BEAVER DAMS. 83 



to them when assailed, and the water connection it 

 gives to their lodges, and to their burrows in the 

 banks. Hence, as the level of the pond must, in all 

 cases, rise from one to two feet above these entrances 

 for the protection of the animal from pursuit and 

 capture, the surface level of the pond must, to a 

 greater or less extent, be subject to their immediate 

 control. As the dam is not an absolute necessity to 

 the beaver for the maintenance of his life, his normal 

 habitation being rather natural ponds and rivers, and 

 burrows in their banks, it is, in itself considered, a 

 remarkable fact that he should have voluntarily 

 transferred himself, by means of dams and ponds of 

 his own construction, from a natural to an artificial 

 mode of life. 



Some of these dams are so extensive as to forbid 

 the supposition that they were the exclusive work of 

 a single pair, or of a single family of beavers : but it 

 does not follow, as has very generally been supposed, 

 that several families, or a colony, unite for the joint 

 construction of a dam. After a careful examination 

 of some hundreds of these structures, and of the 

 lodges and burrows attached to many of them, I am 

 altogether satisfied that the larger dams were not the 

 joint product of the labor of large numbers of beavers 

 working together, and brought thus to immediate 

 completion; but, on the contrary, that they arose from 

 small beginnings, and were built upon year after year 

 until they finally reached that size which exhausted 

 the capabilities of the location ; after which they were 

 maintained for centuries, at the ascertained standard^ 

 by constant repairs. So far as my observations have 

 enabled me to form an opinion, I think they were 



