this, but diminishing upwards by the slope of the sides until the top is only from three to five feet wide. These dams convert even small rivulets into large pools of water, often many acres in extent; and in districts where Beavers abound these pools may occupy neatly the whole course of a stream, one above the other, almost to its source. Their use to the Beavers, as constantly furnishing them with a sufficiency of water in which to carry on their business, and especially to float to their lodges the tree trunks necessary for their subsistence, is easily understood; but it is a more remarkable circumstance that by this means the Beavers exercise a considerable influence upon the external appearance of the locality inhabited by them, which may persist even long after they have themselves disappeared. In and about the pools the constant attacks of the Beavers upon the trees produce clearings in the forest, often many acres in extent; at the margins of the pools the formation of peat commences, and under favourable circumstances proceeds until the greater part of the cleared space becomes converted into a peat-moss. These peaty clearings are known as Beaver-meadows, and they have been detected in various countries where the Beaver is now extinct. As in the case of the majority of Rodents, the chief activity of the Beaver is nocturnal; and it is only when driven from its lodge by a high flood, or in the wildest and most sequestered localities, that it goes about during the day. It swims quickly, but entirely by the agency of the hind feet, the fore feet being used chiefly for carrying and building operations, and for conveying the food to the mouth. Before diving, it is said to slap the surface of the water with its tail, producing a sound that may be heard at a considerable distance. On land it sometimes travels a good way in the warm season, and is then stated to indulge in a change of diet, feeding upon roots and fruits, and sometimes upon corn. The roots of the water-lily (_Nuphar_) are also said to constitute part of its food. The Beaver is hunted--but less now than in former years--for the sake of its skin, the soft under fur of which was much used in the manufacture of hats. It is asserted that the flesh is very good, but according to some authorities, only certain parts of it are palatable; and Audubon declares that the tail, which is regarded as a peculiarly choice morsel, closely resembles marrow, and is so rich that only those whose stomachs are incapable of being upset by greasy food can eat more than a very little of it.