84 THE AMERICAN BEAVER. 



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 become sufficiently enlarged to 

 accommodate more families than one, other families 

 took up their residence upon it, and afterward con- 

 tributed, 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 mainte- 

 nance of which a number of families were at the time 

 depending. 



The great age of the larger dams is shown by their 

 size, by the large amount of solid materials they con- 

 tain, and by the destruction of the primitive forest 

 within the area of the ponds; and also by the extent 

 of the beaver meadows along the margins of the 

 streams where dams are maintained, and by the hum- 

 mocks formed upon them through the annual growth 

 and decay of vegetation in separate hills. These 

 meadows were undoubtedly covered with trees adapted 

 to a wet soil when the dams were constructed. It 

 must have required long periods of time to destroy 

 every vestige of the ancient forest by the increased 

 saturaiton of the earth, accompanied with occasional 

 overflows from the streams. The evidence from these, 

 and other sources, tends to show that these dams have 

 existed in the same places for hundreds and thousands 

 of years, and that they have been maintained by a 

 system of continuous repairs. 



In external appearance there are two distinct kinds 



