The course of the Bronx immediately below the mill is said to have been formerly changed by a large beaver dam, which those industrious animals had erected near die foot of Mr. Underbill's garden. Beaver Pond lies directly north of the mill. Beavers were once very common on the Bronx and neighboring streams, and afford an excellent example of animals not only sociable by dwelling near each other, but by joining in a work which was for the benefit of the community. Water was as needful for the Beaver as for the miller; and it is a very curious fact that long before miller's ever invented dams, or before men ever learned to grind corn, the beaver knew how to make a dam and to insure itself a constant supply of water. The dam was by no means placed at random in the stream, just where a few logs may have happened to lodge -- but it was set exactly where it was wanted, and it was made so as to suit the force of the current ; in those places where the stream runs slowly the dam was carried straight across the river, but in those where the water had much power the barrier was made in a convex shape so as to resist the force of the rushing water. The power of the stream could, therefore, always be inferred from the shape of the dam which the beavers had built across it. Some of these structures were of great size, measuring two or three hundred yards in length and ten or twelve feet in thickness, and their form exactly corresponded with the force of the stream. They made their houses close to the water and communicated with them by means of subterranean passages, one entrance of which passed into the house, or lodge -- as it was technically named -- and the other into the water, so far below the surface that it could not be closed by ice.