58 DYNAMICAL GEOLOGY. 



rocky island in the middle of a glacier or of a tributary will 

 give rise to a separate train. Thus, complex glaciers, 

 with many tributaries, may be covered with these trains. 



Terminal Moraine. Remembering that glaciers are 

 in constant motion and yet never pass beyond a certain 

 point, it is evident that everything which is carried by 

 the glacier must find its resting-place at the foot. Here, 

 then, we find an enormous, irregularly concentric pile 

 of debris, the accumulation of ages. This is called the 

 terminal moraine. It is composed mainly of materials 

 carried on the surface of the glacier (top moraine), but 

 also to some extent of materials pushed out from beneath 

 (ground moraine). 



The Motion of Glaciers and its Laws. That gla- 

 ciers are actually in continual motion downward is proved 

 by the constant change of position, in relation to points 

 on the bounding cliffs, of conspicuous bowlders lying on 

 the surface of the glacier. From day to day and from 

 year to year these are carried farther and farther down 

 the valley. With a good theodolite the movement of 

 objects on the surface may be observed from hour to 

 hour. Thus, not only the fact and the rate but the laws 

 of motion have been determined. The rate of motion of 

 Alpine glaciers is one to three feet per day. The average 

 rate of the Mer de Grlace (Fig. 29) is estimated by Forbes 

 as about five hundred feet per annum. The extreme 

 length of the glacier is ten miles. A stone fallen upon 

 its upper part would find its resting-place on the terminal 

 moraine only at the end of one hundred years. Every- 

 thing upon or beneath or within the substance of the 

 glacier is finally deposited there. A striking and sad 

 illustration of this is found in the fact that, in several 

 cases, the mangled remains of adventurous climbers, who 

 have fallen into crevasses and perished, have appeared, 

 after many years, at the foot of the glacier. 



Laws of Motion. A glacier moves, not like a solid 



