112 ICE AND GLACIERS. 



size, the inclination, the amount of snow-fall, and other circum- 

 stances. 



Such an enormous mass of ice thus gradually and gently 

 moves on, imperceptibly to the casual observer, about an inch 

 an hour the ice of the Col du Geant will take 120 years before 

 it reaches the lower end of the Mer de Glace but it moves 

 forward with uncontrollable force, before which any obstacles 

 that man could oppose to it yield like straws, and the traces 

 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 irre- 

 sistible. 



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 extent corresponding to 

 the increasing distance, it breaks up and forms crevasses, as seen 

 along the edge of the glacier in Fig. 20, which represents the 

 Gorner 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 

 conclusions 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 hundreds. 



