THE WORK OF SNOW AND ICE. 



275 



Assuming that in the high altitudes and high latitudes where glaciers 

 abound, the temperature of the surface may average about — 12° Fahr. 

 (about —25° C.) for the winter half of the year, which is about the case 

 for north Greenland, Spitzbergen, and Franz Josef Land, and that the 

 conductivity of the ice in the C. G. S.^ system is .005, the temperature 



Fig. 250. — Contorted lamination shown at the surface. A small glacier south of 

 Forno hut, Engadine, Switzerland. (Reid.) 



would be lowered appreciably only about 40 feet below the surface at 

 the close of the ^^inter period, conduction only being considered. How 

 far the internal temperature may be influenced by air forced through 

 the ice by mnds and by variations of the barometer is not known and 

 cannot well be estimated. The wave of low temperature descending 

 from the surface in winter would probably become inappreciable 

 before reaching a depth of 60 feet. At this depth the temperature 

 should be about 15° Fahr. — ^the mean annual temperature of the region. 



1 Centimeter-gramme-second system. The rate of conductivity has not been 

 very accurately determined. 



