538 BUILDING INSTINCT OF BEAVER. 



a uniform height ; this they form of branches interlaced one 

 with another, the intervals between them being filled with 

 stones and mud, with which materials they give a coat of 

 rough-cast to the exterior also. When the dam passes across 

 a running stream, they make it convex towards the current ; 

 by which it is caused to possess much greater strength than 

 if it were straight. This dam is usually eleven or twelve feet 

 across at its base, and it is enlarged every year ; and it fre- 

 quently becomes covered with vegetation, so as to form a kind 

 of hedge. 



707. When the dam is completed, the community separates 

 into a certain number of families ; and the Beavers then em- 

 ploy themselves in constructing huts, or in repairing those of 

 a preceding year. These cabins are built on the margin of 

 the water ; they have usually an oval form, and an internal 

 diameter of six or seven feet. Their walls are constructed, 

 like the dam, of branches of trees ; and they are covered on 

 two of their sides with a coating of mud. Each has two 

 chambers, one above the other, separated by a floor ; the 

 upper one serves as the habitation of the Beavers ; and the 

 lower one as the magazine for the store of bark which they 

 lay up for their provision. These chambers have no other 

 opening than one by which they pass out into the water. It 

 has been said that the flat oval tail of the Beavers serves them 

 as a trowel, and is used by them in laying-on the mud of 

 which their erections are partly composed ; but it does not 

 appear that they use any other implements than their incisor 

 teeth and fore-feet. With their strong incisors they cut-down 

 the branches and even the trunks of trees which may be 

 suitable ; and by the aid of their mouths and fore-feet they 

 drag these from one place to another. When they establish 

 themselves on the banks of a running stream, they cut-down 

 trees above the point where they intend to construct their 

 dwellings, set them afloat, and, profiting by the current, direct 

 them to the required spot. It is also with their feet that 

 they dig-up the earth they require for mortar, from the banks 

 or from the bottom of the water. These operations are exe- 

 cuted with extraordinary rapidity, although they are only 

 carried-on during the night. When the neighbourhood of 

 Man prevents the Beavers from multiplying to the degree 

 necessary to form such associations, and from possessing the 



