174 R. A. Daly — Problems" of the Pacific Islands. 



is a section of a sinking island, in which typical levels for a 

 fringing reef (Fr), a barrier reef (Ba), and an atoll reef (At) 

 are indicated, reefs of these types successively appearing at 

 1, 2, and 3. Since corals cannot form massive reefs at depths 

 greater than 150 feet, a bore-hole sunk on the edge of a large 

 atoll, like Funafuti, must enter continuous talus at a level not 

 more than 150 feet below the sea surface. Hence, the boring 

 actually made at Funafuti does not in any case afford a test 

 between the subsidence theory and its competitors. 



What is needed is a series of borings at points situated well 

 inside the atoll and barrier reefs. Several of the Pacific atolls, 



Figs. 13-15. 



ELEV ATE D LAGOON 



J Sea Miles °_ 



Km. 



Figs. 13-15. Sections of uplifted islands. Water shown in solid black ; 

 rocks, including the elevated limestones, are lined. Vertical scale is three 

 times the horizontal. 



13. Elevated atoll of Kambara island, Fiji group. 



14. Elevated island of Nauru, near the main Gilbert group. 



15. Ocean (Paanopa) island, near the main Gilbert group. 



like Jaluit, are provided with coral-knoll islets favorably placed 

 for a really valuable test of the subsidence theory through 

 boring. 



2. How rapidly is reef detritus carried from the growing, 

 oceanward face of a reef into the lagoon, so as to fill the 

 "moat"? How do the inner slopes of reefs agree with the 

 hypothesis that the lagoon floors have been aggraded and flat- 

 tened to the extent demanded by the theory ? What are the 

 actual slopes of the coral knolls dotted over the lagoons, and 

 what is their bearing on this matter of lagoon filling? 



3. What new light can uplifted coral islands throw on the 

 value of the subsidence theory ? How can their repeated asso- 

 ciation with adjacent atolls and barrier reefs be explained ? 

 What is the maximum thickness of true reefs in the elevated 

 islands? Figures 13, 14, and 15 are sections, respectively, of 

 Kambara of the Fijis, and of Nauru and Ocean islands near 

 the main Gilbert group ; all three have been uplifted. 



4. Is there any direct connection between the forms of exist- 

 ing reefs and the Tertiary fragmentation of the Australasiatic 



