596 Summary of Tertiary Formations part ii. 



ordinary vast amount of denudation. We have seen 

 that the highly remarkable fact of the absence of any 

 extensive formations containing recent shells, either on 

 the eastern or western coasts of the continent, — though 

 these coasts now abound with living Mollusca, — though 

 they are, and apparently have always been, as favour- 

 able for the deposition of sediment as they were when 

 the Tertiary formations were copiously deposited, — and 

 though they have been upheaved to an amount quite 

 sufficient to bring up strata from the depths the most 

 fertile for animal life, — can be explained in accordance 

 with the above proposition. As a deduction, it was also 

 attempted to be shown, first, that the want of close 

 sequence in the fossils of successive formations, and of 

 successive stages in the same formation, would follow 

 from the improbability of the same area continuing 

 slowly to subside from one whole period to another, or 

 even during a single entire period ; and secondly, that 

 certain epochs having been favourable at distant points, 

 in the same quarter of the world for the synchronous 

 accumulation of fossiliferous strata, would follow from 

 movements of subsidence having apparently, like those 

 of elevation, contemporaneously affected very large 

 areas. ^ 



There is another point which deserves some notice, 

 namely, the analogy between the upper parts of the 

 Patagonian Tertiary formation, as well as of the upper 

 possibly contemporaneous beds at Chiloe and Concep- 

 cion, with the great gypseous formation of Cordillera ; 

 for in both formations, the rocks, in their fusible nature, 

 in their containing gypsum, and in many other cha- 

 racters, show a connection, either intimate or remote, 

 with volcanic action; and as the strata in both were 

 accumulated during subsidence, it appears at first 

 natural to connect this sinking movement with a state 



