90 SURVEY UNDER OFFICE OF WORKS CHAP, in 



rocks that now form the flattened summit of the range/ 

 Denudation, I uphold, though materially affected by 

 the nature (suddenness and intensity) of disturbances, 

 yet as an independent agency acts in a measure inde- 

 pendently of them. Thus the sea has greater facilities 

 afforded it for acting on a coast subjected to frequent 

 and gradual submergence and emergence ; but the sea 

 would still act, and might, if time were allowed it, 

 utterly destroy a tract of land of any given height, with 

 little or no oscillation of level. In the instance of the 

 Mendip Hills, there were doubtless many minor oscilla- 

 tions after the great catastrophe, and you will observe 

 from the foregoing quotation that I allow great part of 

 the New Red and part of the Liassic epochs for the 

 sea to effect this denudation. 



This surely was a period of time fully equal in 

 extent to those comparatively latter days to which I 

 refer the greater part of the South Wales denudations. 

 I think in the paper I have given physical reasons to 

 show that in South Wales and the neighbourhood the 

 greatest denudation of great part of these tracts did 

 not take place during the first elevation (pp. 317, 323). 



I shall by and by have occasion in subsequent 

 papers on the same subject to prove that in other 

 countries such long- continued denudations did take 

 place during a series of disturbances that affected the 

 Palaeozoic strata during the very period of their forma- 

 tion. The whole matter is merely a question of 

 degree, denudation in both cases being produced by 

 changes of level. 



Respecting the forces that produced the earlier 

 great disturbances, I have perhaps used the words 

 ' conflicting forces ' somewhat hastily. My object was 

 to show that the remarkable and intense curvatures 



