SUBSISTENCE OF BEAVERS. 189 



The tail, which is composed largely of dense, fatty tis- 

 sues, is regarded as a delicacy. 



It is rather remarkable, on general considerations, 

 that the shallow ponds made by beaver dams do not 

 freeze to the bottom during the cold winters of the 

 high northern latitudes. The fixct that they remain 

 unfrozen to this extent, even around Hudson's Bay, 

 is well established. Ca^ptain Wilson informed me that 

 he had found open water along the crest of the dam 

 at Grass Lake, and generally at the lodge before 

 described, in the coldest part of the winter, the ther- 

 mometer in this region standing at an average of 5° 

 below zero for weeks together. There are special 

 reasons for this, among which is the deep covering 

 of snow throughout the winter, which protects the 

 water from the severe temperature of the atmosphere. 

 The first fall of snow lies in the pond partly con- 

 gealed, and afterward freezing at the surface, bears 

 up the subsequent deposits. From this, or some other 

 cause affecting the temperature of the water, the ice 

 formed is not always strong enough in the coldest 

 weather to bear up the weight of a man. Another 

 curious fact observed by the trapper is, that thin ice 

 is usually found over their piles of winter wood. As 

 these ponds are rarely over six feet deep in any part 

 of their area, the consequences of their wood becom- 

 ing ice-bound would not be less fatal than the forma- 

 tion of solid ice in the entrances to their lodcres. 

 There are undoubtedly local causes affecting the tem- 

 perature of ponds and of their different parts, such as 

 springs rising through their beds with their waters at 

 a relatively higher temperature, of the knowledge of 

 which the beavers avail themselves in selecting the 



