248 
STRANGE DWELLINGS 
ing them with stones and earth until they can resist the force of 
the water. Vast numbers of logs are thus laid, and as fast as 
the water rises, fresh materials are added, being obtained mostly 
from the trunks and branches of trees which have been stripped 
of their bark by the Beavers. 
The reader will remember that many persons have thought 
that the dam of the Beaver is only an accidental agglomeration 
of loose logs and branches, without any engineering skill on 
the part of the animals. There is some truth in this statement, 
though the assertion is too sweeping. For, after the Beavers 
have completed their dam, it obstructs the course of the stream 
so completely that it intercepts all large floating objects, and 
every log or branch that may happen to be thrown into the river 
is arrested by the dam, and aids in increasing its dimensions. 
Mud and earth are also continually added by the Beavers, 
so that in process of time the dam becomes as firm as the land 
through which the river passes, and is covered with fertile 
alluvium. Seeds soon make their way to the congenial soil, 
and in a dam of long standing, forest trees have been known 
to grow, their roots adding to the general stability by binding 
together the materials. It is well known that the fertile islands 
formed on coral reefs are stocked in a similar manner. Origi- 
nally, the dam is seldom more than a yard in width where it 
overtops the water, but these unintentional additions cause a . 
continual increase. 
The bark with which the logs were originally covered, is not 
all eaten by the animals, but stripped away, and the greater 
part hidden underwater, to serve for food in the winter time. 
A further winter provision is also made by taking the smaller 
branches, diving with them to the foundations of the dam, and 
carefully fastening them among the logs. When the Beavers 
are hungry, they dive to their hidden stores, pull out a few 
branches, carry them on land, nibble away the bark, and drop 
tne stripped logs on the water, where they are soon absorbed 
by the dam. 
We have now seen how the Beavers keep the water to the 
required level, and we must next see how they make use of it. 
