502 W. M. DAVIS SUBSIDENCE OF REEF-ENCIRCLED ISLANDS 



Eef erence may be made here to other statements by Yaughan, as sequels 

 to the one quoted above; they are to the effect that "many, if not all, 

 barrier reefs stand on marginal platforms [corrected hj^ the author to 

 read "stand on or margin platforms'^] which already existed previous to 

 Recent submergence and the formation of the modern reefs" (1914, a, 

 59 ) ; and that "a study of the charts of barrier-reef islands, as Viti Levu, 

 Fijis, and Tahiti, Society Islands, shows that the platforms are inde- 

 pendent of the presence of reefs, and therefore the relations in these 

 islands are similar to those indicated for barriers off continental shores, 

 for here the reefs are also superimposed on platforms antedating their 

 presence" (1914, &^ 33). As far as I can penetrate the problem, these 

 inferences are not borne out by the facts. 



It is probable enough that pauses in the submergence of a reef, such 

 as could be caused by the coincidence of slow subsidence and the slow 

 lowering of the ocean surface during the oncoming of a Glacial epoch, 

 might have caused a previously narrow barrier reef to widen greatly while 

 its lagoon was nearly or quite filled up with detritus, so that the reef and 

 lagoon together came to form what may be called a mature reef plain. 

 It is also possible enough that during a rapid submergence, such as might 

 be caused by the coincidence of slow subsidence with the slow rising of 

 the ocean surface during the passing of a Glacial epoch, might cause a 

 relatively narrow barrier reef to grow up on or iiear the margin of a 

 previously formed, mature reef plain, and more or less completely encircle 

 it. But the implication of the above quotation is that the platforms there 

 mentioned are not of coral-reef origin; and this is confirmed by the ex- 

 plicit statements regarding many reef -bordered lands, to the effect that 

 "the platforms have an existence independent of coral reefs and were 

 formed by other than coral-reef agencies," and that "an inspection of the 

 Admiralty charts for the eastern coast of Australia shows conclusively 

 that the platform on which the Great Barrier reef of Australia stands has 

 an existence independent of the Great Barrier reef" (1914, 33, 32). 



FACTS AND INFERENCES FROM CRARTS 



Yaughan's opinions regarding reefs in the Pacific are, as the above 

 quotations show, based not on local observation, but on a study of hydro- 

 graphic charts, and such charts do not give enough information- — apart 

 from the occurrence of embayments— regarding the physiographic devel- 

 opment of reef-bordered coasts to lead to safe conclusions. It has been 

 well said that "the principal value of the coral-reef investigation to geol- 

 ogy consists not so much in what has been found out about corals as in 

 the study of a complex of geological phenomena, among which coral reefs 



