THE WORK OF GLACIERS 171 



movement is locally concentrated and therefore increased where the 

 ice finds a relatively narrow outlet between inclosing ridges. 



The contour of this buried continent can be conjectured from the 

 fact that the greatly indented coast with its numerous islands re- 

 sembles that of Norway, so that it is probable that a rough, moun- 

 tainous surface like that of Norway underlies the ice. 



The Antarctic Continent. — The Antarctic Continent is larger than 

 the whole of Europe and differs from Greenland in its greater height, 

 in the greater severity of its climate, and in the absence of a strip 

 of ice-free land bordering the ice. The interior, as in Greenland, is 

 dome or shield-shaped and was found by Amundsen to be 10,500 feet 

 above the sea at the pole. Above the general level of the shield, 

 mountains rise to heights of 15,000 feet. The excess ice is drained 

 by valley glaciers, as well as by the Great Ice Barrier, a floating ice 

 shelf which in Victoria Land forms an ice clifF many miles long and 

 varying in height from 280 feet to places so low that it can be used 

 as a wharf. 



Ancient Glaciation 



The proofs that glaciers at one time covered a large area in North 

 America are so conclusive and the belief is now so universal that it 

 seems remarkable that the theory was not advanced until 1846 (by 

 Agassiz), and that nearly thirty years elapsed before its general accept- 

 ance by geologists. 



Deposition 



(1) Bowlders. — One of the most striking proofs that a region has 

 been covered with glaciers is to be found in the occurrence of bowlders 

 in the soil and on the surface, which differ in composition from the un- 

 derlying rock and consequently were not derived from it. When 

 traced to their parent ledges, some of these bowlders are found 

 to have been carried several hundreds of miles over hill and dale. 

 In regions of rough topography, glacial bowlders are often found at a 

 much higher level than the ledges from which they came. For 

 example, bowlders of quartzite have been found on Mt. Greylock, 

 Massachusetts, which must have been carried into a valley and then 

 to the top of the mountain, a vertical distance of almost 3000 feet. 

 Bowlders of jasper conglomerate, composed of bright red pebbles of 

 jasper embedded in white quartz, have been found from the northern 



