Test Pitting on Hamilton Hill, Nottinghamshire

8/18/2019 Test Pitting on Hamilton Hill, Nottinghamshire

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Test Pitting At Hamilton Hill

Ursilla Spence


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Contents

Summary

1. Introduction, background and geology.

2. The test pits.

3. Methodology.

4. Results.

5. Discussion.

6. Conclusions

Acknowledgements

Thanks are due to Tim Allen and English Heritage for the commission and also to the site

owners, Robert and Jane Thompson.

Report and Archive

The site work was undertaken by Emily Gillott and Ben Crossley of Nottinghamshire

Community Archaeology. The archive is held by Nottinghamshire County Council. The report

was written by Ursilla Spence in 2010, revised 2012, and 2015, with contributions from EmilyGillott.

Written By Read by Signed off Report date and

Revisions

UMS EG UMS 2010, 2012, 2015


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Summary

This report forms one part of a wider project using a range of techniques to investigate

Hamilton Hill and should be read in conjunction with the reports on the other work. Three test

pits were excavated over two days in March 2009 into the top of Hamilton Hill. The purpose

of the test pits was to investigate the nature of the soils, subsoils and geology by comparing

apparently stable areas with one of the areas of ground slumping. No archaeology was

encountered, although fossil gryphaea were recovered from the test pit closest to the

mound. In the first two pits reddish Sandstone bedrock was encountered. In the third, which

was located in one of the slumped areas, soft yellow sandstone was encountered, the upper

levels of which had decayed to a fine sand, only becoming relatively harder with depth. It is

suggested that the processes causing the ground slip originated with the deforestation of

Hamilton Hill, which has led to increased soil erosion, the effects of which are most apparent

where the softest bedrock is exposed to both climatic impacts and animal activity.

1. Introduction, background and geology.

Hamilton Hill is a prominent landscape feature in the District of Ashfield and the parish of

Sutton in Ashfield. It is centred on OS NGR SK 52055894. The hill is ovoid, with relatively

steep sides and a level top, except to the east where the hill-top has been excavated in a

roughly triangular area. In this lowered area, a circular mound has been raised. There are

signs that there have been excavations into the top of the mound. The hill is pocked with a

few small pits, while long the sides of the hill there are a series of slumped areas. These are

worse on the south and east. The underlying geology is the Nottingham Castle formation ofthe Sherwood Sandstones. The surface of the hill is a scheduled monument (NT133317). To

avoid repetition between this and the other reports, only selected information from those

other reports is included in this one. A full bibliography may be found in the main Hamilton

Hill report (Spence, 2010, (a))

2. The Test Pits.

The three 1m test pits were excavated on 29th and 30th March 2009. The work was

undertaken by Emily Gillott and Ben Crossley of Nottinghamshire Community Archaeologyand followed appropriate standards and guidance.

The rationale for the choice of locations was as follows;

TP 1 was sited within the lowered area of the hill top, adjacent to but not on the

mound to try and reduce the risk of encountering archaeology and to provide results

to compare with TP 2.

TP 2 was excavated within the level area of the hill top, to obtain baseline information

on subsoils and geology in an area where ground conditions were believed to be

stable.


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TP 3 was sited within an area of slumping, positioned so as to reduce the risk of the

excavation resulting in any additional erosion or subsidence.

Fig 1. Location of test pits (TP1, 2 and 3) and fixed survey pegs

3. Methodology.

The three 1m test pits were dug in 10 cm spits until a change of soil conditions. The surface

of each interface or clear change in soil conditions was cleaned and photographed. The

excavations proceeded through the bed-rock until digging conditions were made difficult by

the hardness or compaction of the material. Context numbers were given for each change in

soil conditions, but as all three of the test pits reveal information about soil processes, rather

than discrete events, the contexts more properly reflect soil horizons. The northwest corner

of each test pit was recorded by total station, and linked into the grid established for the

topographic survey, which in turn is linked into OS data. An NGR has been derived for each.

4. Results.

TP1


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The topsoil was a dark friable and sandy soil 400 mm deep with infrequent small pebbles,

and occasional fragments of modern material including plastic, fabric and string in its upper

levels. Its humic nature decreased with depth, although it darkened in colour, possibly as a

result of mineral accumulation although there was no sign of an iron pan. At its base was a

pronounced and well developed stone line of rounded pebbles of varying sizes. Included

amongst these were fossil gryphaea, of which a handful were retained by the excavator.Beneath the stone line was a layer of reddish fine loosely compact sand with frequent

pebbles (103), which gradually gave way to the more compacted parent bedrock material.

