1863.] DUNCAN WEST INDIAN COEALS. 453 



although there are genera and species of Corals in Antigua, San Do- 

 mingo, and Jamaica belonging to the great European Miocene Coral- 

 age, still there are a few European Miocene genera of Corals which 

 are not as yet known to belong to the West Indian Miocene. 



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

 the species of remote formations are so frequently closely allied, that 

 the Zoaniharia form better guides for estimating the external phy- 

 sical circumstances of the regions in which they existed, than for 

 determining the age of 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 condi- 

 tions. 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 species 

 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. 



The question of contemporaneity may be fairly considered when 

 the strata are close together in which identical forms, or those closely 

 allied, are found. Thus, JStephanoccenia formosissima, of Gosau and 

 Uchaux, is so closely allied to S. intersepta of the present South Seas, 

 that there is hardly a specific difference. When the latter is broken 

 from recent Coral-limestone, all that can be said is that the modern 

 and the ancient Corals existed under the same circumstances of cli- 

 mate and aqueous distribution. 



But when Stephanoccenia dendroidea is found fossil at San Domingo, 

 and a closely allied species at Antigua, and when the short distance 

 between the formations, and the existence of the equivalents of the 

 Caribbean and of the older and newer Parian formations throughout 

 the West Indian Islands are considered, the sameness of external 

 circumstances may be received as a concurrent testimony of identical 

 age. 



There is nothing anomalous, as would at first appear to be the 

 case, in finding species already classified amongst European Creta- 

 ceous Corals, in West Indian Miocene strata ; nor in finding species 

 of Jurassic Corals closely allied to forms in these Mid-tertiaries. 



The European Miocene contains both Jurassic and Lower Creta- 

 ceous genera, and in some instances the specific relations of the 

 Corals are very close. Thus, Astrcea Lifolensis is hardly worthy of a 

 specific distinction from Astrcea Guettardi, and the Pliylloccenice of 

 the formation at Corbieres greatly resemble those of Dax and Castel 

 Gomberto. 



The Isastrseans from Antigua, whatever may be the geologic age 

 of the Chert, are very closely allied to those of the Oolites, and it is 

 unnecessary to repeat the close resemblance of some and the identity 

 of other San-Domingan Miocene Corals to European Cretaceous forms. 



