VALLEY OF THE AMAZONS. 
197 
the filling of the Amazonian bottom with 
coarse arenaceous materials and finely lami¬ 
nated clays, immediately followed by sand¬ 
stones rising to a height of more than eight 
hundred feet above the sea; the basin mean¬ 
while having no rocky barrier towards the 
ocean on its eastern side. Second, the wear¬ 
ing away and reduction of these formations to 
their present level, by a denudation, more ex¬ 
tensive than any thus far recorded in the 
annals of geology, which has given rise to all 
the most prominent hills and mountain chains 
along the northern bank of the river. Before 
seeking an explanation of these facts, let us 
look at the third and uppermost deposit. 
This deposit, essentially the same as the 
Rio drift, has been minutely described above; 
but in the north it presents itself under a 
somewhat different aspect. As in Rio, it is 
a clayey deposit, containing more or less sand, 
and reddish in color, though varying from 
deep ochre to a brownish tint. It is not so 
absolutely destitute of stratification here as 
in its more southern range, though the traces 
of stratification arc rare, and, when they do 
occur, are faint and indistinct. The mate- 
