Page:A Treatise on Geology, volume 1.djvu/343

 CHAP. VI.

While some, perhaps, reveal to us the inhabitants of the sea before the period of glacial deposits, many certainly contain the reliquiæ of that period, and a few may be admitted as of a later date.

Professor E. Forbes has lately collected into a general view the somewhat scattered information on this subject, which since the date when Linnæus explored Uddevalla (1747), has found no more zealous inquirer than Mr. J. Smith. An extremely valuable contribution to the zoology of the glacial sea was brought by the Geological Survey of Ireland under the direction of Capt. James, In the following table the numbers of testaceous mollusks of four well ascertained modern faunas are compared with a summary of the testacea belonging to the glacial formations of the British Isles.

"This glacial marine fauna is composed of living British species of northern origin, some of which are now confined to climates far colder than our own, with a few forms supposed to be extinct, and one or two shells of southern origin, or known only in the crag." Its analogy to the modern fauna of Greenland and the northern coasts of America is evident.