THE DEEP-SEA FAUNA. 



161 



a former occasion.^ The present comparison does not extend 

 so far. 



Thanks to the researches of Professor Duncan on the fossil 

 corals of the West Indies, we can carry our comparison of the 

 living corals into the tertiary. 



The earHer tertiary fossil corals of the West Indies have but 

 little specific affinity with existing species, and there is some 

 difficulty in comparing the two, owing to the varying condi- 

 tions of preservation in which the fossils are found. This is 

 especially the case in the raised coral beds, which follow the old 

 shore lines, as indicated by the terraces seen at Barbados and 

 many other islands of the Caribbean. These contain a limited 

 number of species of corals generically and specifically identical 

 with the present West Indian coral fauna. According to Dun- 

 can the fossil West Indian corals are related on the one side to 

 the coral fauna which flourished in the oolite, and on the other 

 to a fauna, the first appearance of which is uncertain, but which 

 attained its greatest development in the miocene, and is now 

 represented in the Pacific Ocean and its associated seas. In 

 deep water some of the species with Pacific affinities still live. 



From the oldest periods the faunse of successive reefs had few 

 species in common, but genera were most constant and persis- 

 tent ; and it seems clear that physical conditions which are now 

 absolutely essential to the formation of coral reefs existed dur- 

 ing the mesozoic and cainozoic periods. The presence of these 

 conditions enables us to rebuild the geography of the past, and 

 to imagine in the time of the trias a succession of larger and 

 smaller islands far from continents or large rivers, but having 

 deep and shallow seas, such as we now find in coral areas. The 

 simphcity of the physical conditions and their continuance 

 from one age to another seem a natural explanation of the uni- 

 formity which has evidently prevailed in all coral regions from 

 the earliest times to the present day. 



These conditions offer a ready explanation of the more north- 

 ern extension of the areas of coral reefs, of their disappearance 



1 " Palaeontological and Embryological Association for the Advancement of Sci- 

 Development," Address at the Boston ence. 

 Meeting (for 1880) of the American 



