74 BULLETIN : MUSEUM OF COMPAKATIVE ZOOLOGY. 



explanation of the formation of atolls and of barrier reefs by the growth 

 of the corals of tiie present epoch. Xor would the geological evidence of 

 the great thickness of similar limestones in past periods be of any 

 assistance in the solution of the problem if our explanation of the 

 formation of atolls and of barrier reefs upon platforms of submarine 

 erosion is correct. 



Certainly the analogy of tlie association of volcanic rocks and so 

 called i-eefs in the Devonian and Trias with similar association in the 

 Pacific lias no value, as is suggested by Freeh ^ and Langenbeck. The 

 substratum upon which corals may grow depends upon the geological 

 structure of the country and its latitude. Such an analogy would 

 throw out iu great part the reefs of Australia, those of Florida, of the 

 Bahamas, of Honduras, and of the northern coast of Brazil, which are 

 not in volcanic regions, and where the substratum is either Cretaceous 

 or Tertiary. 



The only evidence we have of the great thickness of coral reefs, such 

 as is required l)y the Darwinian theory of tlie formation of atolls and 

 of barrier reefs, is based upon the great thickness of the so called 

 elevated reefs observed in the Pacific by Dana, Darwin, and others, and 

 upon similar observations in Cuba and other parts of tlie "West Indies, 

 and upon the evidence of the great thickness of the reefs of the Dol- 

 omite. That the latter are true coral reefs is more than doubtful. 

 Those rocks are probably great masses of limestone similar to the huge 

 deposits of so called elevated reefs of the West Indies and of the Pacific. 

 The evidence obtained by boring, and from recent elevated reefs, shows 

 that the modem coral reef attains but a moderate thickness well within 

 tliat of the depth at which reef corals grow. The limestones form 

 the basis or substratum upon which the recent reefs have obtained 

 a footinc;. The elevated reefs of Cuba and of the West Indies have 

 been shown to be Tertiary coralliferous limestones, and the same is the 

 case with the elevated reefs of the Pacific, if we can judge of their 

 aae bv that of the elevated coralliferous limestone reefs resembling 

 them observed by me in Fiji. 



The central depression, noted as characteristic of the summit of so 

 many islands consisting of elevated coralliferous limestones does not show 

 these islands to be elevated atolls as has been supposed. Tlie summit 

 basin representing the former lagoon of the island has been formed since 

 the elevation of the island by atmospheric agencies. This basin is a 

 gigantic banana-hole, as such depressions ai"e called in the Bahamas, 



1 Neues Jalirb. f. Mineral, 1892, Pt. II. p. 173. 



