GLACIERS 



203 



South Pole. Its area is not known, but it is believed to be 

 more than 3,000,000 square miles (about the size of the 

 United States, exclusive of Alaska). The ice moves slowly 

 outwards toward the margins of the ice sheet, where great 

 masses are detached as icebergs, and float away. 



The Greenland ice sheet. Save in a narrow, rugged coastal 

 strip, all Greenland is covered deeply with ice and snow (Fig. 

 212). The area of the ice is probably some 400,000 to 500,000 

 square miles (seven to nine times as large as the state of 

 Illinois), and its thickness toward the center more than a 

 mile. Occasional mountain tops (called nunataks) rise as 

 islands through its marginal portions. Close to its edge the 

 ice contains many crevasses 

 and carries more or less rock 

 rubbish on its surface, but 

 over the vast interior the sur- 

 face is smooth and free from 

 rock material. Thinning to- 

 ward the coast, the ice sheet 

 in places gives off great arms, 

 which move along the valleys, 

 often reaching the ocean. 

 From the ends of these glaciers, some of which rise as cliffs 

 200 or 300 feet above the sea, great masses are detached, 

 and floated away as icebergs (Fig. 213). Icebergs from 

 Greenland are carried south by ocean currents and winds 

 to the latitude of Newfoundland, and sometimes beyond. 

 Rock material that was frozen in the glaciers is carried away 

 by the icebergs and as they melt it is dropped on the ocean 

 floor. Icebergs, however, are not important agents of trans- 

 portation, and most of what they carry is soon dropped. 



Small ice caps occur on various Arctic islands. 



Apart from the geological work which existing ice sheets are 

 doing, and their climatic and other influences, they are inter- 

 esting because they make it easier to understand the former 

 existence of great ice sheets in regions now free from ice. 



FIG. 213. An iceberg. 



