SUBSISTENCE OF BEAVERS. 177 



each cut is found to fit exactly the slight concavity in 

 the inner side of the incisor. It will be observed from 

 the sloping edges of the chip that each cut penetrated 

 deeper than the one preceding it as they severally ap- 

 proach the centre, and that the split surface in the 

 centre is less than an inch in length. From the size 

 of this chip, and the number of distinct cuts upon it, 

 some impression may be formed of the number and 

 power of the bites necessary to gnaw down a tree of 

 the diameter of either of those described; and yet it 

 is said, by those who have witnessed the performance, 

 that a pair of full-grown beavers will accomplish the 

 work in two or three nights. 



Cottonwood-trees are soft and easily cut. The 

 largest trees ever fallen by the beavers are of this 

 kind. I have seen them on the banks of the Upper 

 Missouri twenty inches and two feet in diameter. 

 One specimen in my collection, which I brought down 

 this river from a point about a hundred miles east 

 of the Rocky Mountains, measures sixteen inches in 

 diameter, and was an ordinary specimen. It is re- 

 presented in the group of cuttings (Plate XVI.), 

 but partly concealed from view. Father De Smet, 

 the well-known missionary to the Indians of the 

 Columbia River, informed me that he had seen cot- 

 tonwood-trees, cut down by beavers, thirty inches in 

 diameter; and Dr. F. V. Hay den, that he had meas- 

 ured a cotton wood-tree, on the Yellowstone River, 

 after it was cut down by them, of the same diameter. 

 Lewis and Clarke, remarking upon the tree cuttings 

 at the mouth of the same river, state that "the 

 beavers have committed great devastation among the 



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