6; Z d a n o v i c h

& B a ta n in a 1 9 9 5 ) .

From: POLLARD,A. M. (ed.) 1999. Geoarchaeology: exploration, environments, resources.

Geolog ical Society, Londo n, Special Publication s, 165 , 165-176. 1-86239-053-3/99/$15.00

,,~) The Geolog ical Society of L ondon 1999.



166 V.V . ZAYKOV

ETAL.

~10O0~ ~ _ ~ ~ Il~F~-~--T-as~ol,Ka~go7 0 , 50kin

~/Mo~~ l~l~~i -~ 'k t epn~Tro i l sk

~ ~~

1 l ~ t~~~Cherno , ch,e

i agnitogorsk

~ m~ ineyl ,

odniki

vorov a._

akr-Uzyak "~

Kuysak

Arkaim

Sibay ~

Sokolld

k~ntashta I Andreevka

Alandskoe r/Bersuyt

I | l IDI 4

Fig. 1. M ap of 'the Cou ntry o f towns' showing settlements and ancient copper mines loca-

tions: 1, the modern settlements; 2, large settlements of the Bronze Age; 3, areas of geoarch-

aeological research; 4, ancient surveyed copper mines.

Scop e of research

The research covers the fields of petrog raphy , m ineralogy a nd eco nomic m ineralogy.

Results have contributed to an understanding of patterns of ancient mineral uti l iza-

t ion and economies. Additio nal effort has been put into creating a com pute r database

system. The programme can be described under six headings:

1. Research into the raw ma terial sources for the li thic industry of the ancient com-

munities, devising petrographic maps of the ancient s tone buildings and the determi-

nation of rock sources regionally from geological investigation of possible quarries in

the region.



H I S T O R I C A L R E L I C S O F T H E S O U T H U R A L S 167

2. Minera logica l , geochemica l and pe t ro logica l inves t iga t ion of ores , s lags , and

me ta l s f rom excava ted p ro to - towns and bu r i a l mounds in o rde r to de te rmine the

raw m ater ia l sources and types of meta l lurg ica l technology used .

3 . The prospec t ion for anc ient mines , s tudy of the i r geologica l se t t ing and ore

compos i t ion , and recons t ruc t ion of technologies used in mining.

4 . The s tudy of the com pos i t ion of jewel le ry prod ucts and pa in ts toge ther wi th the

de te rm ina t ion of poss ib le raw mater ia l sources and man ufac tur in g technologies .

5 . The conserva t ion of corroded and a l te red a r te fac ts , de te rm ina t ion of environ-

menta l condi t ions s ince bur ia l and the es t imat ion of the long- te rm s tabi l i ty of

ar te fac ts in museum displays .

6 . The c rea t ion of a geolog ica l -m inera log ica l da ta ban k for the purposes of

archaeology.

Mater ia l sources of the s tone industry

Defin i t ion of raw mater ia l sources for the anc ient s tone indus t ry i s based on the s tudy

of rocks f rom which anc ient a r te fac ts were made . This was carr ied out for a r te fac ts

found a t Arka im and Kuisak . Recent ly , s imi la r work has been carr ied out in the

Alta i and O renb urg d is t r ic ts . Our wo rk was based on a s tudy of the compos i t ion s

and pro per t ies of rocks . The ma in param eters def ined were: minera l comp os i t ion ,

texture, s tructure, density, porosity, durabil i ty, abrasion resis tance and ducti l i ty.

These proper t ies were def ined as those which would have de te rmined whether

Bronze A ge se t tle rs would use them. D urabi l i ty i s mainly inf luenced by the hardne ss

and e las t ic i ty of the com pon ent m inera ls and ho w these combine tog e ther wi th the

degree of jo in t ing . T ools for s t r ik ing were mainly m ade f rom f ine-gra ined rocks ,

for which the combined proper t ies a re h ighly favourable . Cher ts , red-coloured

jaspers , d iabases , gabbro , epidos i tes and dac i tes a re the main rocks wi th su i table

proper t ies . The m os t im por tant s ingle fac tor in the choice of mater ia l for the ma nu-

fac ture of s t r ik ing tools i s the bulk dens i ty of rock . More dense l i thologies such as

diabase wi th a dens i ty of ab out 3 .0 g cm -3 a re h ighly fav oured .

Arkaim

A petrographic s tudy of 192 objec ts col lec ted by S. Ya . Zdanovich was carr ied out .

They comprised 18 types of objec ts made f rom 26 d i f fe rent types of rocks . This

s tudy resul ted in three major conc lus ions . Fi rs t ly , a l l the a r te fac ts a re made of

rocks sourced f rom the a rea of s tudy. Secondly , there a re s t r ic t ru les about which

rocks a re used for which type of objec t . For example , a rrow-heads and dr i l l ing

tools were only made from sil iceous rocks which take a sharp edge. Only clast ic

rocks wi th gra ins of quar tz a re used as abrasives . Tools used for m eta l foun dry

work a re made f rom ta lcose rocks , which have a h igh hea t res is tance . St r ik ing

tools a re produ ced f rom rocks wi th a h igh durabi l i ty and s t rength , namely epidos i tes ,

s i l ica-rich sediments , and jaspers . Thirdly, the uti l ization of the rocks is determined

not only by the i r phys ica l -mechanica l proper t ies , but a lso by the or ienta t ion

and degree of jo in t ing . Fo r th is reason, epidos i tes wi th a d is t inc tive pr ismat ic

jo in t ing was used for the ma nufa c ture of ham mers , whereas basa l t ic and rhyol i t ic

lavas , which have a wedge-shaped in te r locking f rac ture sys tem, were made in to

ma t tocks .



