PHYSICAL HISTORY OF THE AMAZONS. 411 
Verrnejo, 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 Valley 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 
