BEAVER DAMS. 85 



of beaver dams, although they are all constructed on 

 the same principle. One, the stick-dam, consists of 

 interlaced stick and pole work upon the lower face, 

 with an embankment of earth, intermixed with the 

 same materials on the upper, or water face of the 

 dam. This species is usually found on brooks, and 

 upon the larger streams without defined banks. The 

 greater proportion of beaver dams are of this descrip- 

 tion. The other is the solid-bank dam, which is 

 usually found lower down on the same stream, where 

 its banks have become defined, and it has a channel 

 of some depth, and a uniform current. In such places 

 the large amount of earth and mud, used to strengthen 

 the work, buries and conceals the greater part of the 

 brush and poles used to bind the embankment to- 

 gether; thus giving to it, in the course of time, the 

 appearance, on both slopes, of a solid dike, or bank 

 of earth. In the first species the surplus water per- 

 colates through the dam along its entire lengtli, while, 

 in the second, it is discharged through a single open- 

 ing in the crest formed for that purpose. 



At the place selected for the construction of a dam, 

 the ground is usually firm and often stony; and when 

 across the channel of a flowing stream, a hard rather 

 than a soft bottom is preferred. Such places are 

 necessarily unfavorable for the insertion of stakes in 

 the ground, if such were, in fact, their practice in 

 building dams. The theory upon which beaver dams 

 are constructed is perfectly simple, and involves no 

 such necessity. Soft earth intermixed with vegetable 

 fibre is used to form an embankment, with sticks, 

 brush, and poles imbedded within these materials to 

 bind them together, and to impart to them the requi- 



