344 Denudation of 



the present form of the ground. Thus after the forma- 

 tion of the marine plain p p, the Chalk being com- 

 paratively hard, has been partly denuded, and now 

 stands out as the bold escarpments of the North and 

 South Downs. The soft clay of the Gault has been more 

 easily worn away, and forms a hollow or plain between the 

 Chalk and the Lower Greensand. The Lower Greensand, 

 full of hard calcareous bands and ironstone, more strongly 

 resisting denudation, forms a second range of scarped 

 hills, overlooking the more easily wasted Weald Clay, 

 which makes a second and broader plain, from under 

 which rise the subdivisions of the Hastings Sands, forming 

 the undulations of the hills of Ashdown Forest, and other 

 places, in the broad centre of the low anticlinal curve. 

 The absence of flints over nearly the whole of the 

 Wealden area, excepting near the Downs, is easily 

 explained by this hypothesis, for the original marine 

 denudation had removed all the Chalk, except near 

 the margin (see fig. 73), long before the rivers had 

 begun simultaneously to scoop out the valleys of the 

 interior, and to cut the transverse valleys across the 

 North and South Downs. 1 



Given sufficient time, I see no difficulty in this 

 result. But the question arises, how much time, in a 

 geological sense, can be given ? 



It is believed that, excepting for a few feet close 

 upon the coast, this southern part of England was not 

 depressed beneath the sea during any part of the Glacial 

 period. It has, therefore, been above water for a very 

 long time. On the edge of the North Downs there are 



1 The original sketch of these views was published in 1863, and 

 enlarged and much improved in 1864, in a second edition of this 

 work. For greater detail on the same subject, see Foster and 

 Topley, ' Journal of the Geological Society,' 1865, vol. xxi. p. 443. 





