ICE AND GLACIERS. 99 



structure is thereby exposed, the regularly stratified yearly 

 layers are easily recognised. 



But it is clear that this accumulation of layer upon layer 

 cannot go on indefinitely, for otherwise the height of the snow 

 peak would continually increase year by year. But the more 

 the snow is accumulated the steeper are the slopes, and the 

 greater the weight which presses upon the lower and older 

 layers and tries to displace them. Ultimately a state must be 

 reached in which the snow-slopes are too steep to allow fresh 

 snow to rest upon them, and in which the burden which presses 

 the lower layers downwards is so great that these can no longer 

 retain their position on the sides of the mountain. Thus, part 

 of the snow which had originally fallen on the higher regions of 

 the mountain above the snow-line, and had there been pro- 

 tected from melting, is compelled to leave its original position and 

 seek a new one, which it of course finds only below the snow- 

 line on the lower slopes of the mountain, and especially in the 

 valleys, where however, being exposed to the influence of a 

 warmer air, it ultimately melts and flows away as water. The 

 descent of masses of snow from their original positions some- 

 times happens suddenly in avalanches, but it is usually very 

 gradual in the form of glaciers. 



Thus we must discriminate between two distinct parts of 

 the ice-fields; that is, first, the snow which originally fell 

 called firn in Switzerland above the snow-line, covering the 

 slopes of the peaks as far as it can hang on to them, and filling 

 up the upper wide kettle-shaped ends of the valleys forming 

 widely extended fields of snow or firnmeere. Secondly, the 

 glaciers, called in the Tyrol firner, which as prolongations of 

 the snow-fields often extend to a distance of from 4,000 to 5,000 

 feet below the snow-line, and in which the loose snow of the 

 snow-fields is again found changed into transparent solid ice. 

 Hence the name glacier, which is derived from the Latin, 

 glades ; French, glace, glacier. 



The outward appearance of glaciers is very characteristically 

 described by comparing them, with Goethe, to -currents of ice. 

 They generally stretch from the snow-fields along the depth of 

 H 2 



