236 T. C. CHAMBERLIN 



upwards at their extremities to the same degree that was 

 observed in some glaciers that have less free termination. A 

 measurement of the upper limit of the debris-bearing la3^ers at a 

 point about two miles distant from the end of the glacier gave a 

 height of only twenty-eight feet. Between this point and the 

 extremity of the glacier the debris was usually confined to less 

 heights, and at some points near the end it was not visible at all 

 in the lateral face of the glacier. The amount of debris even 

 within the limited range indicated was often relatively small 

 and never very heavy. The accompanying photographs sub- 

 stantiate this. The bowlders of this glacier were usually more 

 rounded than those previously described, and this rounding 

 was of such a nature as to imply very considerable wear. The 

 debris was composed wholly of crystalline rock, so far as 

 observed, no admixture of clastic material being seen. The 

 considerable rounding of the material, the small amount of 

 debris and its low position at the base of the glacier are facts 

 Worthy of special note. They will be seen to have special sig- 

 nificance when it is remembered that this is one of the larger 

 (though not by any means the largest) tongues of the great 

 ice-cap. . 



The rubbing of the glacier against shoulders of rock project- 

 ing from the side of the valley gave opportunity for observing 

 some of the special phenomena of such situations. At one 

 point the process of "plucking" was well indicated (though not 

 actually observed) on the lee slope of a spur of gneissoid rock. 

 Blocks ranging up to three or four feet in width and length and 

 one or two feet in thickness had been detached in considerable 

 numbers. The process involved much breaking and bruising 

 with relatively little wear. Corners and angles were broken off 

 and heavy bruise marks were observed both on the blocks and 

 on the sides and edges of the cavities from which they had 

 been removed. At some points considerable^ crushed rock was 

 observed. On the other hand, systematic grooves and striae were 

 not abundant nor pronounced. The dynamic impression given 

 was that of a forceful tearing out of blocks by the action of a 



