GLACIERS 



211 



FIG. 222. Sketch of a valley glacier in western 

 Canada, showing terminal moraine. 



cracks in the ice toward or to the bottom. On the other 



hand, material may be brought in different ways to the 



surface of a glacier 



from a position 



within or beneath 



the ice, as noted 



above. 



Material carried 

 at the bottom of a 

 glacier may be 

 dropped and picked 

 up again many 

 times before reach- 

 ing a final resting 

 place. Debris may 

 lodge just beyond 



elevations over which the ice has passed. Moving vigorously 

 over surfaces yielding material readily, the ice may obtain a 

 load which later, under new conditions, it cannot carry. At 

 its end, the moving ice is melting continually, the excess of 

 forward movement over melting being the measure of its 

 advance. Material obtained by the glacier back from its 

 end will therefore, if not dropped, find itself sooner or later 

 at the end, where it will be deposited as the inclosing ice 

 melts. Overridden by the advancing glac er, it may be taken 

 up once more, to be dropped again after a longer or shorter 

 journey. Where the end of a valley glacier, or the edge of 

 an ice sheet, remains essentially stationary for a long time, 

 a heavy deposit results at and beneath the margin of the 

 ice. This is called the terminal moraine (Fig. 222 and Plate 

 XII). Obviously, the longer the margin of the ice remains 

 stationary, the larger the terminal moraine becomes. Very 

 massive terminal moraines left by ancient glaciers accord- 

 ingly register very long stands of the margin of the ice. The 

 terminal moraines of valley glaciers are more or less crescentic, 

 the convex side pointing down valley (Fig. 222 j). 



