32. ZOOLOGY. 
ever having seen one built) and cut canals. In the construction 
of their dams, a great deal of mechanical ingenuity is displayed, 
and from which some useful lessons in engineering might be taken. 
No two dams are precisely alike; they vary in form, length, and 
material, according to the situation, size of stream, or number of 
beavers to be accommodated. Very frequently, logs are morticed, 
or dovetailed, together, in order to secure them more firmly in 
their places; and while some are thus engaged on the dam, others 
are employed in cutting canals through higher portions of ground 
that will not be inundated when their dam is finished. These en- 
able them to float logs (after the trees are cut down) from the ad- 
jacent points of timber, to various parts of their pond, for the 
purpose of furnishing themselves with food, and material to build 
their lodges with. Now, it may be asked, without forethought, 
consideration, and conclusion, how would the beaver know that 
this canal, when finished, would be of any practical use or bene- 
fit to him. Some of these canals, lately measured by a Mr. Mor- 
gan, of Lake Superior, were found to be upwards of seventy yards 
in length, and were always filled with water, when the dam was 
completed. It shows plainly, that the beaver, in selecting a place 
for a new colony, takes into consideration the whole surroundings, 
calculates the quantity of food, and material, that can be brought 
into requisition, and after coming to a conclusion, proceeds to 
utilize it to their own wants and requirements. While in Superior, 
I received some fine specimens of beaver, one of the largest of 
which weighed forty-six pounds, although, I believe, they attain a 
much greater size. The beaver of Canada— Castor Canadensis— 
and the beaver of Hudson Bay— Castor Fiber—are identical. 
They are capable ‘of cutting down trees two or three feet in diam- 
eter, the bark of which forms their winter food. They prefer Balm 
of Gilead, White Poplar, and Birch, but will eat many other kinds. 
They have a very powerful pair of incisors in each jaw, but the 
cutting is done with the teeth in the under jaw, turning their head 
sideways, at ight angles with the tree, for that purpose ; and after 
working for an hour, are generally relieved by another beaver. 
Often, two or more beavers work at the same tree. A beaver will 
cut down a tree, one foot through, in two hours and a half, and 
seldom more than one a day. 
