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 by direct observation ; for we 

 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 eight hundred feet above the sea, 

 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 



