Once I found where the beavers had utilized man’s work.  A huge log dam had been built on a wilderness stream to secure a head of water for driving logs from the lumber woods.  When the pines and fourteen-inch spruce were all gone, the works were abandoned, and the dam left—­with the gates open, of course.  A pair of young beavers, prospecting for a winter home, found the place and were suited exactly.  They rolled a sunken log across the gates for a foundation, filled them up with alder bushes and stones, and the work was done.  When I found the place they had a pond a mile wide to play in.  Their house was in a beautiful spot, under a big hemlock; and their doorway slanted off into twenty feet of water.  That site was certainly well chosen.

Another dam that I found one winter when caribou-hunting was wonderfully well placed.  No engineer could have chosen better.  It was made by the same colony the lynx was after, and just below where he went through his pantomime for my benefit; his tracks were there too.  The barrens of which I spoke are treeless plains in the northern forest, the beds of ancient shallow lakes.  The beavers found one with a stream running through it; followed the stream down to the foot of the barren, where two wooded points came out from either side and almost met.  Here was formerly the outlet; and here the beavers built their dam, and so made the old lake over again.  It must be a wonderfully fine place in summer—­two or three thousand acres of playground, full of cranberries and luscious roots.  In winter it is too shallow to be of much use, save for a few acres about the beavers’ doorways.

There are three ways of dam-building in general use among the beavers.  The first is for use on sluggish, alder-fringed streams, where they can build up from the bottom.  Two or three sunken logs form the foundation, which is from three to five feet broad.  Sticks, driftwood, and stout poles, which the beavers cut on the banks, are piled on this and weighted with stones and mud.  The stones are rolled in from the bank or moved considerable distances under water.  The mud is carried in the beaver’s paws, which he holds up against his chin so as to carry a big handful without spilling.  Beavers love such streams, with their alder shade and sweet grasses and fringe of wild meadow, better than all other places.  And, by the way, most of the natural meadows and half the ponds of New England were made by beavers.  If you go to the foot of any little meadow in the woods and dig at the lower end, where the stream goes out, you will find, sometimes ten feet under the surface, the remains of the first dam that formed the meadow when the water flowed back and killed the trees.

The second kind of dam is for swift streams.  Stout, ten-foot brush is the chief material.  The brush is floated down to the spot selected; the tops are weighted down with stones, and the butts left free, pointing down stream.  Such dams must be built out from the sides, of course.  They are generally arched, the convex side being up stream so as to make a stronger structure.  When the arch closes in the middle, the lower side of the dam is banked heavily with earth and stones.  That is shrewd policy on the beaver’s part; for once the arch is closed by brush, the current can no longer sweep away the earth and stones used for the embankment.