220 Professor Forbes on the Leading Phenomena of Glaciers. 



the definition I had given of the direction of the ribboned struc- 

 ture of the ice at different parts of the glacier. The observations 

 formerly made I found to be rigorously exact ; and especially 

 these two facts, which at once put an end to any idea of the 

 ribboned structure being a prolongation or deformation of the 

 strata of the Neve ; viz. (1.) the structure assumed by the ice 

 of the Talefre is extirpated entirely by its precipitous descent 

 to the level of the Glacier de Lechaud, where it reappears, 

 or rather is reconstructed out of the bruised fragments, ac- 

 cording to a wholly different scheme ; (2.) the veined struc- 

 ture often cuts the medial moraines ; i. e.^ a glacier com- 

 posed of two, having originally distinct looped structures, as- 

 sumes finally, after being for some time united, a single looped 

 structure. 



From the heights above the Egralets, which command a 

 most extensive bird's-eye view of nearly the whole Mer de 

 Glace, about 2000 feet below, I was led to make a very in- 

 teresting observation, — on the whole, the newest of the sea- 

 son. I need not remind your Lordship, that I first observed, 

 in 1842, the existence of certain wave-like marks on the sur- 

 face of the Mer de Glace, figured in my map of that year, 

 and represented in the models submitted to the Royal Society 

 last winter. These waves, or " dirt bands," as I termed 

 them, were parallel in their course to the veined or ribboned 

 structure of the ice, and recurred at pretty regular intervals 

 upon the surface of the glacier, — the loops pointing in the 

 direction of its motion, — at an average distance, as I think, 

 of between 600 and 700 feet. [The exact value is stated in my 

 book.] I was prevented, by a premature fall of snow, from 

 tracing these bands (which I also termed " annual rings"), 

 higher up the glacier than the point called Trelaporte. 

 Standing, on the 12th September last, above the precipices 

 of the Couvercle, at the foot of the Aiguille du Moine, as 

 above mentioned, I not only saw with admirable distinctness 

 the " dirt bands'* between Montanvert and Trelaporte deli- 

 neated, as it were, upon a plan ; but I was enabled to count 

 six new ones higher up in the direction of the Glacier du 

 Geant. Then followed a space corresponding to three inter- 

 vals of dirt bands, which were, however, not perceptible. 

 Higher up, on the Glacier du Geant, was a most striking and 



