74 ROMANCE OF THE BEAVER 
in the form of rising ground they are not daunted. 
If the canal is needed it must be made, and the 
work is carried on with the fullest appreciation of 
the water problem, so far as it concerns them. The 
little dams which separate the different levels are 
simple affairs, mostly made of the material excavated. 
Their length depends on the conditions. In flat 
land none are built, for they are not needed. 
Where the rise is very slight they are only the 
width of the canal, increasing according to condi- 
tions, so that in some places they are six or seven 
times the width of the ditch. This presumably is 
to prevent a sudden rush of water which might 
cause injury to the entire system. The dams, 
though quite simple, are strong enough to be used 
as passage-ways ; the animals, swimming down the 
canal, drag their burdens over the dams, which on 
the upper side are but a few inches above the level 
of the water. 
The width of these canals is usually about three 
feet, with a depth of from one to three feet, seldom 
deeper except when small pools are made evidently 
with the idea. of providing a hiding place in the 
event of danger. Burrows are also made in the 
banks probably for the same purpose. Apparently 
every contingency is considered, and little or 
nothing left to chance. The direction of the canals 
must necessarily be variable. Wherever conditions 
are favourable they are as straight as though laid 
out by human engineers, but when there is any 
