234 W. M. Davis — Shale?' Memorial Study of Coral Reefs. 



or more miles. After a careful study of all soundings then 

 available he concluded that a platform, " cut out in the course 

 of ages by the action of the sea," flanked the entire coast before 

 the reef was formed, and that the reef has been built up near 

 the edge of its northern part,* where the ocean is warmer, but 

 without submergence. No reason is given for the change from 

 destructive abrasion to constructive reef building. 



The abundant embayments and the rare cliffs of the Queens- 

 land coast, and the numerous off-shore islands that rise in sub- 

 mountainous form with embayed coasts, little cliffed, in the 

 lagoon of the Great Barrier reef are, as Andrews, Hedley and 

 Taylor have shown, sufficient to disprove the supposition that 

 the part of the platform which they surmount is due to marine 

 abrasion without submergence ; and the consensus of opinion 

 among geologists would, I believe, be strongly against regard- 

 ing the continental shelf farther south along the Australian 

 coast as a surface of abrasion alone, without submergence, rather 

 than as a surface of limited abrasion combined with abundant 

 deposition, followed by submergence. Hence Guppy's explana- 

 tion of the Great Barrier reef without submergence seems to 

 me untenable. 



Reefs and Reef Platforms. — A platform theory for barrier 

 reefs has lately been proposed by Yaughan, who regards recent 

 submergence, proved by the embayments of the central islands, 

 as the determining cause for the upgrowth of existing barrier 

 reefs, but who interprets the deeper and larger part of the 

 entire reef-mass as a " platform" of earlier origin, independent 

 of coral formation. f As this investigator has not yet published 

 his views regarding the origin of the reef platforms, his gen- 

 eral theory will not be here discussed further than to note that 

 it seems inadmissible for many barrier reefs in the Fiji, Soci- 

 ety and other groups, in which the total thickness of the reefs 

 appears to be much greater than the depth of the " plat- 

 forms " ; that the occurrence of certain discontinuous barrier 

 reefs on a submarine platform, as instanced by Yaughan, 

 seems to be explicable by the hypothesis that the platform 

 represents a rapidly submerged reef which had been broadened 

 during a pause or still-stand after an earlier long-continued 

 submergence, and that the present discontinuous reef has grown 

 up imperfectly during the recent and rapid submergence that 

 drowned its predecessor. Like Guppy, Yaughan points to the 

 extension of the continental shelf along the east coast of Aus- 

 tralia, south of the Great Barrier reef, and infers from this 



* H. B. Guppy, "The Origin of Coral Reefs," Trans. Victoria Inst., 

 xxiii, 51-61, 1890. 



f Sketch of the Geologic History of the Florida Coral Reef Tract, Journ. 

 Wash. Acad. Sci., iv, 26-34, 1914; see p. 33. "The Platforms of Barrier 

 Reefs," Bull. Amer. Geogr. Soc, xliv, 426-429, 1914. 



