136 BULLETIN OF THE 



4. Debris from the reef and Keys on the one side, and the mainland 

 already built (Keys) on the other, filling up the successive channels, 

 and converting them first into swamps and finally into dry land, in all 

 of which he agrees with Agassiz's explanation of the causes which have 

 built the Florida Reef. 



Neither was I able, when visiting the Alacran Reef, the reefs of the 

 Windward Islands, 1 the elevated reefs of Barbados, of San Domingo, and 

 of Cuba, the great barrier reef of Cuba, and becoming acquainted with 

 the immense limestone banks so characteristic of the Caribbean region, to 

 satisfy myself that Darwin's theory of subsidence gave an explanation of 

 the condition of things now existing in an area of elevation, and includ- 

 ing all the types of reefs which he considered as characteristic of an area 

 of subsidence. If we pass to the Bermudas, Rein, 2 who carefully ex- 

 plored the islands, came to the same conclusion, and took a most 

 decided stand against the theory of subsidence. Rein is of the opinion 

 that coral reefs may grow wherever the conditions of the bottom are 

 favorable for the development of the corals. In these he includes the 

 temperature, the purity of the water, the supply of food by the sea, aa 

 w r ell as a solid substructure, whether this substructure be due to the 

 subsidence of the coast, or to an elevation of the bottom, this eleva- 

 tion being caused either by volcanic, organic, or other agency. 



Rein also calls attention to the fact, that both Darwin and Dana 

 have assumed a possibility as a fact, and, the theory once given, have 

 attempted to prove the subsidence, instead of bringing the subsidence of 

 coral reefs as a proof of the theory. Proofs of subsidence have nowhere 

 been given except as explanations of existing phenomena, while the 

 proofs of elevations within the regions of coral reefs are innumerable. 

 Darwin and Dana explain the existence of deep channels between barrier 

 reefs and the coast, as well as the formation of atolls by subsidence, and 

 hence conclude from the existence of numerous barrier reefs and atolls 

 that the coasts have sunk, and many islands have been buried in the sea 

 to form atolls. It naturally follows that they calculate the vertical 

 thickness of coral reefs as due to the same cause, and nothing but boring 

 will settle this point. 



Rein further mentions a number of coral reefs from the Tertiary to 

 the Jurassic, none of which were more than thirty meters thick. Rein, 8 



1 Agassiz, A., Three Cruises of the Blake, 1888, Vol. I., "The Florida Reef." 



2 Rein, J. J., Beitrage zur physikalischen Geographie der Bermuda Inseln, 

 Bericht uber die Senkenb. Naturf. Gesell., Mai, 1870, p. 140. 



3 Die Bermudas-Inseln und ihre Korallenriffe, nebst einem Nachtrage gegen die 



