Remarks on Glaciers. 385 



each of them, that of all the beds inferior to it ; so that if the 

 bed at the bottom move with the quickness of 1, the second 

 with the quickness of 2, the third of 3, and so on, the quick- 

 ness of the third, for example, will be 3 + 2 + 1 or 6. 



A glacier, when seen in a vertical section, often exhibits a 

 series of beds of variable thickness, sufficiently distinct in the 

 upper part, less evident in the middle, and more or less obli- 

 terated below, according as the mass, from being exposed to 

 moisture, has been more or less completely converted into 

 transparent ice. These beds diminish in thickness from the 

 top doAvnwards, no doubt by an effect of the tassement, and 

 represent the additional beds which the glacier receives every 

 year. (Upper glacier of the Grindelwald, Trient, &c.) 



In regard to external form, a glacier usually presents a more 

 or less convex surface, particularly at the lower extremity. 

 This form results from the reflection of the heat from the sides 

 of the valley, which accelerates the melting of the ice at the 

 edges of the glacier. When the ground on which the glacier 

 moves, is but little inclined and free from inequalities, the 

 surface continues regular, and the mass is not divided. But if 

 it has some obstacle to surmount in its progress, or if the ground 

 present one of those sudden changes of level so frequent among 

 the Alps, the mass splits transversely into irregular leaves, 

 moving on their lower edge as around an axis, and separated 

 by wide crevices, which close again when the ground becomes 

 less steep, just as the waves of a torrent again become calm 

 after a fall. A glacier, in fact, is a river of ice stereotj^-ped, 

 with its cascades, rapids, storms, and calms ; the superficial 

 mass moving more quickly, and the lateral portions being in- 

 fluenced by the form of the bed in which it moves. 



The destructive action of atmospheric agents on the moun- 

 tain summits from which glaciers descend, and on the crests and 

 declivities which border the valleys in which they move, the fall 

 of avalanches, and the motion of the ice itself, are continually 

 detaching, along the whole basin of the glacier, fragments of 

 rock of every size, which roll into the place which the glacier 

 occupies, and rest upon its surface. These debris, thus depot 

 sited on and carried along with the glacier in its progress, give 

 rise to several remarkable phenomena. The largest of these 



