BEAVER DAMS. Ill 



subsequently incorporated within it; or it may have 

 been seized upon after its fall as a convenient part of 

 a new structure. At all events, the most singular foct 

 connected with it is, that the dam was constructed 

 below the log, so far as sticks and poles are used, while 

 it was banked in above the trunk with earth. The log 

 part of the dam was twenty-five feet long, and the re- 

 mainder sixty-one feet, with a vertical height at the 

 centre of four feet eight inches, and a slope of pole 

 and stick work on the lower face of nine feet. From 

 the nature of the positions in which beaver dams are 

 usually constructed, fallen trees, if cut down on pur- 

 pose, could be of but little advantage; and it is there- 

 fore probable that the use of trunks of trees in build- 

 ing dams was purely accidental, as in the present 

 case. 



In addition to the two species of beaver dams which 

 have been described, there are varieties of each that 

 possess special characteristics resulting from the na- 

 ture of the localities in which they are erected. Some 

 notice of these dams is necessary to complete the ex- 

 position of these structures. 



The beavers do not restrict themselves to the prin- 

 cipal streams, nor yet to the small brooks, but where- 

 ever they find flowing water, however small in quan- 

 tity, they avail themselves of it if the place affords 

 the other requisite advantages. There is one dam, 

 not shown upon the map, situated at a short distance 

 from a spring in the midst of a dense forest, and upon 

 low and swampy ground, which may be called a 

 spring rill dam. As live trees were standing in the 

 pond, it was evidently of recent construction. A de- 

 pression in the ground formed a basin for the water 



