Among the remains of fish in these post-eocene strata of the United States are several large teeth of the shark family, not distinguishable specifically from fossils of the faluns of Touraine. [1] Proceedings of the Geol. Soc., vol. iv, pt. iii, 1845, p. 547. CHAPTER XV. LOWER MIOCENE (OLIGOCENE OF BEYRICH). Lower Miocene Strata of France. — Line between Miocene and Eocene. — Lacustrine Strata of Auvergne. — Fossil mammalia of the Limagne d’Auvergne. — Lower Molasse of Switzerland. — Dense Conglomerates and Proofs of Subsidence. — Flora of the Lower Molasse. — American Character of the Flora. — Theory of a Miocene Atlantis. — Lower Miocene of Belgium. — Rupelian Clay of Hermsdorf near Berlin. — Mayence Basin. — Lower Miocene of Croatia. — Oligocene Strata of Beyrich. — Lower Miocene of Italy. — Lower Miocene of England. — Hempstead Beds. — Bovey Tracey Lignites in Devonshire. — Isle of Mull Leaf-Beds. — Arctic Miocene Flora. — Disco Island. — Lower Miocene of United States. — Fossils of Nebraska. Line between Miocene and Eocene Formations.—The marine faluns of the valley of the Loire have been already described as resting in some places on a fresh-water tertiary limestone, fragments of which have been broken off and rolled on the shores and in the bed of the Miocene sea. Such pebbles are frequent at Pontlevoy on the Cher, with hollows drilled in them in which the perforating marine shells of the Falunian period still remain. Such a mode of superposition implies an interval of time between the origin of the fresh-water limestone and its submergence beneath the waters of the Upper Miocene sea. The limestone in question forms a part of the formation called the Calcaire de la Beauce, which constitutes a large table-land between the basins of the Loire and the Seine. It is associated with marls and other deposits, such as may have been formed in marshes and shallow lakes in the newest part of a great delta. Beds of flint, continuous or in nodules, accumulated in these lakes, and aquatic plants called Charae, left their stems and seed-vessels imbedded both in the marl and flint, together with fresh-water and land shells. Some of the siliceous rocks of this formation are used extensively for mill-stones. The flat summits or platforms of the hills round Paris, and large areas in the forest of Fontainebleau, as well as the Plateau de la Beauce, already alluded to, are chiefly composed of these fresh-water strata. Next to these in the descending order are marine sands and sandstone, commonly called the Gres de Fontainebleau, from which a considerable number of shells, very distinct from those of the faluns, have been obtained at Etampes, south of Paris, and at Montmartre and other hills in Paris itself, or in its suburbs. At the bottom of these sands a green clay occurs, containing a small oyster, _Ostrea cyathula,_ Lam., which, although of slight thickness, is spread over a wide area. This clay