Coral Reefs and Islands. 281 



the present level was consequently within the coral-reef 

 period. It is hence hardly to be doubted that the making of 

 the Florida, Bahama, and other West India coral-reefs was 

 going on during the progress of a great subsidence. None 

 of the facts mentioned by observers are opposed to this 

 view. 



It is of interest to note here that on Cuba and Jamaica 

 there are elevated coral-reefs, the highest on Cuba 1000 feet 

 above the sea, according to Mr. Agassiz, and probably at one 

 point 2000, according to Mr. W. O. Crosby's observations *, 

 and on Jamaica 2000 feet, according to Mr. Sawkins ; 

 indicating that there have been upward movements subsequent 

 to the downward. Mr. Crosby argues that the great thickness 

 of the now elevated reefs could have been produced only 

 u during a progressing subsidence ;" so that " we have 

 apparently no recourse but to accept Darwin's theory." 



C. It has been urged by Mr. Semper, Dr. J. J. Rein, Mr. 

 A. Agassiz, Mr. Murray, Dr. Geikie, and others, that since 

 the growing calcareous deposits of the sea-bottom are slowly 

 rising toward the surface by successive accumulations of the 

 shells and other debris of marine species, they may have been 

 built up locally in various regions of the deep seas (as they 

 actually are now about some islands) until they were near 

 enough to the surface to become next a plantation of corals ; 

 and that in this way atolls became common within the area 

 of the tropical oceans. The method is regarded as setting 

 aside subsidence. 



a. The advocates of this hypothesis have not pointed to 

 such a mound now approaching the ocean's surface on the 

 western border of the Gulf- Stream, where the depth over the 

 remarkably luxuriant region is least ; and none over any part 

 of the tropical Pacific. It is suggested that the Chagos Bank 

 may be one example ; but it is not known to be so. Professor 

 Semper states that he found evidence of pelagic life, instead 

 of modern corals, in the lower part of the elevated reefs of the 

 Pelews. Dr. Geikie cites from letters by Dr. Guppy in 

 < Nature' of Nov. 29, Dec. 6, 1883, and Jan. 12, 1884, the 

 fact that in elevated reefs on the Salomon Islands, 100 and 

 1200 feet high, the coral-rock forms a comparatively thin 

 layer over impure earthy limestone abounding in foraminifers 

 and other pelagic organisms such as Pteropods. Such obser- 



* Proc. Boston Soc. Nat. Hist. xxii. p. 124, (1882), and in abstract in 

 Silli man's American Journal, xxvi. p. 148 (1883). 



