14 ROMANCE OF THE BEAVER 
danger, they trouble themselves but little. But 
the beaver has definite ideas of what is necessary 
for his welfare. He plans months ahead. He 
undertakes stupendous tasks—tasks which demand 
skill of no mean order. Indeed, some of the most 
important work done by them may seem at first 
glance to be superfluous. Why, for instance, does 
he build dams when water is abundant nearly 
everywhere within his natural range? Let us, 
therefore, examine the work and see how it serves 
a very definite purpose, and having done that we 
will follow the beaver throughout a few years of 
their lives and see how they live and how thoroughly 
their various undertakings work out in the best 
possible way. . 
The most conspicuous work, so far as visible 
results are concerned, is the dam ; and the purpose 
it serves is not so much to make a swimming pool, 
as some people imagine, as to keep a body of water 
at a more or less constant level in order to ensure 
certain ends: (1) to conceal the entrances to the 
houses and so prevent the entrance of any land 
enemies, (2) to be a place for the safe storage of 
wood for food during the winter, (3) to render the 
transporting of this wood as simple as possible, and 
(4) to be a place of retreat in case of attack. To 
better appreciate the value of the dam it is necessary 
to understand the structure of the houses, for there 
are several types. The most primitive is simply a 
hole in a bank, with no surface work. This repre- 
