THE GLACIAL THEORY. 



9 



I have examined a cavern beneath the glacier of Urag, extending a 

 quarter of a league." Hugi. 



" The lower glacier of the Aar has two caverns or vaults, one on the 

 right, and the other on the left side/' Agassiz. 



Polished rocks are frequent near the summit and on the sides of 

 the RifFel, St. Bernard, Finsteraar." Agassiz. Charpentier and De 

 Saussure. 



*' The action of glaciers is best remarked in the lias formation of Rosen- 

 laui, where the polish, effected by the passage of the glacier over the 

 rock, is very evident." Agassiz. 



" Polished rocks occur beneath the glacier at Finsteraar and Lauteraar 

 and in immediate contact with the glacier at Bois, Viesch, and Aletsch." 

 Agassiz. 



" Striae occur on polished rocks at St. Bernard." De Saussure. 



"The polished surfaces of the granite in Oberland Bernois are striated." 

 Max. Braun. " The direction of these striae corresponds with the axis of 

 the glacier." Agassiz. 



** The most remarkable pohshed rocks which have been observed in 

 the Swiss Alps, are those at the summit of the Riffel, above the glacier 

 of Zermatt. Studer, Desor. 



Extensive slips of the whole or portions of any glacier, 

 naturally produce an effect upon the remaining portions, or 

 upon the subjacent rock; the alternations of temperature 

 act upon these rocks precisely in the same manner as upon 

 the glacier itself, and from first being cracked in various 

 directions by the absorption and subsequent congelation of 

 water, large pieces next become loosened by succeeding 

 frosts, and in the end, are detached by the first avalanche, 

 or glacial progress ; these, in their descent, become gradually 

 diminished in size, and are subsequently scattered ; the 

 smaller pieces, for instance, acquire a degree of heat which 

 causes them to melt the ice upon which they rested, and 

 penetrate into the mass ; the larger, being impervious on 

 account of their size, often remain isolated upon the ice 

 beneath them, which, from being thus protected, has with- 

 stood the heat ; whilst the surrounding glacier, from being 

 exposed, has long since melted away ; and it is only when 



