AQUEOUS AGENCIES. 55 



shows that the mass of ice is so great that, although mov- 

 ing at a rate of only a few feet a day, it may reach a mile 



FIG. 28. Zermatt glacier. (After Agassiz.) 



below, and many miles beyond, the snow-line before it is 

 all melted. In high latitudes, where the snow-line comes 

 nearer the sea-level, glaciers not only touch the sea, but 

 run far into the sea, and, breaking off, form icebergs. 



General Description of a Glacier. In glacial re- 

 gions, where the summit snow-fields are large, every val- 

 ley is filled for a certain distance with a glacier. In the 

 Alps the glaciers are five to fifteen miles long, one to 

 three wide, and two hundred to six hundred feet thick. 

 In the Himalayas they are twenty to forty miles long. In 

 the United States (exclusive of Alaska) the largest glaciers 

 occur in Washington. White River glacier, on Mount 



