AGASSIZ : FIJI ISLANDS AND CORAL liEEFS. 121 



a fringing reef flat covered with Alcyonariaus (Plato 76), similar to 

 those figured by Keut. 



Gardiner^ has observed the important part which incrusting coralline 

 algae perform in Fiji in supplying the material for a reef rock of compact 

 homogeueous structure ; they iindoubtedly assist materially in prevent- 

 ing the disintegration of dead corals, and their subsequent comminution 

 by the action of the waves. In an intei'esting article on the calcareous 

 algse of the Gulf of Naples,^ "Walther has given an excellent account 

 of the part which coralline algaj like Lithothamnium play in building 

 up amorphous limestone deposits of considerable tiiickness from the 

 obliteration of its structure.^ But he has confused the theory of the 

 formation of reefs with the theory of the formation of limestone deposits 

 of great thickness, one of which is Ixised on an assumption, the other 

 which is not in the least open to doubt. It is evident, however, that 

 those who have examined coral reefs have not attributed to coralline 

 algae the share which they have in building up recent amorphous lime- 

 stone deposits of considerable thickness. 



The following list of algae collected I owe to the kindness of Professor 

 Farlow : Amphiroa fragilissima Lam'x ; Galaxaura fragilis Lam'x, var. 

 fastigiata Decaisne ; Liagora Preissii Louder, var. pacifica Grunow ; 

 Padina Pavonia (L.) Gaillon ; Dictyata ciliata J. Ag. sterile ; Turbina- 

 ria conoides Kg. ; Hydroelathrus cancellatus Borg. ; Sphacelaria furci- 

 gera Kg. 1 sterile ; Caulerpa Freycenetii C. Ag. ; C. clavifera (Turn.) 

 C. Ag. ; C. complanata J. Ag. ; Halimeda macroloba Decaisne ; H. 

 Opuntia (L.) Lam'x; H. polydactylis J. Ag. ; Aurainvillea comosa 

 (Harv.) Murray &, Boodle ; Aur. papuana Murray & Boodle ; Dictyo- 

 sphseria favulosa Decaisne ; Valouia segagropila (Roth) J. Ag. ; Yalonia 

 utricularis J. Ag. 



ISLANDS AND CORAL REEFS DESCRIBED FROM THE CHARTS. 



With the exception of the Argo Reefs (Plates 19, 20), the islands 

 and reefs we did not visit were insignificant in size, or, judging from 

 the charts, presented no point of interest not included in those we ex- 

 amined. I may mention among these Vanua Vatu (Plate 21), a small 

 circular island with a depressed central summit, about a mile and a half 

 long. It is- composed of elevated coralliferous limestone rising to 310 



1 Loc. cit., p. 477. 



2 Zeitsch. d. deutschen geol. Gesell., Heft 2, Bd. XXXVII., 1885, p. .329. 

 8 See also an article by Fresh, Neues Jahrbuch f. Mineral., 1892, II. 169. 



