22 THIRD LETTER ON GLACIERS. [1842. 



careful inspection, are very striking and beautiful when seen at 

 a 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 struc- 

 ture of the ice, which retains the dirt diffused by avalanches 

 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 correspond 

 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 structure 

 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 com- 

 parative absence of these layers of granular and compact ice ; 

 the whole is nearly of uniform consistence, the particles of rock 

 scarcely 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. 



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

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