168 V. V. ZA YK OV

ET AL .

K u i s a k

Fr om Ku isak, 84 ar tefacts, mad e f rom 25 types of rocks and m inerals , have been

invest igated. Th e m ost nu me rous types are percussive tools of some descr ipt ion

(hammers , anvi l s , p icks , pes t les , e tc . ) . The next most numerous are abras ive tools

(gr inders , abraders and pol i shers) , fol lowed by cut t ing and pierc ing tools ( scrapers ,

kni fes , ar row-heads) , then foundry tools , specia l tools ( f i shing s inkers and spinning

weights) and r i tual objects which s imulated tools but which were made f rom sof t

mate r ia l incapable of working. Cher t s , d iabase an d red-colou red jasper are by far

the most f reque nt ly used l i thologies for the manu fact ure of ins t rum ents on the si te

of the anc i en t t own. These rocks a r e t he mos t c om mo n un ive rsa l r aw m ate r ia l fo r

the manu factu re of s tone tools of varying types . Ou tcrop s of si li ceous rocks and dia-

bases are located in the imme diate vic inity of the ancient town. Fra gm ent s o f jaspers

are found in ta lus deposi ts to the eas t of the ancient to wn and in a l luvia l deposi ts o f

the r ivers Kuisak and Zingeika . Talc-conta ining rocks served as raw mater ia l for the

fou ndr y tools . Use of other rocks such as sandstone, daci te , granite and serpentini te i s

un com mo n a t Kui sak . To da t e , on ly r a re ly have too l s made o f gabbro , basa lt , a l euro-

l ites and qu ar tz i tes been found , despi te these l ithologies being co m m on in the region.

Ri tual objects (e .g . , ha tchets , maces) are made f rom eas i ly pol i shed rocks such as

serpent inites and ta lc-schis t . A n um ber of exotic f inds include f rag men ts of fossi l

belemni tes , character is t ic o rganisms in Mesozoic l imestones of the region. How ever ,

the neares t f inds of belemni tes in the Urals l ie some 150 km to the southw est , near to

the Akc hyar se t tl ement .

As d i s ti nct f rom Arka im , t he Kui sak i nhab i t an t s used a l imit ed numb er o f rocks

for manu factu r ing tools and were mo re conservat ive in their choice of s tone

for these products . They used no more than three l i thologies , whi l s t the Arkaim

inhabi tan ts used up to e ight kinds of rock. This ma y have been due to the poo rer

choice of s tone avai lable in the Kuisak area . How ever , in com par iso n w i th

Ark aim , a t Kui sak the inhabi tants used s tone to bui ld the wal ls of the se t tlement .

The ex cavat ions revealed two defensive wal ls mad e f ro m bou lders of s il iceous

rocks , sandstones and basal t s , which can be found in outcrop on the eas t bank of

the Zingeika r iver .

A l a n d s k o e

Am on g the p ro to - town s o f t he S outh Ura l s , t he se tt l ement o f Alandsko e i s d i st in -

guished by the abu nda nce of rocks used in bui lding the se tt lement . Excav at ions

carried out in 1997 have revealed two s trong defensive walls with a height o f the

order of 5-6 m. Th e w al ls are covered by pla tes and blocks of var ious l ithologies,

which are domin ated by grani tes and am phibol i tes . Sources of thi s s tone were

ou tc rops o f g ran i to ids o f t he S uundu k mass i f and metam orph ic rocks i n sca rps o f

the Solonchanka r iver val ley. In bur ia l mounds f lanking the se t t lement , s tone i s

a l so common.

This pet rological work i s only pre l iminary in nature . Only a broad regional pic ture

of the stone used in the set t lemen ts an d po ssible sources of this ma teria l is defined.

Fur ther wo rk i s needed to answer ques t ions ab out sources of raw mater ia l s . Such

prel iminary work i s l imi ted in scale to areas such as I s iney, Rodniki , Kuisak,

S a rym-S akly and Alandskoe .



HISTOR ICAL RELICS OF THE SOUTH URAL S 169

Bronze Age copper mines

The study of ancient mines on the Southern Urals began at the end of the 18th cen-

tury, carried out by the classical Russian geologists I. I. Lepyekhin, P. S. Pallas and N.

P. Rychkov. In 1884, I. P. Aspelin systematized the collected the data on ancient open

pit mines. In the first half of the 20th century, M. V. Malachov, D. Kashintsev, L. P.

