GLACIAL EROSION AND TRANSPORTATION. 231 



ments frozen into the bottom of the ice are not held there by 

 a perfectly firm and unyielding grasp. The same bowlder 

 which plows a furrow in the rock beneath it, plows a louger 

 furrow in the ice which is moving over it. This is finely 

 illustrated by some observations of Professor Xiles. 



In a visit to the great Aletsch Glacier, in the summer of 

 1878, Professor Niles had an excellent opportunity to exam- 

 ine the under side of the ice of this glacier near its front, 

 Here he observed numerous elongated ridges of ruck over 

 which the ice was flowing lengthwise, adjusting itself to all 

 the corrugated surface. When the ice passed the lee end of 

 the ridge it carried with it " the mold of the profile so per- 

 fectly that for more than twenty feet the blue arch presented 

 a series of parallel furrows, like the flutings of a Doric 

 column." 



There was there at that time another highly interesting and 

 instructive exhibition of glacial action. Within a few feet of 

 the down-stream end of one of these elongated roches mouton- 

 nees and upon its crest, there was a bowlder fully three feet in 

 diameter, which evidently had been slowly moving along this 

 ridge for some distance, probably from its upper end. There 

 were two sides of this block of stone which were not incased in 

 ice, viz., the lower one resting upon the rock, and the one 

 facing down the glacier. From the lower end of the ridge of 

 rock I looked at the bowlder through a tunnel of pure, blue 

 ice, which was continued as a deep furrow in the under sur- 

 face of the glacier for fully thirty feet from its beginning. As 

 this was produced by the ice moving over and beyond the 

 bowlder, it was evident that the ice was moving more rapidly 

 than the stone. I a*, erward found other examples of the same 

 kind, but none so favorably situated for a striking exhibition of 

 this property of ice. It will be understood that these stones 

 were sufficiently below the upper surface of the glacier to be 

 removed from the effects of the ordinary changes of the tem- 

 perature of the atmosphere. Although stones which are ex- 

 posed to such changes may be frozen into the ice at the edges 

 of the glacier, yet I believe these were so situated as to cor- 



