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have carefully abstained from saying that sediment is not Letter 483 

 deposited during periods of elevation, but only that it is not 

 accumulated to sufficient thickness to withstand subsequent 

 beach action ; on both coasts of S. America the amount 

 of sediment deposited, worn away, and redeposited, often- 

 times must have been enormous, but still there have been no 

 wide formations produced: just read my discussion (p. 135 

 of my S. American book : ) again with this in your mind. 

 I never thought of your difficulty (i.e. in relation to this 

 discussion) of where was the land whence the three miles 

 of S. Wales strata 2 were derived! Do you not think that 

 it may be explained by a form of elevation which I have 

 always suspected to have been very common (and, indeed, 

 had once intended getting all facts together), viz. thus ? 



Fig. i. 



The frequency of a deep ocean close to a rising continent 

 bordered with mountains, seems to indicate these opposite 

 movements of rising and sinking close together ; this would 



1 See Letter 556, footnote i, p. 222. The discussion referred to 

 (Geological Observations on South America, 1846) deals with the causes 

 of the absence of recent conchiferous deposits on the coasts of South 

 America. 



2 In his classical paper " On the Denudation of South Wales and 

 the Adjacent Counties of England" (Mem. Geol. Survey, Vol. I., p. 297, 

 1846), Ramsay estimates the thickness of certain Palaeozoic formations in 

 South Wales, and calculates the cubic contents of the strata in the area 

 they now occupy together with the amount removed by denudation ; and 

 he goes on to say that it is evident that the quantity of matter employed 

 to form these strata was many times greater than the entire amount of 

 solid land they now represent above the waves. "To form, therefore, 

 so great a thickness, a mass of matter of nearly equal cubic contents 

 must have been worn by the waves and the outpourings of rivers from 

 neighbouring lands, of which perhaps no original trace now remains ' 

 (P- 334). 



