306 SLOPE8 Of RIVER-SYSTEMS. 



it is bounded by plains on the left bank, from the C;.*?siquiare 

 to the mouth of the Atabapo, and flows in a basin which, 

 geologically speaking, according to one great division of the 

 surface of 'South America into three basins, we have called 

 the basin of the Eio Negro and the Amazon. The low 

 regions, which are bounded by the southern and northern 

 declivities of the Parime and Brazil mountains, and which the 

 geologist ought to mark by one name, contain, according to 

 the no less precise language of hydrography, two basins of 

 rivers, those of the Upper Orinoco and the Amazon, separated 

 by a ridge that runs from Javita towards Esmeralda. From 

 these considerations it results, that a geological basin (sit 

 venia verbo) may have several recipients, and several emis- 

 saries, divided by small ridges almost imperceptible ; it may 

 at the same time contain waters that flow to the sea by 

 different furrows independent of each other, and the systems 

 of inland rivers flowing into lakes more or less charged with 

 saline matter. A basin of a river, or hydrographic basin, has 

 but one recipient, one emissary ; if, by a bifurcation, it gives 

 a part of its waters to another hydrographic basin, it is 

 because the bed of the river, or the principal recipient, 

 approaches so near the banks of the basin or the ridge oi 

 partition that the ridge partly crosses it. 



The distribution of the inequalities of the surface of the 

 globe does not present any strongly marked limits between 

 the mountainous country and the low regions, or geologic 

 basins. Even where real chains of mountains rise like rocky 

 dykes issuing from a crevice, spurs more or less considerable, 

 seem to indicate a lateral upheaving. While I admit the 

 difficulty of properly defining the groups of mountains 

 and the basins or continuous plains, I have attempted to 

 calculate their surfaces according to the statements contained 

 "n the preceding sheets. 



SOUTH AMERICA. 



I. MOUNTAINOUS PART: Square 



Marine Lcaguei 



Andes 58.900 



Littoral Chain of Venezuela 1,900 



Sierra Nevada de Merida ~ 200 



Group of the Parime 25,800 



System of the Brazil mountains M .^ 27,600 



114,400 



