Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/152

62 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Nov. 24, Lias of England were formed under very variable bathymetrical conditions; and deposits of Ammonites, deep-sea corals, and clays follow each other. The great coralliferous deposits of Fenny Compton and Cherrington were isolated patches on a very uncoralliferous sea-bottom. The corals of these deposits have no affinities with those of reef-faunas which preceded them; and the coral fauna of the zone of Ammonites angulatus in Glamorganshire was not represented in them, but it was clearly reflected in the assemblage of forms which characterized the upper part of the Inferior Oolite. There are no evidences of reefs or of an abundant deep-sea coral area in western Europe during these times. During the deposition of the Upper Lias and the lower part of the Inferior Oolite, the whole of the area appears to have become nearly uncoralliferous.

The Oolitic Strata.

There are few geological data more evidently true than the occurrence of successive reefs on the same areas of England and Western Europe during the formation of the Oolites. The whole of those districts was occupied by a coral-sea, interspersed with reefs, lagoons, and their associated land; and the bathymetrical conditions which prevailed resembled those now peculiar to reef-areas. The variations in depth on the same portions of the space were very considerable, even during the existence of the same groups of associated species; and successive reefs which still form part of the landscape* are noticed to be separated by the detritus of former ones, by deep-sea deposits, and even by shallow-water formations. Although the character of the sea-bottom varied greatly over the whole space contemporaneously and successively, the general characters of a coral-sea constantly prevailed; and the identity, resemblance, and representative character of the coral species of the consecutive reefs lead to the inference of a continuity of a reef-fauna somewhere or other during the whole Oolitic period. The absence of deep seas close to continental tracts must be admitted; but the presence of such geographical elements as now obtain in the Indo-Pacific may be fairly asserted.

The extent of the coral-sea appears to have reached its maximum during the Great Oolite; and then the conditions which had prevailed so long, and which had furthered the continuance of the successive reefs, began to alter.

The indications of reefs diminish very decidedly in the Oxford group and its continental equivalents in France, Switzerland, Swabia, and Franconia. Moreover our so-called Coral-rag is very poor in species, although it was clearly deposited in a reef-area. Whilst the reefs on our area were in existence there do not appear to have been any in Northern and Western France, Eastern Switzerland, or to the east. There Trigonia limestones, Cidaris limestones, Ammonites limestones and shales appear to have prevailed. But in Western Switzerland there were successive reefs which commenced before our horizon of


 * Wright, op. cit.