AGASSIZ: FIJI ISLANDS AND CORAL 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 Fulanga land to a few large islands left 
isolated in the interior of an encircling reef and connected only by a few 
mushroom-shaped or conical islets, the interior of the lagoon being 
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 Ngele Levu, and the Oneata, Ongea, and Yan- 
gasi 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), Reid Haven, Vanua 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 
Reefs (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 be 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 lagoon? We can thus explain the peculiar formation of 
