GLACIAL-CONTROL THEORY OF CORAL REEFS. 231 



the new theory is correct, the atoll platforms were probably not the 

 loci of pre-Glacial atolls. There is, in fact, no apparent reason for 

 holding that great atolls or barrier reefs ever existed in pre-Pleistocene 

 time. The extent of the massive coral reefs in the Pleistocene islands 

 cannot be definitely stated, though in no case may it have been many 

 times greater than, for example, that of the fringing reef at Rodriguez 

 island in the Indian ocean. (See Fig. 28.) In any case it is unwise 

 to assume that massive reef-rock or any other strong rock capped the 

 whole of any Pleistocene island, which was truncated to form the wide 

 fiats bearing the present atoll reefs. 



In conclusion, the quantity of wave-benching implied by the 

 Glacial-control theory does not appear to represent a fatal objection 

 to that theory, if the varying nature of the Pleistocene islands and 

 shoals is well appreciated. 



Biology of Oceanic Islands. Another published objection is that 

 the existing faunas and floras of the oceanic islands do not accord with 

 a theory involving general crustal stability for the ocean floors during 

 the later geological periods. However, the literature of biogeography 

 shows such a diversity of opinions on this subject that the criterion 

 cannot be fairly described as now having any decisive value. Darwin, 

 Hooker, Salvin, Griesbach, Engler, M. Wagner, Wallace, Peschel, 

 Wolf, A. Agassiz, Stearns, Heller, Dall, and F. X. Williams have con- 

 cluded that the organisms of the Galapagos islands are not such as to 

 necessitate belief in a former connection of this purely volcanic archi- 

 pelago with any continent. Baur, H. Milne-Edwards, Von Ihering, 

 and Van Denburgh, after their biological studies, thought best to 

 assume a former connection with South America. Inasmuch as sharp 

 divergence of views affects one of the best known island groups, any 

 definite opinion regarding the origin of island species throughout the 

 wide coral seas can still have but little - value. Consensus among 

 the expert investigators is reserved for the distant future. The lit- 

 tle that is known about the matter does not appear to weaken the 

 Glacial-control theory, nor to support the subsidence theory, as ap- 

 plied to coral reefs in general. 



Difficulties of the Subsidence Theory. 



A discussion of all published hypotheses concerning the reefs will 

 not here be undertaken. Murray's solution theory, formerly re- 

 garded with favor by leading investigators, is now seen to be weak on 

 the quantitative side and is discounted by recent discoveries in typical 



