Grès de Beauchamp (2. b, Table, [p. 175.]).—In some parts of the Paris basin, sands and marls, called the Grès de Beauchamp, or Sables Moyens, divide the gypseous beds from the underlying Calcaire grossier. These sands contain more than 300 species of marine shells, many of them peculiar, but others common to the underlying marine deposit (No. 2. c.).
Calcaire grossier (2. c, Table, [p. 175.]).—The formation called Calcaire grossier consists of a coarse limestone, often passing into sand. It contains the greater number of the fossil shells which characterize the Paris basin. No less than 400 distinct species have been procured from a single spot near Grignon, where they are embedded in a calcareous sand, chiefly formed of comminuted shells, in which, nevertheless, individuals in a perfect state of preservation, both of marine, terrestrial, and freshwater species, are mingled together. Some of the marine shells may have lived on the spot; but the Cyclostoma and Limnea must have been brought thither by rivers and currents, and the quantity of triturated shells implies considerable movement in the waters.
Nothing is more striking in this assemblage of fossil testacea than the great proportion of species referable to the genus Cerithium (see [fig. 164.]). There occur no less than 137 species of this genus in the Paris basin, and almost all of them in the calcaire grossier. Now the living Cerithia inhabit the sea near the mouths of rivers, where the waters are brackish; so that their abundance in the marine strata now under consideration is in harmony with the hypothesis, that the Paris basin formed a gulf into which several rivers flowed, the sediment of some of which gave rise to the beds of clay and lignite before mentioned; while a distinct freshwater limestone, called calcaire siliceux, which will presently be described, was precipitated from the waters of others situated farther to the south.
Fig. 164.
Cerithium cinctum.[194-A]
EOCENE FORAMINIFERA.