Levitcky and A. A. Iessen researched the origins of ancient metallurgy in the Urals

(Iessen 1948), the sources of ore, and the connections between adjacent mining and

metallurgical operations. Before this, ancient open pits had been located at Bakr-

Uzyak (A. Kh. Ivanov), Elenovka (A. S. Novichenko and I. L. Rudnitsky), and

Ush-Kattyn (A. I. Rybalkin and S. K. Nechitailo). The basis of our modern under-

standing of ancient mining and metallurgy in the Urals was defined by B. G. Tikho-

novr and O. N. Baderr Long-term research on ancient metal lurgy of the region,

particularly the geochemistry of copper ores, was carried out by E. N. Chernykh

(see Chernykh (1992) for an English translation which includes this work). Chernykh

studied about 30 ancient copper deposits on the eastern side of the Urals. The most

prolific work on the metal products of the Bronze Age is by G. B. Zdanovich, who

introduced the term 'metalliferous layers' due to the abundance of bronze artefacts

in horizons excavated at Petrovskaya. The most recent information about copper-

mining production in the South Urals is found in work by S. A. Grigorr E. V.

Zaykova, V. V. Zaykov, and A. F. Bushmakin concerning the mining and recycling

technologies of copper ores in 'the country of towns'. One important result from this

work is the discovery of the Bronze Age mine 'Vorovskaya Yama' near the Zingeisky

settlement (see Fig. 2). The work also links the discovery of tourmaline-containing

copper ores found at the excavations at Arkaim with the Elenovka ore deposit.

Raw material sources for ancient copper production in the South Urals are the

numerous deposits of oxidized sulphide ores, many of them small, in which copper

carbonates (malachite and azurite) are the dominant ore minerals. Ore assemblages

can be classified into the following types:

1. Zones of oxidation of disseminated sulphide ores hosted in ultra basic and basic

igneous rocks that are in crust of oceanic affinity. The mineralization is present as

veinlets and films of malachite and azurite, forming stringers and networks. The

thickness of such zones varies from a few to tens of metres.

2. Oxidation zones of cupriferous massive sulphide ores of volcano-sedimentary

origin in Devonian-age strata. These deposits formed in island arc settings, at the

margins of the Palaeozoic Urals Ocean. These ores are dominated by brown iron

oxide ores in which are masses of copper carbonates, which formed during weather-

ing. Ore bodies are sheet or lens shaped, with a maximum thickness of some tens of

metres. At the base of the oxide zone, primary sulphide ores are usually found.

3. Oxidation zones of copper-bearing hematite-quartz ores which formed as low-

temperature precipitates on the seafloor. One of these sites (Bugodak), where ancient

mining is evident, occurs west of the Magnitogorsk zone near the Aslaevsky settle-

ment.

4. Oxidation zones of irregular disseminated ores in granitoid and gabbroid massifs

of Devonian age, which are cut by porphyry intrusives. The primary ores comprise

copper sulphides. Ore bodies are isometric, linear or annular, from a few hundred

metres to a few kilometres in diameter. Evidence of Bronze Age mining of these

deposits is not yet demonstrated.



170 V. V. ZA YK OV

ET AL.

Fig. 2. Geological sketch of the 'Vorovskaya Yama' mine.

5 . Oxidat ion zones in basal t ic lavas wi th i r regular di sseminated copper mineral iza-

t ion associa ted wi th zeol i tes and nat ive copper .

6 . Oxid at ion zones of i r regular di sseminated sulphide ores in tourm al ine-bea r ing

rocks c lose to the contacts of grani toid mass i fs. E len ovk a depo si t (Oren burg dis tr ict )

i s a typical example . I t has a rarer mineralogical a ssemblage of molyb deni te-chalco-

pyr i te- tourm al ine . Because of this ra ther unique m ineralogy , it has been found tha t

ores f rom or s imi lar to the Ele novk a deposi t , were one of the sources of raw mater ia l

fo r me ta l l u rg i ca l manufac tu re i n Arka im. Th i s was demons t r a t ed by t he i den t i ca l

mine ral compos i t ions an d s imi lar min eral t extures and associa t ions o f some samples

of copper o re found in a rchaeo log ica l excava t ions com pared t o E l enovka o res .

In foun dry s lags recovered f ro m Ar kaim , the presence of high levels of boro n (one

of the main com pon ents of tourm al ine of schor l -dravi te ser ies) is dem onst ra ted

(Bushmakin & Zaykov 1996) .



HISTORICAL RELICS OF THE SOUTH URALS 171

7. Oxidation zones of sulphide-quartz and sulphide-carbonate-quartz veins and

stockworks, usually associated with granitoid bodies of more alkaline affinity. Such

deposits are rather small and low in tenor but are very numerous. Apart form

copper, these veins contain gold, silver, tungsten, molybdenum and other metals.

The presence of the mineral arsenopyrite in the veins is significant, since this may

be the source of arsenic found in the arsenical bronze artefacts.

8. Oxidation zones of garnetiferous skarns at the contacts of granitoid bodes, and

also of rodingites. The Vorovskaya yama mine, 40 kms to the north of Arkaim is

one such deposit (Zaykov et al. 1995) where rodingites are host to rich copper carbo-

nate deposits

9. Oxidation zones of cupriferous sandstones which formed in shallow sedimentary

basins. The Kargala group of deposits in the west of Orenburg district was the

source of large quantities of copper in the Bronze Age and are classical examples

of this type (Chernykh 1970).

Linking geological with archaeological researches shows that in the South Urals it

is quite possible to determine the ancient mines from which the ores are sourced. The

mines are found as anomalies in the relief of the terrain, often as depressions or

rounded knolls and unusual elongate mounds. These are often flanked by overgrown

dumps on which there are fragments of rocks with secondary copper minerals.

