508 KEV. A. lEVING ON A GEjS^ERAX SECTION OF THE 



ness of the London Clay beneath Aldershot may be estimated at less 

 than 200 feet. 



7. A comparison of the sections described in this paper shows 

 that at one horizon (the base of the Lower Bagshots) the beds of 

 flint pebbles are far more widely distributed than at any other 

 horizon. Whether these pebbles are fragments of flint worn by 

 the rolling of a tidal surf and derived immediately from the denuda- 

 tion of the Chalk, or were first imbedded in the Eeading beds and 

 the basement-bed of the London Clay, and supplied to the Bagshot 

 Strata by the denudation of those portions of the Lower London 

 Tertiaries which became more generally exposed to denuding agencies 

 at the incoming of the period marked by the Upper Eagshot Sands, 

 the Bagshot sea must in either case have had access to. older for- 

 mations ; and this could hardly happen without unconformity *. 

 I attach great weight to the evidence afforded by the wide range of 

 the pebble-bed at the base of the Upper Bagshot Sands, as showing 

 at that stage a much greater extension of the area occupied by 

 marine waters, and the consequent overlap of the Upper Sands ; and 

 this is borne out by the numerous casts of diminutive forms of a 

 saltwater fauna t (such as we should find in a shallow sandy estuary 

 open to the sea) which are met with in the buff-yellow sands of the 

 Upper Bagshot, at horizons not far above the pebble-bed at the base. 

 This cumulative evidence seems to show that at the incoming of 

 Upper Bagshot times extensive denudation of the Eeading beds and 

 the base of the London Clay was going- on ; and this view is borne 

 out by the appearance of mottled clays intercalated with the green 

 sands at the foot of Caesar's Camp near Aldershot, which has been 

 already mentioned. 



Purther to the west, along the south side of the valley of the 

 Kennet, there is strong evidence of unconformity. Sections are 

 mentioned in the memoir J where loamy sands with overlying 

 pebble-beds (which agree in character more with the upper bed of 

 the Middle Bagshot and the overlying pebble-bed of the sections 

 described in this paper than with anything we know of in beds of 

 undoubted Lower Bagshot age) rest upon the London Clay within 

 a few feet only of its basement-bed. In one section these loamy 

 Bagshot Sands are said to rest immediately upon the London Clay 

 basement-bed, and in another to overlap even this and to rest 

 immediately upon the Chalk. 



The difficulty in the way of the theory suggested in this paper, 

 arising from the presence of marine shells (e. g. at Yateley) in the 

 Middle Bagshot beds, may be perhaps removed if we recollect that 

 (1) they occur very locally ; (2) they are, as a rule, much broken, 

 •worn, and even comminuted ; (3) they appear to be confined to the 

 coarser sediments of the Middle Bagshot beds. Such results might 



* This was pointed out by Mr. Whitaker when this paper was discussed at 



the Society's Meeting. 



t Comp. Monckton, loc. cit. 



\ Geological Survey Memoirs, vol. iv. pp. 178, 179. 



