Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/148

58 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Nov. 24, water at Aden. A Manicina of the Caribbean is found on the coast of Brazil. Mr. Darwin has given me some deep-sea corals from Cape Verde, and one is identical with a species found in the shallow sea between Cuba and Jamaica. Plesiastroea has species at Panama and Port Jackson. Pocks are often incrusted with reef corals— at Zanzibar and Ceylon for instance.

These exceptions are all within the range of the external conditions favourable for the existence of reefs, and the species retain the structural peculiarities which differentiate them from the deep-sea corals noticed at the commencement of this essay.

VII. Exceptional Relations of the two Faunas.

The genus Flabellum, which has species in the deep seas of western Europe, has others in the deep seas between the coral archipelago and the Asiatic continent, and some which are found in the reefs of the Fidji and other islands. There is a Desmophyllum in the West-Indian coral area, and Caryophyllioe also. Dendrophyllia has a species in the China seas within the range of the conditions favourable for reefs.

There is no well-established instance of any species or variety known to belong to the true coral fauna of reefs, lagoons, and shallows, within the range of the coral seas, which can be identified with any member of the deep-sea coral fauna of the offing of continents and large islands remote from the coral tracts. As yet nothing is known about the corals of the depths between the coral islands of the Pacific Ocean, or of the inhabitants of the great sea-desert to the west of America; but Mr. Christy gave me a collection of corals he had dredged up between Cuba and Jamaica in not very deep water, and I found the species to be closely allied to and. identical with those of the lagoons of the reefs*. From what is known at present, then, the existence of two coral faunas must be admitted—one restricted to large portions of the world, where the conditions favourable for reefs exist, and the other confined to the littoral tracts, and deep and abyssal seas near certain continents. Both depend upon the persistence of definite external conditions, and neither could flourish on each other's area or in such seas as the Baltic or the Black Sea†.

It must be remembered, however, that coral reefs are not invariably found where the physical conditions which accompany them elsewhere exist. The few islands in the Atlantic are not surrounded by reefs, probably on account of the impossibility of the migration of Madeporarian ova to them. The Bermudas are exceptions; but their position in reference to the Gulf-stream explains their having a coral fauna of the reef kind.

When the details of the marine deposits of the Mesozoic and Cainozoic strata are studied, it becomes evident that some of them contain fossil corals belonging (so far as can be judged from the


 * Consult Pourtales, op. cit.

† The abyssal fauna exists off Florida, and enters the reef area. See Pourtales, op. cit.