The composition of copper and bronze artefacts

Significant data on the composition of copper and bronze artefacts from historical

relics of the South Urals has been obtained. On the basis of the study of the chemical

composition of ancient artefacts made from copper and copper alloys, the following

types of metals are distinguished:

Types of copper:

9 pure (where As, Sn, Ag <0.1 wt%)

9 arsenical (where As contents are in the range 0.1-1 wt%)

9 argentiferous (content of Ag 0.1-1 wt%)

Types of bronze:

9 arsenical (content of As 1 -4 wt %)

9 stanniferous (content o f Sn 1-7 wt%)

9 nickeliferous (content of Ni 1-5wt% )

A r k a i m

Research shows the composition of the metal artefacts is mainly of pure copper with

alloying metals less than 0.5 wt%. However, some specimens of awls and knives are

made from arsenical bronze where As is between 1.1 and 2.8 wt%, arsenical copper

where As is between 0.13 and 0.88 wt%, and one specimen of nickeliferous bronze

with a Ni content of 1.10 wt%. Slag material found here contains inclusions of nickel-

iferous bronze, German silver and pure copper. S. A. Grigorr A. F. Bushmakin

and E. V. Zaykova have shown (by composition of slags and fragments of ores)

that at Arkaim, ores from serpentinites, brown iron ore (oxidation zone of massive

sulphide deposits?), quartz veins, and chlorite-tourmaline rock were used. During

the smelting of the ores, quartz and limonite were added to the charge.






The pre l iminary conc lus ions a re tha t the inves t iga ted s i tes y ie lded objec ts made

from pure copper , a rsenica l copper and a rsenica l bronze . The few spec imens found

made f rom s t ann i fe rous b ronze a re ra re and were appa ren t ly impor ted f rom e l s e -

where.

Minerals formed by the corrosion of copper artefacts and their

pseudomorphs

The anc ient coppe r and bronze a r te fac ts a re suscept ib le to a l te ra t ion when bur ied an d

the fo l lowing minera ls have been found as products of th is a l te ra t ion: a tacamite ,

para tacamite , nantoki te , cupr i te , tenor i te , brochant i te , an t le r i te , malachi te and

azur i te . Meta l objec ts found in contac t wi th bur ied corpses or wi th o ther phosphat ic

objec ts of organic or ig in g ive r i se to the l ight -b lue copper phosphate sample i te

NaCaC us (PO4 ) 4 9CI. 5H2 0. This minera l was f irs t sugges ted as a prod uct of corrod ed

ar te fac ts by Bridge

e t al.

(1978) . Sample i te , and somet imes malachi te , replaces both the

meta l and the organic mater ia l in contac t wi th i t . In some cases , th is resul ts in

extremely good preserva t ion of s t ruc tura l de ta i l s of the objec ts (see Fig . 3) . This

replacement a lso inc ludes the organic mater ia l involved. For example , a copper awl

M

k, I~movsky

Ma~. gorsk V~~a rUZt

~~t Varn

:aya gora

~/ ~Ark a im

arnensKy

Chekotay

Sorzhan-Kystau

0 km

0

IAI1

I ~ 12

1 13

Fig. 4. The scheme of burial mounds setting: l, burial mounds; 2, modern settlements; 3,

places of possible ancient gold mining.



1 74 V . V . Z A Y K O V ET AL.

c~

%

9 ~ ~

i,.....,l

o o

r

o o . ~

o

.<

. .

c-. .~

<

tr

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s

<




f o u n d a t t h e B o l ' s h e k a r a g a n b u r i a l s it e w a s a d j a c e n t t o t h e c h i t in o u s c o v e r s o f a f ly

p u p a ( 0 . 5 - 2 m m i n l e n g t h ) , w h i c h b e c a m e r e p l a c e d b y a z u r i t e . T h e m i n e r a l f o r m s

m o u l d s t h a t e x a c t l y r e p r o d u c e m o s t o f th e f in e d et a i l o f t h e p u p a f o r m .

Composition of lead

L e a d w a s f o u n d d u r i n g e x c a v a t i o n s i n t h e K u i s a k s e t t l e m e n t , a s a b e n t s e c t i o n o f

t h i c k w i r e w e i g h i n g 8 . 7 g w i t h a g r e y i s h - b r o w n t o b r o w n c o l o r a t i o n . F r o m t h e

c e n t re o f th e s a m p l e , a s e c t i on a n a l y s e d b y m i c r o p r o b e s h o w s t h a t t h e s p e c i m e n

c o n s is t s o f p r a c t i c a l l y p u r e l ea d . F r o m t h is a n a l y s i s a n d t h e m o r p h o l o g y o f t h e

ob jec t , i t i s conc luded tha t t he m a te r i a l i s pa r t o f a rod- l ike ingo t , i n i t s foundry

f o r m . T h e d e s c r i b e d p a r t w a s s e p a r a t e d f r o m r o d b y u n t w i s t in g a s m a l l s ec t io n .

T h e l e a d w a s p r o b a b l y o b t a i n e d f r o m p u r e g a l e n a , t h e n o r m a l s o u r c e f o r t h e m e t a l

in anc ien t cu l tu res .

