.337

ON BURIED CHANNELS IN THEDARTFORD HEATH GRAVEL.

Together with the Report of an Excnrsion to Dartford Hellth,.May 17th, 1913.

By ARTHUR L. LEACH, F.G.S., Director of the Excursion.

THJo; party, about 60 111 number, assembled at Crayford Station at2.30 p.m., and, before proceeding to the new sections, obtaineda good view over the valley of the Cray from the high groundabove the railway, In the two deep trenches (Fig. 28 A and B)attention was directed to the current-bedded Danford HeathGravel with its ferruginous clayey base resting on Thanet Sand;to those features which prove the existence of the channel X; andto the character of the deposits forming the infilIing of thischannel. Along the sides of trench A an old surface of cultiva­tion, heavily II marled," could be traced by bands of chalkfragments buried upwards of ~~ ft. in drifted soil. The landwash(Fig. 29 d) in both trenches yielded abundant calcined flints (" pot­boilers "), fragments of charcoal, and a few artefacts, but none ofcharacteristic forms. An implement of Le Moustier type wasfound lying upon some fallen gravel in trench A. From thegravel in Wansunt pit the usual non-local cherts and igneousrocks were collected. The upper channel (W) remained trace­able, and a few sharp flakes were taken from its lowest clayeydeposit. Two of the characteristic St. Acheul implements haverecently been found here by members of the Association. Oneof the Vvshaped depressions (prehistoric) full of dark soil, seen onthe south side of the pit, yielded a worked flake. (See Reportsof Excursions in 1907 and 191 I.)

Mr.]. Davies again exhibited his collection of implements,bones, and teeth from the adjacent excavations, and Mr. E. T.Newton drew attention to some broken molars of an elephant,which he has since identified as E. alltiqulIs.

After tea at Bowman's Cottage, an adjacent pit upwards of50 ft. deep, sunk almost to the base of the gravel, aroused muchdiscussion as to the conditions under which this mass of stratifieddrift could have been deposited. A pleasant walk over the Heathand through the fields brought the party to Bexley, where Mr.M. P. Andrew kindly exhibited a number of palreolithic imple­ments collected locally and a fine molar of E. alltiquus obtainedfrom the base of the Dartford Heath gravel in trench B (Fig.28).

The party left' Bexley at 7.30 p.m.Miss Edith Cadmore acted as Excursion Secretary on this

occasion.The Director wishes to express his thanks to !'III'. J. Davies

and Mr. M. P. Andrew, who by the exhibition of their specimensPROC. GEOL. Assoc .• VOL. XXIV, PART 5. 1913.] 24

ARTHUR L. LEACH ON

added very greatly to the interest of the excursion, and toacknowledge the courtesy of Mr. D. E. Corke, by whosepermission the Bowman's Cottage Pit was visited.

Remarks upon the geological points are appended. Nodetails of the extent, thickness, constituents of the DartfordHeath gravel, etc., have been included since these features haverecently been described. (See References.)

~

~~:~~if~~ji?:

THE DARTFORD HEATH GRAVEL.

Near Crayford the Cray trends north-east to join the Darent,the united streams entering the Thames as it passes eastwardabout z} miles north of Dartford Heath. During its HighTerrace stage, the Thames or a powerful distributary current,probably swung in from the opposite side of the main valle}",

s,N.

Cra.yjordRI~.St05.fion

1

FIG. ZS.-SECTION FROM CRAYFORD STATION TO DARTFORD HEATH, SHOWING THF.POSITIONS OF TWO CHANNELS FILLED WITH DEPOSITS OF LATER AGE THANTHE DARTFORD HEATH GRAVEL.

b. Red gravel } Dartford Heath B. Upper trench.a. False-bedded gravel Gravel. W. Channel with.Acheulean implements.A. Lower trench. X. Later channel.

Length 01 Sectionaooul 700 yards. Vertical Scale about thru times the horizontal.

forming a deep loop which curved north-eastward towards Stone.Under such conditions the drift of the Cray and of the Darentwould be deflected eastward, the former chiefly along the presentsouthern border of Dartford Heath, while the Darent Jrift wouldtend towards Dartford, Brent, and Stone, where the abundance ofchert (Hythe Beds) strongly suggests the influence of this river.