Here this was a soft reddish sandstone first met at a depth of about 600mm. The bedrock

(104) became harder and more compacted with depth.

Fig. 2. TP1

TP2.

Here a shallow (


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Fig. 3. TP2

TP3

The shallow (


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Fig. 4. TP 3

5. Discussion.

Possibly the three most striking aspects of the test pitting exercise were

The presence of the gryphaea in TP 1

The thickness of the topsoil in TP1,

The bedrock in TP3, which was significantly different from that encountered in the

other two test pits.

TP1 was sited in the quarried area on the hill top. The soil profile is a clear product ofsignificant worm activity, given the pronounced stone line and the fragments of modern

materials worked into its upper levels. The origin of the humic material is not clear. It is

possible that this derives from leaf litter from the woodland cover believed to have been

present from at least the 18th to mid20th century. Significant depths of leaf litter may have

accumulated through wind blow in this hollowed out area, a position relatively protected from

the elements.

The presence of the gryphaea also raises questions. Gryphaea arctuata derive from Jurassic

limestones. Discussions with colleagues from BGS indicate that the arrival of the gryphaea

has to have an anthropogenic cause (John Carney, pers comm.). It is possible that they


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came to Hamilton Hill as a by- product of liming activity, although it seems unlikely that the

fossils could survive the physical processes involved in refining limestone for use as a

fertiliser. Also, if fossil rich limestone had been spread across the hill, examples should have

been recovered from at least one other of the pits. The test pits were dug in the order in

which they were numbered, and although the gryphaea were not recognised immediately,

they were recognised before the excavation of TP1 was complete and the others started, soadditional examples from other pits would have been spotted. 15 gryphaea were recovered

from TP1 without a deliberate attempt at the recovery of every example. This suggests a

concentration of the fossils in this hollowed out area. In the absence of any additional

archaeological material, an explanation of the presence of the gryphaea can only be pure

speculation.

The final issue is the bedrock in TP3. This is clearly different from that which was

encountered in TPs 1 and 2. As has been noted, this test pit was excavated into a section of

the area which has suffered from ground slumping. The topographic survey clearly indicated

the linearity of this example of slumping, which curves around the eastern end of the hill. Theexcavations suggest that along this line, a strip of this compact and fine sandstone lies at a

relatively shallow depth, which would tend to make it susceptible to erosion. If the humic

material in TP1 does indeed derive from leaf litter accumulated before the deforestation of

the hill in the early -mid 20th century, it is possible also that the recent ground slumping is in

part at least a by-product of the same deforestation. The deforestation will have caused

increased levels of soil erosion. Decaying tree roots or old animal burrows, visible in TP3,

may increase water percolation into the soft bedrock, potentially weakening it further. This

hypothesis fits with the results of the GPR survey, the conclusions of which propose animal

burrowing as the likely main culprit for the slumping. Rabbits are likely to be more active

where the subsoils are softest, concentrating activity in areas which may well already be

most susceptible to erosion from climatic factors, etc. Extensive present day burrowing was

noted by the excavators.

6. Conclusions

The three test pits have provided useful information that may answer the question of why

Hamilton Hill is suffering from patches of land slip. Two of the test pits, dug in areas not

suffering from obvious signs of soil movement, encountered reddish bedrock, whichincreased in hardness and compaction with depth. In the third pit, the bedrock was fine soft

yellow sandstone easily dug to a depth of 400mm, and with signs of root and animal activity

throughout. It is possible that there is a bed of this soft yellow sandstone underlying much of

Hamilton Hill, and that the ground slumping is occurring in those areas where the material is

close to the current ground surface. It is suggested that the land slip is a product of a

process that began 60-100 years ago with the removal of the tree cover, leading to

increased soil erosion and more animal burrowing. Feasibly, the increased rate of soil

movement apparent to the site owners is also a by-product of spells of prolonged

precipitation enjoyed by the East Midlands region over recent years and attributed to climate

change.


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Bibliography

CIfA, 2014, Standard and guidance for archaeological field evaluation

Spence, U, 2010, (a), Hamilton Hill, Sutton in Ashfield, NCC Unpublished Report

Spence, U, 2010, (b), Hamilton Hill Topographic Survey , NCC Unpublished Report

Documents

Test Pitting on Hamilton Hill, Nottinghamshire