1642 THE STORY OF THE UNIVERSE 



"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 careful examination of 

 some hundreds of these structures, and of the lodges 

 and burrows attached to many of them, I am alto- 

 gether satisfied that the larger dams were not the 

 joint product of the labor of large numbers of 

 beavers working together, and brought thus to im- 

 mediate 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 usually, if not invariably, 

 commenced by a single pair, or a single family of 

 beavers; and that when, in the course of time, by 

 the gradual increase of the dam, the pond had be- 

 come sufficiently enlarged to accommodate more 

 families than one, other families took up their resi- 

 dence upon it, and afterward contributed by their 

 labor to its maintenance. There is no satisfactory 

 evidence that the American beavers either live or 

 work in colonies; and if some such cases have been 

 observed, it will either be found to be an exception 

 to the general rule, or in consequence of the sudden 

 destruction of a work upon the maintenance of which 

 a number of families were at the time depending. 



