When the animal has fixed upon a tree which he believes suitable for his purpose, he sits upright, and with his chisel-like teeth cuts a bold groove completely round the trunk. He then widens the groove in exact proportion to its depth, so that when the tree is nearly cut through, it somewhat resembles the "contracted portion of an hour-glass." When this stage has been reached, he looks anxiously at the tree, and views it on every side, as if to measure the direction in which it should fall. Having settled this question, he goes to the opposite side, and with two or three powerful bites cuts away the wood, so that the overbalanced tree comes to the ground. The beaver next proceeds to cut it up into lengths of about a yard or so, employing a similar method of severing the wood. The next part of the task is to make these rounded and pointed logs into a dam. For this purpose the logs are laid horizontally, and covered with stones and earth until they can resist the force of the water. Vast numbers are thus laid; and as fast as the water rises, fresh materials are added, being obtained mostly from the trunks and branches of trees which have been stripped of their bark by the beavers. In those places where the stream runs slowly the dam is carried straight across the river; but where the current is strong, a convex shape is given to it, so as to resist the force of the rushing water. The dam is frequently of great size, measuring two or three hundred yards in length, and ten or twelve feet in thickness. In many localities the streams have been diverted by these erections into entirely different channels. It is in this manner that the beavers keep the water to the required level; we must next see how they make use of it. They build their houses close to the water, and communicating with it by means of subterranean passages, one entrance of which passes into the house, or "lodge," as it is technically named, and the other into the water, so far below the surface that it cannot be closed by ice. It is, therefore, always possible for the beaver to gain access to the provision stores, and to return to its house, without being perceived from the land. "The lodges," says Mr. Wood, "are nearly circular in form, and much resemble the well-known snow-houses of the Esquimaux, being domed, and about half as high as they are wide--the average height being three feet, and the diameter six or seven feet. These are the interior dominions, the exterior measurement being much greater, on account of the great thickness of the walls, which are continually strengthened with mud and branches, so that during the severe frosts they are nearly as hard as solid stone. Each lodge will accommodate several inhabitants, whose beds are arranged round the walls."