463 



the breadth of one of the principal recipients, 

 and the situation of the thalweg, at the very edge 

 of the limit of the two basins. 



If the line of the greatest slope pass through a 

 given point, and if, indefinitely prolonged, it 

 do not meet the river, that point (whatever may- 

 be it's proximity to the thalweg) scarcely belongs 

 to the same basin. In adjacent basins we often 

 see the tributary streams of one recipient rise 

 very near to another recipient, between two tri- 

 butary streams of the latter. These particular 

 relations of coordination, which are observed in 

 alternate slopes, give forms that are more or less 

 sinuous to the boundaries of the basins. The 

 longitudinal furrow, or thalweg, is not neces- 

 sarily found in the middle of the basin : it does 

 not even always occupy it's lowest parts; for 

 these parts may be environed by ridges, that 

 prevent their being reached by the most sloping 

 lines. The unequal length of two tributary 

 streams, that terminate at the two banks of the 

 same river, enables us to judge with some pre- 

 cision of the situation of the thalweg with respect 

 to the boundaries of the basin. When the prin- 

 cipal recipient approaches one of these bounda- 

 ries, when it flows near the ridge that constitutes 

 the line of partition between the two basins, 

 there is the greatest chance of a bifurcation. 

 The least depression of this ridge may then cause 

 the phenomenon which we are discussing, if an 