The lower clean, loose, current-bedded sands and gravels ofDanford Heath are the deposits of rapid and varying streams:the upper gravel, stiffened by ferruginous clay and evenly beddedwith layers of clayey loam, suggests the agency of restrainedcurrents depositing sediments derived largely from the adjacentTertiaries.

On the hill above Crayford lies an isolated patch of gravelwhich presents in its base-level, current-bedding and non-localpebbles, close similarity to the lower part of the main gravel­spread of Dartford Heath, from which it has been cut off by thepost-High Terrace deepening of the newer valley of the Cray,

tHE DAlnrORD HtAUl GRAVEL. 339

The present bed of the Cray at Crayford is about 120 ft.below the surface-levels of the adjacent High Terrace gravelsbut this figure does not express the full post- High Terrace excava­tion, the stream being underlain by a channel eroded in Chalkand choked with gravels of unknown thickness.

To fix the position of the Dartford Heath Gravel in thePleistocene sequence it is necessary to consider (1) its fauna,(2) its erratic constituents or non-local pebbles, (3) its base-leveland relation to older and newer deposits, (4) the characters ofthe contemporaneous implements. No line of inquiry can safelybe neglected. In this report it is only possible to record somefresh facts and to comment briefly upon their significance.

( I) In the summer of 1912 many fragments of bones andteeth, obtained during the excavation of the upper trench(Fig. 28 B), came into the possession of Mr. J. Davies, whokindly placed them at my disposal for examination. I was shownthe gravel in which they were found, and subsequently I dugout bones from the same deposit, which I regard as the undis­turbed basement bed of the Dartford Heath Gravel (Fig. 29 at).The remains were examined by Mr. E. T. Newton, and identifiedas foIlows ;-

Elephas allliquus: one molar, * nearly complete; portionsof (?two) other molars.

Cerous elaphus (Red deer); limb bones and antler.Bas bison or (7) pril1ligmitis: tooth.Ceruus sp.: small antler.Equus cabal/us (horse); tooth.Fragments of limb bones of a large animal, probably elephant.An ulna of Rhiltoceros sp. (identified by Dr. A. S. Woodward)

has since been obtained by Mr. M. P. Andrew.

These fossils are the first to be recorded from an exact horizonin the gravel. In comparing this list with that given by Mr. M. A.C. Hinton t for the High Terrace Drift of Swanscombe, it must beremembered that in the present case the remains came from thebase of the gravel, while the Swanscombe fauna was determinedfrom bones found, with abundant Pleistocene sheIls, in a smaIlpit sunk in a "sheIl-bed," and the relation of this deposit to thegravel in the adjacent Milton Street (Barnfield) Pit t appearssomewhat uncertain. Elephas allliquus occurs in the Crayford §and Grays Thurrock " brick-earths, deposits much later in datethan the High Terrace drift, and it does not necessarily indicatean early Pleistocene age. But in the brick-earths its remains areassociated with those of the mammoth (E. pritlligenius), a later

• This Is In the possessfon of Mr. M. P. Andrew.t Proc, Geol. Assoc••vel. xxt, p. 492.t The pit formerly known as .. Milton Street Pit" is now termed the Barnlield Pit by

Messrs. Smith and Dewey.§ .. Geol, of London," P.336.II M. A. C. Hinton, o], »u; p. 493.

340 ARTHUR L. LEACH ON

and "northern" form of elephant, Dr. Duckworth* remarksthat for a time the two were contemporary, but E. antiquusdisappeared first, and, moreover, this more primitive form ofelephant has "much more definite associations with the southerngroup of mammals than has the mammoth." E. primigemiis hasbeen found at Milton Street t and Dartford Brent.j in each casein deposits of the reo-It. terrace. At present, therefore, if thebones found at Milton Street and Dartford Brent have been cor­rectly assigned to E. pri1lliKe1lius, the Dartford Heath Gravel, onthe evidence of its fauna, cannot be referred to a period anteriorto the introduction of the mammoth.