Composition of the gold artefacts

C o m p o s i t i o n o f th e g o l d o b je c t s f r o m e i g h t b u r i a l m o u n d s r a n g i n g i n a g e f r o m t h e

B r o n z e A g e u p t o t h e E a r l y M i d d l e A g e s h a s b e e n d e t e r m i n e d ( F i g . 4 ) u s i n g t h e

co l l ec t ions o f A . D . T a i rov , S . G . B o ta lov , N . A . P o lu shk in an d D . G . Z d anov ich .

Cu,

n 10

Y Y Y Y Y

Ag

8 Au Ag . ~F__Z e)

F""= . u

71 i" 5

721 _ '

D ~ u 8 "

1

z 3 4 ~ ~ ~

Cu,

w{.%

Ag,

wt. %

A.

30

40

,E

| _ / - -

9

~o so 70 80 Au , wL %

F i 9 . 5 . C o m p o s i t i o n o f q o l d a r t i f a c t s

f r o m b u r i a l m o u n d s o f t h e S o u t h U r a l s

fields of composition

1- Chekotay; 2- Vamensky;

3- B. Klim0vky; 4- Sotzhan-Kystay;

5- Mavrinsky; 6- Krutayagora;

7- Druzhensky; 8- Solonchanka-I.

Fig. 5. Compo sit ion of gold artefacts from burial mou nds of the South Urals.



176 V. V. ZAYKOV ET AL.

The dates, brief description and compositi on of alloys are shown in Table 1. For the

analyses, representative sections of metal with thickness of 0.5-2mm have been

made. After careful polishing, the analysis of each section was carried out at several

points. Gold composition is shown graphically in Fig. 5. The analyses show distinc-

tive variations in the compositions of the objects. Au and Ag, as well as Cu are quite

variable, a testament to the changing technologies for manufacture of the artefacts.

The highest gold contents are found in jewellery where fineness reaches 800-860%o.

For the manufacture of gold foils, middle to low-grade alloys were used.

The authors wish to thank E. V. Belogub, I. G. Zhukov, V. A. Muftakhov, V. A. Popov, I. V.

Sinyakovskaya, O. S. Telenkov, Eu. I. Churin, I. M. Batanina, D. G. Zdanovich, S. Ya.

Zdanovich, A. I. Levit, I. E. Lubchansky, M. V. Kuznetsova, T. S. Malutina and F. N.

Petrov for help in writing this article.

References

BRIDGE,

P. J.,

PRYCE,

M. W.,

CLARKE,

R. M. &

COSTELLO,

M. B. 1978. Sampleite from Jingemia

Cave, Western Australia. Mineralogical Magazine, 42, 369-371.

BUSHMAKIN, A. PH. & ZAYKOV, V. V. 1996. Copper-tourmaline Elenovka deposit is probable

source of the ore for copper-smelting Arkaim production. Ural's Mineralogical Collec-

tions. Miass, 5, 221-232. (in Russian).

CHERNYKH, E. N. 1970. Ancient Metallurgy of the Urals and Povolzhia. Nauka, Moscow. (in

Russian).

-- 1992. Ancient Metallurgy in the USSR. the Early Metal Age. Cambridge University Press,

Cambridge.

IESSEN, A. A. 1948. About ancient production of gold in the Urals. 200 years of gold industry of

the Urals.

Sverdlovsk,

5-34. (in Russian).

YUSHKIN, N. P. (ed). 1990. Mineralogy of the Urals: Elements, Carbides, Sulphides. Urals

Branch RAS USSR, Sverdlovsk. (in Russian).

ZAVKOV, V. V., ZDANOWCH, G. B. & YUMINOV, A. M. 1995. "Vorovskaya yama" copper mine

of bronze century (the Southern Urals). Proceedings of the 3th International Scientific Con-

ference 'Russia and East: the Problems of Interaction'.

Chelyabinsk university, Chelya-

binsk, 2, 157-162. (in Russian).

ZDANOVICH,

G. B. 1996. Arkaim is cultural complex of middle bronze epoch of the Southern

Transurals. Domestic Archeology, 7, 47-62. (in Russian).

- - & BATANINA, I. M. 1995. "Country of towns" is consolidation settlement of bronze epoch

(XVIII-XVII B.C.) in the Southern Urals. Arkaim: Researches, searches, discoveries.

Chelyabinsk, 54-62. (in Russian).



