Studies in the Sierra 



313 



each other with reference to the direction of the glacier's mo- 

 tion, Uke the shingles of a roof. Portions of the sides of rocks 

 or canon walls whose structure is of the latter character always 

 project, because of the greater resistance they have been able 

 to offer to the action of the past-flowing glacier, while those 

 portions whose structure is similar to that of the former exam- 

 ple always recede. 



Fjg. 5, Fig. 7. 



Fig. 5 is a profile view of a past-flowed glacier rock, about 

 1500 feet high, forming part of the north wall of Little Yo- 

 semite Valley near the head. Its grooved, polished, and frac- 

 tured surface bears witness in unmistakable terms to the enor- 

 mous pressure it has sustained from that portion of the great 

 South Lyell Glacier which forced its way down through the 

 valley, and to the quantity, and size, and kind of fragments 

 which have been removed from it as a necessary result of this 

 action. The dotted lines give an approximate reconstruction 

 of the rock as far as to the outside layer at A. Between A and 

 B the broken ends of concentric layers, of which the whole 

 rock seems to be built, give some idea of the immense size of 



