146 RODENT WATER TRESPASSERS- 



they fell a tree on each side of the water so as to meet 

 in the centre. They then float sticks from six to four 

 feet long down to the dam, and lay them horizontally, 

 filling in the spaces with roots, tufts of grass, leaves, 

 and clay or mud. The branches of the first tree are 

 the perpendicular supports, almost all the remaining 

 sticks being placed horizontally and crosswise. The 

 last six or eight inches in height is very insecurely con- 

 structed, being nothing but mud and leaves. 



" The highest dam I ever saw was only about four 

 feet six inches ; but the generality of them are not above 

 two or three feet. The action of the water, by bringing 

 down mud, gravel, or fallen leaves, strengthens the 

 dam by making a sloping bank against it ; and, the 

 willow sticks of which it is composed sending forth their 

 roots and shoots, the dam in course of time becomes 

 a fixture, bound together as strongly as well could be. 



" The winter floods almost invariably destroy the 

 upper part of the dam, which is reconstructed afresh 

 every year. The shape of the dam is almost always 

 semicircular, with the crown of the arch down stream, 

 thus reversing the order of things ; but I have no doubt 

 this is in consequence of the heads of the first or 

 principal trees being floated down stream when they 

 are first thrown. 



" The body of water raised by these dams varies, 

 of course, according to the fall of the original stream, 

 from a small hole of 20 feet diameter to a lake of miles 

 in length. In the former case, the Beaver builds his 

 house close to the dam, so as to get depth of water, 

 and there saves himself from any hungry panther 

 (Felis concolor, L.) or wolf who might feel inclined to 



