Wood— Structure of the Thames Valley, 



103 



the valley. Let us take a section from the 

 Thames over this hill to the Chalk in Surrey^ 

 forming the northern edge of the tract of 

 denuded Chalk through which the Weald 

 valley is cut. (See Section 7.) 



In this section we see that the denudation 

 has acted principally to the south, i.e., in the 

 opposite direction from tJie river, the hill having 

 been cut down and a newer gravel (a5 5) cor- 

 responding in position (relatively to the 

 Thames gravel, a; 4''') with that of the Cray 

 valley, formed below it ; the denudation also 

 is equally decided on the east and West sides 

 of the hill. The gravel x5 extends in a 

 continuous sheet from Mitcham, where it rests 

 on 100 feet of London clay, to the Chalk at 

 Carshalton. It is unlike the Thames gravel, 

 being composed of very angular flints, and is 

 of inferior thickness, becoming whiter and 

 more chalky as the Chalk is approached, being 

 nearly white over that formation itself. 



If this section be prolonged it will reach 

 the north scarp of the Weald to which the 

 Carshalton Chalk extends continuously, and 

 there is nothing by which this gravel (x5) 

 can be disconnected from the sea that denuded 

 the Chalk, and covered the Weald area, prior 

 to the excavation of its valley. It would, 

 therefore, appear from this section that the 

 Thames gravel, prior to the convulsions which 

 destroyed so much of the south side of the 

 valley, had, in addition to its exit by Dartford 

 and Gravesend, another opening to the Weald 

 towards Carshalton, from which it was eventu- 

 ally cut off by the upcast of the country there, 

 and the gravel (a; 5) formed. The gravel of 

 Mitcham (x5), however, mingles, towards 

 the north-east by the Tootings and in the 

 Wandle valley, with the Thames gravel (a; 4"), 

 so that it would ajopear that the sea continued 

 to have access to a part of the area occupied 

 by the Thames gravel after the elevation of 

 the Richmond and Wimbledon Hills and the 

 denudation of their southern sides. ^ 



£ 

 ^.2 



too 



'^ o 

 "do 





S^ 



^ 



^1 



w 



"^i 



^ Although when the gravel at Beddington or Car- 

 shalton is compared with that near the Thames the con- . <,. 

 trast is considerable, yet from the flatness of the inter- ^ h\ 



vening country it is impossible to say where one begins | 



and the other ends ; indeed, if the partial continuity ._ ^ 



with the sea remained, the two must have blended. The fe; ^ 



railway cutting at Peasemarsh, near Tooting, shows the 



same coarse gravel as the Mitcham cuttings ; but it is too shallow to disclose whether 



this rests on any different gravel. 



