BEAVER DAMS. 131 



described. Dams constructed of cotton-wood and wil- 

 low, of which I have seen a number of specimens 

 on the tributaries of the Upper Missouri, between the 

 Yellowstone and the Rocky Mountains, are inferior 

 in appearance to those in which hard wood is used, as 

 in the Lake Superior region; but the differences do 

 not affect the stability or efficiency of the structures. 

 Before concluding the subject of beaver dams, one 

 other variety remains to be noticed, which in novelty 

 surpasses all others. In Montana Territory three 

 beaver dams have been discovered in a petrified state. 

 They were found upon a small stream that runs 

 through the Point Neuf Canon, and empties into the 

 Snake River, one of the tributaries of the Columbia. 

 This canon is about three hundred miles north of Salt 

 Lake City. In length these dams are from fifty to 

 sixty feet, with a fall of water over two of them, at 

 the centre, of from three to four feet, and over the 

 third of about one foot. They were not in that com- 

 plete and final state of petrifaction which involves the 

 change of every particle of the original woody mate- 

 rials, and the substitution of solid substances; but 

 rather incrusted with lime, which, penetrating and 

 solidifying the entire structures, had given to them a 

 permanently durable form. It seems not a little sin- 

 gular that Nature should thus wrap up with her kindly 

 and preserving hand these memorials of the skill and 

 labor of the beaver, and hold them as a part of her 

 vast record of the past. My friend. Prof, Henry A. 

 Ward, of the University of Rochester, discovered these 

 dams while engaged in a geological exploration in 

 Montana, in the year 1865, and from him I received 

 the above account. 



