Observations on the Recent Glacial Drift of the Alps. 269 



distance of about one hundred miles, where it terminated on the 

 declivity, and its waters continued on across the driftless area, 

 leaving gravel terraces along their course. We must, therefore, 

 seek elsewhere for an adequate illustration of the essential prin- 

 ciples involved. 



At the foot of the Yiesch glacier, the ice stream divides and the 

 branches pass through valleys on either side of a ridge, tho'ugh 

 the ice at the point of branching is higher than the ridge. For- 

 merly the branches extended much further, and probably united 

 below the ridge. This would be an approach to an illustration of 

 the phenomena in question, but, unless the ice moved over the 

 ridge, and terminated on its slope, it would fail of an essential 

 element. 



The right hand branch of this glacier is antagonized by a prom- 

 inence, and the greater portion of the ice passes through lower 

 channels on either hand ; and these subordinate streams approach 

 each other below, leaving an island, or nearly so, on the slope. 

 Above this island the ice terminates on the declivity. On one 

 side the slope is so steep that the ice breaks away and rolls to the 

 bottom, marring the perfection of the illustration, but not destroy- 

 ing its force. The ice, while not really split in twain, is so far 

 thinned by the combined action of the prominence and the adja- 

 cent depressions, as to be unable to maintain itself against the 

 wasting to which it is subjected. If the slope were somewhat less 

 precipitous the illustration would be more complete. 



Near the termination of the upper Grindenwald glacier, there 

 has recently been a similar instance of an island ia a glacial 

 stream with higher ice on either side and above it. In this case, 

 the slope was so great that a portion of the ice above the island 

 became loosened and rolled down to the ice below. The amount 

 which thus passed over was less than an equivalent of the melting 

 capacity of the area of the island, so that, had not the cohesion 

 of the ice been overcome, it would have been melted on the 

 upper margin of the island. 



In all the foregoing instances, the areas have formerly been 

 glaciated, and thus differ from the Wisconsin driftless area. They 

 have force, however, as illustrating, in a miniature and imperfect 



