98 
NATURE S CRAFTSMEN 
king. So the beaver, like the wise little engineer 
that he is, builds a dam to keep back the water 
and thus raise it to the required depth. These 
dams, as the paper has just stated, are often 
massive affairs, and in their construction the lit¬ 
tle animals often show great engineering ability. 
“ The beavers live in colonies, you know; so 
that what looks like a gigantic undertaking for 
so small an animal is not such a terrible problem 
when two hundred or more go at it. Indeed, a 
dam ten feet thick and three hundred feet in 
length is often constructed in what seems an in¬ 
credibly short time. The first job, of course, is 
to fell the trees necessary for the log part. Six or 
eight of the workmen chiseling with might and 
main on a tree is an interesting sight! So sharp 
are their teeth and so strong their jaws that even 
large trees cannot long stand against their tireless 
onslaught. Moreover, they know enough to fell 
their tree so that it falls into the water where 
they can handle it, and they always cut it far 
enough up-stream to give them plenty of oppor¬ 
tunity to swing it into the position they want it. 
An instance is on record of a poplar tree, nine 
feet in circumference, that was felled by the bea¬ 
vers on the upper Missouri. Doubtless among 
the beaver colonies of the Northwest, where great 
trees are the rule, this feat is often exceeded. 
“After enough trees have been interlocked 
