PHYSICAL HISTORY OF THE AMAZONS. 



411 



Vermejo, and Salado rivers, to the river Platte, the Ar- 

 kansas, and the Red River in the United States ; while 

 the rivers farther south, emptying into the Gulf of 

 Mexico, represent the rivers of Patagonia and the south- 

 ern parts of the Argentine Republic. Not only is there 

 this general correspondence between the mountain eleva- 

 tions and the river-systems, but as the larger river-basins 

 of North America — those of the St. Lawrence, the Mis- 

 sissippi, and the Mackenzie — meet in the low tracts 

 extending along the foot of the Rocky Mountains, so do 

 the basins of the Amazons, the Rio de la Plata, and 

 the Orinoco join each other along the eastern slope of 

 the Andes. 



But while in geographical homology the Amazons com- 

 pares with the St. Lawrence, and the Mississippi with the 

 Rio de la Plata, the Mississippi and the Amazons, as has 

 been said, resemble each other in their local geological 

 character. They have both received a substratum of cre- 

 taceous beds, above which are accumulated more recent 

 deposits, so that, in their most prominent geological fea- 

 tures, both may be considered as cretaceous basins, con- 

 taining extensive deposits of a very recent age. Of the 

 history of the Amazonian Yalley during the periods im- 

 mediately following the Cretaceous, we know little or 

 nothing. Whether the Tertiary deposits are hidden under 

 the more modern ones ; or whether they are wholly want- 

 ing, the basin having, perhaps, been raised above the 

 sea-level before that time ; or whether they have been 

 swept away by the tremendous inundations in the valley, 

 which have certainly destroyed a great part of the creta- 

 ceous deposit, — they have never been observed in any part 

 of the Amazonian basin. Whatever Tertiary deposits are 



