202 nature's 



I remember walking* across one of the gla- 

 ciers in the Alps, called the Mer de Glace, one 

 clear day in summer, when I suffered so much 

 from the heat, although standing upon a sea 

 of ice, that it was necessary to carry an 

 umbrella. In fact, during my stay there was a 

 case of sunstroke that occurred upon this same 

 glacier. This intense heat during the day 

 melts the surface of the ice, which forms 

 streams that run along on the top of a glacier 

 until they come to a crevasse or riffle in the 

 ice river, where they plunge down and become 

 a part of the glacial stream that is flowing 

 underneath the ice. 



The speed at which these ice streams flow 

 varies greatly with the size of the glacier as to 

 width and depth and the steepness of the 

 grade, and many other conditions. In its 

 movement the glacier is constantly bending 

 and freezing and being torn asunder by ten- 

 sional strain, yielding and liquefying at other 

 points by pressure, only to freeze again when 

 that pressure is removed. This, taken in con- 

 nection with the friction of the great ice 

 bowlders, produces a movement that is exceed- 

 ingly complicated in its actions and inter- 

 actions. 



According to Professor TyndalFs investiga- 

 tions, the most rapid movement observed in 

 the glaciers of Switzerland is thirty-seven 

 inches per day at the point of greatest move- 



