342 ART H UR L. LEACH,

north-east, and commented upon the difficulty of conn ecting thiswith the Badshot knoll without assuming a fault in between ;but no such fault is shown on the map of the Geological Survey,nor has any decisive proof of its existence yet been found. Aftertea at Messrs. Ransom's, the relief map was again studied , andthe question discussed of the causes which led to the diversion ofthe river, the Director maintaining that earth movement s hadplayed no part in it, but that it was a simple case of river captureby an obsequent stream growing out from the sou th along theline of an old consequen t river-the power of capture rest ing withthe Wey by reason of its shorter course to the sea, and conse­quent lower level at the critical point. Some Paleeoliths fromT errace D were also shown, all in a water-worn condition, excepttwo of a late St. Acheul type found on no other terrac e. LeMoustier, though present at a higher level, is apparently absenthere . As there was no time left for further work in the field, theparty proceeded directly to the station in time for the 7. 15 train.

Mr. A. H. Williams acted as Excursion Secretary.

REFE R EN CES.

Ordnance Surv ey Map, I in. scale . No . 26g.Ord nance Su rvey Map, 6 in. scale, Surrey xxx, N .W. & N .E . Geo logical

Su rvey Ma p, O ld Ser ies, No .8.Ig08. Y OUNG , G. W.-"The Cha lk Area of Western Surrey." Proc, Grot.

Assoc., vol. xx, part 6, pp. 435-8.Ig08. BURY. H._HNotes on t he River Wey." Quart. :J0ur1l . Geoi, Soc.,

vol. lxiv , p. 318. .IgIO. - - - -.- " The Relat ions of the R iver Wey to the Blackwater

and the Arun ." 7ran s. •'iouth-E astr1'n Union oj Sci. Soc., p. 14.1913. . _ H The Gra vel Beds of Farn ha m in Rela tion to Pal reolith ic

Man " Proc, Ceol A ssoc., vol , xxiv, p. 178.

GE OLOGICAL AND GEOGR APHICAL NOTES ONWELL HILL, KENT.

S EPT EM BER 11TH, 1915.

By A RT H UR L. L EACH, F.G.S., D ine/or oj the Excursion.

F ROM Chelsfield sta tion the party walked over Well Hill intoShoreham, halting near Chel sfield Church, in the gravel-pit onWell Hill, beside a swallow-hole a little to the east of this pit , inTimberden Bottom, and on the eastern slope of Meenfold Hill,to observe various points of interest. After tea, at the" GeorgeHotel," Mr. H. W. Monckton, on behalf of the party, thanked theDirector for his services. T he Director's remarks on thegeological and geographi cal features of the district are summarisedbelow.

GEOLOGICAL AND GEOGRAPHICAL NOTES ON WELL HI LL. 3-B

WELL HILL.

Geographically this hill forms the summit of a ridge west of theDarent and between that river and its tributary, the river Cray. Inits present stage the Darent, beginning as a strike-stream in theVale of Holmesdale, becomes a consequent or dip-slope river onlyafter its sudden northward deflection and passage through theNorth Downs. The consequent Cray, which rises now atOrpington, has a dry valley extending several miles above thestream-head to a gentle depression barely a mile west of theDarent Valley, and on the northern edge of the Clay-with-Flintsarea of the North Downs. From this point the dry valley of theCray bends westward to Green Street Green, takes thence a

TrihuTory (dry)uolleysCraY{dry}vo/ley

. R. Dare"r Magpie Bolio'" AWell Hill CarJerhursf HDarent 8

FtG. n.-PARALLEL SECTlQNS ACROSS THE VALLEYS OF THE CRAY AN[)DARENT.-A. 1. Leach.

Section A, through the plateau I mile south of Shoreham.Section B, I mile north of Shoreham.Section C, ro miles north of E.The letter M indicates the Maplescombe dry-valley.

Vertical scale, about r o times the horizontal.Length of section, 8 miles.

northerly course to Orpington, and the stream, which here isformed by a group of springs, flows through St. Mary Cray,St. Paul's Cray, Foot's Cray, North Cray, Bexley, Crayford, andBarnes Cray, to join the Darent in the marshes below Dartford.The two valleys present many interesting geological and geo­graphical features. The inter-stream district, an undulating anddiversified area of about 50 square miles, falls northward fromWell Hill (610 O.D.) to the Dartford Marshes (6 O.D.).

In its geological aspect Well Hill may be described as anoutlier of Eocene formations lying on the northern flank of the\V ealden anticline, To the south rises the feature-convenientlytermed the plateau-formed by Chalk uplands (North Downs)overlain by Clay-with-Flints. The Chalk has a general dip north­ward towards the synclinal axis of the London Basin. In thevicinity of the deep transverse valley of the Darent the Eoceneformations, which west of the Cray have a broad outcrop and a

344 ARTHUR L. LEACH,

well-defined southern margin here and there resembling anescarpment in character, have undergone great denudation, andin the inter-stream district Eocene deposits remain only as out­liers, ranging from small patches of sands and pebbles to areas ofmore than a square mile in which Thanet, Woolwich, and Black­heath Beds may be recognised. The larger outliers are well­wooded in contrast with comparatively treeless adjacent areas ofChalk.

