FIG. 25.—PLESIOSAURUS.
FIG. 26.—NAUTILUS INEQUALIS.
FIG. 27.—ORGANISMS FROM CHALK.
The chalk is interstratifìed with lines of sand, and the lower part is almost entirely sandy, forming the gault and greensand deposits; these each contain organic remains, and must have been the original sand of the sea-bottom before the chalk was deposited on it. These seas must have been the residence of a vast number of reptiles, for the gault contains an enormous number of nodules of what appears to be stone, but which upon closer examination, prove to be coprolites, or portions of the excrement of those creatures partly fossilised, but still retaining phosphate of lime enough to render them valuable manure, and these—like the coal—after being buried in the earth for thousands of years, are now being brought into use. In these coprolites may be constantly seen the teeth and bones of fishes, together with portions of echini and crustaceans, which had passed through the intestines of these saurian reptiles. Fig. 26 is the shell of a small nautilus (Nautilus inequalis) thus found.
FIG. 28.—AMMONITE FROM THE CHALK.
This chalk is of a white colour, very light and porous; under the higher powers of the microscope, it appears to be made up of organic forms, as "Foraminifera," and portions of various kinds of shells, crushed and broken into minute fragments (fig. 27). Dr. Carpenter, in his work on the microscope, says: "Many parts of it (the chalk) consist in a great measure of the minuter parts of the smaller kinds of Foraminifera, whose shells are imbedded in a mass of apparently amorphous particles, many of which nevertheless present indications of being the worn fragments of similar shells, or of larger calcareous organisms. In the chalk of some localities, Foraminifera constitute the principal part of the minute organisms which can be recognised with the microscope; in other instances the disintegrated prisms of Pinnæ, or other large shells of the like structure (as Inoceramus), constitute the great bulk." The fossil remains in the chalk are very numerous and are all of a marine character, the ammonites (fig. 28), belemnites, and other cephalopods, were very prevalent, as were the various Echinodermata, as the Hemicidarus intermedia (fig. 29), together with numerous univalve and bivalve mollusca, various crustacea, fish and reptiles. There was some considerable wonderment a few years ago expressed at the skeletons of men being found in the chalk at Guadaloupe; but it has been ascertained that this chalk is a modern formation, being produced by the sea washing and disintegrating the adjacent coral reefs, and depositing a fine white sediment of broken coral on the shore which can hardly be distinguished from ancient chalk; the same process is taking place at the Bermudas and other islands of the West Indies.
