GLACIAL SHEETS 



325 



Ice caps, or glacial sheets, are expansions of ice, covering and 

 concealing the underlying topography, to which their surfaces do 

 not correspond. They may be compared to a flood, not confined 

 within banks, but spreading over antl uniformly submerging hills 

 and valleys alike. The smaller glaciers of this type are the plateau 

 glaciers, such as are found in Iceland, parts of Scandinavia, etc., 

 while the larger constitute the continental glaciers or ice sheets. 



Fig. 60. Map of Greenland, showing the ice cap and the ice-free borders. 

 (After Stieler, from Chamberlin and SaHsbury.) 



Of these the great ice cap of Greenland, with an area of nearly 

 2,000,000 square kilometers, is a well-known example. (Fig. 60.) 

 Another example of a little explored ice sheet is the continental ice 

 sheet of Antarctica, which ends seaward in ice cliflfs 50 meters or 

 more in height, (i.) In Pleistocenic time several huge ice caps 

 covered the northern part of North America. (Fig. 61.) They 

 were contiguous along their margins, where they interfered the one 

 with the others in respect to freedom of movement, interferences 

 now expressed in the distribution of their transported material and 

 frequently by the absence of erosion along the line of contact. 

 From the margins of the ice caps of the present day numerous 

 glaciers descend, many of them into the sea, where their ends may 

 break off and become icebergs. In continental glaciers no bounding 

 rock walls hem in the ice, though occasionally in the thinner mar- 



