PHYSICAL HISTORY OF THE AMAZONS. 419 
primitive altitude. On the banks of the Rio Japura, in the 
Serra of Cupati, Major Coutinho has found the same beds 
rising to the same height. It thus appears, by positive 
evidence, that over an extent of a thousand miles these 
deposits had a very considerable thickness, in the present 
direction of the valley. How far they extended in width 
has not been ascertained bv direct observation ; for we 
7 
have not seen how they sink away to the northward, and 
towards the south the denudation has been so complete 
that, except in the very low range of hills in the neighbor- 
hood of Santarem, they do not rise above the plain. But 
the fact that this formation once had a thickness of more 
than eight hundred feet within the limits where we have 
had an opportunity of observing it, leaves no doubt that 
it must have extended to the edge of the basin, filling it 
to the same height throughout its whole extent. The 
thickness of the deposits gives a measure for the colossal 
scale of the denudations by which this immense accumu- 
lation was reduced to its present level. Here, then, is a 
system of high hills, having the prominence of mountains 
in the landscape, produced by causes to whose agency 
inequalities on the earth's surface of this magnitude have 
never yet been ascribed. We may fairly call them denuda- 
tion mountains. 
At this stage of the inquiry we have to account for two 
remarkable phenomena, first, the filling of the Amazonian 
bottom with coarse arenaceous materials and finely lami- 
nated clays, immediately followed by sandstones rising to a 
height of more than eiorht hundred feet above the sea. 
o o 
the basin meanwhile having no rocky barrier towards the 
ocean on its eastern side; secondly, the wearing away and 
reduction of these formations to their present level by a 
