70 TJie Home of the Wolverene and Beaver. 



fabric is conn^letely water-tight, and so firm and 

 compact that even men armed with ice-chisels and 

 such hke tools find great difficulty in breaking 

 through them. In height the dams average from 

 seven to nine feet, according to the depth of water, 

 being broad at the base, and the sides sloping 

 inward towards each other, so as to form a narrow 

 platform about two feet wide at the top. The 

 object of these curious structures is that they may 

 possess a sufficient quantity of water at all seasons, 

 and the skill displayed by the animals in the shape 

 of their dams is a triumph of engineering science. 

 If the stream runs gently they throw the barrier 

 boldly athwart it, but if the current rushes past 

 swiftly, and is liable by floods to be converted 

 into a destructive torrent, they build the dam in 

 a crescent form, its convex side opposed to the fury 

 of the stream. Some idea of the extent of these 

 works may be formed when Audubon states that 

 they are sometimes found three Jiiindred yards in 

 length, and often extend beyond the bed of the 

 stream in a circular form, so as to overflow all the 

 tim'ber near the margin, which the beavers cut 

 down for food during the winter, heap together 

 in large quantities, and so securely fasten to the 

 shore, under the surface of the water, that even a 

 strong current cannot tear it away. Some of the 



