374 
ANIMAL INTELLIGENCE. 
in itself considered, a remarkable fact that he should have 
voluntarily transferred himself, by means of dams and ponds 
of his own construction, from a natural to an artificial mode 
of life. 
In external appearance there are two distinct kinds of 
dams, although all are constructed on the same principle. 
One, the more common, is the 4 stick dam, 5 which is com- 
posed of interlaced stick and pole work upon the low T er 
face, with an embankment of earth mixed with the same 
materials on the upper face. The other is the 4 solid-bank 
dam, 5 which differs from the former in having much more 
brush and mud worked into its construction, especially 
upon its surfaces ; the result being that the whole formation 
looks like a solid bank of earth. In the first kind of dam 
the surplus water percolates through the structure along 
its entire length ; but in the second kind the discharge 
takes place through a single furrow in the crest, which, 
remarkable though the fact unquestionably is, the beavers 
intentionally form for this purpose. 
In the construction of the dam, stones are used here 
and there to give down-weight and solidity. These stones 
weigh from one to six pounds, and are carried by the 
beavers in the same way as they carry their mud — namely, 
by walking on their hind legs while holding their burden 
against the chest with their fore-paws. The solid dams 
are much firmer in their consistence than the stick dams ; 
for while a horse might walk across the former, the weight 
of a man would be too great to be sustained by the latter. 
Each kind of dam is adapted to the locality in which it is 
built, the difference between the two kinds being due to 
the following cause. As a stream gains water and force in 
its descent, it develops banks, and also a broader and 
deeper channel. These banks assume a vertical form in 
the level areas where the soil is alluvial, thus, an open 
stick-wwk dam could not in such places be led off 
from either bank ; and even if it could, the force and depth 
of the stream would carry it away. Therefore in such 
places the beavers build their solid-bank dams, while in 
shallow and comparatively sluggish waters they content 
