l>ALEOZOiC CORAL REEFS 251 



special reason, perhaps, excepting very early stages in the earth's his- 

 tory, why the composition of the salts in solution in the ocean should 

 have varied from one geologic age to another. Because of the lithologic 

 similarity of material in suspension laid down as sediments in the oceans 

 from Paleozoic to Recent time, it appears probable that the material in 

 solution was also similar throughout the geologic ages. The marine 

 organisms of the earlier geologic ages, although different from those of 

 the later, represent the same zoologic groups, and their skeletons indi- 

 cate the extraction of salts from the medium in which the animals lived 

 by similar physiologic processes. The available evidence indicates that 

 the oceanic salts in Paleozoic time were not essentially different from 

 those of the ocean of today. 



SPECIFIC GRAVITY 



There are no means of directly obtaining light on the specific gravity 

 of the oceanic waters in Paleozoic time, but we may reach an opinion on 

 the subject through inference. The specific gravity of ocean water is 

 determined by the quantity of salts in solution, and of these the calcium 

 salts are important. As the Paleozoic lime-secreting organisms required 

 calcium salts to be in solution in the medium in which they lived, a spe- 

 cific gravity of the oceanic water considerably above that of pure water 

 was necessary. Although a quantitative estimate can not be given of the 

 specific gravity of Paleozoic oceanic waters, it may be stated that salts 

 were contained in solution, calcium salts were important constituents, and 

 it appears probable that there has been no great variation in the specific 

 gravity of the water of the ocean since that time. 



8VMMARY 



All the data obtainable from various sources indicate that the Paleo- 

 zoic coral reefs were formed under conditions similar to those under 

 which Recent reef corals live.^^ 



The conclusions may be summarized as follows: 



(a) Depth, maximum, 25 fathoms; light, strong. 



(6) Temperature, annual minimum not lower than between 60 and 

 70 degrees Fahrenheit and probably above 70 degrees Fahrenheit. 



(c) Water, agitated and circulating. 



" Bonney says in his appendix to Darwin's "Structure and distribution of coral reefs," 

 p. 331 : "Moreover, the aporosa and madreporaria, which are now the chief reef-builders, 

 have only become common since the conclusion of Paleozoic ages, so that the largest 

 volume of the gelogical history of the earth is excluded from consideration, because in 

 the time which it covers the habits of the reef-builders may have been different." The 

 evidence here presented shows, in my opinion, that the habits of reef-building corals 

 have always been similar. 



XVUI— Bull. Gbol. Soc. Am., Vol. 22, 1910 



