Coral Reefs and Islands. 153 



11. Since a fringing reef is, by the theory of Darwin, the 

 first stage in the origin of an atoll, it was naturally regarded 

 by him as, in general, evidence of little or no subsidence, and 

 even, at times, of elevation. But since (1) bold shores are 

 an occasion for narrow reefs and for their absence, (2) sub- 

 marine volcanic disturbances and eruptions about volcanic 

 lands would destroy living reefs or retard their progress 

 where begun, (3) islands of active volcanoes have small or 

 no reefs, and (4) abrupt subsidences of only 120 feet would 

 put reef-corals below a surviving depth and so lead to the 

 beginning of a new reef, I was led to regard the evidence 

 from a fringing reef for no, or little, change of level as of 

 very doubtful value. But the doubts, while making such 

 evidence generally useless, do not affect the value of the pre- 

 ceding arguments for subsidence. Darwin used the evidence 

 from fringing reefs only to mark off the limits of the area of 

 Central-Pacific subsidence to which his coral-island theory 

 had led him ; and the same limits essentially are reached not- 

 withstanding the doubt. Instead of concluding that the 

 region along these limits was one of recent elevation or at 

 least of no subsidence, I was led to speak of it as one either 

 of no subsidence or of less subsidence than over the central 

 area referred to. The difference between us is small. 



12. The true value of fringing-reefs as evidence in the 

 question of change of level should be appreciated in this dis- 

 cussion, as is apparent from the objections to Darwin's theory 

 which have been urged; and I mention a few facts from the 

 Pacific islands in its elucidation. 



On Darwin's map, the Marquesas group is left uncoloured, 

 which means, doubtful as to subsidence or not. The Tahitian 

 group (Society Islands) is coloured blue; that is, it is included 

 within the area of coral-reef subsidence. The Navigator or 

 Samoan Islands are coloured red, or placed in the area of 

 elevation ; the Feejees blue ; the Sandwich Islands red. The 

 facts are these. 



The Marquesas Islands are an example of absence of reefs 

 to a large extent, with only small reefs where any. But the 

 shores are mostly too bold for reefs ; and hence their small- 

 ness bears no testimony as to elevation. Along the bold 



the belt on its north side may continue eastward of the ( Challenger ' 

 route. Many more lines of soundings are needed to substitute sure con- 

 clusions for the above suggestions. 



The existence in the ocean of parallel belts of deeper and shallower 

 waters, such as are here inferred to exist, and such as are actually in- 

 dicated by the parallel lines of high islands and atolls, is in accordance 

 with the facts over the continents. 



