Fig. 126.—Chalk of Meudon (magnified).
Much of this curious information was unknown, or at least only suspected, when Ehrenberg began his microscopical investigations. From small samples of chalk reduced to powder, placed upon the object-glass, and examined under the microscope, Ehrenberg prepared the designs which we reproduce from his learned micrographical work, in which some of the elegant forms discovered in the Chalk are illustrated, greatly magnified. [Fig. 126] represents the chalk of Meudon, in France, in which ammonite-like forms of Foraminifera and others, equally beautiful, appear. [Fig. 127], from the chalk of Gravesend, contains similar objects. [Fig. 128] is an example of chalk from the island of Moën, in Denmark; and [Fig. 129], that which is found in the Tertiary rocks of Cattolica, in Sicily. In all these the shells of Ammonites appear, with clusters of round Foraminifera and other Zoophytes. In two of these engravings ([Figs. 126] and [128]), the chalk is represented in two modes—in the upper half, by transparency or transmitted light; in the lower half, the mass is exhibited by superficial or reflected light.
Chalk under the Microscope.
Fig. 127.—Chalk of Gravesend. (After Ehrenberg).—Magnified.
Observation, then, establishes the truth of the explanation we have given concerning the formation of the chalky or Cretaceous rocks; but the question still remains—How did these rocks, originally deposited in the sea, become elevated into hills of great height, with bold escarpments, like those known in England as the North and South Downs? The answer to this involves the consideration of other questions which have, at present, scarcely got beyond hypothesis.
Chalk under the Microscope.