Index

Note: page numbers in italic type refer to illustrations and tables

Alandskoe, southern Urals 168

al luvial tin mining on Da rtmo or 91-101

barytes and galena 97

climate deterioration 101

docum entary evidence of mining 91, 92

field site sele ction 93, 94

l abora tory methods 94-5

palaeochannels

River Avon 98-100, 99, 100, 101

River Erme 98,

99,

100-101,100

radiocarbon dating 93, 95, 97, 98-100, 99

Ringarooma River, Tasmania 93, 97

sediment sampling 93-4

Taw M arsh terrace s ite 95-6, 96

Teign valley site

middle terrace 96-8, 97, 98

upper terrace 93, 97

tin concentrations 96, 96, 97-100, 9 7 -1 0 0

correlated to s il t percentage 97-8, 97

tin slag 92

t in s t reaming (hydraul ic mining of placer

deposits) 92

downstream environmental impact 92-3, 97

alum extraction processes, geochemistry of 12,

139-45

alum industry 139-40

alum shales of North Yorkshire 139, 140

sulphur content 145

alunite 139-40

Carl ton Banks Alum Works 142-3, 145

geochemical analysis 142-5

EDXRF (energy dispersive X-ray

fluorescence) 143-5, 144

method ology 143

variations in fresh shale compo sition 143, 145

magnetic susceptibility 143, 144, 145

product ion process 140-2,

141

extraction 140

extraction efficiency 142, 143, 145

purification 140-2

waste tips of calcin ed shale 142

Spence process 140

anthropology, and archaeology 8

archaeological chemistry 7

archaeological geology 9

Archaeological Prospection 9

archaeometry 7

Ariconium Roma no-Bri t ish i ron w orking s i te 156,

159-63

Arkaim, southern Urals 167, 169, 170, 171

Australopi thecine s ite at L imeworks Cave,

Makapansgat 10-11 , 61-76

bones derived from hyena dens 71

breccias 62, 71-2, 74, 75-6

cave deposits 65-74

Mem ber 1 (A and B) 65-9, 65, 67, 68, 70,

72, 75-6,

Member 2 69-70 , 70, 71, 75-6

Member 3 70-1 ,

70,

75-6

Member 4

66, 71-4, 72, 73

cave s t rat igraphy 63-5, 65

cave topography 63-5 ,

64

chronology 61-2

locat ion 62

mud-crack po lygons 68, 69, 75

palaeomagnetism 62, 63, 72, 73, 74, 76

palynological analysis 62

rhythmites 73-4

speleothem deposi t ional e nvironments 66,

67-9, 71, 74-5

standing water and water tables 75

Australopithecus africanus remains 61, 63, 70-1

Blaengwynlais ore deposi t, G lamorg an i ron

orefield 112, 116, 117

bloome ry furnace mass balance and efficiency 12,

155-64

contribution of furnace lining to slag 155,

163

mass balance of smelt ing componen ts 155-63

equat ions 157-9

errors in best fit solution 161-3

fuel ash contribution 159, 163

graphical solut ions 155-9, 161, 162, 163

ma jor elemen~ts 159,

161

rare-eartl~, elements 161,162

trace elements 161,162

major e lement compos it ion of components

159,

160

brass alloys see zinc isotope fract ionat ion

Bristol Channel Orefield 103-20, 155-64

geological back ground 111,111, 156-7

Brouage see geochemistry of grani te bal last

Bute ore deposi t , Glam orga n i ron orefield 111,

112, 117,

120

Carl ton Banks Alum Works 142-3, 145

see also alum extract ion processes



178 INDEX

cave deposits

see

Australopithecine site at

Makapansgat

Dacre , lead sm elting site 16, 18, 27-9, 28, 30, 31

D ar t m o o r

see

al luvial t in mining on Da rtmo or

Darwin, Charles 8

depth to buried features see Euler deconvolut ion

in depth est imat ion

environme ntal geochem istry 11

environme ntal reconstruct ions 10, 79-89

Euler deconv olut ion in depth est imat ion 10,

35-40, 55 7

Euler deconvolut ion theory 37-8, 38

fluxgate gradiom eter data 35 -6

GPR (ground penetrat ing radar) 38-40,

39

Fforest Fawr ore deposi t , Glamorgan i ron

orefield 111-12, 115, 116, 117

fluxgate gradiometer surveys

del ineat ion of wal l foot ings 35-6,

36

Euler deconvolut ion methods appl ied to 37-8,

38, 40

metal working sites 16-17, 18, 19-27,

21 5,

27 8,

29,

30

Geoarchaeology 9

geoarchaeo logy

definition 7

in the United States 8

geoch emical analysis 11

geochemistry

early alum extraction processes 12

modelling of bloom ery iron smelting 12, 155-64

geochemistry of grani te bal last boulders 11-12,

123-36

archaeological dat ing 125, 126

ballast boulders

cabotage 127, 136

in dated building structures (Brouage) 125,

126, 127

evidence for direct travel 124, 127

mari t ime pract ices 123-4

in ore furnace l ining (La R ochel le) 125,

126,

127

un-mixed sample types 124, 127

laboratory methods 124

muscovi te-bearing grani te 127-34, 135-6

Carnmenel l is intrusion 133-4,

133

geochronology 133-4

geographical origin 133-4

petrograp hy 127, 129, 129, 131, 132

rare-earth element pat terns 133, 133

single magmatic series 129-32

trade between Falmouth and La Rochel le

and Brouage 136

muscovite-fre e granite 134 6, 127

Donegal bathol i th 134

geochrono logy 135

geographical origin 134-5

petrography 127, 129, 134, 135

t rade between Donegal and Brouage 134-6

site deta ils

128

syenite bould ers 127

trade routes 123, 136,

136

geochron ology 11-12, 61-2, 133-4, 135

The Geological Evidences of the Antiqui ty of Man

(Lyell) 8

geology 7

and archaeo logy 9

geomo rphology 7, 9

geophysics in u rban areas

see

microgravi ty in

industrial archaeology

georadar (GPR; ground penetrat ing radar) 9, 10,

36, 38-40, 39, 45

Glamorgan orefield 103, 104, 111

evidence of exploi tat ion 117-18

geology of 111-12, 111

historical context of exploitation 119-20, 119

ore characteristics 112-18,

113, 114

t race element data 115-17

see also i ron ore

Grinton lead smelting site 18, 26-7,

27,

31

historical relics of the south U rals 12, 165-76

Alandskoe 168

Ark aim 167, 169, 170, 171

burial mounds

173,

175-6

composi t ion o f artefacts

copper and bronze 171-3

lead and gold 174, 175-6, 175

conservation of artefacts 167

corrosion products of copper and bronze

artefacts 173

geological-mineralogical data b ank 167

Kuisak 167, 168, 172-3

locations of settlements 166

materia l sources for lithic indus try 166, 167 8

mining and metal w orking 167, 169-70

Bronze Age copper mines 169-70,

170

ore assemblages 169-71

Sintashta 172

Vorovskaya Yama, Bronze Age mine 169,

170,

171

ICP-MS (Induct ively Coupled Plasma-Mass

Spectrometry) 107, 109, 115 17, 149 , 150 -1,

152, 155, 156

iron ore, provena ncing in Bristol Channel

Orefield 11,103-20, 156

de Clare family, Lords of Glamorgan 119-20

Trelech industrial centre 119-20

exploitation evidence 117-18

Glam organ i ron orefield 111,111

geology 111-12, 111

ore characteristics 112-18

orebodies worke d out 111-12

Pb/Ba data 116-17,

116

under control of de Clare family 119, 119

historical context 119-20

locat ion

104

Magor Pill boat 103

date of found ering 119

iron ore cargo 103,

108, 109, 110,

116, 118

grade 107

lump ore facies 104, 106-7

ore genesis 118

powder ore 107,

107



INDEX 179

provenancin g within Glamo rgan ore f ield

111-18, 120

majo r elemen t analysis (XRF) 108, 113, 114,

116

rare earth e leme nt analysis

110

trace elemen t analysis (ICP-MS) 107, 109,

115-17

iron smelt ing technology

blast furnace (indirect process) 16, 19, 29, 117

bloomery process (direct process) 16, 18-19,

18,

29, 1178

finery/chafery 16, 18, 19

see also bloom ery furnace mass balance;

