136 



THE FORMS OF WATER IN 



moment. Let the adjacent figure represent the channel 

 of the glacier moving in the direction of the arrow. 

 Suppose three circles to be marked upon the ice, one at 

 the centre and the two others at the sides. In a glacier 



of uniform inclination all these circles would move 

 downward, the central one only remaining a circle. By 

 the retardation of the sides the marginal circles would 

 be drawn out to ovals. The two circles would be elon- 

 gated in one direction, and compressed in another. 

 Across the long diameter, which is the direction of 

 strain, we have the marginal crevasses ; across the short 

 diameter m n, which is the direction of pressure, we have 

 the marginal veined structure, 



473. This association of pressuie and structure is 

 invariable. At the bases of the cascades, where the 

 inclination of the bed of the glacier suddenly changes, 

 the pressure in many cases suffices not only to close the 

 crevasses but to violently squeeze the ice. At such 

 places the structure always appears, sweeping quite 

 across the glacier. When two branch glaciers unite, 

 their mutual thrust intensifies the pre-existing marginal 

 structure of the branches, and developes new planes of 

 lamination. Under the medial moraines, therefore, we 



