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 Valley 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. 
