Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/151

1869.] DUNCAN—CORAL FAUNAS OF WESTERN EUROPE. 61 of Madreporaria, including compound forms of reef species. A large coral bank, from 8 to 10 metres in thickness, runs obliquely through a vast depth of marine deposits, and it may be traced as far as the south side of the Lake of Geneva. The position of this bank, which is nearly composed of one species of coral, is such that it must have grown during a slow subsidence of the area. All these deposits contain fossils which are closely allied to the St-.Cassian forms; and some are identical species.

Lias.

1. Zone of Ammonites planorbis and its equivalents.—The corals of this zone in England belonged to reef-species; and it is therefore probable that some scattered reefs were formed on our area during the considerable alterations in depth which the Ostrea and Ammonites zones indicate. Probably the reefs of the Alpine area still continued.

2. Zone of Ammonites angulatus.—The formation of fringing reefs and coral banks took place in the Glamorganshire area*; and the mountain-limestone supported them. Other reefs were formed in the north about Skye, and eastwards in Worcestershire. In Lincolnshire there were deep-sea conditions, and they prevailed also in the north of Ireland. Sparsely distributed reefs and deep seas may be traced in Northern and Eastern France and into Germany. The reefs on the Lombardo-Alpine area persisted. It must be remembered that Triassic fish lived through the Rhaetic period into the times when the deposits now being considered were forming, and that species of Triassic corals and mollusca formed part of their fauna. There were 61† species of corals on the British area. It would appear that the seas were full of a very rich invertebrate fauna during this period, and that the British, French, Belgian, and northern Italian districts were reef-areas.

3. Zone of Ammonites Bucklandi (bisulcatus).—The reefs appear to have diminished, and to have been worn down, before the peculiar deposits containing this Ammonite were formed. In England, the remains of the scanty coral fauna of the reefs of this period are seen to cover up those of the reefs of the zone of Ammonites angulatus in Glamorganshire. The sea of the age of Ammonites Bucklandi contained a few of the molluscan species of the previous reefs; but the bulk of their coral fauna is not to be recognized in its deposits, even by allied species. Tbe area of England was losing the external conditions which hitherto and since the Trias had been gradually becoming more and more favourable for reef-formation. The coralliferous deposits of Western Europe are as scanty in Madreporarian remains as those of England; and it therefore would appear that the reefs initiated during the Muschelkalk age had, after a long continuance, gradually broken up, the variation in their consecutive faunas having been slight.

The other divisions of the Lower Lias and those of the Middle


 * Quart. Journ. Geol. Soc, Feb. 1867.

t Duncan, Pal. Soc. Monog. Liassic Corals, vol. xx.