Mr. Prestwich has obtained it in low-level deposits of river gravels in the valleys of the north of France and south of England, and it has been obtained from the Löss, a loamy, usually unstratified deposit, which is extensively distributed over central Europe, in the valleys of the Rhine, Rhone, Danube, and other great rivers. This deposit is considered by Mr. Prestwich to be equivalent to other high-level gravels of the Pleistocene period. THE MASTODON.--The generic title Mastodon has been applied to a number of species allied to the elephants, but distinguished from them by a peculiar structure of the molar teeth; these are rectangular, and in their upper surfaces exhibit a number of great conical tuberosities with rounded points disposed in pairs, to the number of four or five, according to the species; whereas in the elephants they are broad and uniform, and regularly marked with furrows of large curvature. The mastodons, in addition to large tusks in the premaxillæ, like those of the elephant, had also in most instances, a pair of shorter ones in the mandible. [Illustration: FIG. 11.--MASTODON'S TOOTH (WORN). (_After Figuier._)] Cuvier established the name Mastodon,[51] or teat-like toothed animals, for the gigantic species from America which Buffon had already described under the name of the animal or elephant of the Ohio. [Illustration: FIG. 12.--MASTODON'S TOOTH. (_After Figuier._)] The form first appears in the Upper Miocene of Europe, five species being known, two of them from Pikermi, near Athens, and one, _M. angustidens_, from the Miocene beds of Malta. Mastodon remains have also been found in the beds of the Sivalik hills, and four species of mastodon in all are known to have ranged over India during those periods. In Pliocene deposits we have abundant remains of _M. arvernensis_, and _M. longirostris_ from the Val d'Arno in Italy, and the _M. Borsoni_ from central France. The _M. arvernensis_ may be considered as a characteristic Pliocene species in Italy, France, and Europe generally. In Britain it occurs in the Norwich Crag and the Red Crag of Suffolk. Species of mastodon occur in the Pliocene of La Plata, and of the temperate regions of South America; on the Pampas, and in the Andes of Chili. The _Mastodon mirificus_ of Leidy is the earliest known species in America; this occurs in Pliocene deposits on the Niobrara and the Loup fork, west of the Mississippi. The remains of the _Mastodon americanus_ of Cuvier occur abundantly in the Post Pliocene deposits throughout the United States, but more especially in the northern half; they are also found in Canada and Nova Scotia. [Illustration: FIG. 13.--THE MASTODON.]