127

SUPPLEMENTARY NOTES ON THE GEOLOGYOF SHOOTER'S HILL, KENT.

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

(Read March 5th, 19:10.)

PLATE g.

pREVIOUS papers's incorporating the results of several years'observations of temporary sections drew attention to features

of more than local interest in each of the formations-LondonClay, Claygate Beds and post-Eocene gravel-represented onShooter's Hill. During the last eight years fresh temporarysections have been opened: one in London Clay has yielded severalspecies of fossils hitherto unrecorded from the hill and, more­over, has revealed small landslides by which the beds have beendisturbed to quite appreciable depths. 1\0 new excavationof importance has been made in the gravel-cap, but recent workby Mr. G. Barrow and Mr. G. McDonald Davies, on the high­level sands and gravels of the Chiltern Hills and North Downsrespectively, has aroused new interest in these fragmentarydeposits and the occasion seems opportune to place on recordMr. Davies' determination of the mineral composition of thesands associated with the Shooter's Hill Gravel.

I.-EXCAVATION IN CASTLE WOOD, SHOOTER'S HILL.

In December, 19I4, excavations began on the site of a newreservoir (for the Metropolitan Water Board) in Castle Woodon the western slope of Shooter's Hill. Below a surface washof gravel the excavation passed through London Clay mingledwith Claygate Beds and gravel, all disturbed, into normal Lon­don Clay.

The following section was noted in January, 1915, on theeastern side of the pit :-Pebbly soil, 1-2 feet. } S1" dSoft greenish yellow clays, slightly loamy, zft. ippe fmassesBrown clay .blue streaked, containing ferru- CI ~ B d

ginous clay concretions and lenticles of ~~a ~ hsfine yellow sand, 6feet. an on on ay

Stiff brown and blue clay, 7ft. =: London Clay altered andprobably slipped.

Dark blue clay, at approximately 315 O.D., seen to a few feet." Note on a Section in probable Bagshct Beds on Shooter's Hill," Gwl. Mag. Dec. V. Vol.

vii., No. sss. Sept. '910, p. +9~.til On the Geology of Shooter's Hill, Kent." Proc. Geol. Assoc., vo!. xxiii (1912), p. II2-1:Z04·tOO Report of an Excursion to Shooter's Hill and Eltbaro." Proc, Geol. Assoc.,vo!. xxiii (1912)

p. 180-182.tOO On some Fossiliferous Nodules from the Oaygate Beds of Shooter's Hill." Proc, Geol,

A-., vol. xxiv (1913), p, 115-111.

128 A. L. LEACH.

only, containing septarian nodules, abundant selenitecrystals and fragments of pyritised wood, and shells.:=:London-Clay, undisturbed.

Fossils were obtained only from the dark blue clay, IS to20 feet below the original ground level. The overlying brownclay appeared quite barren of organic remains, but in the un­weathered blue clay thrown out from the deepest part of the pit,at about 315 a.D., the following species were identified :- 'Dentalium sp., Cassidaria (Cassia) ambigua, Sol., Metula juncea,

SHOOT ERS H ILL.

5001 ,

o, I

F IG. 20.-SKF.TCll ",rAP O F SH OOTER'S HILL

(R eproduced from Proc. Gcol, Assot ., Vol. xxiii., 1912. )

Naiica label/ala, Larn ., Pleurotoma of, terebralis, Lam ., Pleuro­lorna sp ., Voluta nodosa ].de C Sow., Pedunculus (Axinea) decus­satus, ]. Sow., Astarte rugata, .J. Sow., Leda oblata, S. Wood., .Apporrhais Soteerbyi (Mant.), Nucula Wetherelli,.J. de C Sow.

All the concretions in the brown clay were ellipsoids of fer­ruginous clay resembling those of the Claygate Beds ratherthan the septarian nodul es common in the London Clay and thelenticles of sand (one a few feet in length) had clearly slippeddown from Claygate Beds higher up the hill. An adjacent partof the same face of the pit showed that superficial movements-

THE GEOLOGY OF SHOOTER'S HILL, KENT. 129

had affected the beds to a depth of at least 12 feet and had pro­-d uced repetitions of the beds in inverse order.

With the exception of the lowest brown clay, not any of theintermingled masses of sand, clay and gravel shown in thissection were in place. Claygate Beds and gravel followed uponthe London Clay in their natural order, but all were masseswhich had slipped and above the gravel came more Claygateloams, followed by London Clay, the order being thus reversed.The beds had evidently yielded to soil-creep in successive slices,but nothing on the surface gave any indication of these sub­siol disturbances. (See Plate 9).

II.-TELEPHONE CABLE TRENCH, SHOOTER'S HILL,MARCH, 1915.

In March, 1915, a trench, cut along the path on the north sideof the main road over Shooter's Hill, exposed shallow sections,which, while not adding any new facts, confirmed and extendedthe observations previously recorded. Claygate Beds wereseen near Christ Church, a little above the site of the milestones(6-inch map, Kent 2S. W., B.M. 330.2 .), the level of their baseagreeing closely with that on Eltham Common. Oppositethe private road to Castle Wood House the cutting enteredShooter's Hill Gravel, apparently undisturbed, resting on Clay­gate Beds at about 355-360 O.D., a level in accord with that ofits base at the Fire Station as previously recorded. On thesummit of the hill fine yellow and orange-coloured sands wereagain seen, as in 1905 and 1910; but in a much longer sectionextending from Shrewsbury Lane to the Water Tower. Theunderlying Claygate loams were noted further east, nearly wherethe 400 O.D. contour crosses the road at Summer Court. Belowthis level, to the east, nothing but London Clay seems to occur.

