504 W. M. DAVIS SUBSIDENCE OF REEF-ENCIKCLED ISLANDS 



Agassiz alone has given an adequate description. The barrier reef of 

 Tahiti surmounts the margin of the abraded platform, now submerged 

 to a depth of a hundred fathoms or more, as I have shown in detail in an 

 article to be published in the Annates de Geographie during 1918; but 

 no other member of the Society Islands is similarly cut back in sea-cliffs, 

 and hence no other reef in that group rests on a submerged abraded plat- 

 form — unless, as will be shown on a later page to be eminently possible, 

 the submergence of the platforms has been so great as completely to drown 

 the cliffs that must have risen to heights of 1,000 feet or more from their 

 inner margin ; and platforms so greatly submerged have no close relation 

 to the shallow platforms inferred by Yaughan, which are supposed to lie 

 about 40 fathoms below present sealevel. 



According to the best application that I could make of Andrews' physio- 

 graphic studies of eastern Australia during my journey there in August, 

 1914, the Great Barrier reef of the Queensland coast has been formed by 

 upgrowth during the long continued but intermittent down-warping of 

 the continental margin; and the conditions for reef growth during the 

 earlier stages of down-warping appear to have been just as good as they 

 are today. The total thickness of this vast reef may well be thousands 

 rather than hundreds of feet. The present reef is more probably con- 

 structed on or near the margin of a preexistent, mature reef plain than 

 any other reef that I have seen, as I have shown elsewhere in some detail 

 (1917, c). Thus the reefs of Yiti Levu, Tahiti, and northeastern Aus- 

 tralia have been formed under diverse conditions that do not by any 

 means support Yaughan's conclusions. All of these reefs owe their oppor- 

 tunity of upgrowth to the subsidence of their foundations, whatever the 

 previous form of the foundations may have been. 



DETAILS CONCERNING FIJI REEFS 



As my acquaintance with the reefs of the Fiji Islands is more extended 

 than v^ith those of most of the other groups that I visited in 1914, it is 

 particularly with respect to the Fiji reefs that I must take exception to 

 Yaughan's opinion, quoted above, that they are "superimposed on plat- 

 forms antedating their presence'^ ; and especially to his later statement to 

 the effect that "Andrews has essentially confirmed" this opinion (1916, 

 133). There is nothing in Andrews' recent article on Fiji to warrant 

 such an assertion; his brief summary regarding the largest island of the 

 group is that its "present great barrier reef, which rises to the level of 

 the sea, has thus, in all probability, been built up by coral-reef organisms 

 on the submerged lowlands of Yiti Levu" (1916, 138) ; but the lowlands 

 that are submerged along the southern border of the island, where An- 



