70 BULLETIN : MUSEU:M OF COMPAEATIYE. ZOOLOGY. 



these islands without having recourse to subsidence. Yet other writers 

 upon coral reefs would look upon some of these islands as instances of 

 raised atolls. 



The gradual transformation of islands, composed either wliollv or in 

 part of elevated limestone, into islands with large interior sounds like 

 Fulanga can be readily followed by examining such islands as Waufava 

 (Plate 22), Tuvutha, Xaiau (Plate 20), or Vanua Vatu (Plate 21), in 

 which the interior basin is still surrounded by a high rim. Xext fol- 

 lowed such islands as Mango (Plate 19), in which the interior basin has 

 at one extremity been transformed into a diminutive sound ; then follow 

 such islands as Xamuka (Plate 22), the rim of the basin of which has 

 been eroded so as to leave only .parts of it, and the outline of which has 

 been deeply cut into by a large outer sound. We pass next to such a 

 group as Ongea (Plate 22), and next to such groups as Yangasa (Plate 

 22), of which the rim of the basin is represented only by four small 

 islands scattered within the encircling reef; next to Oneata and Aiwa, 

 where a single island, comparatively small, represents the former extent 

 of the elevated limestone area of those groups. And a still further stage 

 of erosion and denudation is represented, as stated above, by Xgele 

 Levu, Wailangilala, and other atolls in Lau. 



Vatu Leile (Plate 9) must have sloped very rapidly eastward to have 

 attained its present condition, and we can readily follow it to a time 

 when it will be flanked on the west side by a line of narrow islets very 

 similar to those now existing on the north side of the lagoon. "WJien 

 the island and islets in Yatu Leile, !N'gele Levu, Wailangilala, Katavanga, 

 Eeid Reef, Aiwa, Oneata, Yangasa, and Ongea have disappeared by sub- 

 sequent erosion, it will be wellnigh impossible to detect the nature of the 

 substratum upon which the modem reef is growing. At that time the 

 lagoon will probably have become gouged out much as Xgele Levu has 

 been. A similar difficulty will naturally be encountered, though at a 

 later period, in determining the geological composition of the substratum 

 underlying the modern coral reef in the atolls of Wakaya, Makongai 

 (Plate 15), Mbengha (Plate 8), North and Great Astrolabe Reefs (Plates 

 9, 10, 11), Budd Reef (Plate IS), Totoya (Plate 16). Kimbonibo 

 (Plate 19), Xairai (Plates 12, 14), Komo (Plate 22), and others, when 

 the islands now existing on the edge or within the encircling reefs have 

 disappeared from denudation and submarine erosion. 



This is another instance of the eri'eat varietv of causes which have been 

 active in producing the present physiognomy of the reefs of the Fijis, 

 and shows the impossibility of assigning any one factor, like subsidence. 



