Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/149

1869.] DUNCAN—CORAL FAUNAS OF WESTERN EUROPE. 59 analogies of their structures and specific affinities) either to the deep-sea or to the reef fauna. When the fossils are evidently not derived from older strata, and not rolled or drifted, their having once lived on the area of their fossilization must be conceded.

If the general arrangement and grouping of forms peculiar to the reefs of the existing seas is evidently to be traced in those of the Mid-tertiary age, it is logical to admit that the very definite physical conditions peculiar to modern reefs existed formerly. This general arrangement may be instanced in the vast coral strata of the Nummulitic age; and the reefs of that period cannot be distinguished by the shape of the species from the coral remains of the Gosau reef area, or those of the Neocomian and the Oolites.

Still earlier in the world's history, the nature of the coral faunas may be estimated by scantily dispersed specimens which possess the peculiarities of one or other of the types.

The relation of high land, older strata, and intrusive rocks, their drainage, vegetation, and fauna to coral reefs may be learned inmost works on physical geography and on the principles of geology*; and there is a possibility, which depends upon the imagination of the geologist, of forming ideal landscapes whenever corals abound in strata.

VIII. Genera of Reef-Faunas, Ancient and Modern.

The following is a List of Genera whose species form the existing and also composed some of the Tertiary and Mesozoic reefs.

Euphyllia. Barysmilia. Pectinia. Galaxea. Stephanocoenia. Symphyllia. Mycetophyllia. Ulophyllia. Maeandrina.

Diploria. Leptoria. Coeloria. Hydnophora. Favia. Heliastraea. Brachyphyllia. Cyphastraea. Solenastraea.

Astraea. Prionastraea. Agaricia. Pachyseris. Mycedium. Madrepora. Turbinaria. Astraeopora.

Porites. Alveopora. Pocillopora. Millepora. Heliopora. Cycloseris. Trochoseris. Lithophyllia.

Many of the genera are allied to other fossil forms with which they were associated; and by comparing and enumerating the extinct genera which lived with those whose species still exist, an extended list of reef-makers can be obtained. Such genera as Pachygyra, Rhipidogyra, Astrocoenia, Phyllocoenia, Calamophyllia, Rhabdophyllia, Montlivaltia, Thecosmilia, Cladophyllia, Latimoeandra, and Thamnastroea were associated with many of those in the list given above in the reefs of the Miocene, the Nummulitic, the Lower Chalk, the Neocomian, and the Oolitic periods.

The genera characteristic of the deep sea, and whose species do not form reefs, may be very well represented by the following list:— the genera of the families Turbinolides, Oculinides, many Trochosmiliaceae, Lithophylliaceae simplices, Cladocoraceae, Eupsammiacese, and some Fungiaceae.

IX. Coral-sea Conditions in different Periods.

The following is a list of the geological periods, showing the rela-


 * Lyell; Dana; Jukes.