THE WORK OF SNOW AND ICE 



265 



and left there, for it is to be remembered that the ice continues to 

 move though the end is stationary. If the glacier moves forward 

 500 feet per year, and if its end is melted at the same rate, all the 

 debris in the 500 feet of ice which is melted is deposited, and all ex- 

 cept that which has been washed away has been deposited at and 

 beneath the end of the glacier (Figs. 218-219). If the end of the 

 glacier is retreating, the retreat means that the waste at the end 



Fig. 221. The moraines about the lower end of a glaciated mountain valley. 

 Bloody Canyon, Cal. (U. S. Geol. Survey.) 



exceeds the forward movement. If the ice advances 500 feet per 

 year and is melted back 600 feet in the same time, all the debris 

 carried by the 600 feet which has been melted has been deposited, 

 and largely in the narrow zone (100 feet) from which the ice has 

 receded. If the end of the glacier is advancing 500 feet per year 

 while it is being melted but 400 feet, all the drift in the 400 feet 

 melted has been deposited, and chiefly at or beneath the immediate 

 margin of the ice. To the marginal and sub-marginal accumula- 

 tions made in this way, the material carried on the ice is added 

 whenever the ice is melted from beneath it. Deposition beneath 

 the lateral margins of a glacier is much the same as beneath its ter- 

 minus (Fig. 221). 