(2) The most probable intermediate source for the palreozoicand igneous rocks found in the gravel appears to be Plateau andGlacial Drifts*(Boulder Clay and Glacial Gravels) lying to thenorth and west. The age of the Danford Heath Gravel maythus be later than the Chalky Boulder Clay, a view in harmonywith Mr. Whitaker's opinion 1/ and with Mr. T. Holmes' interpre­tation of a section at Hornchurch.f] This view, however, may becontested in the near future. In support of the suggestion thatthe Dartford Heath Gravel contains material derived from glacialdrifts the characters of some flints may be cited. Several water­worn fragments obtained U in Wansunt Pit show well-markedscratches and striations indistinguishable i~ character from theglacial strire exhibited by pebbles in boulder clay and terminalmoraines. These striations existed upon the flint before thefragments became embedded in the gravel; remembering theextreme hardness of flint, and the comparative rarity of striatedflints in boulder-clays, the glacial origin of the striations appearsvery probable, and at the same time the infrequency of theiroccurrence is explained. The Dartford Heath Gravel, therefore,appears to be later than some of the glacial deposits of south­eastern England.

(3) There is nothing to add to what has been stated ti inreference to the base-level of the Dart ford Heath Gravel. Noreason connected with its base·level has yet been shown forregarding its age as different from that of the Milton Street(Barnfield Pit) Gravel, which Messrs. Kennard and Hinton.j ]

• .. Prehlstorle Man," '91', p, SS.t ..Geology of the London District," p, 90. In tbls pit (now known as Barnfield Pit)

E. aniiqnus was obtained by Messrs. Smtth and Dewey.t. Quart. JOIll'. Geot, Soc., vol. U,p, 521.§ See H. W. Monckton "On the Occurrence of Boulders and Pebbles from the

Glacial DrIft In Gravels South of the Thames," Qllart. JOII,n. Geol, Soc., vol. xllx,H. B. Woodward, "Geolol\Y of the London District," p, 73. Mem, Geol, Smv.

II .. Geol. of London," p. 386.'IT Quart.Journ. Geol. Soc., vol. xlvlll(ISg21, p. 370.

•• By Mr. ]. Davies, Mr. R. H. Chandler, and the writer. Mr. Chandler's speelmen Isstrongly striated, and was exhibited at a Geologists' Association Conversazione. Awell.strlated Illnt was shown during the Excursion Ofay ,Sth), and a large 1IInt nodulefrom Barnfield Pit deeply scratched. was exhibited by Mr. P. A. B. ~Iarlln at a Conver­sazlone. A strongly striated Illnt was found In Milton (Barnfield) Pit on the occasion 01the Excursion, ] une 7th.

tt Proc, Geol, Assoc., vol, xxlii, p. '04.n Proc, Geol, Assoc., "01. xlx, p. 76.

THR D.\RTFORD HEATH GRAVEL. 341

Dewey and Reginald Smith* agree in describing as the reo-footterrace.

(4) There is again nothing to add under this head. Thenumerous implements from the section in trench B were obtained,not from the Dartford Heath gravel, but from a reconstructeddeposit of later date.

The facts summarised above appear somewhat contradictory,for while the position, fauna, and base-level of the DartfordHeath Gravel suggest close correspondence with the Swanscomberoo-foot terrace deposits, the lithological succession appearsdissimilar, and implements are almost unknown; certainly nonehave been recorded from definite positions.

FIG. 29.-SECTION ALONG THE SOUTH·WEST SIDE OF TRENCH B,DARTFORD HEATH.-A. L. Leach.

a. Current-bedded gravel } Dartford Heatha1 Fossiliferous and ferruginous base Gravel.R Reconstructed implementiferous gravel.c Pale friable loam.d Landwash,

BURIED STREAM-CHANNELS IN THE HIGH TERRACE GRAVEL.

The new sections are shown in two trenches, each aboutr a ft, wide, driven into the hillside for about 60 yards on alevel, the floor of the upper (B) being 8 ft. below the base ofthe Dartford Heath Gravel, i.e., approximately at 800 a.D., whileA lies perhaps 10 ft. lower. At their eastern ends these trencheswere each about 18 ft. deep when first cut. In Fig. 29 thesection along the south-western side of trench B will do also forthe opposite face; and if this figure be divided into thirds byvertical lines, the right-hand division gives very nearly the sectionat the eastern end of A (disturbed Dartford Heath Gravel restingon an eroded slope of Thanet Sand). The channel X has beeninserted on the evidence of the features shown in these sections:it is of later date than W, and, in contrast with this channel,appears to be wholly choked with subaerial landwash, but itslowest part contains a pale friable loam (Fig. 29 c),t which maybe a water-laid sediment, but little of it can be examined.

