MODE OF FORMATION OF CREVASSES. 353 



correspondence of the curve in the stratifica- 

 tion with that of the line of stakes confirmed 

 this result. The study of the stratification 

 of the snow was a marked feature of the sea- 

 son's work, and Agassiz believed, as will be 

 seen by a later letter, that he had established 

 this fact of glacial structure beyond a doubt. 



The origin and mode of formation of the 

 crevasses also especially occupied the observ- 

 ers. On the 7th of August, Agassiz had an 

 opportunity of watching this phenomenon in 

 its initiation. Attracted to a certain spot on 

 the glacier by a commotion among his work- 

 men, he found them alarmed at the singu- 

 lar noises and movements in the ice. "I 

 heard," he says, " at a little distance a sound 

 like the simultaneous discharge of fire-arms ; 

 hurrying in the direction of the noise, it was 

 repeated under my feet with a movement like 

 that of a slight earthquake ; the ground 

 seemed to shift and give way under me, but 

 now the sound differed from the preceding, 

 and resembled a crumbling of rocks, without, 

 however, any perceptible sinking of the sur- 

 face. The glacier actually trembled, never- 

 theless ; for a block of granite three * feet in 

 diameter, perched on a pedestal^two feet high, 

 suddenly fell down. At the same instant -a 



23 



