AGASSIZ: FIJI ISLANDS AND CORAL KEEFS. 131 



pltuuitiou of the formation of such remarkably sliaped reefs as the Nanuku 

 and Nukusemanu Eeefs (Plate 18), from the denudation and erosion of 

 an extended ridge or line of the summits»of independent islands, elevated 

 at the time wlien the great masses of ancient limestones were raised to 

 various heights perhaps np to one thousand feet. 



The Great Sea Eeef (Plate l) appears on the cliart as the continuation 

 of the chain of which the Yasawa group of islands are the only rem- 

 nants, and it may be that it represents its eastern continuation after its 

 denudation and erosion, and transformation into a submarine platform 

 for the growth of corals. Similarly the reefs extending to the east of 

 Vanua Levu towards the Yasawa group may be the western extension of 

 a range of which Sesaleka Peak and Yendua Islands formed prominent 

 points. 



GENERAL SKETCH OF THE FIJI ISLANDS AND CORAL REEFS. 



I went to the Fijis under the impression that I was to visit a charac- 

 teristic area of subsidence ; for according to Dana and Darwin there is 

 no coral reef region in which it is a simpler matter to follow the various 

 steps of the subsidence which has taken place. Dana, in his last dis- 

 cussion ^ of the coral reef question, states that it is impossible to find a 

 better sei*ies of islands than the Pijis to illustrate the gradual changes 

 (brought about by subsidence) which take place in transforming a a'oI- 

 canic island with a frino'ing: reef to one with a barrier reef, or to one with 

 an encircling reef ring, and finally to one in which the interior island 

 has disappeared and has left only a more or less circular reef ring. For 

 these reasons one of the Fiji atolls promised to be an admirable location 

 for boring and settling the question of the thickness of the coral reef of 

 an atoll. 



My surprise was great, therefore, to find within a mile from Suva an 

 elevated reef about 60 feet thick, and 120 feet above the level of the sea, 

 the base being vinderlaid by what is locally called " soapstone," ^ a kind 

 of volcanic mud. The western extension of this reef can be traced at 



1 Am. Journ. of Science, Vol. XXX., August and September, 1885. Dana says: 

 " The large Feejee group bears abundant evidence of subsidence in its very broad 

 reef grounds, barrier islands, and atolls." 



" The "soapstone" is largely composed of volcanic deTsris, mixed with tests of 

 Foraminifera, Pteropods, and Mollusks. Brady (Q. J. Geol. Soc. London, 1888, Vol. 

 XLIV. p. 1 ) considers the Ehizopod fauna such as one would expect from a depth 

 of 150 to 200 fathoms. 



