NO. 1193. SOME NEOCENE COB ALS—GANE. 181 



fill whether any truly deep sea forms are represented. The few genera 

 that might be so classed are also frequently found living in shallow 

 depths. When we add to the above the fact that they occur in the 

 deposits side by side with true reef builders, we may consider that the 

 corals living in the Oligocene and Pliocene periods flourished as shallow- 

 water forms with preponderating reef-building tendencies. 



Both from their kind and the relations which the coral genera and 

 species of a particular area bear to one another, it is possible to judge 

 ot the similarity or of the variation of the physical conditions ])revail- 

 iiig in the region. 



Eegarding this hypothesis, Prof. P. M. Duncan,^ in his first article 

 on the West Indian fossil corals, says : 



The range, in strata, of the genera of corals is often so great, and the species of 

 remote formations are so frequehtlj^ closely allied; that the Zoantharta form better 

 guides for estimating the external physical circumstances of the regions in which 

 thejr existed than for determining the age of the strata. There are few subjects 

 better understood than the relation between the presence of certain genera and 

 species of coral and certain definite, external physical conditions. Depth of sea, 

 purity of sea water, its intense aeration, force of wave, absence of fresh water, the 

 climate and nature of the coast line, with all their possible varieties, appear to 

 determine, according to their mutual reactions, the presence and persistence of spe- 

 cies and genera. Indeed, very slight variations from the general rule of the external 

 circumstances in a coral sea would appear to prevent the development of certain 

 genera. It is a reasonable induction that, if a species be found in strata of any 

 age and distant in space, the two sets of strata were formed under the same external 

 physical circumstances. 



If this be true, then the conditions prevailing upon the Atlantic 

 coast during Neocene time were most varied, both from a geological 

 and a geographical standpoint; for we find that in the fauna under dis- 

 cussion the genera of the corals are quite varied, and that the indi- 

 vidual species are very limited, both vertically and horizontally, in their 

 stratigraphic distribution. In this distribution the Pliocene species 

 are perhaps more liable to be limited in their geographical range than 

 in their geological, since a number of the forms are either found as 

 recent or having closely related living allies, whereas the Miocene 

 species appear to be about equally confined both from a geographical 

 and a geological aspect. 



A majority of the corals represented belong to extinct species. A 

 few are now found living in the Caribbean Sea, and some belong to 

 closely allied fossil forms from iSanto Domingo and other West Indian 

 islands. 



We should expect that the Neocene corals of the United States would 

 have close kinship with those of like age in the West Indies, but such 

 does not seem to be generally the case. On the other hand, according 

 to Professor Duncan the fossil Oligocene corals of the West Indies are 

 closely related to those of the Miocene of Europe a^d the recent faunas 

 of the Pacific and Indian oceans. Eegarding the affinities of. the Neo- 



1 Quart. Jour Geol. Soc, XIX, p. 453. 



