200 
PHYSICAL HISTORY OF THE 
idea that the two formations belong to distinct 
geological periods, and are not due to the 
same agency, acting at successive times. One 
feature, however, shows their close connection. 
The ochraceous clay exhibits a remarkable 
identity of configuration with the underlying 
sandstones. An extensive survey of the two, 
in their mutual relations, shows clearly that 
they were both deposited by the same water- 
system within the same basin, but at different 
levels. Here and there the clay formation has 
so pale and grayish a tint, that it may be con¬ 
founded with the mud deposits of the river. 
These latter, however, never rise so high as 
the ochraceous clay, but are everywhere con¬ 
fined within the limits of high and low water. 
The islands also in the main course of the 
Amazons consist invariably of river-mud, while 
those arising from the intersection and cut¬ 
ting off of portions of the land by diverging 
branches of the main stream always consist 
of the well-known sandstones, capped by the 
ochre-colored clay. 
It may truly be said that there does not exist 
on the surface of the earth a formation known 
to geologists resembling that of the Amazons. 
