256 W. M. Davis — Shaler Memorial Study of Coral Reefs. 



various volcanic islands in the Fiji group, the thickness of the 

 limestone at the margin of Mare must be at least 5000 or 6000 

 feet. 



Uvea, the northwestern member of the group, is a gently 

 tilted atoll about 40 kil. in diameter ; its eastern half is uplifted 

 in an irregularly crescentic ridge, highest and broadest at the 

 middle, lowest and narrowest at the horns ; the depressed west- 

 ern half is marked by a series of small islands that presumably 

 grew up to the sea surface as down-tilting took place. The 

 lagoon deepens very gradually from east to west ; its eastern 

 border is marked by a long beach composed very largely of 

 delicate shells and their fragments, without corals. 



Testimony of Elevated Reefs. — The glacial-control theory 

 seems to have little or no application in explaining the elevated 

 reefs above described ; some of them must have been formed 

 and placed out of reach by emergence before its processes 

 came into operation. Let it be remembered, however, that the 

 glacial-control theory does not attempt to explain coral reefs in 

 the larger sense of the term, which includes not merely the 

 visible reefs at the sea surface, but the whole submarine lime- 

 stone mass under the lagoon as well as under the reef; the gla- 

 cial-control theory accepts the reef-masses as completed in 

 preglacial time — presumably on still-standing foundations — and 

 merely gives a special explanation of their lagoons and of so 

 much of the reef-mass as now encloses the lagoons. 



As to other theories of coral reefs, it is certainly significant 

 that the only one of them which receives any support from the 

 facts here stated regarding elevated reefs is Darwin's theory of 

 upgrowth during subsidence. This is the more important when 

 it is remembered that the above-named elevated reefs were not 

 visited because they were supposed to present evidence in favor 

 of one theory or another, but simply because they were accessi- 

 ble in the course of my voyage. All of them — except the 

 little reefs of Walu bay, near Suva, Fiji, which are intercalated 

 in a series of inclined delta-front strata, and the great elevated 

 atoll of Lifu in which no foundation is visible — rest uncon- 

 formably upon eroded foundations, which must have subsided 

 before the reefs were formed upon them. The entrance of 

 the Oahu reef-limestones into the valleys of that well-dissected 

 island, the horizontal attitude of the strata deep in the mass of 

 the reef-limestones of Vanua Mbalavu, and the freedom of the 

 central limestones of Lifu from fossil corals, all testify against 

 the theory of out-growing reefs on still-standing foundations. 

 The large thickness of the limestones of Yanua Mbalavu, 

 Mango, and the Loyalties testifies against the theory of veneer- 

 ing reefs on wave-cut platforms. Hence although the testi- 

 mony here presented by elevated reefs is more varied and more 



