BEAVER DAMS. 107 



the dam was of uniform width and height, as the bed 

 of the channel was level. At the base of the struc- 

 ture its average Avidth transversely was sixteen feet, 

 diminishing to twelve feet at the original surface level 

 of the stream, which here was twenty inches deep, 

 and to four feet in width at the height of three feet 

 from the bottom. Above this last level the crest was 

 rounded up about sixteen inches higher, where it was 

 still two feet wide, the embankment having a total 

 height of four feet and four inches. 



In constructing dams where the water is of such 

 depth, larger quantities of brush and poles are used 

 than in dams of the other class, and it is also neces- 

 sary to use larger amounts of earth. The brush is 

 required to hold the earth where it is placed, which 

 otherwise would be dissolved and flow away with the 

 current : and the earth in turn anchors the brush, and 

 when packed around it, the two together form a firm 

 and solid embankment. The principle on which 

 brush and sticks are used for their binding properties 

 is the same which led to the use of straw in mud 

 brick. Neither, separately, would answer the end 

 designed. So much earth was used upon this dam 

 that the brush and poles upon the lower face, as well 

 as on the water slope, were buried and concealed from 

 view, except the ends which projected in different 

 places. So firm and solid had the embankment be- 

 come, and such was its breadth near the summit, that 

 a horse and wagon might have been driven across the 

 river upon it in safety, but for the opening on the 

 left side for the passage of the surplus water. The 

 only differences, therefore, in the two species of dams, 

 consist in the filling in of the interstices on the lower 



