+ 
AGASSIZ: FIJI ISLANDS AND CORAL REEFS. 85 
crease in width, and encroach upon the lagoon, but that is a different 
proposition, as shown by Gardiner, from the filling up of the lagoon. 
Gardiner! assumes that the limestones of the Fijis cannot have had 
any different origin from that of many of the atolls and barrier and 
fringing reefs of the present day.” But it seems to me that, inasmuch 
as these elevated limestones are of tertiary age and have been uplifted 
to heights varying from a few feet above the level of the sea to nearly a 
thousand feet to form subsequently platforms of submarine erosion upon 
which the recent reefs have grown, we cannot claim that they have been 
deposited, as recent corals have been, within comparatively narrow batliy- 
metrical limits, the dolomitization of the elevated tertiary limestone 
having gone on to a considerable extent, while that of the recent reefs 
is insignificant. 
Gardiner® looks upon Naiau, Tuvutha, and other islands as perfect 
specimens of raised atolls. I have elsewhere given my reasons for not 
accepting such a view, and for considering the interior depressions of 
such “elevated atolls” as huge sinks similar to those formed in the 
A£olian hills of the Bahamas and Bermudas, and which eventually result 
in the formation of sounds or lagoon-like depressions. Gardiner* does 
not think it possible that denudation owing to climatic causes could 
have been of sufficient importance to have greatly affected the position 
of the summits. It seems to me that the gradation we can trace in the 
summits and outlines of such old island masses as Naiau, Kambara, 
Mango, Fulanga, Ongea, Aiwa, and others indicate, on the contrary, 
a most extraordinary denudation and accompanying submarine erosion. 
Gardiner ® himself has given very much the same examples which I used 
in tracing the gradual changes hinted at above, only he attributes them 
wholly to the solvent action of the sea, while I am inclined to call into 
action in addition the effect of denudation and erosion, and to attribute 
to them a more important share than to the solvent action of the sea 
in the successive stages of the changes in the elevated limestone land 
masses, from an island with a fringing reef to a true atoll. 
Under what conditions these tertiary coralliferous limestones of great 
thickness have been deposited is a distinct question from that of the 
formation. of atolls through subsidence by the upward growth of corals 
during the present geological period. Neither the borings through a 
coral reef growing upon a substratum of tertiary limestone, nor the 
1 Loe. cit., p. 467. 4 Loe. cit., p. 470. 
2 Loe. cit., p. 467. 5 Loc. cit., p. 471. 
4 Loe. cit., p. 470. 
