GLACIAL FEATURES OF THE ALPS 17 



will be formed in the place of a former dome-shaped elevation. This 

 surface will, however, not reach below the snow limit. Thus by the 

 action of isolated hanging glaciers mountain summits may be degraded 

 nearly to the level of main glaciers, so far as they lie above the snow- 

 line. 



Open corries prevail in the highest parts of the Alps, in Tyrol and 

 in Switzerland. Their forms vary according to the height of the 

 valley slopes above the level of the main valley glaciers. The higher 

 these slopes are, the steeper they become, and the steeper then the 

 slope of the bottom of the corrie. The steeper this slope, the smaller 

 becomes the angle between it and the surrounding cliffs, and in those 

 parts of the western Alps which reached highest above the surfaces 

 of the neighboring valley glaciers the cliffs and the steep bottoms of the 

 open corries nearly unite, to form very steep cliffs, the feet of which 

 are and were constantly attacked by steep hanging glaciers formed 

 by snow avalanches and interspersed with stones which have fallen 

 down. The cliffs of two opposite glaciers of this kind usually inter- 

 sect at a very acute angle, and form very sharp ridges whose summits 

 are needle-like. These are the features in the Mont Blanc region, 

 with its aiguilles. The height of all these sharp crests is determined 

 by their elevation above the neighboring valley glaciers. Neighboring 

 crests have, therefore, nearly uniform heights, and all rise in height 

 in that direction from which the ice radiates or radiated. Therefore, 

 seen from a distance, the centers of glaciation of the Great Ice Age, 

 which are still today the scenes of a very strongly developed glaciation, 

 appear as extended domes, which are very much dissected by glaciated 

 valleys, and from which rise only a few isolated peaks, in places 

 where the rocks resisted best the attacks of weathering. The Mat- 

 terhorn and the Gross-Glockner are types of these horns of highest 

 resistance. They show clearly that the actual height of the sharp 

 mountain crests of the Alps is far from being an original one. It is 

 determined by destructive processes, the attacks of which still go on 

 above the actual glaciers, constantly lowering the crests and the 

 summits. The latter fact leads to the conclusion that our process 

 of destruction is a rather modern one, for if it had lasted for a longer 

 time, it would long ago have removed the whole of those crests pro- 

 jecting above the glaciers. It was believed that the crests of the 