medieval iron and lead smelting; metal

wor king sites

Kuisak, so uthern Urals 167, 168, 172-3

Kyloe Co w Beck, i ron bloo mery 16, 22-4, 23, 24,

31

La Rochelle

histor ical developm ent 124-5

see also geochemistry of gran ite ballast

lead smelting sites 10, 16, 26-9, 31, 32

see also i ron and lead smelt ing works

Lesser Garth ore deposit , Glamorgan iron

orefield 111,112, 115, 116, 117

Limeworks Cave , Makapansga t see

Australopithecine site at M akapans gat

Llanharry ore deposit , Glamorgan iron oref ield

111,115, 116, 117, 157

Lock Farm, reburied iron bloomery furnace 16,

19-21, 20, 21, 22, 24, 31

Lyell, Sir Charle 7-8

magnetic gradiometery (m agnetostrat igraphy) 10

Ma gor Pill boat , i ron ore cargo see i ron ore,

provenanc ing

medieval iron and lead smelt ing works 15-32

charcoal storage areas 29

Dacr e lead sm elting site 16, 18, 27- 9, 28, 30,

31

furnace area calculations 24

geophysical techniques and m ethod ology

16-18

earth resistance 17, 29

fluxgate gradiometer surveys 16-17,

18,

19-27, 21-5 , 27-8 , 29, 30

magn etic susceptibility determin ations 16-17,

19, 26, 27, 29, 31,

32

pulse induction surveys 17

Grinton lead smelting site 18, 26-7, 27, 31

Hendy -isaf bloom ery 117

Kyloe Cow Beck 16, 22-4, 23, 24, 31

Lock Farm experimental site 16, 18, 19-21, 20,

21, 22, 24, 24, 31

Mwyndy bloomery 117

previous work 15-16

site locations 17-18, 17

technology

iron smelt ing 18-19, 29-30

lead smelt ing 26, 29-3 0

Timberholme High Bloomery 25-6, 25, 31

tin proces sing sites 16

metal working sites

Ariconium Rom ano-B rit ish iron smelt ing site

156, 159-63

Fforest Fawr 117

Glam organ oref ield 112-15, 117

Hendy -isaf 117

Mwyndy 117

remo te sensing techniques

earth resistance 15, 16, 29

fluxgate gradiometer surveys 16-17, 18,

19-27, 21-5, 27-8, 29, 30

gamm a-ray spectroscopy 16

mag netic susceptibility surveys 15, 16 -17,

19, 26, 27, 29, 3l, 32, 143, 144, 145

magnetometer surveys 15-17

pulsed induction 16

southern Ura ls 167, 169-71,170

Trelech, i ron -makin g centre (Gwent) 119

see also

medieval i ron and lead smelt ing works

microgravity in industr ia l archaeology 10, 41-58

Bouguer anomaly maps 48, 49, 51, 53

regional anomaly removal 51, 53, 57

second horizontal derivative 49, 51, 52, 54-5,

54,

55, 57

terrain correction 49-50, 50, 53, 57

data

acquisi t ion 48-9

enhancement 49-51, 57

interpretat ion 53-5, 54

reduction 49

sources of noise 52 3

Eule r deconvolut ion method 55-57,

56

geolo gy of site 52, 53

gravimeter resolution 47

gravity modell ing in 3D 55-7, 56

previous microgravity surveys 46

previous si te invest igations 43-4

principles of microgravity 45-6

site reconnaissance 44, 48

survey design 46-8

techniques for void detect ion 44- 6

Will iamson tunnels, history and redevelopment

41-4, 43, 44, 53

Miskin ore deposit , Glamor gan iron oref ield 111,

115-16

Mwyndy ore deposit , Glamorgan iron oref ield

111,112, 1t5, 117

On the Origin of Species (Darwin) 8

palaeoindian sites, ephem eral nature 9

palynology 10, 62

see also soil-strat igraphic palyn ology in

podsols

pedology 7

Principles of Geology

(Lyell) 8

radioc arbon d ating 8, 88

remo te sensing (archaeological prospection) 7,

9 - 1 0

aeria l photography 9

earth resistance 15, 16, 29

georadar 9, 10, 36, 38-40, 39, 45

grou nd based techniques 9



180 INDEX

remo te sensing (archaeological prospection) (cont . )

high-resolution microgravity 10, 45-58

magnetic ( f luxgate) gradio metry

see

fluxgate

gradiometer surveys

magnetic susceptibility 15, 16-17, 19, 26, 27,

29, 31,

32,

143,

144,

145

