dam is built of poles to-day ; it speedily becomes 

 earthy and is planted by nature to grass, willows, 

 and flowers. On old, large dams it is not uncom- 

 mon to see old forest-trees. The roots of these 

 entangle the constructive materials, penetrate 

 deeply, and help to anchor securely the entire 

 dam. 



In only a few cases are the water-fronts of 

 dams at once plastered or filled in with mud. 

 This is done only where there is a scarcity of 

 water. It is the aim of the beaver to raise the 

 water in the pond to a certain height and there 

 maintain it, the chief purpose of the dam being 

 to regulate the height or the depth of the water. 

 The water, in streaming through new dams, de- 

 posits therein quantities of sticks, trash, and sedi- 

 ment, so that in a year or two these choke the 

 holes, almost stop the leakage of the water, and 

 help to solidify the dam. The discharge from 

 dams is regulated by the beaver. In some in- 

 stances water leaks through a dam in numerous 

 places from bottom to top; in others it seeps 

 through only close to the top ; and in still others 

 the dam is so solid that the water pours over the 



