Professor Forbes' s ^ixth Letter on Glaciers. 239 



the same noise, (?) and in the same manner, as the melting 

 glaciers roll into the valley of Chamouni ; indeed, this awful 

 and extraordinary scene would have brought to mind the base 

 of the Montanvert, had it not been for the crimson glare and 

 excessive heat of the surrounding scoriae."* 



Mr Auldjo, the author of a Narrative of an Ascent of Mount 

 Blanc, and therefore acquainted with the appearance of gla- 

 ciers, has renewed Mrs Starke'^s comparison in very similar ex- 

 pressions, in a work more recently published upon Mount 

 Vesuvius. Captain Basil Hall has, if I mistake not, in more 

 than one part of his writings suggested the picturesque ana- 

 logy of volcanoes and icy mountains, the cradle of glaciers. 



We have seen how far there is a real analogy between the 

 mechanism of these two terrible scourges of Almighty power 

 — the ice-flood and the fire-flood, both of which invade the 

 homes and the labours of man, with a force alike irresistible. 

 But to render the analogy more than apparent or poetical, i^ 

 was required that several difficulties, very obvious, and seem- 

 ingly insuperable, should be removed ; and the chief of these 

 was the texture of ice compared to the texture of lava — the 

 former passing from a brittle solid into limpid fluid by heat, 

 the latter passing like sealing-wax through every intermediate 

 degree of viscidity. This difficulty could only be met by an 

 exact determination of the question — Of how far a glacier is 

 to be regarded as a plastic mass % Were a glacier composed 

 of a solid crystalline cake of ice, fitted or moulded to the 

 mountain bed which it occupies, like a lake tranquilly frozen, 

 it would seem impossible to admit such a flexibility or yielding 

 of parts as should permit any comparison to a fluid or semi- 

 fluid body, transmitting pressure horizontally, and whose parts 

 might change their mutual position, so that one part should 

 be pushed out whilst another remained behind. But we know, 

 in point of fact, that a glacier is a body very diff*erently con- 

 stituted. It is clearly proved by the experiments of Agassiz 

 and others, that the glacier is not a mass of ice, but of ice and 



* Starke's Travels. French edit., p. 311. 



VOL. XXXXVII. NO. LXXIV. OCTOBER 1844. Q 



