Geological and Geographical Notes on Well Hill, Kent: September
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342 ART H UR L. LEACH, north-east, and commented upon the difficulty of conn ecting this with 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. After tea at Messrs. Ransom's, the relief map was again studied , and the question discussed of the causes which led to the diversion of the river, the Director maintaining that earth movement s had played no part in it, but that it was a simple case of river capture by an obsequent stream growing out from the sou th along the line of an old consequent river-the power of capture resting with the Wey by reason of its shorter course to the sea, and conse quent lower level at the critical point. Some Paleeoliths from T errace D were also shown, all in a water-worn condition, except two of a late St. Acheul type found on no other terrac e. Le Moustier, though present at a higher level, is apparently absent here. As there was no time left for further work in the field, the party proceeded directly to the station in time for the 7. 15 train. Mr. A. H. Williams acted as Excursion Secretary. REFER 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 Chalk 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 Relations 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 Palreolith ic Man " Proc, Ceol A ssoc., vol, xxiv, p. 178. GE OLOGICAL AND GEOGR APHICAL NOTES ON WELL HILL, KENT. S EPT EM BER 11TH, 1915. By A RT H UR L. LEACH, F.G.S., D ine/or oj the Excursion. F ROM Chelsfield station the party walked over Well Hill into Shoreham, halting near Chelsfield Church, in the gravel-pit on Well Hill, beside a swallow-hole a little to the east of this pit, in Timberden Bottom, and on the eastern slope of Meenfold Hill, to observe various points of interest. After tea, at the" George Hotel," Mr. H. W. Monckton, on behalf of the party, thanked the Director for his services. T he Director's remarks on the geological and geographi cal features of the district are summarised below. GEOLOGICAL AND GEOGRAPHICAL NOTES ON WELL HI LL. 3-B WELL HILL. Geographically this hill forms the summit of a ridge west of the Darent and between that river and its tributary, the river Cray. In its present stage the Darent, beginning as a strike-stream in the Vale of Holmesdale, becomes a consequent or dip-slope river only after its sudden northward deflection and passage through the North Downs. The consequent Cray, which rises now at Orpington, has a dry valley extending several miles above the stream-head to a gentle depression barely a mile west of the Darent Valley, and on the northern edge of the Clay-with-Flints area of the North Downs. From this point the dry valley of the Cray bends westward to Green Street Green, takes thence a TrihuTory (dry)uolleys . R. Dare"r Magpie Bolio'" A CraY{dry}vo/ley Well 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 is formed by a group of springs, flows through St. Mary Cray, St. Paul's Cray, Foot's Cray, North Cray, Bexley, Crayford, and Barnes Cray, to join the Darent in the marshes below Dartford. The two valleys present many interesting geological and geo graphical features. The inter-stream district, an undulating and diversified area of about 50 square miles, falls northward from Well Hill (610 O.D.) to the Dartford Marshes (6 O.D.). In its geological aspect Well Hill may be described as an outlier of Eocene formations lying on the northern flank of the \V ealden anticline, To the south rises the feature-conveniently termed the plateau-formed by Chalk uplands (North Downs) overlain by Clay-with-Flints. The Chalk has a general dip north ward towards the synclinal axis of the London Basin. In the vicinity of the deep transverse valley of the Darent the Eocene formations, which west of the Cray have a broad outcrop and a 344 ARTHUR L. LEACH, well-defined southern margin here and there resembling an escarpment in character, have undergone great denudation, and in the inter-stream district Eocene deposits remain only as out liers, ranging from small patches of sands and pebbles to areas of more than a square mile in which Thanet, Woolwich, and Black heath Beds may be recognised. The larger outliers are well wooded in contrast with comparatively treeless adjacent areas of Chalk. At Well Hill, Eocene deposits control the cultivation and impart to the landscape a distinctive character. A narrow, steep-sided outlier of Thanet Sand extends for three miles north and south, with a narrower strip of Woolwich Beds on its central and higher parts. The cap of plateau gravel remains only in small disconnected patches, which, although probably occupying an area greater than that shown on the Geological Survey Map, are yet too limited in extent to affect directly the aspect of the ridge. From either side Well Hill appears thickly clothed with woods, orchards, and fruit gardens, the margin of the tree-clad area agreeing roughly with the boundary of the outlier. Well Hill, where the sub-Eocene Chalk might have been expected to show the characteristics of a high zone, supplies an instance of the value of zonal stratigraphy. Marsupites occurs on the west at Farnborough, and Uintacrinus at Orpington, to the north-west; but according to Mr. H. Dewey, of the Geological Survey, the Chalk at Well Hill is low down in the zone of M. cor-anguinum, or even in that of Holaster planus These zonal features indicate pre-Thanet Sand movement of the Chalk.'*' 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 beds are poorly exposed. A brickyard, where Woolwich clays were worked half-a-century ago, has disappeared. Diversity of soils and good natural drainage have favoured the high cultivation of Well Hill and its surrounding district. Pears, apples, plums, bush fruit and strawberries, thrive on the outlier. Lavender is grown at Chelsfield, potatoes in large quantities on the Thanet Sand areas, grain on the chalk soils, and an important centre of cultivation under glass has developed near Swanley. The rainfall decreases with the northward fall of the ground from 35-30 in. on the adjacent plateau to 35'2-30 near Wen Hill, 30-27 near Swanley, 27-25 about Dartford 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," by W. Whitaker. 'g08. CEOLOGICAL AND GEOGRAPHICAL NOTES ON WELL HILL. 345 THE WELL HILL GRAVEL. On the highest ground of Well Hill are several patches of coarse gravel. The greatest thickness of the deposit is unknown, but Woolwich Beds come within a few feet of the ground surface on the summit of the hill. Possibly, as at Shooter's Hill, the gravel rests on an irregularly convex floor, and thickens along the sides of the ridge. The constituents are large battered chalk flints, subangular and angular flint fragments, white and deep brown in colour, flint pebbles (probably from Eocene beds), small quartz pebbles, rolled and angular pieces of chert from the Hythe Beds (Lower Greensand). These materials lie confusedly in a coarse red sand. The isolated position of this gravel, the absence of northern rocks (such as occur abundantly in the High Terrace gravels of the Thames), and its elevation above the adjacent river-valleys, indicate a remote period for its formation, but its mode of origin and age remain unknown. Mr. J. R. Larkby" treated it as an old deposit of the Darent; Prestwich,t at least in his earlier view, regarded it as a relic of "a marine gravel, of Glacial age, which once stretched over Kent" All its materials may have come from the south, and two modes of transport may be suggested-ice and water. Evidence is altogether lacking that ice carried Hythe Beds cherts from the Lower Greensand outcrop, over the Holmesdale and across the Plateau to Well Hill, and under the present geographical con ditions water could not have done so. The gravel must have been deposited while a land surface, unbroken by a depression along the Gault outcrop, connected the Lower Greensand source of the cherts with Well Hill.