Fig. 233.—Portion of the skeleton of Vespertilio Parisienis. Eocene Tertiary, France. of the Gnawing Mammals (Rodentia), the Insect-eating Mammals (Insectivora), and the Monkeys (Quadrumana).[24]
[Footnote 24: A short list of the more important works relating to the Eocene rocks and fossils will be given after all the Tertiary deposits have been treated of.]
CHAPTER XIX.
THE MIOCENE PERIOD.
The Miocene rocks comprise those Tertiary deposits which contain less than about 35 per cent of existing species of shells (Mollusca), and more than 5 per cent—or those deposits in which the proportion of living shells is less than of extinct species. They are divisible into a Lower Miocene (Oligocene) and an Upper Miocene series.
In Britain, the Miocene rocks are very poorly developed, one of their leading developments being at Bovey Tracy in Devonshire, where there occur sands, clays, and beds of lignite or imperfect coal. These strata contain numerous plants, amongst which are Vines, Figs, the Cinnamon-tree, Palms, and many Conifers, especially those belonging to the genus Sequoia (the "Red-Foods"). These Bovey Tracy lignites are of Lower Miocene age, and they are lacustrine in origin. Also of Lower Miocene age are the so-called "Hempstead Beds" of Yarmouth in the Isle of Wight. These attain a thickness of less than 200 feet, and are shown by their numerous fossils to be principally a true marine formation. Lastly, the Duke of Argyll, in 1851, showed that there existed at Ardtun, in the island of Mull, certain Tertiary strata containing numerous remains of plants; and these also are now regarded as belonging to the Lower Miocene.
In France, the Lower Miocene is represented in Auvergne, Cantal, and Velay, by a great thickness of nearly horizontal strata of sands, sandstone, clays, marls, and limestones, the whole of fresh-water origin. The principal fossils of these lacustrine deposits are Mammalia, of which the remains occur in great abundance. In the valley of the Loire occur the typical European deposits of Upper Miocene age. These are known as the "Faluns," from a provincial term applied to shelly sands, employed to spread upon soils which are deficient in lime; and the Upper Miocene is hence sometimes spoken of as the "Falunian" formation. The Faluns occur in scattered patches, which are rarely more than 50 feet in thickness, and consist of sands and marls. The fossils are chiefly marine; but there occur also land and fresh-water shells, together with the remains of numerous Mammals. About 25 per cent of the shells of the Faluns are identical with existing species. The sands, limestones, and marls of the Department of Gers, near the base of the Pyrenees, rendered famous by the number or Mammalian remains exhumed from them by M. Lartet, also belong to the age of the Faluns.
In Switzerland, between the Alps and the Jura, there occurs a great series of Miocene deposits, known collectively as the "Molasse," from the soft nature of a greenish sandstone, which constitutes one of its chief members. It attains a thickness of many thousands of feet, and rises into lofty mountains, some of which—as the Rigi—are more than 6000 feet in height. The middle portion of the Molasse is of marine origin, and is shown by its fossils to be of the age of the Faluns; but the lower and upper portions of the formation are mainly or entirely of fresh-water origin. The Lower Molasse (of Lower Miocene age) has yielded about 500 species of plants, mostly of tropical or sub-tropical forms. The Upper Molasse has yielded about the same number of plants, with about 900 species of Insects, such as wood-eating Beetles Water-beetles, White Ants, Dragon-flies, &c.
In Belgium, strata of both Lower and Upper Miocene age are known,—the former (Rupelian Clays) containing numerous marine fossils; whilst the latter (Bolderberg Sands) have yielded numerous shells corresponding with those of the Faluns.