VALLEY OF THE AMAZONS. 
173 
in the United States ; while the rivers farther 
south, emptying into the Gulf of Mexico, rep¬ 
resent the rivers of Patagonia and the south¬ 
ern parts of the Argentine Republic. Not 
only is there this general correspondence be¬ 
tween the mountain elevations and the river 
systems, but as the larger river basins of 
North America — those of the St. Lawrence, 
the Mississippi, 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 compares 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 geo¬ 
logical character. They have both received 
a substratum of cretaceous beds, above which 
are accumulated their more recent deposits, so 
that, in their most prominent geological fea¬ 
tures, both may be considered as cretaceous 
basins, containing extensive deposits of a very 
recent age. Of the history of the Amazonian 
