THE BEAVERS OF NORTH AMERICA 35 



done, and beavers vary in the quality of their work 

 just as men do, the structure is finally practically 

 watertight. Yet the word finally is scarcely the 

 right word to apply to a dam, for so long as the 

 beaver have any need of it they continue adding 

 to both its height and length. What begins by 

 being a perfectly complete dam, perhaps twenty 

 feet long and a foot or two in height, ends with 

 a length of many hundreds of feet and a height 

 of six or seven feet or even more. Besides the 

 above-mentioned materials stones are frequently 

 employed in the construction of dams. In fact it 

 is rare to find any that have not at least a few 

 stones worked in with the sod, particularly 

 towards the ends. When so few are used it is 

 hard to say what purpose they serve. But 

 there are instances of dams being built in 

 which stones form the larger part of the 

 material. These are not common and I have 

 never seen but one example. Unfortunately the 

 photograph shows only those stones which are above 

 water, where there is a fair proportion of other 

 material, but below the surface there was little 

 else than stones of small size, none weighing more 

 than three or four pounds. Very much larger 

 ones are frequently used ; in fact, I have been 

 told by trappers of some that weighed about thirty 

 or forty pounds and even more, and Mills speaks 

 of stones weighing upwards of one hundred and 

 twenty pounds being moved into position on the 



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