Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/159

1869.] DUNCAN—CORAL FAUNAS OF WESTERN EUROPE. 69 group of islands, receives additional force from the study of the successive reef-areas of the Nummulitic, Oligocene, and Miocene periods. The first of these contained a coral fauna which was as representative of that of the Cretaceous reefs as this was of the Oolitic; and thus there is another example of the remarkable return of closely allied forms to the same area after great alterations in its physical geography had occurred. The Oligocene and Miocene reefs were the last on the European area; and the present deep-sea coral fauna of the Mediterranean, North Sea, and north-eastern Atlantic is representative of the deep-sea coral fauna of the White Chalk.

The alliances between the consecutive coral faunas which were separated by deposits containing the evidences of conditions most unfavourable to coral-life indicate that there has been an unbroken series of reef-areas within the scope of the emigration of Madreporarian ova ever since the Trias. Sometimes the reef-bearing seas were on the European area; and then it probably resembled, in its geography and natural history, a modern coral-sea. At others the physical conditions which characterize the existing state of things prevailed; and then the coral-tracts were remote, and either deep-sea forms existed or none at all. Doubtless the continental land was very persistent in Northern Europe, and the Arctic sea was shut out until the termination of the Mid-tertiary age. The land probably often encroached upon the coral tracts, and determined their partial or entire destruction.

Its influence may have been like that of the American continent upon the Caribbean Sea. During the Miocene, Trinidad was a vast reef, hung on to the older Parian hills, which were submerged and far away from land, and it was one of a series. But as the South- American coast uprose and the drainage of the new continent was poured out through the valley of the Orinoco, so great a mass of fresh water and muddy sediment contaminated the Trinitatian area, that hardly any corals grew around its old reefs after they they had been upheaved in common with the Miocene deposits of the Caribbean Sea. A short distance to the north, however, the new coral fauna encircles the old.

Discussion.

Prof. Alexander Agassiz accounted for the circumscribed area of many corals in the Atlantic from the young of many coral species attaching themselves within a few hours of their becoming pelagic. He traced to the great equatorial current which must have traversed the Isthmus of Panama and the Sahara in a precretaceous period the distribution of certain forms, which the rising of the Isthmus of Panama eventually checked. He mentioned the formation of a reef at the present time off the coast of Florida, which threw light on the manner in which mudflats were formed, and the sea eventually filled.

Mr. Gwyn Jeffreys objected to the term "deep sea" being applied to a depth of 1 fathoms only, when the tide in some places rose to that extent, and the laminarian zone extended to 15. He