AGASSIZ: FIJI ISLANDS AND COKAL REEFS. 69 



summits nearly as high on the southwest coast, and sloping seaward 

 towards the east (Plate 80). Atmospheric agencies gradually reduced 

 its height, cutting out at the same time an interior basin, the eastern 

 rim of which (Plate 81), being lowest, was soon denuded and eroded in 

 part. One can readily see (Plate 22) how longer denudation and ero- 

 sion would reduce the existing Fulauga land to a few large islands left 

 isolated in the interior of an encircling reef and connected only bv a few 

 mushroom-shaped or conical islets, the interior of the lagoon bciuo- 

 dotted with coral heads, the recent corals on the outer edge of the sub- 

 marine flat forming a reef crust of moderate thickness. This coral rim 

 has been broken through, and the action of the sea has gradually 

 hollowed out in the interior a circular sound resembling an extinct crater 

 (Plate 22), which has arisen solely from the disintegration of the inner 

 part of the elevated limestone. Many parts of this still exist as small 

 mushroom-shaped or conical islands (Plate 83). 



It is also probable that some of the ancient elevated reef flats may 

 have been converted into atolls by causes similar to those which have 

 produced the crater-like Sound of Fulanga. This has perhaps been the 

 case with such atolls as Xgele Levu, and the Oneata, Ongea, and Yan- 

 gasa groups. In both Ongea Levu and Ongea Ndriti (Plate 22), incipient 

 sounds are forming which will cut these islands into two or more com- 

 ponents, each one of which will in its turn be dissected into smaller 

 islands or islets, till finally the remaining land may be all reduced to 

 insignificant islands and islets, as on Ngele Levu (Plate 17), or on "Wai- 

 langilala (Plate 18), Pteid Haven, A'anua Masi (Plate 20), Motua Levu 

 and Motua lai lai. Duff" and Adolphus Reefs (Plate 18), or the islets may 

 have totally disappeared and no vestige of the former land area remain 

 except the sunken coral heads and rocks of such atolls as Thakau Levu, 

 Thakau Motu (Plate 22), Thakau Lekaleka (Plate 21), the Ongea 

 Eeefs (Plates 20, 21), Thakau Tambu (Plate 20), Thakau Mata Thuthu, 

 and Thakau Vutho Vutho (Plate 17), with the reservation that some of 

 these atolls may be the result of the denudation and submarine erosion 

 of volcanic islets or peaks or ridges, and not necessarily of elevated 

 coralliferous limestones. 



Are not islands such as Phoenix, Birnie, Kean, Howland, Baker, and 

 Enderbury, which have depressions in the centre and no lagoons, islands 

 which are gradually being denuded to the level of the sea, and the next 

 stage of which will V)e the formation of a lagoon (sound) by the cutting 

 in of the sea across the rim at one or more points, forming islands or 

 islets round the lagoonl We can thus explain the peculiar formation of 



