THE SOUTHERN PORTION OF THE WEALDEN AREA. 



655 



have not been considerably lowered since the Glacial period is to be 

 found in the existence of Crag deposits at Lenham, on the edge of 

 the Chalk escarpment, which points to the conclusion that the whole 

 Wealden valley has been excavated since the Pliocene period *. 



When we come to consider the origin of the plateau-drift, we 

 are met by considerable difficulty. The flints are the residue of the 

 Upper Chalk which still covered a certain portion of this area after 

 marine denudation had exposed the Hastings beds of the central 

 dome, and probably also the higher portions of the Lower Greensand 

 escarpment. Similar flints, many of them, angular and broken, still 

 lie in great quantities upon the summit of the Chalk escarpment, 

 and in many places, as at Beachy Head, build up a considerable 

 thickness of angular, ferruginous gravel, not unlike the drift-gravels 

 just described. The broken and shivered condition of the flints of 

 the Wealden area has been attributed by Mr. S. V. Wood to the 

 result of alternating frozen and warmer conditions of the surface of 

 a soil which remained permanently frozen below f . 



But to account for the distribution of the beds of angular gravel 

 on the higher grounds, and the evident traces of stratification which 

 they in many cases present, appears to require something more 

 than a mere letting down of the angular flints, in proportion as the 

 Chalk disappeared, upon an eroded surface of the inferior strata ; 

 for if such a process has been going on during the recession of the 

 Chalk escarpment, it should also be going on now, and flints should 

 occur, along the base of the escarpment, upon the Upper Greensand 

 and Gault. Yet it is just here that the flint-drift is absent, except 

 in certain instances near the watersheds, as near Chanctonbury and 

 Clayton. An examination, moreover, of the diagrams of the water- 

 shed gravels is sufficient to show that such phenomena as contorted 

 stratification, intercalated beds of sand or clay, and alternations of 

 fine and coarse materials require some more powerful agent than 

 mere subaerial deposition, however angular and confused the general 

 character of the drift may be. 



It seems necessary therefore to look upon the watershed gravels 

 of Heath Common, Ditchling, and Berwick as the remains of an 

 eastern extension of the angular drift of Rogate and other parts of 

 West Sussex, and as a true subaqueous deposit. 



SrililAKY. 



It will be convenient, in conclusion, to sum up the results which 

 it has been the object of the present paper^to prove, viz. : — 



1. That the highest and oldest gravels of this area occur only in 

 patches in or near the watersheds : that, although appar- 

 ently without fossils, these gravels exhibit some traces of 

 subaqueous origin, and may possibly be contemporaneous with 

 similar deposits occurring throughout the southern counties of 

 England. 



* Prestwich, Quart. Journ. Geol. Soc. vol. xiv. p. 322 ; C. Eeid, ' Nature,' vol. 

 xxxiv. p. 342. 



t Geol. Mag. 1882.. pp. 339, 441. 



