44 ROMANCE OF THE BEAVER 
» chosen proves entirely satisfactory it will continue 
_ to grow as the years go on, each year seeing the 
extending of the dam, and, if necessary, the number 
of subsidiary dams increased. The trees whose 
base has been flooded by the rising water gradually 
die, and the gaunt grey columns bear witness to the 
effect that beavers’ work has on the land. So long 
as the supply of suitable food trees is to be found 
the colony remains, unless killed off or driven oft 
by the trappers, and so it is that such immense 
dams are found, some over two thousand feet in 
length with a height of from two to about fourteen 
feet, the result of countless generations of indus- 
'.. trious beavers, not necessarily working continuously, 
for they often abandon a pond for many: years, 
apparently to give time for the food trees to grow. 
On their return, or if a new colony takes possession, 
they have a busy time repairing the dam and 
getting everything in proper order. 
The solidity of the structures is perhaps best 
proved by the fact that some have been found in 
Montana which were in a partially petrified state. 
As a rule, however, the life of a dam is but 
a few years beyond the period during which it is 
used ; owing to the nature of the material employed; 
constant supervision and repair are absolutely neces- 
sary. The beaver realise this and seldom allow 
a night to pass, during the autumn, without 
making a tour of inspection and building up 
and strengthening any part that shows signs of 
