The fur of the beaver, like that of other animals, may be divided into two parts: the guard hair, up to two inches in length, and the underhair or fur, at most an inch. According to Lahontan, "a beaver has two lays of hair; one is long and of a shining black color, with a grain as big as that of Man's Hair; the other is fine and smooth, and in Winter fifteen lines long. In a word, the last is the finest Down in the world." Examined through a microscope the fur has numerous small barbs. It was these barbs which made it unusually suitable for the manufacture of felt and of felt hats. (The Fur Trade in Canada, Harold A. Innis, paperback edition, p. 4)

The significance of the habit of the beaver in the development of the fur trade may be suggested. Since the beaver was an amphibious animal, its fur was thick and abundant and it could be hunted in summer, although the fur was then much less valuable. The length of time required to arrive at maturity was an important factor in the destruction of the supply of fur and its non-migratory tendencies and elaborate housing facilities made destruction certain. In the language of economists, the heavy fixed capital of the beaver became a serious handicap with the improved technique of Indian hunting methods, incidental to the borrowing of iron from the Europeans. Depreciation through obsolescence of the beaver's defense equipment was so rapid as to involve the immediate and complete destruction of the animal. (The Fur Trade in Canada, Harold A. Innis, pp. 3-4)