AGASSIZ: FIJI ISLANDS AND CORAL REEFS. 81 



where we can begin the study at the very base of the elevated limestoue 

 reef at its point of contact with tlie underlying volcanic rock, will teach 

 us a great deal regarding the interior structure of a coral reef. This we 

 can follow to the surface, or nearly so, by following the faces of exposed 

 cliffs or the slopes of the ridges. Of course, the uppermost part of the reef 

 rock, that which formed the original surface of the reef, will have been 

 denuded and eroded to a considerable depth. Eut it ought to be possible 

 from the study of an extensive area of an elevated reef, both vertical 

 and horizontal, to settle the question of the growth of a reef seaward by 

 its gradual extension upon a talus formed at a comparatively shallow 

 depth (say twenty fathoms) from the fragments and masses which have 

 dropped at the foot of the sea slope of the reef, after having been de- 

 tached by the action of the breakers from the edge of the reef. It is 

 natural to suppose that there must exist at the base of the reef a num- 

 ber of coral masses, judging from the multitude which are thrown upon 

 the sea face of any modern reef when exposed to violent breakers. 



Dr. William H. DalP has been kind enough to examine the fossil 

 mollusks which I collected from the elevated limestone reefs in the 

 Fijis. He coutirms the impression I had formed of their late tertiary 

 age. Dr. Dall writes : " The fossils comprise Turbo, Cassis, Lithophaga, 

 Macha, Teilina, Meretrix, Dosinia, Chama, Pholas, and fragments of 

 Pecten. None of the genera are extinct. The rock, however, looks 

 decidedly too old for Pleistocene. I should say the fossils were younger 

 than Eocene, and might be either Miocene or Pliocene." 



The boring which I started at Wailangilala Island in the atoll of the 

 same name reached at forty feet a limestone similar in all respects to 

 that composing the elevated reefs we had observed at Ngele Levu, 

 at Yanua Mbalavu, at Mango, at Yangasa, at Oneata, at Ongea, at 

 Kambara, at Yatu Leile, and at different points along the eastern, 

 southei'n, and western shores of Yiti Levu. At some points the elevated 

 limestones attain a height of over 1,000 feet (Yatu Yara Island 1,030 

 feet), and the volcanic rocks underlying the elevated limestone reefs 

 were observed at Yanua Mbalavu, at Mango, at Kambara, and at several 

 points along the southern and western coast of Yiti Levu. A renewed 

 examination of tlie elevated reefs of the Paumotus, of the Friendly 

 Islands, of the Gilbert, Ellice, and other groups of atolls in the Pacific 

 will be needed to determine their age and correlation to the Fiji ele- 

 vated limestones. At any rate, it is evident that the tertiary corallif- 

 erous limestones of Fiji have not played any part in the formation of 

 1 See Am. Journ. Science, Vol. VI. p. 165, 1898. 



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