The upper branches are
then trimmed close to the trunk, and are woven with alders among the
long stubs sticking down from the trunk into the river bed. Stones,
mud, and brush are used liberally to fill the chinks, and in a
remarkably short time the dam is complete.
When you meet such a dam on the stream you are canoeing don't attempt
to break through. You will find it shorter by several hours to unload
and make a carry.
All the beaver's cutting is done by chisel-edged front teeth. There
are two of these in each jaw, extending a good inch and a half outside
the gums, and meeting at a sharp bevel. The inner sides of the teeth
are softer and wear away faster than the outer, so that the bevel
remains the same; and the action of the upper and lower teeth over
each other keeps them always sharp. They grow so rapidly that a beaver
must be constantly wood cutting to keep them worn down to comfortable
size.
Often on wild streams you find a stick floating down to meet you
showing a fresh cut. You grab it, of course, and say: "Somebody is
camped above here. That stick has just been cut with a sharp knife."
But look closer; see that faint ridge the whole length of the cut, as
if the knife had a tiny gap in its edge. That is where the beaver's
two upper teeth meet, and the edge is not quite perfect.
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