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.[1] 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,[2] 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.
| Orders of Mollusca. | Comparative Table of Testacea Inhabiting | ||||
| Mediterranean. | British Seas. | Seas of Massachusetts. | Seas of Greenland. | Fossil in British glacial Beds. | |
| Cephalopoda with shells | 1 | 1 | 1 | ||
| Pteropoda | 13 | 1 | 2 | ||
| Nucleobranchiata | 6 | 1 | |||
| Gasteropoda | 368 | 248 | 100 | 74 | 63 |
| Lamellibranchiata | 200 | 210 | 83 | 44 | 63 |
| Palliobranchiata | 10 | 4 | 2 | 1 | 1 |
| Totals | 598 | 465 | 186 | 121 | 124 |
"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."[3] Its analogy to the modern fauna of Greenland and the northern coasts of America is evident.