At Well Hill, Eocene deposits control the cultivation andimpart to the landscape a distinctive character. A narrow,steep-sided outlier of Thanet Sand extends for three miles northand south, with a narrower strip of Woolwich Beds on its centraland higher parts. The cap of plateau gravel remains only insmall disconnected patches, which, although probably occupyingan area greater than that shown on the Geological Survey Map,are yet too limited in extent to affect directly the aspect of theridge. From either side Well Hill appears thickly clothed withwoods, orchards, and fruit gardens, the margin of the tree-cladarea agreeing roughly with the boundary of the outlier.

Well Hill, where the sub-Eocene Chalk might have beenexpected to show the characteristics of a high zone, supplies aninstance of the value of zonal stratigraphy. Marsupites occurs onthe west at Farnborough, and Uintacrinus at Orpington, to thenorth-west; but according to Mr. H. Dewey, of the GeologicalSurvey, the Chalk at Well Hill is low down in the zone ofM. cor-anguinum, or even in that of Holaster planus Thesezonal features indicate pre-Thanet Sand movement of theChalk.'*'

The Thanet Sand appears in several road-side sections,notably in Hollows (Hollard's) Wood. Broken shells of Cyrena,a characteristic Woolwich Beds species, occur in the north bank,where the road to Cockerhurst crosses the ridge, but these bedsare poorly exposed. A brickyard, where Woolwich clays wereworked half-a-century ago, has disappeared.

Diversity of soils and good natural drainage have favouredthe high cultivation of Well Hill and its surrounding district.Pears, apples, plums, bush fruit and strawberries, thrive on theoutlier. Lavender is grown at Chelsfield, potatoes in largequantities on the Thanet Sand areas, grain on the chalk soils,and an important centre of cultivation under glass has developednear Swanley. The rainfall decreases with the northward fall ofthe ground from 35-30 in. on the adjacent plateau to35'2-30 near Wen Hill, 30-27 near Swanley, 27-25 aboutDartford Heath, 25-22 around Dartford. t

• Mem. Geol, Survey. "Summary of Progress of the Geological Survey for '9'4,"p.28.

t See Rainfall Map in Me... Geol, Survey," The Water Supply of Kent," byW. Whitaker. 'g08.

CEOLOGICAL AND GEOGRAPHICAL NOTES ON WELL HILL. 345

THE WELL HILL GRAVEL.

On the highest ground of Well Hill are several patches ofcoarse gravel. The greatest thickness of the deposit is unknown,but Woolwich Beds come within a few feet of the ground surfaceon the summit of the hill. Possibly, as at Shooter's Hill, thegravel rests on an irregularly convex floor, and thickens along thesides of the ridge. The constituents are large battered chalk­flints, subangular and angular flint fragments, white and deepbrown in colour, flint pebbles (probably from Eocene beds), smallquartz pebbles, rolled and angular pieces of chert from theHythe Beds (Lower Greensand). These materials lie confusedlyin a coarse red sand.

The isolated position of this gravel, the absence of northernrocks (such as occur abundantly in the High Terrace gravels ofthe Thames), and its elevation above the adjacent river-valleys,indicate a remote period for its formation, but its mode of originand age remain unknown. Mr. J. R. Larkby" treated it as anold deposit of the Darent; Prestwich, t at least in his earlier view,regarded it as a relic of "a marine gravel, of Glacial age, whichonce stretched over Kent"

All its materials may have come from the south, and twomodes of transport may be suggested-ice and water. Evidenceis altogether lacking that ice carried Hythe Beds cherts from theLower Greensand outcrop, over the Holmesdale and across thePlateau to Well Hill, and under the present geographical con­ditions water could not have done so. The gravel must havebeen deposited while a land surface, unbroken by a depressionalong the Gault outcrop, connected the Lower Greensand sourceof the cherts with Well Hill. Again, either ice or water may haveborne the gravel down such a slope. There is no convincingevidence of ice-action, and under the conditions indicated, water­carriage by streams appears an efficient and sufficient mode oftransport. In its present state, however, the gravel may not he anundisturbed river-drift, for its materials, even if brought downand deposited by streams, may have been re-arranged by the seaupon an old plane of marine action. Nothing in the character ofthe gravel allows any light on this point.

