DIRECTIONS OF RIVERS. 
217 
some way from it, and will diverge further and 
further as erosion proceeds. 
It is a remarkable fact that great folds by no 
means always determine the watershed, but, on the 
contrary, rivers often cut through ranges of moun- 
tains. 
Thus the Elbe cuts right across the Erzgebirge, 
the Rhine through the mountains between Bingen 
and Coblenz, the Potomac, the Susquehannah, and 
the Delaware through the Alleghanies. Even the 
chain of the Himalayas, though the loftiest in the 
world, is not a watershed, but is cut through by 
rivers in more than one place. The case of the 
Dranse will be alluded to further on. In these in- 
stances the rivers probably preceded the mountains. 
Indeed, as soon as the land rose above the waters, 
rivers would begin their work, and having done so, 
if a subsequent fold commenced, unless the rate of 
elevation exceeded the power of erosion of the river, 
the two would proceed simultaneously, so that in 
many cases the river would not alter its course, but 
would cut deeper and deeper as the mountain range 
gradually rose. 
In some other cases where we speak of a 
river suddenly changing its direction, it would be 
more correct to say that it falls into the valley of 
