GLACIERS. 683 



solid ice. The melting of the surface sometimes leaves the more solid 

 layers projecting. The structure is due, as shown by Tyndall, to the 

 pressure to which the glacier is subjected, in making its way between 

 the walls of a valley, especially where there is a contraction in width, 

 or a projecting point against which pressure is exerted, and particularly 

 below a place of steep descent. It may be formed when two great 

 glaciers unite, the pressure between the meeting streams being here 

 the cause. In the lower part of the glacier of the Rhone, the lam- 

 inated structure is produced, according to Tyndall, between the capes m 

 and n (Fig. 1103, p. 676), — the structure-mill, in his language. It ap- 

 pears first in the section s, and is fully developed in the following one, 

 s'. The radiating lines in the view represent crevasses. The resis- 

 tance to motion in a glacier is not continuously overcome, as in the 

 case of a perfect fluid, but intermittently. This is evinced in the 

 •successive transverse crevasses of a cascade-glacier, like that of the 

 Rhone, or in the dirt-bands which are registers of the successive 

 crevassing. Each movement, moreover, must cause a series of vibra- 

 tions, of great force, in the ice. Such intermittent action is especially 

 calculated to produce a laminated structure. As Tyndall has observed, 

 the air-ceils appear to have been in part expelled from the bluish lay- 

 ers by the pressure, and in part to have been obliterated by an incipient 

 liquefaction and refreezing of the layer. 



II. Transportation and Erosion. 



1. Transportation. — The moraines of glaciers are made from (1) 

 the stones and earth which fall from the cliffs along their borders ; 

 (2) the material received from falling avalanches ; (3) that which is 

 taken up by the "ice from the surface of the valley against which 

 it moves. They form in all the stages of progress of a glacier, 

 though usually the least in the region of the neve, where the area of 

 bare peaks is often small, compared with the extent of snow. The 

 surface in this upper part is always peculiarly white and clean, owing 

 to the frequent falls of snow. 



From their mode of origin, it follows that moraines are situated 

 primarily along the margin of a glacier. But, when two glaciers 

 coalesce, the two uniting sides join their moraines in one ; and this 

 one is remote from the borders, and may be central — as in the glacier 

 of the Aar — if the two coalescing streams are about equal. It fol- 

 lows from the above that the number of moraines on a glacier can 

 never exceed the number of coalesced glaciers by more than one. 



The nearest moraine, in the view of the Glacier of Zermatt, on page 

 677, is that of the Riffelhorn ; the second is a union of moraines of 

 the Gornerhorn and Porte Blanche ; the third, a union of two mo- 



