FORMATION OF REEFS. 231 



Darwin himself recognises the force of my objections ; though 

 he certainly attempts to set them aside by means of an assump- 

 tion of which the fallacy is amply proved by the very obser- 

 vations I have published. 



The latest labours of the American naturalist prove that 

 his views with regard to the origin of reefs differ very consider- 

 ably from Darwin's, and in a very essential point. Darwin, as 

 is well known, assumes that wherever fringing reefs occur, a 

 period of elevation or of repose now prevails, while atolls and 

 barrier-reefs can be formed only in regions of recent subsidence. 

 As an essential argument for the correctness of this view he 

 adduces the fact, prominently brought out in a map of his con- 

 structing, that active volcanoes occur only in those regions 

 which, from the structure of their reefs, must also be regions of 

 elevation. 



Dana agrees with Darwin in so far that he also assumes 

 that atolls or barrier -reefs can only be formed in regions of sub- 

 sidence ; but fringing reefs, according to him, indicate not merely 

 no upheaval in recent times, but, on the contrary, a more con- 

 siderable subsidence than is pointed to by other reef formations. 

 For instance, he says expressly : ' I still hold that, while barrier- 

 reefs are proofs of subsidenca, small or fringing reefs are in 

 themselves no certain evidence of a stationary level, and are 

 often evidence of subsidence, even a greater subsidence than is 

 implied by barrier reefs. I have already stated that one cause 

 limiting the distribution of reefs is bold shores ; a wall of rock 

 of even a hundred and fifty feet producing a complete exclu- 

 sion. . . . Such bold shores ate evidence of subsidence ; and 

 as only very small reefs, if any, could find footing about such a 

 shore, the narrow reef would be another consequence .of the 

 subsidence, and no evidence of a stationary condition.' * 



Now, although Darwin admits that, under certain circum- 

 stances, narrow (i.e. fringing) reefs might be formed on such 

 steep and precipitous shores, he adheres to his former opinion 

 that this does not occur, as a rule, and that, in most cases, reefs 

 of this class prove upheaval in the most recent periods, or even 



* Am. Journ. Sci. Ser. III. vol. viii. p. 316. 



