GLACIAL FEATURES OF THE ALPS 13 



as is the confluence. In the same way, as steps were formed at the 

 places where glaciers met, other steps occur where branches occurred, 

 for here there was a sudden diminution of the ice. There are steps 

 of confluence in the region of .confluence, and steps of diffluence in 

 the region of diffluence. The steps of confluence are seen in the hang- 

 ing mouths of side valleys; the steps of diffluence are hanging openings 

 of those valleys which were entered by a branch of the ice. The 

 height of both kinds of steps will generally be more considerable, 

 the greater the difference between the main glacier and its affluent 

 or diverting branch. Thus the step of diffluence of Yalsassina east 

 of Lake Como is higher than that of Porlezza west of this lake, and 

 the branches of Como and Lecco divided at about the same level, 

 since they were of nearly equal size. Here is a true bifurcation of 

 branches, and a bifurcation of valleys follows the diffluence of the 

 ice, if the openings of the neighboring valleys passed by the ice are 

 so deeply eroded that they will be easily buried by the accumulation 

 of river material which is being deposited in all overdeepened valleys 

 since they were vacated by the ice. The bifurcation of the Rhine 

 valley near Sargans, that of the Isere valley at Montmelian, and that 

 of the Salzach valley near Zell am See are fine samples of valley 

 bifurcation caused by glacial diffluence, and not, as often said, by 

 capturing. 



The establishment of a reversed drainage in consequence of 

 glacial diffluence is very much helped by the accumulation of moraines. 

 They surround the dissipating part of the glacier. They follow its 

 sides as lateral moraines and surround its end as frontal moraines. 

 In the glacier fans north of the Alps they form conspicuous land- 

 scapes. They are often watersheds between the reversed drainage 

 of the fan and the drainage of its surroundings, which corresponds 

 to the drainage of the ice-fan during its existence. Thus, for example, 

 the terminal moraines of the Rhine glacier form part of the great 

 European watershed between the northern seas and the Mediter- 

 ranean. On the south side of the Alps the terminal moraines are 

 still more conspicuous, and form amphitheaters around the ends of 

 the overdeepened glacier beds. These are the so-called morainic 

 amphitheaters of upper Italy, whose deposits partially dam up the 

 Italian lakes. Those glaciers which ended in the Alps left their 



