VALLEY OF THE AMAZONS. 
199 
over the whole basin at one level. Though it 
is now worn down in many places, and has 
wholly disappeared in others, its connection 
may be readily traced; since it is everywhere 
visible, not only on opposite hanks of the 
Amazons, but also on those of all its tributa¬ 
ries, as far as their shores have been exam¬ 
ined. I have said that it rests always above 
the sandstone beds. This is true, with one 
exception. Wherever the sandstone deposits 
retain their original thickness, as in the hills 
of Monte Alegre and Almeirim, the red clay 
is not found on their summits, but occurs only 
in their ravines and hollows, or resting against 
their sides. This shows that it is not only 
posterior to the sandstone, but was accumu¬ 
lated in a shallower basin, and consequently 
never reached so high a level. The boulders 
of Errere do not rest on the stratified sand¬ 
stone of the serra, but are sunk in the un¬ 
stratified mass of the clay. This should be 
remembered, as it will presently be seen that 
their position associates them with a later 
period than that of the mountain itself. The 
unconformability of the ochraceous clay and 
the underlying sandstones might lead to the 
