654 MR. J. V. ELSDEIST ON THE SUPERFICIAL GEOLOGY OF 



also show abundant traces of plateau-gravels, at heights varying 

 from 300 to 1200 feet above sea-level. The m; terials of these 

 gravels are mostly of local origin, and, while the slopes of the hills 

 are free from drift, the valleys have abundant gravel-deposits up to 

 100 feet above sea-level *. 



JSTow when we look for an explanation of these phenomena, 

 which are seen to be general over the whole of Southern England, 

 it is evident that we must accept one of two views. Either the 

 higher plateau-gravels are the oldest, and the lower valley-gravels 

 represent former river-beds, and are consequently a measure of the 

 denudation which has been effected since their deposition ; or all 

 these patches of gravel have been deposited since the excavation of 

 the valleys, their sporadic character being due either to a kind of 

 selective deposition, or to a subsequent process of selective denuda- 

 tion. The former theory has been sufficiently proved by Mr. 

 Topley to hold good for the gravels of the northern portion of the 

 Wealden area, and the phenomena described in this paper respect- 

 ing the southern portion tend to a similar conclusion. 



The chief advocate of the marine theory is Mr. Searles V. "Wood, 

 who, in an elaborate contribution to this subject as late as 1882 f, 

 discredits the view that there has been any considerable excavation 

 of the Wealden valleys since the deposition of these gravels, which, 

 he states, were accumulated either under the sea, or in estuaries as 

 the sea was invading or retiring from the land. 



An examination, however, of the facts described in the earlier 

 portion of this paper shows the extreme difficulty of accounting for 

 the gravels of the southern portion in this manner. Whether we 

 examine the valley of the Bother at Fittleworth, the Arun at Hen- 

 field, Wickham, and Steyning, or the Ouse between Barcombe and 

 Bodmell, the terrace-gravels always slope gently towards the rivers, 

 and terminate abruptly in the opposite direction. Could any process 

 of selective deposition or selective denudation by the sea explain 

 this fact ? Again, let us consider the plateau-gravel of the Adur 

 watershed at Ditchling. Here we find three or four isolated hills, 

 close together, each capped with gravel, and in each case the inter- 

 vening valleys are free from drift. Is it not more in accordance 

 with the fundamental principles of geology to see in this fact the 

 excavation of the valleys subsequently to the accumulation of the 

 drift, than to imagine some unintelligible process of selective depo- 

 sition on the summits of these hills, when submerged beneath the 

 sea, or a peculiar process of denudation, which during emergence 

 swept the valleys clear and left each hill-top covered with drift ? 

 An exactly similar but still more striking instance of the 

 same kind is seen in the Cuckmere valley, where we find isolated 

 hill-tops capped with drift, even when an area of only a few square 

 yards reaches above the particular contour to which the gravels are 

 confined. 



Another argjment against the view that the Wealden valleys 



* Belt, Quart. Journ. Geol. Soo. vol. xxxii. p. 83. 

 t Quart. Journ. Geol. Soc. vol. xxxviii. p. 600. 