• A tc'ltzologia (1913). See also H. B. Woodward, op. cit, P.90.t This Ieam Is very IIltht and porous, and one sample was calcareous. In the

Pleistocene gravel at Foot's Cray a band of loam very shu liar In appearance Is stronglycalcareous. I am inclined to regard these (now) porous, fine-grained loams as dacalelfiedslits which contained ori~lnally much chalky mud intermixed with clay and fine sand,but In some respects they appear to resemble wind-blown deposits (loess). Similarfine sandy loams occur In small channels on the j:ravds above Greenhithe and in severalsmall channels on Dartforcl Heath.

AR1'HUR L. L~ACH ON

Both Wand X were probably cut out by small streamsdraining the gravel-spread long after it had become dry land, butalso long before the formation of the Crayford brick-earths. Suchstreamlets would successively cease to flow, as the Darent andCray by deepening their valleys limited their gathering groundsand concurrently lowered the level of the underground water.They may be compared with the" Palreolithic brook" describedby Mr. W. G. Smith. '*

The date of the stream-deposits in W appears to be fixed bythe character of the implements-St. Acheul II. and early LeMoustier types-s-found therein: the landwash which overlies theseimplementiferous deposits is of uncertain age. The infilling ofX, as far as can be seen, is almost wholly landwash, and although

s

oI

$

I

FIG. SO.-SECTION 100 YARDS N.N.E. OF EDITH VILLAS, DARTFORDHEATH.-A. L. LrQch.

lJ. Upper red gravelQ. False-bedded gravel }

DartfordHeathGravel.

e. Unstratified loamy gravel } Deposits in thed. Stratified loams and clay ImplementiferousG. Dark clay Channel W.

the upper part (to a depth of 5 ft. at most) is recent soil-washdueto the cultivation of the slopes above, the stiffly-packed materialbelow the "chalk-line" appears to be much older and due todifferent conditions of sub-aerial downwash. It contains calcinedflints (" pot-boilers") in abundance. fragments of charcoal, andmany flint artefacts, some of palreolithic types, while others aresimple flakes and rough tools, such as when found upon thesurface are commonly termed "neolithic." At one point nearthe eastern end of the trench A a layer of charcoal and calcinedflints was observed by Mr. Davies, fully 5 ft. deep in the land­wash below the marl-line (i.e., 10 feet from the surface), butprimitive methods of cooking by hot stones may have continuedin use in historic times, and this discovery does not prove theinfilling land-wash to be prehistoric. Some help is given bythe characters of certain of the artefacts. There appears to me

* See W. Whitaker, "Geology of London," vel, I, p. 404. and references there given.

THE DARn'ORD HEATH GR,\VEL. 343

to be a strong probability that the lower part of this land wash isprehistoric in age.

AN IMPLEMENTIFEROUS AND RE-CONSTRUCTED GRAVJo:L.

Several implements of early palreolithic types, obtained bythe workmen during the excavation of trench B, are now in thepossession of Mr. J. Davies. They include two of Chelles types,a few of St. Acheul I. and several of St. Acheul II. The type ofLe Moustier is also represented.

After the Excursion of May rSth, Mr. M. P. Andrew foundin situ in trench B (Fig. 29) a fine ovate implement of St.Acheul type, 6 inches long, 4 inches broad, and in its greatestthickness not exceeding I ~ inches; it is neither appreciablyabraded nor patinated.

It was found at the eastern end of trench B, 7 ft. above thetop of the Thanet Sand. Subsequently Mr. Davies found, about2 ft. below the ground-surface, an implement similar in size andshape, and others of St. Acheul II. types. The implements ofChelles type are patinated, all others unpatinated (some an:ochreously stained), and many of the St. Acheul II. type are indis­tinguishable in character from the implements of the channel W.The specimens referred to Le Moustier are thick, heavy flakes,trimmed only on one face, and of much rougher workmanshipthan the smaIl Le Moustier implements of the channel W.

