Notice of Prof. Forbes' s Travels in the Alps. 183 



icicles of ten or twelve feet in length — hang from the roof, and give to 

 these singular vaults all the grotesque varieties of outline which are 

 so much admired in calcareous caverns, but which here show to far 

 greater advantage in consequence of their exquisite transparency and 

 lustre, and from being illuminated, instead of by a few candles, by the 

 magical light of a tender green, which issues from the very walls of 

 the crystal chambers." 



" Considering then the glaciers as the outlet of the vast reservoirs of 

 snow of the higher Alps — as icy streams moving downwards, and con- 

 tinually supplying their own waste in the lower valleys, into which 

 they intrude themselves like unwelcome guests, in the midst of vegeta- 

 tion and to the very threshold of habitations — it is a question of the 

 highest interest to explain the cause of this movement of the ice. 



" The glacier moves on, like the river, with a steady flow, although 

 no eye can see its motion ; but from day to day, and from year to year, 

 the secret silent course produces the certain slow effect ; the avalanche 

 .feeds it and swells its flowing tide ; the mightiest masses which lightning, 

 or the elements roll from the mountain side upon its surface, are borne 

 along without pause ; when the glacier advancing beyond its usual 

 limit, presses forward into the lower valleys, it turns up the soil, and 

 wrinkles far in advance the green sward of the meadows, with its 

 tremendous ploughshare ; it brings amongst the fields the blasts of 

 winter, and overthrows trees and houses in its ruthless progress ; no 

 combination 'of power and skill can stay its march, and who can define 

 the limits of its aggression ! Its proud waves are however stayed, and 

 by causes as mysterious as those of its enlargement ; it retreats year 

 by year within its former limits ; but where the garden and the meadow 

 were, it has left a desolate spread of ruin, like the fall of a mountain, 

 which never again may be tilled, and over which for at least half a 

 century, not even a goat shall pick the scanty herbage." 



The transporting power of glaciers is wonderful — superior to that of 

 any other power — unless it be that of icebergs, those floating glaciers, 

 which however exhibit only another mode of the same action. 



Vast masses of primitive rocks, that have apparently undergone little 

 wear and tear in ti-avelling, are found upon secondary or alluvial sur- 

 faces, at a great distance from their origin. These masses have obvi- 

 ously been deposited during the more recent periods of the earth's 

 physical history, and no considerable changes of surface have occurred 

 since. They are superficial, naked, often lying upon bare rock, or 

 upon sand or gravel, and often they are in such delicate positions as to 

 equilibrium, that earthquake or deluge would have easily displaced 

 them. Perhaps Prof. Playfair, of Edinburgh, first pointed out the im- 

 portance of glaciers as a moving power ; he understood their motion, 



