‘> iP, 
AGASSIZ: FIJI ISLANDS AND CORAL REEFS. 137 
directions, and which has undoubtedly played a great part in the lifting 
of the island masses and their subsequent shaping to their present out- 
lines. From this evidence I am inclined to think that the corals of to- 
day have actually played no part in the shaping of the circular or irregular 
atolls scattered among the Fiji Islands, that they have had nothing to do 
in our time with the building up of the substructure of the barrier reefs 
encircling either wholly or in part some of the islands, that their modi- 
fying influence has been entirely limited in the present epoch to the 
formation of fringing reefs, and that the recent corals living upon the 
outer margin of the reefs, either of the atolls or of the barriers, form only 
a crust of very moderate thickness upon the underlying base. This base 
may be either the edge of a submarine flat, or of an eroded elevated 
limestone, or of a similar substructure composed of volcanic rocks, the 
nature of that base depending absolutely upon its character when ele- 
vated in a former period to a greater height than it now has ; denudation 
and erosion acting of course more rapidly upon the elevated coralliferous 
limestones than upon those of a volcanic character. It is therefore natu- 
ral to find that the larger islands, like Kandayu, Ovalau, and Taviuni 
(Plates 1, 3, 4,7, 10, 11), are of volcanic origin, while the islands which once 
occupied the area of the lagoons of Ngele Levu, Nanuku Reefs, Vanua 
Mbalavu, the Argo Reefs, the Oneata, Yangasé, Aiwa, Ongea, and Vatu 
Leile clusters, were composed of elevated coralliferous limestones. They 
have disappeared almost entirely, leaving only here and there a small 
island to attest to the former existence of a more extensive elevated 
limestone, once covering the whole area of what is now an atoll (Plates 
1, 17, 18, 19-21). Smaller volcanic islands, like Matuku, Moala, Ngau, 
Nairai, and Koro (Plates 1, 12, 13, 14, 16), also show the greater or 
smaller extent to which each has been eroded after its elevation, being 
least in Koro (Plate 3*) and Matuku (Plate 16), and somewhat more in 
Moala (Plate 16) and Ngau (Plate 13), and still more in Nairai (Plate 
14), while in such volcanic islands with atolls as Mbengha (Plate 8), 
Wakaya, and Makongai (Plate 15) the denudation and submarine ero- 
sion’ has been still greater, the islands covering but a comparatively 
1 Dana (p. 280) accounts for the formation of the shore platform by the action of 
the sea. We goa little further, and assign to the action of the breakers and of the 
currents in carrying loose material to sea the formation of channels between the 
outer reefs and the shore ; these become lagoons inside of barriers or encircling reefs, 
and finally scoop out the lagoons of atolls. Dana (p. 181) insists fully as strongly as 
Darwin upon the identity of origin of the encircling atoll reef and the outer reefs 
enclosing high or low islands: “The lagoons are similar in character and position 
