The beaver is of interest to the geographer not only on account of its wide distribution, which embraced the entire continent wherever the willow, birch, alder, etc., on which it subsisted, could grow, from northern Mexico to the Arctic Ocean, but for the reason that it made more conspicuous and lasting changes in the minor features of the surface of the land than any other mammal. One of its peculiar habits is that it gnaws down trees frequently 6 or 8 inches in diameter, and after cutting them into sticks a few feet in length, uses them in making dams across small streams. These dams were built in thousands and tens of thousands all through the forested regions, and being plastered with mud, and still further enlarged and strengthened by the accumulation of driftwood and leaves, held the waters of the streams in check and caused them to expand so as to form small lakes, ponds, and swamps. These beaver-dam lakes are common even at the present day, and many of them which have been filled with sediment or drained furnish rich lands, now utilized for gardens and cultivated fields. In Michigan these beaver-dam lakes furnish the rich black soil so favourable for the raising of celery and other vegetables. The beaver has disappeared from all but the wilder and more inaccessible portions of the continent, but the influence of the changes it made in the drainage of the land will endure for many generations to come.
Of the fur-bearing animals mentioned above, none are more definitely American than the skunks, or, to use a more felicitous name, _Mephitis_, which ranges from central Canada to central Mexico, and is represented by four or five species. As stated by Elliott Coues in his instructive monograph on the North America _Mustelidæ_, the skunks are closely related to the badgers, being heavy-bodied, short-legged, stout in build, with hairy tails and generally loose pelage. They neither climb trees nor swim in water; their gait is slow, and they do not allow themselves to be hurried, even in the face of danger; their retreats are burrows in the ground or dens in rocks and hollow logs, and sometimes in the nooks and corners of dwellings and outhouses. Their most common representative, _Mephitis mephitica_, is a beautiful animal some 15 or 20 inches in length, exclusive of its bushy tail, which is usually 12 to 15 inches long. The head is small, the ears low and short, and the hair of a glossy black, relieved by conspicuous white markings which are not only irregular in shape, but vary with individuals. The most marked characteristic of the skunks is their ability to emit at will a fluid which has the most disagreeable and sickening odour known. This fluid is secreted in two glands, each about one inch in diameter, situated at the base of the tail and opening into the rectum, but has no connection with the secretions of the kidneys, and is probably seldom discharged except when the animal is annoyed. It is a unique and most efficient means of defence. In this connection it is to be remembered, however, that the skunks belong to the family _Mustelidæ_, which is characterized in part by the odoriferous secretions present in its various species, but, above all others, the odours emitted by the genera under consideration are the most dreadful. The stench produced by these animals when startled or enraged is not only horrible beyond description, but endures for months and even a year or more. The yellow liquid which is ejected is squirted in a fine spray for a distance of some 6 or 8 feet, but its odour may sometimes be perceived, even when the wind is still, for a distance of a quarter of a mile.