idea of an avalanche is derived from heartrending accounts of great sweepings away and annihilation of whole villages, and few of the general run of people seem to realise that in Alpine work almost any little descending mass of rock, snow, or ice is dignified by the name of avalanche. Snow avalanches are most frequent after fresh falls of snow followed immediately by warm weather, and after a little experience amongst the mountains one soon learns to detect their customary tracks. Ice avalanches are mainly caused through the overhanging portion of ice at the terminals of secondary glaciers—that is, glaciers which break off before descending to the valley or to the parent glacier below. The tracks of ice avalanches are almost invariably unmistakable and are swept night and day without cessation, and very frequently at regular intervals.
Rock avalanches are more treacherous, and one never knows when to expect them from above; generally in the early morning the frost holds the stones above in an icy grip, but as the sun melts the ice in the chinks the hold is released and a stone will descend into the couloirs or ditches which scarp the mountain side. If one happens to be below then it is a case of sauve qui peut and a rush for the nearest protection, for there is no saying how many tons, or indeed how many hundreds of tons, of loose rocks or stone may start in a wild and dusty rattle down the hillside.
But some snow avalanches almost crawl down the couloirs, and make a strange and ever-continued hissing as they move. These are composed of heavy and sodden snow, and begin after the sun has been up for some hours, continuing until nightfall. These are not
