VALLEY OF THE AMAZONS. 
203 
even this does not cover the whole ground, 
and that some future writer may say of my 
estimate, as I have said of Humboldt’s, that it 
falls short of the truth ; for, if my generaliza¬ 
tions are correct, the same formation will be 
found extending over the whole basin of the 
Paraguay and the Rio de la Plata, and along 
their tributaries, to the very heart of the 
Andes. 
Such are the facts. The question now 
arises ; how were these vast deposits formed ? 
The easiest answer, and the one which most 
readily suggests itself, is that of a submersion 
of the continent at successive periods to allow 
the accumulation of these materials, and its 
subsequent elevation. I reject this explana¬ 
tion for the simple reason that the deposits 
show no sign whatever of a marine origin. No 
sea-shells nor remains of any marine animal 
have as yet been found throughout their whole 
extent, over a region several thousand miles 
in length, and from five to seven hundred miles 
in width. It is contrary to all our knowledge 
of geological deposits to suppose that an ocean 
basin of this size, which must have been sub¬ 
merged during an immensely long period in 
