PHYSICAL HISTORY OF THE AMAZONS. 441 



enclosed, and the identity of the materials contained 

 in it. 



A glance at any geological map of the world will show 

 the reader that the Yalley of the Amazons, so far as 

 an attempt is made to explain its structure, is repre- 

 sented as containing isolated tracts of Devonian, Triassic, 

 Jurassic, cretaceous, tertiary, and alluvial deposits. This 

 is wholly inaccurate, as is shown by the above sketch, 

 and whatever may be thought of my interpretation of the 

 actual phenomena, I trust that, in presenting for the first 

 time the formations of the Amazonian basin in their natu-- 

 ral connection and sequence, as consisting of three uniform 

 sets of comparatively recent deposits, extending throughout 

 the whole valley, the investigations here recorded have con- 

 tributed something to the results of modern geology. 



