362 Glaciers. 



land we see certain white patches here and there 

 on the higher mountain ranges of the Alps. These 

 are more or less covered by snow and glaciers. The 

 highest mountain in the Alps, Mont Blanc, rises 

 more than 15,000 feet above the sea, and there are 

 many other mountains in this great chain which 

 approach that height, ranging from 10,000 to 15,000 

 feet high. The mean limit of perpetual snow upon 

 the Alps, is about 8,500 feet above the level of the sea. 

 Above that line, speaking generally, the country is to a 

 great extent covered with snow, excepting where the 

 tall cliffs are too steep to hold it, or on those sides of 

 even high valleys that face the southern sun. In the 

 higher regions it gathers on the mountain slopes, and 

 in the large cirques or recesses, which like vast amphi- 

 theatres, are characteristic of all true mountain groups 

 or ranges that I have seen. By force of gravity, and the 

 alternate melting and regelation of the molecules of 

 ice, especially in summer, the gathered snow presses 

 downwards into the main valleys; where, chiefly in 

 consequence of the immense pressure exerted by the 

 vertical weight and onward pressure of the accumu- 

 lated mass, the snow year after year is converted into 

 moving ice. Without entering on details, it is enough 

 if I now state that this is proved by well-considered 

 observations made by the best observers of the icy 

 phenomena of the Alps. 1 



Still accumulating, year upon year, by degrees this 

 ice slides down the valley, and is often protruded in 

 great tongues far below the limits of perpetual snow ; 

 for some Swiss glaciers descend as low as from three to 

 four thousand feet or thereabouts above the level of 



1 See Dr. James Croll's work on ' Climate and Time.' 



