The Theory of Glacier motion, 117 



bruise over a considerable space of the yielding body. 

 According to this view, the delicate veins seen in the 

 glacier, often less than a quarter of an inch wide, have 

 their couysq parallel io the direction of the sliding effort of 

 one portion of the ice over another." He goes on to quote 

 the case of the Glacier of La Brenva, which at a point where 

 the ice is forcibly pressed against the naked rocky face of an 

 opposing hill is turned into a new direction, and in thus 

 shoving and squeezing past a prominence of rock the ice 

 developes a veined structure so beautiful that it is impos- 

 sible to resist the wish to carry off slabs, and to perpetuate 

 it by hand specimens. This perfectly-developed structure 

 was visibly opposite the promontory which held the glacier 

 in check, and past which it struggled, leaving a portion of 

 its ice completely embayed in a recess of the shore behind it. 

 Starting from this point as an origin, the veined laminae 

 extended backwards and upwards into the glacier, but did 

 not spread literally into the embayed ice. They could, 

 however, be traced from the shore to some distance from 

 the promontory into the icy mass. The direction of lam- 

 inae exactly coincided with that in which the ice must 

 have moved if it was shoved past the promontory at all. 

 Having proved experimentally that it had so moved, he 

 continues, " No rigid solid body can advance in such a 

 manner, it is therefore plastic, and the veined structure is 

 unquestionably the result of the struggle between the 

 rigidity of the ice and the quasi-fluid character of the 

 motion impressed upon it. That it is so, is evident not only 

 from the direction of the laminae, but from their becoming 

 more distinct exactly in proportion to their nearness to the 

 point from where the bruise is necessarily strongest." 



In regard to the state of the crevasses formed by the 



laminae, Forbes shewed them to be owing to the differential 



motion of the parts retarded by lateral friction, and to the 



fact that the friction being least where the motion is fastest^ 



H 



