206 
THE BEAVER. 
current is very gentle, the dam is carried 
nearly straight across ; but when the stream 
rapid, it is uniformly made with a considerate^ 
curve, having the convex part opposed to tb^ 
current. With the trunks and branches 
trees they intermingle mud and stones, to 
greater security ; and, when dams have beeH 
long undisturbed and frequently repaired, th^) 
acquire great solidity, their resistance to tb^ 
pressure of water and ice being increased by 
the willow, birch, and other cuttings, occa' 
sionally taking root, and growing up into ^ 
regular hedge. The materials used in coU' 
structing the dams are secured solely by tb® 
branches resting against the bottom, and tb^ 
subsequent accumulation of mud and stoB^^ 
either by the deposit of the stream or by tb<^ 
industry of the beavers. 
Their dwellings are formed of the same m^' 
terials as the dams, and are very rude, though 
strong, and adapted to the number of theb' 
