Geology, in the magnitude and sublimity of the objects of which it treats, ranks next to Astronomy in the scale of the sciences.
Sir J. F. W. Herschel.
[SUPPLEMENTARY NOTES.]
[Note I.] [Page 13.] Shells in Chalk.
The shells of mollusca, in consequence of their durability, are the most abundant fossils in the sedimentary strata;[X] entire layers of marble and other limestone, of great thickness and extent, are wholly composed of an aggregation of a few species or genera: in some instances of fresh-water snails—as, for example, the Sussex and Purbeck marbles;[Y] in others, of marine bivalves and univalves, as the oyster-conglomerate of Bromley, and the shelly limestones of Portland, Dorsetshire, &c.
[X] For an account of the geological value of fossil shells, see 'Medals of Creation,' vol. i. p. 363.