THE DAM. 



211 



Putting aside the natural dams made by accumulations of the 

 various debris that are washed down by a swollen stream, and 

 which sometimes raise the water to a very great height, we 

 have an example of a natural dam in the curious structure 

 made by the Beaver, for the same purpose as that of the lock in 

 the mill-stream, namely, to insure a depth of water sufficient 

 for the needs of the beings that make them. 



Every one has heard of the Beaver's dam, but there is so 

 much misconception on the subject, that a few words will not 

 be out of place. 



Ingenious as is the animal in the construction of its dam, it 

 is not nearly so accomplished an architect as was once supposed. 

 We were told in the earlier books of Natural History that the 

 Beaver felled trees, cut off their branches into convenient lengths, 



DAM MADE BY BEAVER. 



DAM MADE BY MAN, 



and sharpened one end, like an ordinary stake. Then they were 

 said to drive the sharp end of the stakes into the bed of 

 the river, to set them side by side, to interweave smaller 

 branches among them, and lastly, to fill up the interstices with 

 mud, leaves, and similar materials. In fact, they were supposed 

 to build a " wattle-and-daub " wall, like that which is in use at 

 the present day in Southern Africa. 



The Beaver does nothing of the kind. It needs a dam, and 

 it makes one which is far stronger than the wattle-and-daub 

 could be. It begins by felling a tree, and letting it lie across the 

 stream, in some place where the banks are high and tolerably 

 steep. A bend of the river is usually chosen for the new dam. 

 Should not the tree be long enough for the Beaver's purpose, 

 two trees are felled, one on either side, so that their branches 

 meet in the middle. 



p 2 