No palseoliths have been found in the gravel, but Mr. J. R.Larkby, in his interesting and well-illustrated report.] figures aseoliths several flints obtained from the pit on the summit of the hill.As the origin of the" eolithic" edge-chipping on flint remains indebate, the occurrence of eoliths cannot at present be acceptedas evidence of a definite geological age. But an idea of thegreat antiquity of the deposit may be gained by considering

,; Proc, Geol, Assoc., vol, xix, '905-6. Excursion to Chelsfield and Well Hill.t lbid.; vol. tv, See the report by H. Walker, F.G.S., of an excursion to Well Hill

in 18i4.I See above.

PROC. GEOL. Assoc., VOL. XXVI. PART 5. 1915.] 25

ARTHUR L. LEACH,

what great geographical changes have occurred since LowerGreensand cherts were incorporated in the Well Hill gravel.The Vale of Holmesdale and the escarpment of the NorthDowns are important land-forms developed after the depositionof the gravel, which thus must belong to a very early, andprobably pre-Pleistocene, cycle of surface changes.

SWALLOW-HoLES ON "YELL HILL.

Springs issue at the margin of the gravel-cap on each side ofthe Well Hill ridge, giving rise to streamlets, which in someinstances have incised steep-sided valleys on the Eoceneformations. On reaching the Chalk outcrop these valleys widenconsiderably, but no water now flows through them. The wholerainfall on Well Hill is absorbed directly or indirectly, and theridge thus forms a watershed from which no visible streamsproceed. An explanation of this anomaly lies in the geologicalconditions. Rainwater falling on the Thanet Sand or on theChalk becomes at once absorbed; that which descends upon thehighly permeable gravel, although thrown out as springs by theclayey Woolwich Beds, is finally and completely re-absorbedby the Thanet Sand and Chalk. The diagram illustrates theconditions :-

Highly permeable Gravel.Impermeable Woolwich Beds.

Permeable Thanet Sand.

Highly permeable Chalk.

The re-absorption of the spring waters may be gradual, thestreamlet merely dying away, or sudden, as when the drainagedisappears in a swallow-hole. Two of these are mentioned byMr. Whitaker," but others are known. One example, visited onSeptember I r th, receives surface drainage only after heavy rains.A few years ago the bottom of the funnel-shaped hollow sub­sided about 20 ft., but the pit has since been filled up with refusefrom the adjacent farm.

The streamlets in their courses towards the swallow-holeserode their channels and carry sand and silt down into under­ground water-channels. Hence the upper rim of a swallow-holemust extend up-stream. The lower rim tends to be raised bysoil-drift, and thus the funnel-shaped aperture may graduallymove up the valley. By this process swallow-holes reachpositions considerably within the boundary of the Thanet Sand.

The diagram given above shows that the conditions arefavourable for the shallow wells,whence, doubtless, the hill receivedits name.

" "Water Supply of Kent," p. 50.

GEO LOGICA L AND GEOGRAPH ICAL NOTES ON WELL HI LL. 347

MEEl\"FOLD HIL L AN D THE DARENT V ALLEY.

Meenfold H ill, a steep-sided ridge of Chalk, cap ped byClay-with-flints, is separated from Well Hill by a dry valleykno wn as Timberden Bot tom. A pat h runs from Timberd enFarm through the woods on the ridge and emerges on the steephillside above Shoreham in the valley of the Darent. T heview tha t opens suddenly to th e south is very fine in its merelypic turesq ue aspect, and whe n the geological significance of th ephysical features can be appreciated the landscape acqui res ahigh inte rest. In the distance, to the south, through the wideand deep gap by which the Darent breaks th rough the NorthDowns, lies the wooded ridge of Lower Greensand rocks .The gap in the Chalk contracts and becomes a steep- sidedvalley, through which the river goes northward towards theT hames. The diagram (Fig . 27) indicates the remark ablechange in the form of the valley as it passes from the highChalk Plateau district to the neighbourhood of the Th ames, whereloose Eocene sands and pebble-beds border the river. Thegorge-like character of th e passage through the North Downscontrasts strongly with the subdue d relief of the valley nearDartford Heath_

T he intermediate character of Sec tion B, although somewhatobsc ured by the Well Hill ridge, brings into prom inence the geo­graphical character of this relic of the high platea u. A shelf­like feature at Cockerhu rst (Section B), describe d by Mr. Larkbyas a "flood-plain," is connected by him with an early stage ofthe Daren t. T here seems but sligh t evidence of flood-pla indep osits on this shelf, but it clearly lies with in the valley ofth e Darent, and dou btless represents an old base-level of river ­erosio n transformed into a shelf or rock-terrace by subsequentdeepening of the valley.

R E FE R EN CE S.

Geolog ical Survey Map, I inch . London Dis trict (Drift) Sheet 4.Ordnance Surv ey Ma p, I inch, Sh eet 271.18go. PRESTWICH, J. "On the Relati on of the We stle ton Shing le," etc.

Pa rt 3. Qllart. J ourn. Grot. Soc., vol, xlvi. pr. 155. 157. 170.rq ro, LEACH , A. L. " N orth Kent," etc . Ceology in the Fidd, pr .

236, 246.