CHAPTER XV. 



REGELATION AS A CAUSE OF GLACIER MOTION. 



Why the Problem of Glacier Motion is so difficult. — Heat in Rela- 

 tion to Glacier Motion. — Regelation as a Cause of Motion. — 

 Theories of the Cause of Regelation. — How Regelation pro- 

 duces Motion. — Heat transformed into Glacier Motion. 



The conditions which make the question of the cause 

 of the descent of glaciers so perplexing seems to be 

 this : — The ice of a glacier is not in a soft and plastic 

 state, but is solid, hard, brittle, and unyielding. It 

 nevertheless behaves in some respects in a manner very 

 like what a soft and plastic substance would do if 

 placed in similar circumstances, inasmuch as it 

 accommodates itself to all the inequalities of the 

 channel in which it moves. The ice of the glacier, 

 though hard and solid, moves with a differential 

 motion ; the particles of the ice are displaced over 

 each other, or, in other words, the ice shears as it 

 descends. It had been concluded that the mere 

 weight of the glacier is sufficient to shear the ice. 

 Canon Moseley several years ago investigated this 

 point* and showed that it is not. He found that for 

 a glacier to shear in the way that it is supposed to do, 

 it would require a force some 30 or 40 times greater than 

 the weight of the glacier. Consequently, for the glacier 

 to descend, a force in addition to that of gravitation is 

 required. What, then, is this force ? It is found that 



f Memoir read before the Royal Society, Jan. 7, 1869. 



