108 THE AMERICAN BEAVER. 



face with mud and earth, which turns it into a solid 

 embankment on both slopes, and throughout its whole 

 extent, and in the special method resorted to for dis- 

 charging the surplus water, which remains to be 

 noticed. 



From the solidity of these dams the water is not 

 able to percolate through them as before stated, 

 neither was it allowed at ordinary stages to pass over 

 their summits. A regular opening is left in the crest 

 of the dam, usually in the line of the thread of the 

 current, several inches lower than its summit. On 

 the water face above the opening is found the ordi- 

 nary embankment, while on the lower face it is con- 

 structed of interlaced stick-work precisely in the form 

 of the dam first described. This opening is usually 

 from three to six feet long, so that the water passes 

 over its top, and also through this narrow portion of 

 the structure by percolation. It is evident, from the 

 existence and peculiar character of these openings, 

 that the beavers understood the injurious effects of 

 allowing the surplus water to flow over the crests of 

 their solid-bank dams, and also the importance of 

 regulating the amount of the discharge, which could 

 be effected by the enlargement or contraction of the 

 openings. The dam was cut through at this point, 

 which nearly obliterated this feature of the structure. 

 This species of dam, when completed, might possess 

 some advantages over the other in the matter of re- 

 quiring less frequent repairs, and yet with each freshet 

 it would suffer more or less of waste. 



The pond above is narrow, it being confined with- 

 in the natural banks of the stream, with the excep- 

 tion of shallow water upon portions of the beaver 



