126 ICE AXD GLACIERS. 



of which are distinctly seen even on the granite walls 

 of the valley. If, after a series of wet seasons, and 

 an abundant fall of snow on the heights, the base of 

 a glacier advances, not merely does it crush dwelling 

 houses, and break the trunks of powerful trees, but the 

 glacier pushes before it the boulder walls which form 

 its terminal moraine without seeming to experience any 

 resistance. A truly magnificent spectacle is this motion, 

 so gentle, and so continuous, and yet so powerful and so 

 irresistible. 



I will mention here that from the way in which the 

 glacier moves we can easily infer in what places and 

 in what directions crevasses will be formed. For as 

 all layers of the glacier do not advance with equal 

 velocity, some points remain behind others : for instance, 

 the edges as compared with the middle. Thus if we 

 observe the distance from a given point at the edge 

 to a given point of the middle, both of which were 

 originally in the same line, but the latter of which 

 afterwards descended more rapidly, we shall find that 

 this distance continually increases ; and since the ice 

 cannot expand to an ex'tent corresponding to the in- 

 creasing distance, it breaks up and forms crevasses, 

 as seen along the edge of the glacier in Fig, 20, which 

 represents the Grorner Glacier at Zermatt. It would 

 lead me too far if I were here to attempt to give a 

 detailed explanation of the formation of the more regular 

 system of crevasses, as they occur in certain parts of all 

 glaciers ; it may be sufficient to mention that the con- 

 clusions deducible from the considerations above stated 

 are fully borne out by observation. 



I will only draw attention to one point — what extremely 

 small displacements are sufficient to cause ice to form 

 hiuidreds of crevasses. The section of the Mer de Glace 

 (P'ig. 21, at g, c, h) shows places where a scarcely 



