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position of the great slopes, which compose 

 the polyedrical surface of the plains. The 

 chains of mountains do not rise like walls on 

 horizontal plains; their masses, more or less 

 prismatic, are always supported by table-lands, 

 and these are lengthened out into slopes, more 

 or less inclining toward the thalweg of the 

 river. It is therefore because the plains rise 

 toward the mountains, that the rivers so seldom 

 break against the mountains ; and that they feel 

 in some sort the influence of those lines of ridges 

 at very great distances. The geographers who 

 have studied topography in nature, and who have 

 taken levels of the ground, will not be surprised 

 to see 3 that in maps, the scale of which does not 

 admit of marking the inclinations of slopes from 

 three to five degrees, nothing materially indicates 

 the causes of the great inflexions of rivers. The 

 Oroonoko, from the confluence of the Apure to 

 it's mouth on the eastern coast of America, 

 runs in a line parallel to it's first direction, but in 

 an opposite course. It's thalweg is formed on 

 the north by an almost imperceptible slope, 

 which rises toward the chain on the shore of 

 Venezuela ; and on the south by the short and 

 steep counter-slope, which rests on the Sierra 

 Parime. By this particular disposition of the 

 ground, the Oroonoko surrounds the same 

 group of granitic mountains on the south, the 

 west, and the north ; and, after a course of 



