162 HEAT OF HIGHER LAYERS OE AIR. 



proper glacier region, the layers, which are at first 

 level, become bent ; since they sink in from the two 

 borders to the middle, and down the slope of the 

 valley. Farther below, this bending of the middle 

 increases ; the cropping out of the several layers^ 

 (which, in general, may be readily distinguished 

 by the somewhat different condition of their ice, 

 and of the sand which still clings partially to the 

 surfaces which were formerly uppermost,) falls 

 more and more into acute angles towards the 

 middle, and is there in some places even perpendi- 

 cular, according to the stretching of the glacier in 

 its progress. Thus the outcrops of the layers on . 

 the surface of the glacier get the appearance of a 

 broken zig-zag line, whose general convexity how- 

 ever is always downwards, showing the quicker 

 progress of the ice in the middle of the glacier. 



The origin of the glacier-ice is entirely con- 

 fined to the firn region. During the cold season 

 the water, filling the hollows, or soaked into 

 the glacier-ice, freezes, it is true, as for as the 

 cold can penetrate, but the belts of ice thus formed 

 are denser, and are distinguished by their trans- 

 parency and sky-blue colour, from the porous and 

 opaque glacier-ice in whose mass they form riband- 

 like bands. 



Since every glacier loses every year a consider- 

 able portion of its mass by the thawing which 

 goes on at its surface, its thickness must generally 



