218 ICE ITS FORMS AND FUNCTIONS. 



duration, and every peak and precipice would be rounded 

 and worn down by its power.* 



In all the higher latitudes, snow, we have said, falls less 

 or more during winter, and melts away during summer, t 

 But in all latitudes there is an elevation at which it lies 

 perennially, and this elevation will differ, of course, with 

 the latitude. This limit, above which snow lies at all 

 seasons, is known as the snow-line, or line of perpetual con- 

 gelation; and though it ascends a little higher during sum- 

 mer, and descends a little lower in winter, it is, on the 

 whole, pretty stationary in every region of the globe. Of 

 course, it will come nearer the sea-level in high latitudes, 

 and ascend higher and higher as we approach the equator ; 

 and thus it is that we have it at 1500 feet in Spitzbergen, 

 2400 at North Cape, 5000 in the Dovrefelds, 9000 in the 

 Alps, 12,000 in the Atlas range, and on an average about 

 16,000 feet under the equator. In all the higher regions, 

 therefore, this snow accumulates enormously, and would 

 continue to accumulate were it not for three causes which 

 tend as incessantly to prevent it. These are, first, atmo- 

 spheric causes, such as summer's heat, warm winds, and 

 occasional rainfalls, which partially dissolve it ; second, the 

 mechanical pressure of the accumulating mass, which ever 

 tends to urge it forward and downward to lower levels; and, 

 third, the land-slopes, which afford greater or less facilities 

 for its descent. As it descends by these means, so it melts 



* The reader who takes interest in this matter will find marvellous illus- 

 strations of the power of frost in such works as Von Wrangell's ' Siberia, ' 

 Scoresby's 'Arctic Voyages/ Ross's 'Antarctic Voyages/ and Dr Hooker's 

 ' Himalayan Journal.' 



*{ Though snow is the necessary product of cold, yet in all temperate 

 and coldly-temperate latitudes a good heavy snowfall is beneficial in pro- 

 tecting vegetation from the severity of long- continued frosts. Such a cover- 

 ing is usually known as the snow-blanket, and in central and northern 

 Europe its absence in early spring is often followed by most destructive 

 results to the young growths of the farmer and gardener. 



