115

ON SOME FOSSILIFEROUS NODULES FROMTHE CLAYGATE BEDS OF SHOOTER'S HILL,

KENT.

By ARTHUR L . LEACH, F.G.S.

(Read December sn; 1912.)

T H E loams and fine sands which succeed the London Clay of. Shooter's Hill were, in January of this year, described by

me* as Claygate Beds, from their correspondence in stratigraphi­cal position and lithological character with the deposits, which, inWest Surrey, constitute the passage-beds between the London Clayand the Bagshot Beds. The exposures on Shooter's Hilll wereexamined, under rather unfavourable conditions, by some mem­bers of this Association in March, t and in June the admirablesections at Claygate were visited under the guidance of Mr. H.Dewey, to whom we are indebted for the application of the term"Claygate Beds" to these transition deposits. In his Report] ofthe Excursion Mr. Dewey has given an excellent account of thedevelopment of these beds in the locality whence they derivetheir name.

It is not now necessary to dwell upon the reasons for theclassification of these beds, since the disadvantages and apparentinconsistencies which followed when the passage-beds were notseparately mapped have been indicated by Mr. H. B. Woodward,§and those lithological characters, which distinguish Claygate Bedsfrom London Clay on the one hand and from Bagshot Beds onthe other, are summarised by Mr. Dewey in his Report.

At Claygate, and likewise in the neighbourhood of Esher andChessington, the passage-beds appear to be unfossiliferous.Recently, nowever, the loamy beds overlying the London Clay ofShooter's Hill have yielded a few fossils, and my purpose is toshow that this fossiliferous horizon lies within the Claygate Bedsof that locality.

Upon Shooter's Hill the Claygate Beds are nowhere exposedin clear section, but on Eltham Common the sequence appears tobe as follows:

1Buff and orange-streaked sandy loam.Grey clayey sand, very fine, with streaks of clay .

CLAYGATE BEDS Orange-coloured loam, with much fine sand .Pale-brown and orange-coloured loams.Brown clayey loam, with" boxstones."

LONDON CLAY . Stiff yellowish-brown clay .

• "The Geology of Shooter's Hlll, Kent." Pro c. Geo], Assoc., vol, xxlll ([gu), p , 11 2.t Proe. Geol. Assoc., vol. llxlll (Igl.), p, 180.t Ibid, p. 237.§ Mem . Geol, Survey. Geology of the London District, p. 36.

PROC. GEOL. Assoc., VOL. XXIV, PART 3, I9I3.J 10

116 ARTHUR L. LEACH ON

The fossils were obtained from boxstones in the lowest loamybeds at the point marked (4) in the sketch-map accompanyingmy paper. None of the few nodules which I had found last yearyielded fossils, but after the heavy rains of the late summer partof a band of scattered boxstones* became exposed, and onbreaking up some of the new material indications of fossils wereobserved in the form of interior casts and impressions oflamellibranchs and small gasteropods. The shelly substance hasunfortunately been completely decalcified, but the followingspecies appear to be represented:

Axinea (Pectunculus) decussatus Sow., one interior cast and a fewfragmentary impressions of the external surface.

Natica (7), a few tiny internal casts.Aporrhais sotoeroyi Mant., external cast of a small part of the

spire.Cyprina morrisii Sow., one large internal cast and impressions of

the exterior of the same shell were examined by Mr.E. T. Newton, and referred "almost certainly" to thisspecies. I have since obtained portions of two smallercasts of a similar shell.

One nodule shows a number of small dark circles about2 millimetres in diameter with dark cores; these are arrangedin pairs, and probably represent the" burrows of habitation" ofsmall marine worms such as have been observed in the rocks ofmany formations. See for example the tubes assigned toArenicolites by Nicholson.f

The most interesting shell in this brief list is Cyprinamorrisii. Mr. Newton, who kindly compared it with somelamellibranchs in the Jermyn Street Museum, informs me thatamong the specimens found by Mr. R. S. Herries at Tunnel Hill,Aldershot, there are several portions referred to Cytherea, butnone that can be satisfactorily compared with the Shooter's Hillspecimen, nor does it resemble any of the lamellibranchs foundat Ascot in 1887 by Mr. H. W. Monckton,

Cyprina morrisii abounds in the Thanet Beds of East Kent.It has been observed in the Thanet Sand at Plumstead andLewisham, but, except for these instances, it appears to be knownnear London only in the basement-bed of the London Clay, inwhich deposit it has been recorded from Bennet's End, WatfordHeath, Hampstead, Bushey, and other localities. Mr. H. B.Woodward'[ does not include it amongst the noteworthy fossils

*This term is used in various senses by different writers. In this paper it isapplied to hard concretions of ferruginous loam, enclosed usually by harder and moreferruginous shells of limonite. The nodules sometimes, but not frequently, contain smallhollows, due to contraction of the nucleus or, and more usually, to the disappearance offossils by solution of the shells,

t Manual of Palaontology, Fig. Igo.

lap. cit., p. 3'.

THE CLAYGATE BEDS.

of the London Clay, nor does it figure amongst the shellsobtained at Bracknell, '*' where the fossiliferous septaria comeprobably from near the top of the London Clay. We have,therefore, the recurrence of a shell which is associated not withthe main mass of the London Clay, but with the shallow-waterbeds at its base. Mr. Newton informs me that the species isfound also in the Bracklesham Beds. The species of Pedunculus,Natica, and Aporrhais are common London Clay fossils.

The question now arises whether these fossils belong to theLondon Clay or to the Claygate Beds. I believe them to berightly assigned to the latter, for two reasons-

I. The fossiliferous nodules (boxstones) occur in a brownloam, which passes upwards into more sandy beds, showing noreturn to clay of the character of' London Clay.

2. The boxstones are small concretions of ferruginous loam,usually less than 6 in. in diameter, often enclosed by thin shellsor crusts of limonite. They differ in size, shape and mineralcharacters from the massive, ellipsoidal septarian concretions (or"cement stones") of argillaceous limestone found in the LondonClay.

The occurrence of these marine fossils on Shooter's Hillshows that in this district the marine conditions of the LondonClay continued during the deposition of the Claygate Beds. Itmay be recalled that Prestwich regarded the sandy beds at thetop of the London Clay merely as indicating a recurrence ofthe conditions under which the basement-bed was deposited.The presence of Cyprina morrisii certainly tends to supportthis view as to the conditions of deposition, but the lithologicalcharacters of the passage-beds are sufficiently definite to justifytheir separate classification as Claygate Beds.

NOTE.-In the first week of January of this year a trenchfor the new London to Canterbury telephone mains was cutover the summit of Shooter's Hill. At the south end ofShrewsbury Lane the fine clean or slightly loamy sands of theClaygate Beds were well shown, and beds of fine yellow loamunderlay the pavement near the Water Tower. The loamsappeared to pass into definite London Clay slightly belowWaldstock Road.

* Proc, Geol, Assoc., vol, xxii (19Il), p, 176.