Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/154

64 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Nov. 24, ceded them; and at the same time there must have been a persistence of reef conditions within the limit of the migration of corals during the Kimmeridge and Portland period, and without the area of Western Europe.

If the Neocomian is regarded in a general sense as the marine equivalent of the Wealden, some insight may be obtained concerning the great elevation of parts of the Jurassic sea-bed which occurred before the commencement of the Cretaceous era. The opinion of Elie de Beaumont, that a great upheaval, which he has named the system of the Cote d'Or, took place before the sediments of the lower Cretaceous seas began to form, is worthy of careful consideration. It would appear that long ranges of the Jura and Cevennes, and granitic rocks covered with Oolitic outliers were tilted and elevated before the sediments of the Neocomian period were deposited uncomformably and horizontally in relation to them. If this was so, the varying bathymetrical conditions already noticed as characterizing the sea-bottoms of the Upper Oolites culminated in an upheaval, which produced land in one portion of the area of Western Europe, and determined the presence of the physical conditions favourable for coral-life in another. The Gault.

When the species forming the Coral-fauna of the Gault are compared with recent forms, there is no difficulty in asserting that they were dwellers in deep water, and not within the range of reefs. Some of them, probably, were littoral kinds. All are specifically distinct from the Neocomian corals, and present a different facies. Nothing is known concerning the reefs of this period; and the few species of the generally very uncoralliferous strata of the Continent are deep-sea forms.

Upper Green Sand.—Upper and Lower White Chalk Strata.

The gradual subsidence of great spaces of the sea-bottom, which probably determined the peculiar fauna of the Gault, and the absence of reefs, appears to have continued in some localities during the deposition of the Upper Green Sand strata; whilst it was preceded in others by an elevation of the old sediments. The coral fauna of the English Upper Green Sand is representative of that of the Gault, but the species differ. There were littoral and deep-sea forms in both; and in the south-west of England, at Haldon, there was a reef. On the Continent, the strata of the period indicate every known variety of deposit, and very varying bathymetrical conditions. Reefs succeeded various deposits, and occupied different geological horizons; and all had a definite relation to each other, both in the identity of the species and the accompanying mollusca.

It is impossible to separate the English Upper Green Sand and Lower White Chalk from the formations at Gosau, in Austria, and the reefs in the south of France, where Hippurites are mixed up, like gigantic Chamas, with masses of compound corals to form reefs. Few generalizations have been more useful than those of Messrs. R.