THE VOYAGE OF THE BEAGLE 365 



escarpments or ancient sea-cliffs at different levels, one 

 above another, on that same line of coast. 



The old underlying tertiary formation at Coquimbo, 

 appears to be of about the same age with several deposits 

 on the coast of Chile (of which that of Navedad is the 

 principal one), and with the great formation of Patagonia. 

 Both at Navedad and in Patagonia there is evidence, that 

 since the shells (a list of which has been seen by Professor 

 E. Forbes) there entombed were living, there has been a 

 subsidence of several hundred feet, as well as an ensuing 

 elevation. It may naturally be asked, how it comes that, 

 although no extensive fossiliferous deposits of the recent 

 period, nor of any period intermediate between it and the 

 ancient tertiary epoch, have been preserved on either side of 

 the continent, yet that at this ancient tertiary epoch, sedi- 

 mentary matter containing fossil remains, should have been 

 deposited and preserved at different points in north and 

 south lines, over a space of 1100 miles on the shores of the 

 Pacific, and of at least 1350 miles on the shores of the Atlan- 

 tic, and in an east and west line of 700 miles across the 

 widest part of the continent? I believe the explanation is 

 not difficult, and that it is perhaps applicable to nearly analo- 

 gous facts observed in other quarters of the world. Consid- 

 ering the enormous power of denudation which the sea 

 possesses, as shown by numberless facts, it is not probable 

 that a sedimentary deposit, when being upraised, could pass 

 through the ordeal of the beach, so as to be preserved in 

 sufficient masses to last to a distant period, without it were 

 originally of wide extent and of considerable thickness : now 

 it is impossible on a moderately shallow bottom, which 

 alone is favourable to most living creatures, that a thick 

 and widely extended covering of sediment could be spread 

 out, without the bottom sank down to receive the successive 

 layers. This seems to have actually taken place at about 

 the same period in southern Patagonia and Chile, though 

 these places are a thousand miles apart. Hence, if pro- 

 longed movements of approximately contemporaneous sub- 

 sidence are generally widely extensive, as I am strongly 

 inclined to believe from my examination of the Coral Reefs 

 of the great oceans — or if, confining our view to South 



