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Ch. VI.] 



OF ANCIENT DEPOSITS. 



113 



inconstancy in mineral composition of the ancient formations, 

 and equally so of the wide spaces over which the same kind 

 of sediment is now actually distributed by rivers and currents 

 in the course of centuries. The persistency of character in 

 the older series was exaggerated, its extreme variability in 

 the newer was assumed without proof. In the chapter which 



treats of river-deltas and the 



sediment 



currents, and in the description of reefs of coral now growino- 

 over areas many hundred miles in length, I shall have oppor- 

 tunities of convincing- the reader of the danger of hasty 

 generalisations on this head. I may also mention in this 

 place, that the vast distance to which the white chalk can be 

 traced east and west over Europe, as well as north and south, 

 from Denmark to the Crimea, seemed to some geologists a 

 phenomenon, to which the working of causes now in action 

 could present no parallel. ~ 



^marine telegraph have taught us that 



But the soundings made in 



the 



white mud, formed of similar organic bodies and of like 

 character, is in progress over spaces still more vast * 



But in regard to the imagined universality of particular 

 rocks of ancient date, it was almost unavoidable that this 

 notion, when once embraced, should be perpetuated ; for the 



■J • *m g^ _ _ ** 



same 



kinds of rock have occasionally been reproduced at 

 successive epochs : and when once the agreement or disagree- 

 ment in mineral character alone was relied on as the test of 

 age, it followed that similar rocks, if found even at the 

 antipodes, were referred to the same era, until the contrary 



could be shown. 



impossible to combat 



on geological grounds, so long as we are imperfectly acquaint- 

 ed with the order of superposition and the organic remains 

 of these same formations. Thus, for example, the red marl 

 and red sandstone, containing salt and gypsum (the Triassic 

 group of the Table, p. 139), being interposed in England be- 

 tween the Lias and the Coal, all other red marls and sand- 



them 



,.^ AA «u;i^ CL11U. ULIieitt Willi 



gypsum and occurring not only in different parts of Europe, 



North 



VOL. I. 



* Elements of Geol., 6th edit. p. 318. 



t 





