ON THE LAND. 219 



away, and is carried by runnel and river to the ocean, again 

 to be raised as vapour, again to be frozen and fall as snow, 

 and again to be urged downward and melted to water. 

 Occasionally its descent from the mountains is sudden and 

 abrupt, as in the avalanche, which breaks away when the 

 gravity of the mass becomes too great for the slope on which 

 it rests, or when fresh weather' destroys its adhesion to the 

 surface. These snow-slips, or rather snow-and-ice slips, 

 are frequently most destructive in their effects, and are the 

 dread of the traveller and inhabitant on mountain regions 

 like the higher Alps and Himalaya. These are usually 

 distinguished as drift 9 or those caused by the action of the 

 wind on the snow while loose and powdery ; rolling, when 

 a detached piece of snow rolls down the steep, licks up the 

 snow over which it passes, and thus acquires bulk and im- 

 petus as it descends ; sliding, when the mass loses its adhe- 

 sion to the surface, and descends like a land-slip, carrying 

 everything before it unable to resist its pressure; and glacial, 

 when masses of frozen snow and ice are loosened by the 

 heat of summer, and precipitated with crushing effects into 

 the valleys below. 



The great and persistent result, however, of this moun- 

 tain-snow, is the glacier the " ice-sheet " of the flatter 

 heights, and the " ice-river " of the glens and ravines 

 which is ever pushing and grinding its downward way till 

 it finally melts and becomes the gladdening stream of the 

 lower valleys. The snow that falls on the higher peaks, 

 being partially softened by the warmth and rains of sum- 

 mer, is converted into a sort of " snow-broth," or " slush," 

 as the Scotch would call it, and has necessarily a tendency 

 to move downward by its own gravity, however gentle the 

 slope on which it rests. Pressed on summer after summer 

 by newer masses, it gradually assumes greater consistence, 

 loses the dull aspect of frozen snow, and passes into the hard 



