AGASSIZ: FIJI ISLANDS AND COKAL EEEFS. 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 compai-atively narrow bathy- 

 metrical limits, the dolomitization of the elevated tertiary limestone 

 having gone on to a considerable extent, while that of the recent reefs 

 is insio'uificant. 



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 tlie 

 ^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 tho 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 b}' 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 Loc. dt., p. 467. * Loc. at., p. 470. 



■■^ Loc. dt., p. 467. ^ Loc. cit., p. 471. 



•' Loc. cit., p. 470. 



