GEOLOGY. 671 



Avalanches are generally formed by enormous masses 

 of snow which from the height of the mountains precipi- 

 tate themselves into the valleys. It is particularly in 

 spring and during summer that they occur, at the time 



305. Mount Erebus, Antarctic Regions. 



when the heat of the day makes itself most felt. At such 

 times the least agitation in the air produces the fall. 

 There has been only too often occasion to regret their 

 ravages ; they frequently engulf travellers, and sometimes 

 carry with them forests and villages. 



In the mountain passes where there is most reason to 

 dread them, the muleteers always travel before day, the time 

 when they are least to be feared ; and in order not to agi- 

 tate the air, they observe absolute silence, and even stuff 

 the little bells on the harness with linen. But notwith- 

 standing these precautions, the avalanches engulf every 

 year a certain number of victims. At different times 

 hundreds of men have perished at once, criished imder 

 their mass. The most deplorable accident due to this 

 cause upon record is that which befell 400 Austrian 

 soldiers who, in the fifteenth century, were buried under 

 one of these falls of snow. 



