Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/156

66 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Nov. 24, that now occupy definite positions in the reefs of the Indo-Pacific. Even the great reef-making genera Millepora, Porites, Alveopora, Madrepora, and Heliastroea are represented in the Eocene reefs by numerous species. The number of species in the old reefs quite equals that in the existing ones. The stragglers from the reefs which formed a part of the British Eocene coral fauna are of the genera Stereopsammia, Dendracis, Porites, Litharea, and Axopora. These forms, associated as they are with the Dendrophyllioe, would not be out of place in such an area as the sea-bottom to the south of China, or the Gulf of Mexico.

Great variations of depth occurred in these coral areas; for deep sediments containing Nummulites overlie the reefs either directly or by inference, and there is a profound flysch superior to the Oberburg, but not in the same district. The Nummulites appear to have favoured the reef-areas.

Oligocene.

The coralliferous deposit at Brockenhurst, in Hampshire, rests upon a freshwater formation which is the equivalent of the fresh-water beds of the Lower Headon series. The species of corals are of genera which now characterize reefs, and the most prominent are Madrepora and Solenastroea. The mollusca associated with the corals are identical, for the most part, with those which are found in the Oligocene strata of Tongres, Magdeburg, and Latdorf; and they belong to a well-characterized horizon between the Nummulitic and the Faluns. The corals of the three localities just mentioned are deep-sea and littoral forms more or less under the influence of a reef; but the true reefs were in Hampshire and in the Castel-Gomberto district, where they can still be recognized in great masses.

These reefs contain no less than 50 genera of corals; and there are many species there which are found in the Nummulitic and Miocene reefs associated with characteristic forms. The Oligocene reefs differed, in species, about as much from those which immediately preceded and followed them as the existing West-Indian reefs do from those of the Pacific and South Sea.

The relation of the Oligocene reefs to certain great bathymetrical changes is obvious; and the Brockenhurst reef was located upon an area which had been upheaved after the Barton deposits had been completed and again slightly depressed. The deep water in the German area covered extensive Brown-coal strata.

The reef-corals began to diminish in the number of their species after this time; and the Miocene reefs formed in south-western France, northern Italy, Austria, Hungary, Spain, and Malta, do not present so varied an assemblage as those of the two preceding formations. The oscillations of the south-western area of Europe were very great between the Oligocene and the Miocene; and during this age reefs and barriers were associated with considerable land-surfaces, and with very variable conditions of sea-bottom. The partial upheaval of the Alps (which had been a reef-supporting series of hills for two periods) into mountain-ridges, and the general volcanic