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ground, on a surface of less than fifteen hundred 

 square leagues, another great river, the Oroo- 

 noko, forms a distinct hydraulic system. The 

 central plain of South America comprehends 

 consequently, two basins of rivers ; for a basin 

 is the whole of all the surfaces of circumjacent 

 lands, the lines of the greatest slope in which 

 terminate in the thalweg, that is to say, in the 

 longitudinal depression, which forms the bed of 

 the principal recipient. In the short space be- 

 tween the longitude of sixty-eight and seventy 

 degrees, the Oroonoko receives the waters which 

 flow down the southern slope of the Cordillera 

 of Parime ; but the streams * which issue from 

 the same slope east of the meridian of sixty- 

 eight degrees, between Mount Maraguaca, and 

 the mountains of Portugueze Guyana, flow to 

 the Amazon. It is therefore only on a length of 

 fifty leagues, that, in this immense equatorial 

 valley, planes situate immediately at the foot of 

 the Cordillera of Pari me have lines of the great- 



* The Padaviri and the Rio Branco (tributary streams 

 of the Rio Negro) ; the Rio Trombetas, the Gurupataba, 

 and the Rio Para, which fall immediately into the Amazon. 

 These rivers, all belonging to the same basin, rise from the 

 continuation of the Cordillera of Parime, east of the sources 

 of the Oroonoko, where this Cordillera stretches along by the 

 Sierra Pacaraimo (the poiut of division between the waters 

 of the Rio Branco and those of the Rio Carony) toward 

 French and Portugueze Guyana, that is, toward the sources 

 of the Essequibo and the Oyapoc. 



