471 



sufficient to remind us of the progressive dimi- 

 nution of the running waters. We every where 

 see ancient traces of branches dried up, and 

 bifurcations* of which scarcely an historical 

 document remains. The different furrows more 

 or less parallel, which compose the beds of the 

 American rivers, and make their waters appear 

 far more ample than they are in reality, gradu- 

 ally change their direction ; they grow wider, 

 and are confounded together by the erosion of 

 the longitudinal ridges, by which they are sepa- 

 rated. What was at first but a branch, soon 

 becomes the only recipient ; and, in streams 

 that have little velocity, the bifurcations or 

 interbranchings between two hydraulic systems 

 disappear in three ways ; either the outlet, or 

 channel of communication, draws the whole of the 

 bifurcated river into it's basin ; or the channel is 

 choked up by deposits, where it issues from the 

 principal recipient ; or, finally, in the midst of 

 it's course it forms a transverse ridge, a point of 

 partition, which gives a counter-slope to the 

 upper pari, and occasions the waters to flow 

 back in an opposite direction. Very low coun- 

 tries subject to great periodical inundations, like 



* Those of the Gihon (Ritter, Geogr., vol. 2, p. G65 — 693), 

 and of the Nile, near the opening of Fayoum (Roziere, Const, 

 phys. de VEgypte, p. 32 — 53; Girard, Vallee de I'Egypte, p. 4). 



f This is at present the case in the Arno Teverin, between 

 Chiusi and Citta della Pieve in the Val de Chiana. 



