VALLEY OF THE AMAZONS. 
215 
foundation, and even cutting through it into 
the underlying sandstone, were, in the end, 
reduced to something like their present level, 
and confined within their present beds. This 
is shown by the fact that in this ochre-colored 
clay, and penetrating to a greater or less depth 
the sandstone below, are dug, not only the 
great longitudinal channel of the Amazons 
itself, but also the lateral furrows through 
which its tributaries reach the main stream, 
and the network of anastomosing branches 
flowing between them ; the whole forming the 
most extraordinary river system in the world. 
My assumption that the sea has produced 
very extensive changes in the coast of Brazil 
— changes more than sufficient to account for 
the disappearance of the glacial wall which I 
suppose to have closed the Amazonian Valley 
in the ice-period — is by no means hypothetical. 
This action is still going on to a remarkable 
degree, and is even now rapidly modifying the 
outline of the shore. When I first arrived at 
Para I was struck with the fact that the Ama¬ 
zons, the largest river in the world, has no 
delta. All the other rivers which we call great, 
though some of them are insignificant as com- 
