Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/237

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Mr. Webster on the Strata lying over the Chalk.

admitted of removal from their original situations without being broken.

These organic remains therefore most distinctly mark the nature of the place where the strata enveloping them have been deposited. It must unquestionably have been the bosom of an extensive lake in some period of the earth far antecedent to human history; nor can we refrain from emotions of extreme astonishment when this conviction is forced upon us, nor help indulging in speculations on the revolutions which the earth must have undergone, when we consider how very differently these strata are now situated. Instead of being found in a hollow, they now compose the upper part of a hill; nor are they any more surrounded by those elevations which must have been essential to the confinement of the vast body of fresh water which furnished a habitation to myriads of animated beings, and of which we have nothing to demonstrate the former existence, except the nature of its depositions, which remain a faithful record.

Over this bed is a stratum of clay 11 feet in thickness, containing numerous fragments of a small bivalve shell. The hinge of this shell is of so peculiar a structure that Mr. Parkinson was not able to refer it to any known genus. The shells are thin, and unmixed with any other species whatever. It is impossible therefore to say whether they have belonged to marine or freshwater animals, and I have preferred for the present to keep them among the latter, rather than to suppose another alternation of which there is no direct proof.

Upon this lies another bed of yellow clay without shells, and then a stratum of friable calcareous sandstone, also without shells.

To this sandstone succeed other calcareous strata having a few freshwater shells. In these, which, like those mentioned above,

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