370 Professor Fournet's Besearches on the 



branches on the borders of the Sahara. According to Mol- 

 lien, the altitude of some of these summits is such as to reach 

 the limit of perpetual snow. 



There results, then, from the position of the plane of gene- 

 ral slope of this continent, combined with that of the fractures 

 and rugosities of the coasts, a sort of immense central valley, 

 which, commencing near the southern point of Africa, opens 

 to the north upon the broad low plain of the Sahara ; but 

 the altitudes scarcely appear to be such as to perform any 

 other part but that of an epanouissement in the regulation of 

 the rains ; the form of the plateau may accord with the phy- 

 siognomy of the desert : the two intumescences of the east 

 and of the west might alone occasion greater disturbances ; 

 but their opposite position, on very neighbouring parallels of 

 the equator, is such, that, by favouring the atmospheric afflu- 

 ence of the two heteronymous poles, they only contribute to 

 the establishment of the trade-winds, and consequently to the 

 symmetry of the zones without rain and of the deserts. 



The structure of the New World differs materially from 

 the preceding ; the essential forms no longer correspond, either 

 in a parallel manner or symmetrically, with reference to the 

 equator : the arrangement of the principal masses is even at 

 right angles ,* the meteorological phenomena likewise are no 

 longer everywhere identical. 



In fact, for the east and west protuberances of Africa, 

 situated in the neighbourhood of the equator, there is sub- 

 stituted the vast depression of the basins of the Amazon 

 and Orinocco, to which the entrance of east winds is pre- 

 vented, for a certain distance, by two mountain masses : the 

 one, the Cordillera of Parima or of the Guianas, is comprised 

 between the Orinocco, the Amazon, and the mouth of the 

 Meta, and is composed of a mass of mountains, among which 

 the Sierra of Duida attains nearly the height of the St 

 Gothard ; the other forms the Sierras of Amanbahy, of Mar, 

 of Montequerra, of Vertentes, of Epinhaco, &c., which cover 

 a portion of Uruguay, of Entre-Rios, of Oorrientes, of Para- 

 guay, and of Brazil, and comprehends, from the mouth of the 

 Plata to Cape San-Roque, an extent of 30^ lat. This vast 

 plateau, having a mean height of about 2600 feet, on which 



