THE DAM 29 
in by the stream, which naturally lessens the depth of the 
water, and hence the dam must be raised in order to retain 
the water at the desired depth. Raising the height of the 
dam almost invariably means lengthening it, and thus a dam, 
which was originally straight, comes to have a curve up or 
down stream, or, if it be a long one, may have several 
angles in it. 
In constructing the dam the beaver brings up such mate- 
rials as mud and stones from the bottom by carrying them 
held against its chin by its fore feet, which are pretty efh- 
cient handsin such work. MiZills speaks of seeing his young 
pet beaver carry mud and sticks clasped between the tail 
and belly. ‘The branches used are conveyed by holding them 
in the mouth and letting them trail alongside on the ground 
or in the water until the dam is reached, where the paws may 
be used to place them properly. In building dams beavers 
will often take advantage of any natural elevations which 
may be of use to them. At one place in Colorado, where a 
low dam was extended across a wide flat or meadow, and 
where numerous clumps of willows stood a little higher than 
the surrounding surface, the animals built their dam from 
one of these clumps to another, saving themselves consider- 
able labor, though I must confess I thought their work was 
wasted, for only a very shallow pond was created, of which I 
was unable to see the use. It was one of those cases where 
it seemed as if the beaver had made a mistake and failed to 
accomplish anything. 
I have little doubt that at the beginning of the construc- 
tion of a dam most of the brush used is laid longitudinally 
with the current, not transversely. Some dams may pos- 
sibly have all the material laid in this manner. In many 
cases, however, where dams have been cut through by man 
or a stream, the ends at the banks remaining, one sees the 
ends of sticks projecting from the break as if they had been 
