MAX AND THE GLACIAL PERIOD. 



A glacier is a mass of ice so situated and of such size as 

 to have motion in itself. The conditions determining the 



Fig. 1.— Zermatt Glacier (Agassiz). 



character and rate of this motion will come up for state- 

 ment and discussion later. It is sufficient here to say that 

 ice has a capacity of movement similar to that possessed 

 by such plastic substances as cold molasses, wax, tar, or 

 cooling lava. 



The limit of a glacier's motion is determined by the 

 forces which fix the point at which its final melting takes 

 place. This will therefore depend upon both the warmth 

 of the weather and upon the amount of ice. If the ice 

 is abundant, it will move farther into the region of warm 

 temperature than it will if it is limited in supply. 



Upon ascending a glacier far enough, one reaches a 



