Ingenious as is the animal in the construction of its dam, it is not nearly so accomplished an architect as was once supposed. We were told in the earlier books of Natural History that the Beaver felled trees, cut off their branches into convenient lengths, and sharpened one end, like an ordinary stake. Then they were said to drive the sharp end of the stakes into the bed of the river, to set them side by side, to interweave smaller branches among them, and lastly, to fill up the interstices with mud, leaves, and similar materials. In fact, they were supposed to build a “wattle-and-daub” wall, like that which is in use at the present day in Southern Africa. [Illustration: DAM MADE BY BEAVER. DAM MADE BY MAN.] The Beaver does nothing of the kind. It needs a dam, and it makes one which is far stronger than the wattle-and-daub could be. It begins by felling a tree, and letting it lie across the stream, in some place where the banks are high and tolerably steep. A bend of the river is usually chosen for the new dam. Should not the tree be long enough for the Beaver’s purpose, two trees are felled, one on either side, so that their branches meet in the middle. These branches, and not any supposed stakes, are really the upright supports of the dam. The trees being thus laid, the Beaver cuts down branches from four to six feet in length, and lays them horizontally among the boughs of the fallen trees. Having thus made the foundations, so to speak, of its dam, the Beaver then proceeds to fill in the spaces with roots, grass-tufts, leaves, mud, and, indeed, almost anything on which it can lay its paws. After this, the Beaver has to take but little trouble, for the stream itself becomes a silent, slow, but constant labourer, lodging floating debris against the dam, and making a sloping bank which much adds to its strength. By degrees, seeds that lodge on the dam spring into life, and their roots act like chains, binding the materials more closely together. Willow twigs too, if they lodge on the dam and be left undisturbed, are sure to “strike,” as the gardeners say, and further to bind the structure together. It is evident, from this short description, that the lower part of the dam is more solid than the upper. In fact, the floods are tolerably sure to wash away some eight or ten inches of the upper part every year, and the Beavers have to make it afresh. The height of these dams is not nearly so great as is generally supposed. Mr. Green, a practical trapper, states that the highest which he ever saw was only four feet six inches in height, and that the average is under three feet.