. Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments. Geology. Ch. XVI.] EOCENE STRATA OF FRANCE. 303 Sables inoyens, divide the gypseous beds from the calcaire grossier proper. These sands, in which a small nummnlite (JV. variolaria) is very abundant, contain more than 300 species of marine shells, many of them peculiar, but others common to the next division. Calcaire grossier, upper and middle (B. 1, p. 298).—The upper divis- ion of this group consists in great part of beds of compact, fragile limestone, with some intercalate
. Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments. Geology. Ch. XVI.] EOCENE STRATA OF FRANCE. 303 Sables inoyens, divide the gypseous beds from the calcaire grossier proper. These sands, in which a small nummnlite (JV. variolaria) is very abundant, contain more than 300 species of marine shells, many of them peculiar, but others common to the next division. Calcaire grossier, upper and middle (B. 1, p. 298).—The upper divis- ion of this group consists in great part of beds of compact, fragile limestone, with some intercalated green marls. The shells in some parts are a mixture of Cerithium, Cyclostoma, and Corbula ; in others Limnea, Cerithium, Paludina, &c. In the latter, the bones of reptiles and mammalia, Paleotherium and Lophiodon, have been found. The middle division, or calcaire grossier proper, consists of a coarse lime- stone, often passing into sand. It contains the greater number of the fossil shells which characterize the Paris basin. No less than 400 dis- tinct species have been procured from a single spot near Grignon, where they are embedded in a calcareous sand,- chiefly formed of com- minuted 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 figures, p. 240). There occur no less than 137 species of this genus in the Paris basin, and almost all of them in the calcaire gros- sier. Most of the living Cerithia inhabit the sea near the mouths of rivers, where the waters are brackish ; so that their abundance in -the marine s
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