SNOW. GLACIERS 323 



relationship between latitude, the lower limit of snowfall, and 

 the snow-line. (Hann-4:j/j.) 



Altitude of Siicncfall and of Snozi^'-Iinc (Meters). 



Latitude 



0° 

 20° 

 40° 



These figures a.re approximate and represent average condi- 

 tions. Many temporary and local variations from these averages 

 occur. 



The equatorial limits of regular snowfall (at sea-level) are as 

 follows, the figures in parentheses giving the range of occasional 

 snowfall: On the west coast of America, 45° (34°) N. to 45° 

 (34°) S.; east coast, 35° (29°) N. to 44° (2^?) S. Interior, 30° 

 (19°) N. to near tropics in South America. For the Old World, 

 on the west coast of Europe, 45° (33°) N., on the east coast of 

 Asia, 30° (22.5°) N.; on east and south coast of Australia, 34° S. 

 (occasional). For the interior of Asia snow falls to 24° (22°) N. 

 latitude; on the Mediterranean to 7,"/° (29°) N. latitude, while 

 in the interior of South Africa it falls occasionally at 24° S. lati- 

 tude. (Hann-4: ?7^.) That the distribution of snow and ice 

 resulting from it was different in former geologic periods is shown 

 by the extent of former glaciation. 



Conversion of Snozv into Ice. The deeper portions of the 

 snowfield are gradually converted into snow ice through the inter- 

 mediate state of firn or 7ieve. The process of transformation of 

 snow into ice involves the partial melting and regelation of the 

 granules and the cementation of the remainder by the reconsoli- 

 dated snow water. This is a process of diagenetic metamorphism 

 or diagenesis. 



GLACIERS. 



When the mass of ice resulting from the consolidation of snow 

 begins to spread, creeping or flowing away from the center of 

 accumulation, it gives rise to glaciers. From their mode of occur- 

 rence, glaciers may be divided into, A. true glaciers or glacier 

 streams, and 15. ice caps, or glacier sheets. True glaciers are com- 



