230 
ELEMENTS OF GEOLOGY* 
CHAPTER XV. 
LOWER MIOCENE.* 
Lower Miocene Strata of France.—Line between Miocene and Eocene.— 
Lacustrine Strata of Auvergne.—Fossil Mammalia of the Limagne d’Au- 
vergne.—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.— 
Kupelian Clay of Hermsdorf near Berlin.—Mayence Basin.—Lower Mio¬ 
cene of Croatia.—Oligocene Strata of Beyrich.—Lower Miocene of Italy. 
—Lower Miocene of England.—Hempstead Beds.—Bovey Tracy 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 
faliins 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 su23erposition implies 
an interval of time between the origin of the fresh-water 
limestone and its submergence beneath the waters of the Up¬ 
per Miocene sea. The limestone in question forms a part of 
the formation called the Calcaire de la Beauce, which consti¬ 
tutes 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 plat¬ 
forms 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 Etarapes, south of 
* Oligocene of Beyrich. 
