Beaver dams are solid structures always, built up of logs, brush, stones, and driftwood, well knit together by alder poles.  One summer, in canoeing a wild, unknown stream, I met fourteen dams within a space of five miles.  Through two of these my Indian and I broke a passage with our axes; the others were so solid that it was easier to unload our canoe and make a portage than to break through.  Dams are found close together like that when a beaver colony has occupied a stream for years unmolested.  The food-wood above the first dam being cut off, they move down stream; for the beaver always cuts on the banks above his dam, and lets the current work for him in transportation.  Sometimes, when the banks are such that a pond cannot be made, three or four dams will be built close together, the back-water of one reaching up to the one above, like a series of locks on a canal.  This is to keep the colony together, and yet give room for play and storage.

There is the greatest difference of opinion as to the intelligence displayed by the beavers in choosing a site for their dam, one observer claiming skill, ingenuity, even reason for the beavers; another claiming a mere instinctive haphazard piling together of materials anywhere in the stream.  I have seen perhaps a hundred different dams in the wilderness, nearly all of which were well placed.  Occasionally I have found one that looked like a stupid piece of work—­two or three hundred feet of alder brush and gravel across the widest part of a stream, when, by building just above or below, a dam one-fourth the length might have given them better water.  This must be said, however, for the builders, that perhaps they found a better soil for digging their tunnels, or a more convenient spot for their houses near their own dam; or that they knew what they wanted better than their critic did.  I think undoubtedly the young beavers often make mistakes, but I think also, from studying a good many dams, that they profit by disaster, and build better; and that on the whole their mistakes are not proportionally greater than those of human builders.

Sometimes a dam proves a very white elephant on their hands.  The site is not well chosen, or the stream difficult, and the restrained water pours round the ends of their dam, cutting them away.  They build the dam longer at once; but again the water pours round on its work of destruction.  So they keep on building, an interminable structure, till the frosts come, and they must cut their wood and tumble their houses together in a desperate hurry to be ready when the ice closes over them.

But on alder streams, where the current is sluggish and the soil soft, one sometimes finds a wonderfully ingenious device for remedying the above difficulty.  When the dam is built, and the water deep enough for safety, the beavers dig a canal around one end of the dam to carry off the surplus water.  I know of nothing in all the woods and fields that brings one closer in thought and sympathy to the little wild folk than to come across one of these canals, the water pouring safely through it past the beaver’s handiwork, the dam stretching straight and solid across the stream, and the domed houses rising beyond.