SNOW-MUSHROOMS AND CAHOTS 221 



culty in dislodging them. The circumstance that 

 the overhanging caps do not when overloaded 

 break off close against the tree-trunk is due to 

 the fact that the material which has accumulated 

 during many snowfalls is stratified, and that the 

 strata bend down steeply near the edge of the 

 cap. Thus if there be an overloading at the rim 

 or edge a small break occurs at once without any 

 extension of fracture to the main mass. Moreover, 

 the dome-shaped top is so steeply inclined at its 

 margin that an additional load of snow would 

 readily slide off. The photographs show clearly 

 the contrast between the smooth surface of the 

 upper stratum of snow, bent into a dome shape, 

 and the rough edges of the pendent strata below, 

 where the snow breaks away. The tree-stump 

 pedestals had generally a diameter of 2 feet, and 

 the caps were of the nearly uniform diameter of 

 9 feet— /.^., the snow projected 3I feet all round. 

 The depth of the snow upon the pedestal was about 

 4| feet. Perhaps the most striking of all the snow- 

 caps was one which had formed upon an unusually 

 large tree which had been broken off by lightning, 

 or some other agent, at a height of more than 

 20 feet above the ground. The diameter of this 

 tree where broken was about 4 feet, and the 

 diameter of the cap was about 1 2 feet. It must 



