266 GEOLOGY 



Types of Moraines 



The terminal moraine. The thick accumulation of drift made 

 at the end of a glacier or at the edge of an ice sheet, especially where 

 its end or edge is stationary or nearly so for a considerable time, 

 is the terminal moraine. Terminal moraines are of more importance, 

 relatively, in connection with ice-caps than in connection with 

 valley glaciers, for streams are more effective in destroying the 

 moraines of the latter than those of the former. 



The ground moraine. When a glacier disappears, all its debris 

 is deposited. All the drift deposited beneath the advancing ice, 

 and all deposited from the base of the ice during its dissolution, 

 constitutes the ground moraine. The thickness of the ground 

 moraine is notably unequal. In general, it is thicker toward the 

 terminus of the glacier and thinner toward its source, but consid- 

 erable portions of a glacier's bed are often left without debris when 

 the ice melts. In general, the ground moraine is thinner than the 

 terminal moraine, and less irregularly disposed. The ground mo- 

 raine is of relatively slight importance in valley glaciers as compared 

 with ice-caps, since conditions for erosion under the body of a valley 

 glacier are, on the average, better than under an ice-sheet, and 

 those for deposition less favorable. 



The lateral moraines. Lateral moraines are the product of val- 

 ley glaciers. The lateral moraines on such glaciers are let down on 

 the surface beneath when the ice melts; but the lateral moraines 

 in a valley from which the ice has melted are not merely the lat- 

 eral moraines which were on the glacier at a given time. They are 

 often far more massive than any which ever existed on the ice 

 (Figs. 216, 221, and 222). Furthermore, much of the material of 

 lateral moraines left after the ice is gone is as well worn as that of 

 the ground moraine. The massive lateral moraines left after the 

 ice is gone are made up chiefly of the drift accumulated beneath 

 the lateral margins of the valley glaciers. This accumulation is 

 the result of the lateral motion of the ice from the center to the side 

 of the valley. Such sub-lateral accumulations are akin to terminal 

 moraines. Some of the lateral moraines of ancient valley glaciers. 

 such as those of the Uinta, Wasatch, and Bighorn mountains are 



