698 



DYNAMICAL GEOLOGY. 



ating lines in the view represent crevasses. The resistance 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 move- 

 ment, moreover, must cause a series of vibrations, of great force, in 

 the ice. Such intermittent action is especially calculated to produce 

 a laminated structure. As Tyndall has observed, the air-cells appear 

 to have been in part expelled from the bluish layers by the pressure, 

 and in part to have been obliterated by an incipient liquefaction and 

 refreezing of the layer. The cause is the same that has produced slaty 

 cleavage in some fine-grained rocks. 



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 a glacier's progress though 

 smallest in the region of the neve, where the area of bare peaks is us- 

 ually small, compared with the extent 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. An 

 isolated peak rising above a glacier may send off its stones and earth 

 all in a single line or moraine. 



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

 691, 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- 

 raines from two Mt. Rosa Glaciers ; the fourth, the great moraine of 

 the Breithorn, the summit in the middle of the view. Other moraines 

 may be seen in the distant part of the glacier. In Fig. 1101, on page 

 690, representing a section of the Bois Glacier near Trelaporte, there 

 are six distinct moraines. 



Toward the lower extremity of a glacier, the several moraines 

 usually lose their distinctness, through the melting of the ice ; for this 

 brings the stones and earth that were distributed at different depths to 

 one level, and thus produces a coalescence of the whole over the sur- 

 face. 



