464 



acquired velocity do not retain the whole of the 

 river in it's bed. The bifurcation takes place, 

 when the limit of the two basins crosses the bed 

 of the principal recipient longitudinally : it is 

 then that a part of the thalweg of a contains some 

 points, the most sloping lines of which lead to 

 the thalweg of b. The branch which is separated 

 can no more return toward a ; for a stream of 

 water, which has once entered a basin, can 

 never extricate itself, without having passed 

 through the bed of the river, where ail the waters 

 of the basin unite. 



It remains to examine, how in similar cir- 

 cumstances the breadth of a river favours the 

 chance of these bifurcations, which, like canals 

 with points of partition *, furnish, from the na- 

 tural disposition of the ground, a navigable line 

 between the basins of two neighbouring rivers. 

 On sounding a river in a transverse line, we ob- 

 serve, that it's bed is ordinarily composed of 

 several furrows of unequal depths. The broader 

 a river is, the more numerous are these furrows; 

 they even preserve at great distances a parallel- 

 ism more or less perfect. Hence it results, that 

 rivers may for the most part be considered as 



* In canals dug by the hand of man, the summit line (ligne 

 de faites) is placed between the two recipients - y on the con- 

 trary, in the branches that unite naturally tv/o systems of 

 rivers, the line of ekvation 3 or the ridge of partition, cuts the 

 bed of one of the two rivers longitudinally. 