The occurrence of this strange 'admixture of implements ingravel only a. few feet above the unquestionable base of the HighTerrace drift, led me to re-examine very closely the whole sectionin trench B, and I am now satisfied that this implementiferousgravel is not true Dartford Heath gravel but a deposit recon­structed from the constituents of that gravel and much later indate. A fairly definite line can be traced between the originalundisturbed gravel and the re-arranged material j below this linethere remains from .; ft. to 6 ft. of Dartford Heath gravel, con­sisting of its ferruginous fossiliferous base (Fig. 29 a,) and patchesof the clean current-bedded sandy gravel (Fig. 2902)'

The reconstructed gravel (Fig. 29 R), upwards of 10 ft. th ick, isnot current-bedded nor even clearly bedded. When looked atfrom the opposite side of the cutting it appears faintly stratifiedand presents a deceptive resemblance to the lower part (0\1 of theHigh Terrace drift, but upon close examination the pebbles arefound lying, closely packed at all angles, in a stiff loamy matrix,no traces of sorting into fine and coarse materials being dis­cernible. There is little in its arrangement to suggest depositionin water. Its characters rather suggest subaerial accumulation.The condition of the implements supports this view, since theyare not rolled nor abraded, and clearly have not been subjectedto stream action. The deposit could not have been formed until

344 ARTHUR L. I.EACH ON THE DARTf'ORD HEATH GRAVI<:L.

long after the High Terrace stage; this is proved by the fact thatthe Dartford Heath gravel had been eroded to its base before theformation of the reconstructed gravel. The occurrence in it ofimplements of the types of Chelles, St. Acheul I. and II., andearly Le Moustier, suggests accumulation during the Le Moustierstage, which is quite in agreement with its position between theHigh Terrace gravel and the Crayford brick-earths. The relationof this reconstructed gravel to the channel W, which has yieldedso many implements exactly similar in type, cannot yet beascertained, but it is not improhable that the deposits belong toone group, and that W is a larger physical feature than was atfirst suspected. Further excavations alone can remove theuncertainties in the following scheme, which is suggested by theinformation at present available :-

Channel X II sLandwadsh-~rehisthoric in lowedr part. .. trearn- eposrts-s-c aracter an age uncertam.

{

Landwash-unimportant.Channel \V Stream-deposits-St. Acheul II. and early Le

Moustier.Gravel R ? Sub-aerial deposit-early Le Moustier,Dartford {upper or red gravel (b)-? St. Acheul I.Heath Lower or current-bedded gravel (02)-? age.Gravel Base (Ol)-? age.

It is of the utmost importance to distinguish deposits (such asthose of channels \V and X) laid down sub-aerially or as stream­sediments in channels eroded in the High Terrace Gravels, fromthose which are true High Terrace deposits. The detection ofreconstructed gravels such as R, especially when they are imple­mentiferous, is of equal importance. The difficulty, in theabsence of sections transuerse to the channels, may be verygreat. This point has been emphasised by Mr. H. Bury,· andobviously in such cases implements obtained at low levels maysuggest erroneous conclusions as to the date of the maindeposits.

REFERENCES.

Ordnance Survey Map, 6 inch (1910 edition), Kent. Sheet ix, N.W.Geological Survey Map, I inch, London District (Drift edition), Sheet 4.1889. WHITAKER, W.-hGeology of London," vol. i, /l/~m. Geo). Surue»,1907. CHANDLER, R. H .• and LEACH, A. L._h Excursion to Dartford

Heath." Proe. Geo], Assoc., vol. xx, p. 122.1907. NEWTON, E. T.-" Note on Specimens of I Rbaxella-Chert ' or

I Arngrove Stone' from Danford Heath." Proc. G~ol. Assoe.,vol. xx, P: 127.

1912. CHANDLER, R. H., and LEACH, A. L.-" On the Dartford HeathGravel and on a Palseolithic Implement Factory." Proc. G~ol.

Assoc., vo xxiii, p. 102.• Proc, Geol. Assoc., vel, xxlv ('913), p. 200.