THE WORK OF SNOW AND ICE 



111 



even where thickest it is but a few hundred of feet. Larger alpine 

 glaciers occur in the Caucasus Mountains and in Alaska. Seward 

 Glacier in Alaska is more than 50 miles long, and three miles wide 

 at the narrowest part. The glaciers of the western mountains of 



Fig. 113. A type of a glacier system. Snow-fields above send out tongues of 

 moving ice which unite to form the Mer de Glace, which is a well-defined 

 valley glacier. The white part represents snow and ice. (Robin.) 



the United States south of Alaska are mostly shorter than the longer 

 glaciers of the Alps. Many of them are cliff glaciers, or interme- 

 diate between valley glaciers and cliff glaciers. 



Disposition of surface debris. The rock and earthy debris on 

 a glacier is sometimes scattered irregularly over the surface, but it 

 is often arranged in definite belts. When these are near the sides 

 they are called lateral moraines; when near the middle, medial 

 moraines (Fig. 110 and Fig. 1, PL XXXII, p. 109). When there is 

 much debris on the ends of a glacier it makes terminal moraines. 



Ice-caps 



As already stated, ice-caps may lie on plains or plateaus, and 

 may be large or small. Very large ones, like that of Antarctica, 

 are sometimes called continental glaciers. 



