NOTES ON THE SECTIONS EXPOSED IN THESIDCUP BY·PASS ROAD.

By E. E. S. BROWN, F.G.S., and ARTHUR WRIGLE Y.

Received Nov. 17th, 1924.

IN the spring of 1924 the construction of the new Sidcupby-pass road from Longlands to Ruxley Corner, exposed

some sections of sufficient importance to justify a bri ef des­cription of them.

The principal cu ttings were on either side of th e junctionof the new road with the old Chis lehurst- Sidc un road kn own asPerry Street. In examining these cuttings from eas t to westthe following strata were observed, in ascending order :-

Woolwich Beds.(1.) Dark, olive-green, glauconitic loam, i.e ., Woolwich

" bottom-bed," seen in an isolated trench beyond the easternend of the cutting. ... ... ... ... 10 ft . exposed

Th e dark green colour of the unweathered material thrownout was strikingly different from the much pal er hu e usuallyseen in well-weathered sections exposing the base of the WoolwichBeds.

Very irregular junct ion.

(2.) Pebble-bed ; flint pebbles in purplish bro wn clay withan upper impersist ent st ra tum of flint pebbles in pink sand.

2 ft. average.A large proportion of the flint pebbles are bright red within,

with a semi-translucent black cortex. The irregular junctionbetween (1) and (2) cannot be due to disturbance subsequen tto deposition, as the junction between (2) and (3) is qu ite straightand bed (3) above shows wholly regular bedding.

(3.) Yellow and grey mottled clay, becoming loamy west-ward 3 ft.

(4.) Grey clay passing irregula rly upward into black ligniticclay which becomes a conspi cuous soft lignite at thetop .. .4ft.max.

Distinctly une ven junction.

(5.) Cyrena Beds, the lower part sandy and ferruginous,crowded with large Cyr ena cordata Mor., and C. cunei/armis Fer., allvery friable. The upper part passes westward into a black Cyrenad ay, yielding many examples of a variety of Tympanotomus[unatus (Mant.) in which the post erior band of tubercles on eachwhorl is strongly dev eloped and thickened, thus giving a turretedaspect to the spire. 3 ft.

(6.) Unfo ssiliferous grey clay 1l ft.

SECTIONS EXPOSED IN SIDCUP BY-PASS ROAD. 77

(7.) Grey clay with broken Ostrea, Cyrena spp. and Tympano-tomus junatus (Mant.) ... I ft.

(8.) Cyrena clays of various colours, crowded with shells :­Cyrena cuneijormis Fer., C. [orbesi Desh., C. cordata Mor.,Tympanotomus junatus (Mant.), Melanatria inquinata (Defr.).The top of this division is locally indurated and yields Scrobi­culabra condamini (Mor.). The upper surface of the induratedpart is covered with a thin layer of M odiola mitchelli Mor....6t ft.

(g.) Loams, striped in the lower part, limonitic in themiddle 7ft.

(ro.) Yellowish grey sand, weathering white 3ft.*

(II.) Brown loams with limonite 6tft.*

In the middle is a 2t ft. bed of sand, with great numbers ofOstrea and a few other shells :-Ostrea bellovacina Desh.(abundant), O. tenera, J. de C. Sow., Modiolasp., Barbatia striatu­laris (Desh.), Serpula sp., Cyrena sp., Calyptraa sp. An" oysterrock" from this bed was noticed on a neighbouring dump.At one stage of the excavations the oyster band was separatedinto two layers by a seam of unfossiliferous sand.

(12.) "Paludina" band; brown clay with decayed clay­stone, calcareous" race" and claystone casts of mollusca. Thisbed seems to be a residuum from the decay of a band ofsoft stone. [PaludinaJ Vioiparus sp. (abundant), Tritonidea lata(J. Sow), Calyptrea sp., Hydrobia sp., Melanopsis sp., Tympano­tomus [unatus (Mant.), Corbula regulbiensis Mor., Cyrena sp .... 1 ft.

Irregular junction, the scooping of the pebble beds aboveprobably being arrested by the stony band 12.

(13.) Flint pebbles in day, apparently a drift of the hillwashtype resulting from a denudation of Blackheath beds. Thereare traces of a sandy pebble bed with very small pebbles atthe bottom. ... ... ... ... ... ... 3 ft.

All the beds rise gently eastward over the greater part of thesection, flattening out horizontally at the western end.

In the main section of the Woolwich Beds the upper two­thirds of the strata were seen to be disturbed by a small anti­clinal fold the crest of which, on the western face of the cutting,had broken and collapsed obliquely. Presumably this fold isnot tectonic, but merely local and due to a slipping of the clayson the hillside in a manner similar to that well displayed in therailway cutting between Brockley and New Cross.j Mr. H. G.Dines, of H.M. Geological Survey, to whom our thanks are due,made a scale drawing of the disturbance at a time when the fold

t On an early visit, in beds 10 and II we noticed a channel 12 feet wide, containing thinseams of grey clay.+T. N. BROMEHEAD, 1922. Proc, Geol; Assoc., vol. xxxiii, p. 77 and illustration, pI. 4.,

E. E. S. BROWN AND A. WRIGLEY.

was seen to be br oken by two faults, which let down the bedsbetween them for about tw o feet.

