THE GLACIERS OF MOUNTAIN AND CONTINENT 267 



controlled by retaining rock walls, and it now assumes a form 

 largely independent of the irregularities in the upland. Expe- 



FIG. 294. Section through a mountain glacier (in solid black), showing how its 

 surface is determined by the irregularities in the rock basement (after Hess). 



rience shows that this surface is approximately that of a flat dome 

 or shield, and as it covers all the upland, save where the ice thins 

 upon its margins, this type of glacier is called an ice cap (Fig. 

 295). All types of glacier in which rock projects above the 

 highest levels of the ice and snow are known as mountain glaciers. 



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FIG. 295. Profile across the largest of the Icelandic ice caps, with the vertical 

 scale greatly exaggerated (after Thoroddsen and Spethmann). 



The flat domes of ice which mantle the continents of Green- 

 land and Antarctica, though resembling in form the smaller ice 

 cap, are yet because of their vast size so distinct from them, par- 

 ticularly in the manner of their nourishment, that they belong in 

 a separate class described as inland ice or continental glaciers. 

 Though they have some affinities with ice caps, they are most 

 sharply differentiated from all types of mountain glaciers. Of them 

 it is true that the lithosphere projects through them only in the 

 neighborhood of their margins (Fig. 296), whereas in the case of 



FIG. 296. Ideal section across a continental glacier, with the vertical scale and 

 the projecting rock masses of the marginal zone greatly magnified. 



