VALLEY OF THE AMAZONS. 
213 
in consequence of some turbulent action from 
within, a break was made in this defence, and 
the waters rushed violently out. It is very pos¬ 
sible that the waters, gradually swollen at the 
close of this period by the further melting of 
the ice, by the additions poured in from lat¬ 
eral tributaries, by the rains, and also by the 
filling of the basin with loose materials, would 
overflow, and thus contribute to destroy the 
moraine. However this may be, it follows 
from my premises that, in the end, these waters 
obtained a sudden release, and poured seaward 
with a violence which cut and denuded the 
deposits already formed, wearing them down 
to a much lower level, and leaving only a few 
remnants standing out in their original thick¬ 
ness, where the strata were solid enough to 
resist the action of the currents. Such are 
the hills of Monte Alegre, of Obydos, Almei- 
rim, and Cupati, as well as the lower ridges of 
Santarem. This escape of the waters did not, 
however, entirely empty the whole basin; for 
the period of denudation was again followed 
by one of quiet accumulation, during which 
was deposited the ochraceous sandy clay rest¬ 
ing upon the denudated surfaces of the under- 
