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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, that in maps, the scale of which does not 

 admit of marking the inclinations of slopes from 

 three to five degrees, nothing materially indi- 

 cates 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 