III.-MIXERAL COMPOSITION OF THE SHOOTER'S HILLGRAVEl..

In my former paper (2), the Shooter's Hill sands and pebble­beds were excluded from the Bagshot Beds, original or remanie ;distinguished from some of the Pebble Gravels] from the PlateauGravels of the North Downs, and from the Glacial Drifts, andregarded as probably estuarine, or even marine deposits, certainlypre-Pleistocene and probably Pliocene in age, presenting manypoints of similarity with the sands and gravels of Headley Heathand other U) Pliocene formations on the Korth Downs, andrelated by their elevation" structure and lithology to the Lenhamor Older Pliocene Beds.

-This milestone has been remo ved to the enclosure 01 Christ Church on the opposite side 01tile road.

tM..... Gtol. S..",ey, "Geology of London," vol, i.

13° A. L. LEACH,

Sand on 30 mesh sieve ..60

" go" "" through 90 "

Mud (and fine silt)

The interesting results obtained by recent developments ofsana analysis and the application of these methods to the investi­gation of beds of doubtful age made an examination of the sandof the Shooter's Hill Gravel desirable as a means of testing thesuggestions put forward in regard to its age. Mr. G. McDonaldDavies kindly undertook to analyse some specimens which Ihad obtained in 19II from the excellent sections on the L.C.C.Fire Station site. In his report , which follows, the exact posi­tions where the samples were obtained are stated by referenceto the figures and plates in my paper of 1912 (2).

REPORT ON THE MINERAL COMPOSITION OF TWOSAMPLES OF SAND FROM THE SHOOTER'S HILL

CRAVEL.

By G. MACDoNALD DAVIES, M.Sc., F.G.S.

"A," Bottom bed ,= "a" in Fig. 2I." B " Ferruginous sand = "c" in Fig. 2I.

A, is a laminated yellow to buff sand with thin clay partings.B, is a red loamy sand with a streak of buff.

A B0·3 % 0.5 %

33.2 44·724·9 29·41.g 2.9

39·7 22·5

100.0 100.0

Diam eter of largest grain 2 . 5 mm. 3 .2 mm.Heavy minerals (mostly limonite) 0.36% 0.48 %

II aft er treatment with hydrochloric acid0.07 % 0.04 %

Th e samples contain more" mud" and less fine sand (through90 mesh) than is usual in the supposed Pliocene Beds on theChalk of Kent and Surrey, but the red loamy sand of RanmoreCommon is not very different in this respect. Both samplesconsist mainly of quartz, with some glauconite (rather oxidisedin A) and small amounts of mica, flint and felspar.

B is not more micaceous than A.The heavy minerals are rather scarce as compared with other

Pliocene deposits, but here again Ranmore Common givesthe nearest comparison, with 0.04% in one sample. It wasnecessary to boil in HCI to remove abundantlimonite concretions;The heavy minerals are chiefly tourmaline, staurolite, zircon.rutile, kyanite, andalusite, ilmenite, and opaque whitish grains.

THE GEOLOGY OF SHOOTER'S HILL, KENT. 131

with small amounts of monazite, magnetite, garnet, sillimanite,and yellow anatase. Hornblende and spinel were also noticedin A. Andulusitc is particularly abundant in B, which in thisrespect resembles the sand of East Kent, more than the sandsof Surrey.

Both samples have, on the whole, a similar mineral composi­tion and appear to be derived from the same source, and to bepart of the same deposit.

They have a Pliocene, not an Eocene composition, and notsuch as is associated with the Plateau gravels of the LondonBasin. They resemble the Pliocene (Lenham) sands of Surreyand East Kent in the scarcity of flint and felspar, coml?arativeabundance of andalusite and monazite, and presence of spinel andsillimanite in small amount. But the presence of garnet is veryunusual in the Lenham Sands, though Professor Boswell speaksof garnet as a type mineral of the Pliocenes of Suffolk. I had

N.W. __380..~__

FIG. 2I.-SECTION O~ THE SITE OF TilE NEW FIRE STATIm" EAGLESFIELD ROAD,

SHOOTER'S HILI..

(From Proc, Geol, Assoc., Vol. xxiii., 1912).

seen only two grains of it in dozens of samples of that sand untilI examined one from the cliff edge at Folkestone, where therewas a good deal. The presence of garnet in the Shooter's Hillmaterial may indicate that it is formed mainly from LenhamSands with some admixttire in post-Lcnham times, or that it isPliocene, but rather later than the other Lenham Beds. ButI think we may regard it as probably of true Lenham age, butincluding a little material derived from the Eocene beds, on whichit rests. That would account for the high percentage of mud aswell as the garnet. This is the first instance known of LenhamBeds resting on anything but Chalk and one might expect evenmore variation from the normal composition.

132 THE GEOLOGY OF SHOOTER'S HILL, KENT.

With Mr. Davies' conclusion, based on the mineral analysis,I am in agreement. His report furnishes an interesting- andlong-needed completion to the description of the Shooter'sHill Gravel given in 1912, and strengthens greatly the case therebrought forward on other grounds for grouping this depositwith the Older Pliocene or Lenham Beds.

My thanks are due to Mr. G. Me.cD. Davies for his veryinteresting report.

PROC. GEOL Assoc., VOL. XXXI. PLATE 9.

A.--ExCAVATIO:> I:> CASTLE WOOD, SilOOTER'S HILL.

Photo, A. L. Leach.

CLAYGATE BE esHILL GRAVEL

CLA'iGATE BEDS

LONDON CLAY.

LONDON CLAY

B.-KEY TO TilE A130VE.

A. L. Leach.

[To face p. 132.