Page:Memoirs of the Geological Survey of Great Britain, Volume 1.djvu/391

378 proved the barrier to the migrations of many species of Mollusca. Several genera and numerous species, which are separated by the intervention of only a few miles of land are effectually prevented from intermingling by the cape, and do not pass from one side to the other. No specimen of Cochlodesma, Montacuta, Cumingia, Corbula, Janthina, Tornatella, Vermetus, Columbella, Cerithium, Pyrula, or Ranella, has yet been found to the north of Cape Cod; while Panopæa, Glycimeris, Terebratula, Cemoria, Trichotropis, Rostellaria, Cancellaria, and probably Cyprina and Cardita, do not seem to have passed to the south of it. Of the 197 marine species (of the Massachusetts fauna), 83 do not pass to the south shore, and 50 are not found on the north shore of the cape. The remaining 64 take a wider range, and are found on both sides." (p. 315). A little farther north and we have the contrast still more evident on each side of Cape Breton, the true boundary southward on the coast line of the Boreal fauna, which north of it ranges on to Greenland, and is probably very nearly the existing representative of the ancient fauna of our seas during the glacial epoch.

The probability of the peculiar fossils noticed as occurring only in the southernmost Irish beds of the glacial epoch, indicating a proximity of the glacial sea with one peopled by mollusks of a Lusitanian type, is supported by the fact that in the newer pliocene beds of southern Italy, we find associated with the characteristic existing mollusca of the Mediterranean certain Red Sea and Indian Ocean species on the one hand, and Celtic species on the other, both now extinct in that region. It is worthy of notice, that the Celtic fossil species found in the Sicilian beds, Mya truncata, Lutraria solsnoides, Cyprina islandica, Ostrea edulis, Patella vulgata, Fusus antiquus contrarius,, and Buccinum undatum, present the association of species characteristic of the southern bounds of glacial beds in Britain; and it can scarcely be doubted that during the newer pliocene epoch, which I regard as synchronic with the glacial period in the north, there was a communication open between the Mediterranean and North Seas on the one hand, by which this influx of Boreal or Celtic forms was acquired, whilst, on the other, there was, or had lately been, a free communication with the Indian Ocean through the Red Sea,—the Isthmus of Suez not existing.