34 GLACIERS 



form, and becomes granular or powdery. It is known as 

 the " nevd," or " firn." Occasionally it is coloured red by 

 a microscopic plant called Sphcerella nivalis, and when it 

 melts a certain kind of wheel animalcule often inhabits the 

 small pools so formed both in the Alps arid on the Arctic 

 and Antarctic snows. Generally the nev6 remains firm 

 and hard ; the foot sinks but little into j>. The water 

 which results from its melting sinks through it and 

 freezes with the snow below into a solid layer. Each 

 year's deposit forms a layer from i ft. to 3 ft. in thickness, 

 and is covered up to a great depth by the next year's 

 snow, which again during the warmer weather contributes 

 its frozen layer. Thus below the surface the nevd has a 

 banded or stratified structure, and when it has passed in 

 the course of years far from the place of its original 

 formation down the rocky bed of the creeping glacier, you 

 may still observe this laminated or stratified structure of 

 annual layers. The nevd is often of very great depth or 

 thickness. At the top or " source " of many Alpine 

 glaciers it is as much as 1000 ft. thick. Avalanches are 

 falls of the imperfectly consolidated snow on slopes too 

 steep to permit more than a small thickness of the 

 powdery material to lie at rest. An immense quantity of 

 snow is thus regularly brought down by avalanches to the 

 lower regions, and is melted every spring, when there is a 

 loosening of frozen bonds by the daily sunshine. The 

 deeper layers of the nevd are under vast pressure from the 

 overlying layers, and become crushed and regelated into 

 solid ice. They slowly slide as a continuous layer of 

 great thickness down the slopes on which they have 

 accumulated, and as they advance the powdery snow on 

 the surface both evaporates and melts until the deeper- 

 lying ice is bare aqd shows on the actual surface. The 

 nevd now ceases to exist as such ; it has become a 

 glacier, a slowly-moving river of solid ice. It is this 



