128 /. C. Russell — Expedition to Mount St. Elias. 



diagonal Ti of the square ; in the lower position this diagonal, if the ice 

 could stretch, would be lengthened to T^ ?/. But the ice does not stretch ; 

 it breaks, and we have a crevasse formed at right angles to T^ i\ The mere 

 inspection of the diagram will assure you that the crevasse will point 

 obliquely iqnvard" * 



Figure 4 — Diagram illustrating the Formation of marginal Crevasses. 



The explanation given above applies especially to the lower 

 or icy portion of a glacier ; above the snow-line other facts appear. 

 When a glacier floAvs through fields of snow on a level with its 

 surface, crevasses are formed in the adjacent banks. These trend 

 down stream for the same reason that the crevasses in the glacier 

 proper trend up stream — that is, the friction of the moving 

 stream against its banks tends to carry them along, while the 

 portions at a distance are stationary. Fissures are thus opened 

 which trend in the direction in which the glacier moves. The 

 angle made by these crevasses with the axis of the glacier is 

 about the same as those of the marginal crevasses, but in an 

 opposite direction. They are widest near the margin of the 

 glacier and taper to a sharp end towards the stationary snow- 

 banks above. The crevasses in the two series thus fall nearly 

 in line, but are separated by a narrow band of irregularly broken 

 snow, marking the actual border of the glacier, f 



After leaving Blossom island the party was divided, and we 

 began a new series of numbers for our camp above the snow-line, 

 although in this narrative and on the accompanying map a single 

 series of numbers for all the camps will be used. While in the 

 field the camps in the snow were usually termed, facetiously, 

 " sardine camps,"- in allusion to the uncomfortable manner in 

 which we were packed in our tent at night. 



*The Forms of Water: International Scientific Series, New York, 1875, 

 pp. 107-108. 



t Crevasses in snow-fields through which ice-streams flow will be men- 

 tioned again in describing the Seward glacier. 



