CHAPTER V. 



THE WORK OF SNOW AND ICE. 



A PART of the atmospheric precipitation falls as snow, and this, 

 like the rain, does its appropriate work in degrading the land. Over 

 the larger part of the land surface the snow of the mnter does not 

 endure through the succeeding summer, and when it melts it follows 

 the same course as the precipitation which falls as rain; but in cold 

 regions w^here the fall of snow is heavy some of it remains unmelted 

 and constitutes perennial snow-fields. 



SNOW- AND ICE-FIELDS. 



Snow-fields. — Mountain heights and polar lands are the most com- 

 mon habitats of snow-fields, though they are not confined to these 

 situations. In North America there are numerous small snow-fields 

 in the western mountains, from Mexico on the south to Alaska on the 

 north, their number and size increasing in the latter direction. In the 

 United States there are few snow-fields south of the parallel of 36° 30', 

 and most of the many hundreds north of that latitude (excluding Alaska) 

 are small (PL XVIII, Fig. 1, Washington, lat. 48° 5', long. 121° 5'; 

 Fig. 2, lat. 41° 25', long. 122° 12'. From Glacier Peak and Shasta Special 

 Quadrangles, U. S. Geol. Surv.). Farther north, especially in Alaska, 

 the snow-fields of the western mountains attain much greater size. In 

 Europe snow-fields comparable to those of the northwestern part of 

 the United States and British Columbia occur in the Alps (Fig. 221), 

 the Pyrenees, the Caucasus, and the Scandinavian mountains. In Asia 

 snow -fields occur in the Himalayas and in many of the high mountains 

 farther north, from Turkestan on the southwest nearly to the coast 

 on the northeast. In South America there are snow-fields of small size 

 even in equatorial latitudes, and farther south in the Chilean Andes 

 there are some of considerable size. Small snow-fields occur on the 

 highest peaks of tropical Africa, and in the mountains of New Zealand. 

 For reasons which will appear later, much of every considerable snow- 

 field is really ice. 



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