2 



GLACIERS. 



gESSy. <* uence of the alternating seasons and of frequent daily 

 Tabl^ase *}""" and ni S htl 7 f ^sts, becomes converted into ice. The 

 n BeoeH a. slopes of valleys occupied by glaciers are various ; some- 

 times only from 3° to 5° 



the descents are exceedingly abrupt. 



sometimes steeper, and sometimes 



A large glacier 



passes down these slopes in a manner that may be compared 

 to a broad and deep river of ice. Accordingly the whole 

 mass bends and accommodates itself to the sinuosities and 

 varying width of the valley, and its rate of progression has 

 been ascertained to be fastest in the middle and slowest at 

 the sides. Professor J. D. Forbes' theory of glacier motion 



is this 



rfect fluids 



if 



->/ 



>» 



On the other hand, it has 



mg 



of the ice 



lately been maintained by Professors Tyndall and Huxley 

 that the progressive motion of glaciers is not due to a vis- 

 cous movement of particles in the strict sense of the term, 

 but to numerous and repeated fractures of the entire mass! 

 and to rapid regelation, by means of which the general 

 continuity of the glacier is maintained. In summer, on 

 the surface of a glacier there is much waste by the thaw- 



At the lower extremity it is finally 

 melted by the heat. This waste is replenished by the fall 

 of snow on the high grounds, and thus it happens that a 

 glacier drains a certain area of snow, much in the same 

 manner that in lower or milder regions a river drains a 

 certain area of water. Numerous stones and blocks fall on 

 the marginal surfaces of glaciers from the mountain sides, 

 and as the ice progresses, these are carried, as it were, 



regular, and often very 

 broad lines, termed moraines. Where the ice of two 

 valleys coalesces, two of these side moraines also unite, and 

 generally form one central moraine, which passes down the 

 mid-surface of the glacier. Where glaciers finally melt at 

 their lower extremities curved terminal moraines are formed 

 by the stones and finer substances, that find their way 

 so far, and are there shed by the glaciers. The surfaces 



floating on the surface in long. 



i 



