COAST ICE 115 



as from that which gathers upon the surface of the snow or n£ve" 

 and is covered up by subsequent snowfalls. The materials carried 

 by a glacier are as characteristic as the marks left upon the rocks 

 over which the ice has flowed. Aside from the substances swept 

 along by the sub-glacial stream, the various fragments are not 

 rounded and water-worn, as is the sediment of rivers. The 

 moraines on the top of the ice (lateral and medial) are little or 

 not at all abraded, but are deposited as angular blocks and frag- 

 ments. The ground moraine, on the other hand, is abraded in 

 a peculiar way ; the larger fragments retain their angular shape 

 more or less distinctly, though the angles and edges are rounded 

 off, and the side of the pebble or boulder which was in contact 

 with the rocky bed is itself scored and polished. The finer frag- 

 ments produced by the grinding and crushing of the rocks against 

 one another are angular. In all this work of glacial denudation 

 the process is entirely mechanical, — chemical disintegration plays 

 no part in it. 



Certain other forms of transportation by ice may be conven- 

 iently mentioned here. 



Ground Ice forms in rivers and ponds on the bottom, freezing 

 around stones and boulders, and when broken up by thaws, this 

 ice may float for long distances, carrying with it burdens far 

 greater than the stream which transports the ice could carry 

 unassisted. The shores of the St. Lawrence River are fringed 

 with lines of large boulders which have thus been brought down. 



Coast Ice. — In Arctic regions the shallow water along the coast 

 is frozen in winter into a broad shelf of ice called the ice-foot. In 

 the spring landslips cover the ice with debris, while the bottom is 

 studded with stones and pebbles. When the ice-foot is broken up 

 in summer, part of it is drifted away and transports its load of rock 

 for long distances. Other parts are worked backward and forward 

 by the waves and tides, scoring the rocks of the coast and grind- 

 ing and polishing the fragments of rock frozen in the ice, in much 

 the same fashion as glacial pebbles are scored and ground. Over 

 comparatively limited areas the marks of coast-ice often have a 

 deceptive resemblance to those left by glaciers. 



