70 BULLETIN : MUSEUM OF COMPARATIVE 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 wholly or in 
part of elevated limestone, into islands with large interior sounds like 
Fulanga can be readily followed by examining such islands as Wangava 
(Plate 22), Tuvutha, Naiau (Plate 20), or Vanua Vatu (Plate 21), in 
which the interior basin is still surrounded by a high rim. Next 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 Namuka (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 smal] 
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 Ngele 
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. When 
the island and islets in Vatu Leile, Ngele Levu, Wailangilala, Katavanga, 
Reid Reef, Aiwa, Oneata, Yangas4, and Ongea have disappeared by sub- 
sequent erosion, it will be wellnigh impossible to detect the nature of the 
substratum upon which the modern reef is growing. At that time the 
lagoon will probably have become gouged out much as Ngele 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 18), Totoya (Plate 16), Kimbombo 
(Plate 19), Nairai (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 great variety 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, 
