GLACIERS 



209 



face of the ice. The material moved in the bottom of a 

 glacier or lodged beneath it constitutes the ground moraine. 

 The ground moraine deposits of the ancient ice sheets were 



FIG. 219. Diagram to show how debris in the body of a glacier may come 

 to be on top through the lowering of the surface of the ice by melting. 



frequently pressed by the weight of the overlying ice into very 

 dense, compact beds. These are sometimes called hardpan. 



Valley glaciers often carry heavy loads of rock debris on 

 their surfaces. This is partly material weathered from the 

 mountain slopes above, partly material worn from elevations 

 in the bed of the glacier and brought to the surface by the 

 melting of the ice above (Fig. 219), and partly also material 



FIG. 220. Moraine on south side of Hayden Glacier, in west-central Ore- 

 gon. Note the constitution of the moraine. West Sister Peak, Cascade 

 Mountains, in background. (Russell, U.S. Geol. Sun.) 



