58 M. Ch. Martins on the 



speak, wliich descend into the valleyl^ in the form of masses 

 of ice, resembling frozen torrents. These masses are glaciers. 

 Their lower extremity is often more than 1500 metres below 

 the limit of perpetual snow, and sometimes approach to the 

 vicinity of large villages, such as those of Chamonix, Cour - 

 mayeur, and Grindelwald, the mean height of which is about 

 1120 metres above the sea. At the same time, a great num- 

 ber of glaciers exist which do not descend so low, and rest 

 on elevated slopes, where we find only a few scattered cha- 

 lets, inhabited only a few months in the year. 



What are the relations that exist between these glaciers 

 and the fields of snow with which they are connected ? is the 

 first question we have to examine. Science has already an- 

 swered it. In winter, spring, and autumn, considerable 

 masses of snow fall on the summits of the Alps.* These 

 snows, driven about by the winds and whirlwinds, accumu- 

 late, particularly in the great depressions in the vicinity of 

 the high peaks. These depressions are known by the name 

 of amphitheatres or cirques^ for they commonly terminate 

 in a semicircular enclosure, surrounded with elevated sum- 

 mits. Of this description, in the environs of Chamonix, are 

 the cirque which terminates at the Col du Geant ; the great 

 plateau, which is only 800 metres below the peak of Mont 

 Blanc ; near Grindelwald, the amphitheatre which leads to 

 the Strahleck ; at the Grimsel, those of the Lauteraar and 

 Finsteraar. The snows that accumulate in these regions do 

 not remain immoveable ; they have a progressive motion, 

 which makes them tend towards the valley. Like the lakes 

 which feed a river, and whose waters begin to flow slowly, as 

 soon as the influence of the declivity is felt, these fields of snow 

 can slide over ground but very slightly inclined. In propor- 

 tion as this snow descends into the more temperate regions, 

 it undergoes, particularly in the warm season, important modi- 

 fications, which completely change its nature and aspect : it is 



* The height of the snow fallen at Grimsel, at 1880 metres above the sea 

 level, was 16 metres 6 decemetres, from the mouth of November 1845 to Aj)ril 

 1846. The sheet of water arising from the melting of this snow would be 1 

 metre 4 decemetres in thickness. 



