The authors add the curious observation that the beavers of the present day seem to be a degenerate race, as they neither fell huge trees not construct great dams, while their progenitors cut down trees two feet in diameter and dammed up rivers a hundred feet in width. The change in the habits of the beaver is probably due to the diminution of their numbers since the introduction of fire-arms, and to the tact that their hydraulic operations are more frequently interrupted by the encroachments of man. In the valley of the Yellowstone, which has but lately been much visited by the white man, Hayden saw stumps of trees thirty inches in diameter which had been cut down by beavers. --Geological Survey of Wyoming, p. 135. The American beaver closely resembles his European congener, and I believe most naturalists now regard them as identical. A difference of speceies has been inferred from a difference in their modes of life, the European animal being solitary and not a builder, the American gregarious and constructive. But late careful researches in Germany have shown the former existence of numerous beaver dams in that country, though the animal, having becaome rare to form colonies, has of course ceased to attempt works which require the co-operation of numerous individuals.--Schleiden, Fur Baum und Wald Leipzig, 1870, p. 68. On the question of identity and on all others relating to this interesting animal, see L.H. Morgan's important monograph, The American Beaver and his Works, Philadelphia, 1868. Among the many new facts observed by this investigator is the construction of canals by the beaver to float trunks and branches of trees to his ponds. These canals are sometimes 600 to 700 feet long, with a width of two or three feet and a depth of one to one and a half.] INFLUENCE OF ANIMAL LIFE ON VEGETATION