106 



PHYSIOGRAPHY 



Glaciers sometimes occur at the bases of mountains, being 

 formed by the union of the spreading ends of valley glaciers. Such 

 glaciers are piedmont glaciers. Another type of small glaciers, 



Fig. 109. Small ice-caps in the northwestern part of Iceland. 



called cliff glaciers, is shown in Fig. 2, PL XXIX, p. 100. Cliff 

 glaciers grade into valley glaciers. Of these types, valley glaciers 

 are most common and most familiar, but the large ice-caps con- 

 tain much more ice. 



The Valley Glacier 



The general form of a valley glacier (Fig. 110) is determined 

 chiefly by the valley in which it lies. If the valley is crooked the 

 glacier turns to match it, and if the bottom is very uneven the sur- 

 face of the ice is uneven too. Valley glaciers have sometimes been 

 called " rivers of ice," but the differences between glaciers and rivers 

 are so much greater than their likenesses that this definition is not 

 a good one. 



The surface. The upper end of a valley glacier is in the snow- 

 field, and is always covered with snow. The lower end may be 

 covered with snow in winter, but not as a rule in summer. Some 

 glaciers carry so much rock rubbish on their surfaces as to almost 

 conceal the ice, especially near their lower ends. 



