274 



EARTH FEATURES AND THEIR MEANING 



FIG. 302. Edge of the Greenland inland ice, 

 showing the nunataks diminishing in size toward 

 the interior. The lines upon the ice are medial 

 moraines starting from nunataks (after Libbey). 



Rock fragments which travel with the ice. Rock surfaces 

 which are exposed to the atmosphere are in high latitudes broken 



_____ down through the freez- 

 ing of water within their 

 crevices. The frag- 

 ments resulting from 

 this rending process fall 

 upon the glacier surface 

 and are carried forward 

 as passengers in the di- 

 rection of the ice mar- 

 gin. They are either 

 visible as long and nar- 

 row ridges or trains fol- 

 lowing the directions of 

 the steepest slope (Fig. 

 302), or they become buried under fresh falls of snow and only 

 again become visible where summer melting has lowered the glacier 

 surface in the vicinity of its margin. These longitudinal trains of 

 rock fragments upon the glacier surface always have their starting 

 point at the lower margin of one of the nunataks, and are known 

 as medial moraines (Fig. 301, p. 273, and Fig. 302). Inside 

 the zone of nunataks the glacier surface is, however, clear of rock 

 debris except where dust has 

 been blown on by the wind, 

 and this extends for a few 

 miles only. The material of 

 the medial moraines is a col- 

 lection of angular blocks whose 

 surfaces are the result of frost 

 rending, for in their travel 

 above the ice they are sub- 

 jected to no abrading pro- 

 cesses. 



A contrasted type of surface 

 moraines upon the Greenland FlG - 303 - Moat ^rounding a mmatak in 



. . . , . , . Victoria Land (after Scott). 



glacier, instead of being par- 

 allel to the direction of ice movement, is directed transversely or 

 parallel to the margins. The materials of these moraines are 



