CORAL REEFS 229 



continues, and as with increasing knowledge the problems 

 concerned appear to become more and more complicated, 

 demanding more extended investigations of ever-increasing 

 diiliculty and expense, it is impossible that a complete set 

 of explanations of the phenomena will be discovered in our 

 generation. 



It has been suggested by some of the bitter critics of 

 evolution that Darwin has been discredited by his theory of 

 coral reefs. Nothing could be more absurd. The simple 

 and beautiful theory which he expressed was the starting- 

 point of a great scientific movement and has led to the 

 discovery of an immense store of facts about the physical 

 geography of the tropical seas of the greatest interest and 

 importance. If it is borne in mind that at the time he 

 wrote his famous book on coral reefs and islands our know- 

 ledge was far less than it is now, his work stands out as a 

 model of scientific reasoning and inference. 



The evidence afforded by the embayments of islands that 

 are surrounded by barrier reefs, by the unconformable 

 relation of elevated reefs to the rocks on which they rest, 

 and by other geological considerations, appears to support 

 the view that subsidence of the earth's crust in the coral 

 reef zone has occurred over even a wider area than Darwin 

 himself believed. 



The doubts that have been expressed, as the result of 

 more recent investigations, that solution or scouring could 

 have produced lagoon depths of over 20 fathoms, appear to 

 have turned the scale of opinion in favour of Darwin's 

 explanation of these depths by subsidence. 



The principal conclusion made by Darwin, which has not 

 been confirmed, and will probably be abandoned, is that the 

 reefs were formed by long-continued depression of the lands 

 on w'hich they rest, and are consequently, in some cases, a 

 few thousands of feet in thickness. There is no evidence 

 either from borings in modern reefs or from the study of 

 elevated reefs of the existence of such vast masses of con- 

 tinuously formed coral rock. It appears much more prob- 

 able that in most parts of the coral zone periods of subsi- 

 dence of relatively short duration have alternated with 



