TEXTURE OF GLACIER-ICE. 161 



rapidly than that which surrounds it, and thus 

 little hollows are formed, which, when once filled 

 with water, are soon increased in depth by the 

 liquid, which is heated at the top to above 0° C. 

 P.) and then sinks to the bottom. 

 Although the proper ice of the glacier holds to- 

 gether as a solid mass, yet it appears, on closer 

 examination, to be quite full of cracks as fine as 

 hairs : it has not, therefore, in the mass, the trans- 

 parency of common ice, and differs from it too in 

 being somewhat less brittle, if, as generally happens, 

 its little cracks are soaked full of water. Farther 

 up it takes a granular texture, and in the highest 

 parts of the glacier you find only a mass of very 

 line grains, partially frozen together,— the Firn. 

 The firn is formed from the snow fallen during the 

 pear, by the water thawed upon the surface, which 

 again and again first soaks into it and then freezes* 

 By these changing influences, which last during 

 its downward movement, it is turned into the solid 

 glacier-ice, which, therefore, is not marked off from 

 the firn by any sharp boundary line. 



In the firn region the ice forms horizontal layers, 

 which probably consist of the snow-beds of each 

 winter, and their levels are marked by the dust 

 and sand, which are blown in the summer time 

 by the wind from the naked walls of rock. Each 

 layer, therefore, shows the passage of a year. As 

 the firn reaches downward in the valleys to the 



M 



