316 



streams, and augment their inundations ; but 

 at length these deposites obstruct entirely the 

 branches of the rivers, and the narrow channels, 

 that connect the neighbouring streams. The 

 substances washed down by rainwaters form by 

 their accumulation new bars, isthmuses of depo- 

 sited earthy and points of division, which did not 

 before exist. It hence results, that these natu- 

 ral channels of communication are by de- 

 grees divided into two tributary streams, and 

 from the effect of a transverse rising acquire 

 two opposite slopes. A part of their waters 

 is turned back toward the principal reci- 

 pient, and a buttress rises between the two paral- 

 lel basins, which occasions all traces of their 

 ancient communication to disappear. From 

 this period the bifurcations no longer connect 

 different systems of rivers ; and, where they 

 continue to take place at the time of great in- 

 undations, we see that the waters diverge from 

 the principal recipient only to enter it again 

 after a longer or shorter circuit. The limits, 

 which at first appeared vague and uncertain, 

 begin to be fixed ; and in the lapse of ages, from 

 the action of whatever is moveable on the sur- 

 face of the Globe, from that of the waters, the 

 deposites, and the sands, the basins of the 

 rivers separate, as the great lakes are subdivided*, 



* For instance, the lakes of the valley of Mexico since the 

 sixteenth century. 



