THE WORK OF SNOW AND ICE 113 



large, the total amount of ice in them is small compared with that 

 in the great ice-cap from which they move. 



The Antarctic snow-and-ice cap is far more extensive than that 

 of Greenland, but its area is not so well known (Fig. 108). It is 

 probably several million square miles in extent, and the thickness 

 of its ice probably exceeds that of Greenland. The ice descends 

 to the sea at many points, and huge blocks of it become icebergs. 



Piedmont Glaciers 



In Alaska, a number of alpine glaciers come down adjacent 

 valleys in the St. Elias range and spread out upon a low plain at its 

 base. So much do their ends spread, that they unite to form a 

 single body of ice, 70 miles long and 20 to 25 miles wide, called the 

 Malaspina Glacier. Its area is greater than that of the state of 

 Delaware. Its central portion is free from rock debris, but is inter- 

 rupted by thousands of deep, wide cracks. On warm summer days, 

 hundreds of rivulets flow in channels of clean ice until they lose 

 themselves in yawning crevasses. The deep roar of some stream 

 in its tunnel far below the surface is frequently heard. 



Nearer the margin, where the ice is not so broken, there are 

 many small ponds with high walls of ice. A belt along the margin 

 five miles or less in width is covered by rocky and earthy debris, 

 and parts of it are clothed with vegetation. The undergrowth is 

 here so thick that travelers have to cut their paths, and on the 

 edge of the ice there are trees three feet in diameter (Fig. 2, PL 

 XXXII, p. 109). Another large but unexplored glacier of the same 

 type lies a few miles west of the Malaspina, and others occur about 

 North Greenland. 



THE WORK OF GLACIERS 



Glaciers do a twofold work; they erode the surface over which 

 they pass, and they deposit the material which they get by erosion. 



Erosion 



The ice gets its load in many ways. 



1. As the snow-field accumulates, it often lies upon an uneven 

 surface covered with loose pieces of rock. All these pieces are 