multispectral data (airborne and satellite) 9

resistivity 9

shallow seismic techniques 9

in urban areas 10, 41-58

salt trade, Brouage 125

sedimentology 7, 9

Sintashta, southern Urals 172

slag deposits 30

assimilation of furnace lining 155

chem ical analysis 10, 12, 25 -6, 28

iron con tent 19

low ano mal y values of lead slag 27, 29,

30, 31

magnetic susceptibility surveys 15, 16, 26, 27,

29, 31,

32

in mass balance equations 157-9

soil-strat igraphic palynology in podso is 79- 89

14C dat ing 88

biological activity 80

field site (Lour 7; ferric podsol) 80-3, 81

dated inputs to podsol

137Cs 82, 84-5, 86

depth and rate of mixing 86-7, 88

non-native pollen 81, 84, 86

spheroidal carbonaceous particles (SCPs)

82, 84-5, 86

stratigraphic locations 84, 85

earthworms absent 85, 87, 88

enchytraeids 85-6, 87

faunal excrement 85-6, 87

location of te trad p ollen grains 84, 85- 6

methodology 82

physical and soil-faunal data 83, 84

soil profile description

83

Lour Peat Profile 81, 82, 87

mor hor izons , format ion of 80

pollen assemblages 79-80

trapped within organic horizons 86, 87, 88

unreliable for interpret ing vegetat ion

histories 87, 88-9

pollen mixing processes 80, 86-7, 88

near-surface fe eding inverteb rates 86, 88

previous work 80

soil-m icrom orph ologica l analysis 80, 82, 83, 85

vegetat ion histories 79-80

stratigraphy 7

in cave deposits 10-11, 6 1-76

in soil profiles 79-89

Timberh olme, high bloomery si te 25-6, 25, 31,

31

tin mining

see

alluvial t in mining on D artmo or

trade patterns see geochemistry of granitic ballast

boulders; historical relics of the south Urals;

iron ore

Trecastell ore deposit , Glam organ iron oref ield

111, 115, 117

Trelech, i ron-mak ing centre 119-20

tunnels see microgravity in industr ia l archaeology

Urals see historical relics of the south Urals

void detect ion see microgravity in industr ial

archaeology

Vorovsk aya Yama, Bronze Age copper mine 169,

170, 171

Will iamson, Joseph 42

Will iamson tunnels, Edge Hil l , Liverpool

see

microgravity in industr ia l archaeology

Wroxeter Hinter land project 35-40, 36

X-ray fluorescence (XRF) 94, 108, 143-5, 144,

156

zinc isotope fractionation in liquid brass alloys

12, 147-53

brass-making 147-8

cemen tat ion process 147 -8

direct process 148, 152

fractionation factor est imates 149, 151-2,

151

ICP-MS ( inductively coupled plasma-mass

spectrom etry) 149, 150-1, 152

isotopic zinc f ract ionation during evaporation

147, 148 , 152

experimental methodology 149-51

mathem atical modell ing 148-9, 152

zinc isotope analyses ( ICP-MS) 150-1,150,

151,

152

Rayleigh fraction ation 148-9 , 152



Geoarchaeology:

e x p l o r a t i o n , e n v i r o n m e n t s , r e s o u r c e s

edited y

A. M. Po l la rd

(Dep ar tme n t o f A rch aeo log i c a l Sc iences , Un i ve rs i t y o f B rad fo rd , UK)

Geology and archaeology have a long h is tory of f ru i t fu l co l laborat ion

stretching back to the ear ly 19th century. Geoarchaeology - the appl icat ion

of the geosciences to solve research prob lem s in archa eolog y - has no w

emerged as a recognized sub-discipl ine of archaeology, especial ly in the

USA. Tradi t ional ly , methods used inc lude geomorphology, sedimentology,

pedology and strat igraphy, ref lect ing the fact that most archaeological

evidence is recovered f rom the sedimentary environment. As ref lected in

the sub- t i t le , th is volume embraces a broader def in i t ion, inc luding

geophysics and geochemistry.

Geophysical techniques, both ter rest r ia l and remote, are now used

Documents

Geoarchaeology Exploration Enviroment