The section is br oken by the comparatively low groundwhere th e new road crosses Perry Street. To the west of this-crossing, t races are seen of th e " Paludina " band 1 2 , and a pitshowed th e oyst er bed II cove red by a pebbly wash from theadjacent hill . Another pit exposed flint pebbles in sandy claywith a pebble-oys ter conglomera te . Much of this materiallooks like a mixture and redeposition of Blackheath beds andLondon Clay. There is no room for more than 3 to 4 feet ofdeposits between bed 1 2 and the London Clay , so the typicallocal development of the Blackh eath Beds seems to be missingat this point.

Proceeding westward the new road cuts through the patch ofLondon Clay marked on the lin. map by the note " 234 a.D."and from the new section this patch appears to extend a littlefurther east than there shown. Here the cutting shows :-

(14.) London Clay, weathered brown and slightly sandy atthe base of the section, The clay is finely jointed, and containsmuch decaying pyrites, selenite and many ferruginous box stones .A few sept aria were observed 2 feet below the sub soil at theeastern end of the main London Clay cutting, but no fossils werefound either in them or in th e clay of which about IS feet wasseen in a sloped sec tion .

Continuing westward, normal Blackheath Beds were welldeveloped on the western side of the London Clay hill , but theirjunction with the clay was not visible, nor could their thicknessbe accurate ly estimated.

E astward from the eas tern end of th e main cutting thenew road is formed on top of a bank of dumped material. Atthe end of this bank, on the side of the Cray valley, a shallowsection exposed 4 feet of gravel , composed mainly of Eocenepebbles, with a small but not iceabl e admixture of subangularpatinated flints, the whol e in a clayey matrix . From surfaceindications , and in th e absence of a sect ion, this dri ft gravelmight have been taken for a spread of Blackheath Beds .

The excellent sect ion of th e Woolw ich Beds seen in the maincut ting indicates an unusually thick development of th esedeposits; beds 2 to 12 inclusive have a total thickn ess of 36 feet,to which must be added the thickness of the " bottom-bed "which could not be accurately measured. This notable thi ckn esswas a feature of similar sections in the railway cuttings, a miledistant, at St. Mary Cray, which have been fullv recorded by1'1r. Whitaker.* In the Woolwich Beds here described , beds

• W . WH rrAKER, 1889. Geology of London, 1vl em . Grot . Svrv., vol, L, pp. 136- 8, whered etails will be found of a similar succession of ligniti c clay , Cyrena beds, oyster bed and. 1 PtIludina " band.

SECTIONS EXPOSED IN SIDCUP BY-PASS ROAD. 79

3--8 may be correlated with beds 1-3 and the upper portion of bed4 at Swanscombe,* while the occurrence of a strong lignite band(bed 4) is noteworthy, as it has now been recorded at Park Hill,Croydon (a trace), Mottingham, Sidcup (zft.), St. Mary Cray(l~ft.), Swanscombe (11ft), Shorne Wood (2~ft.), and Upnor (atrace). At each of these places it occurs in the same relativeposition in the Woolwich series, i.e., between the" bottom-bed"and the lowest of the Cyrena clays.

Mr. A. G. Davis, who greatly aided us in collecting, has washedseveral samples from various parts of the section to determinewhat small organisms were present. He kindly sends us anote of the Ostracoda he has found :-

(Bed 8.) Cytheridea mulleri, Munst, and its variety torosa,Jones, both abundant.

(Bed II.) Cythere wetherellii, Jones,C. plicata, Munst.Cytheridea debilis, Jones.C. mulleri Munst, and its variety torosa, Jones.

In 1854, in an appendix to Prestwich's paper on the WoolwichBeds, C. wetherellii and C. plicata were described by RupertJones as occurring in an Oyster Clay from Woolwich, t but in alater monographj this author considered that he was mistaken,and that the oysters and their associated Ostracods really camefrom Colwell Bay (Middle Headon Beds), and in the text andtabular appendix to the monograph these species are restrictedto Middle and Upper Eocene deposits. That they have againbeen found in an oyster bed of the Woolwich series suggeststhat Jones' original opinion was the correct one.

Our thanks are due to Mr. Davis for this note and for his helpin the field, to Mr. S. Priest, who inserted a notice of the sectionin the Side up District Times of June 13, 1924, and to Mr. A. J.Bull for directing our attention to the section, on informationreceived by him from the Ministry of Transport in connectionwith the desire of the Excursion Committee of the GeologistsAssociation to keep members informed of temporary road sectionsopened in their respective districts .

• E. E. S. BROWN and S. PRIEST, 1924, Proc, Geol, Assoc., vol, xxxv, p, 142.'t Q .. ,.". lou".. Geol, Soc., vol. x, p, 161, pI. 3, figs. 9 and 11.~ The Tertiary Entomostraca, Mon, Pal. Soc., 1856, p. 26, note 1.