Observaduns on Glaciers. 349 



distance by a light not too strong", as in the afternoon or by 

 moonlight. They are evidently bands of dirt on the surface 

 of the ice, having nearly the form of very elongated parabolas 

 merging in the moraines on either side, -widest apart from one 

 another in the centre, and confounded towards the edge. For 

 some time I was at a loss to conceive how these sort of false 

 moraines could spread from side to side of the glacier, but I 

 at length assured myself that it was entirely owing to the 

 structure of the ice, which retains the dirt diffused by ava- 

 lanches and the weather on those parts which are most porous, 

 whilst the compacter portion is washed clean by the rain, so 

 that these bands are nothing more than visible traces of the 

 direction of the internal icy structure, and of course corre- 

 spond with what has been already stated as to the forms in 

 which the conoidal surfaces intersect the plane of the glacier. 

 I counted distinctly sixteen of these bands on the surface of 

 the ice then in view. I afterwards traced them to the higher 

 part of the ice-field ; and the only distinction which I there 

 observed was, that the loops of the curves were less acute, or 

 more nearly circular, fig. 5. All glaciers do 

 not shew this external evidence of their struc- Fig. 5. 



ture equally, as there are some glaciers which 

 possess the structure itself more developed than 

 others. The cause of the dazzling whiteness 

 of the Glacier des Bossons at Chamouni is 

 the comparative absence of these layers of gra- 

 nular and compact ice ; the whole is nearly of 

 uniform consistence, the particles of rock scarce- 

 ly find a lodgment, the whole is washed clean 

 by every shower. The superficial bands are 

 well seen on the Mer de Glace of Chamouni, 

 and, to quote another example, one of the last I have seen, 

 very admirably on the Glacier of Ferpecle in the Valley of 

 Erin, where I counted above thirty in view at once. 



1 am quite persuaded that these bands, and of course the 

 structure which they represent, have their origin in the move- 

 ment of the glacier ; and if the laws of movement, ascer- 

 tained independently, shall coincide with, or confirm, the phe- 

 nomena of structure, we shall be better able, from the compa- 



