THE CORAL-REEF PROBLEM. 77 



subsidence to nearly this amount. Mr. Agassiz, commenting 

 on this important observation, says (p. 150, note) that it does 

 " not throw any additional light on Darwin's theory of sub- 

 sidence ; it is of the same character as all the statements 

 which prove the subsidence by the existence of coral reefs, and 

 while there may have been coral reefs formed during sub- 

 sidence, it does not prove that their growth is due to subsidence 

 any more than the presence of elevated reefs proves them to 

 be due to elevation." This criticism is in a measure valid ? 

 but it must be remembered that one of the " strong " points 

 urged by Guppy and others against the subsidence theory was 

 the (supposed) non-existence of massive deposits of coral-lime- 

 stone, or such as indicated formation through protracted sub- 

 sidence. But here we surely have such a limestone (provided 

 the observation is correctly made), and its presence removes 

 what might have been a valid argument against the Darwin- 

 ian hypothesis. And further, there is reason to believe that 

 the thousands of feet of reef-structure which have been do- 

 scribed by Sawkins in Jamaica are largely, if not mainly, of 

 coral growth, and represent a formation produced during a 

 long period of subsidence. 



In the foregoing discussion of the structure of coral reefs, as 

 also in the chapter treating of the physical history of the Ber- 

 mudas, I have used the term "subsidence" (and necessarily its 

 opposite elevation) in a relative sense, indicating a depression 

 or submergence of the land beneath the sea. But whether 

 this submergence was due to a positive movement on the part 

 of the land, or to a change of level (rise) in the water, cannot 

 readily be determined, as the phenomena attending either 

 form of movement would be practically identical. The broad 

 problem of oceanic transgression and continental stability, 

 which has been so forcibly outlined by Suess, cannot be 

 properly treated in this place. 



