THE WORK OF SNOW AND ICE 241 



valley, nor is there evidence of rotatory motion, as in the water 

 of a river. Furthermore, the glacier is readily fractured, as the 

 numerous gaping crevices on many glaciers show. The crevasses 

 are sometimes longitudinal, sometimes transverse, and sometimes 



Fig. 197. Takakrow Falls, Yoho Valley, British Columbia. The glacier 

 above feeds the stream which falls. (Detroit Photographic Company.) 



oblique. In the case of arctic glaciers, longitudinal crevassing is 

 especially conspicuous. Crevasses appear to be developed wherever 

 there is appreciable tension, and the causes of tension are many. 

 An obvious cause is an abrupt increase of gradient in the bed (Fig. 

 198). If the change of gradient is considerable, an ice-fall or cas^ 

 cade results, and the ice may be greatly riven. Transverse crevasses 



