Agassis — Islands and Coral Beefs of the Fiji Group. 117 



north to Ongea on the south, have been subject to an elevation 

 of at least 800 feet ; as there is abundant proof that a great 

 part of the thickness of the elevated reef has been eroded to 

 reduce it in certain localities to the level of the sea or to leave 

 at others bluffs and islands or islets, the occurrence of which 

 we have traced at so many points. 



But the evidence of a very considerable elevation is not 

 limited to that furnished by the remains of the elevated reefs 

 just mentioned : it is natural to assume that the elevation we 

 have just traced was but a part of a more general elevation 

 which perhaps took place in late Tertiary times and in which 

 the whole group was involved. It is plain that there must 

 have been most extensive denudation and erosion going on 

 throughout the group for a very considerable period of time, 

 geologically speaking. The outlines of the islands deeply 

 furrowed by gorges and valleys, the sharp and serrated ridges 

 separating them, the fantastic outlines of the peaks of Viti 

 Levu, Vanua Levu and Ovalau, all attest to the great work of 

 atmospheric agencies which has been going on for so long. 

 The separation of islands, islets or isolated rocks from the 

 points or spurs of the larger islands also bears witness to the 

 great length of time during which action of the sea necessary 

 to bring about their separation has been at work : adding to 

 this the fact that we are in a region of a former powerful and 

 extensive volcanic activity, the traces of which can still be 

 seen in all directions, forces which have undoubtedly played a 

 great part in the lifting of the island masses and their subse- 

 quent shaping to their present outlines. 



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; 

 furthermore that they have had nothing to do in our time with 

 the building up of the barrier reefs surrounding either wholly 

 or in part some of the islands; I also believe 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 reefs either of the atolls or of the barriers 

 form only a crust of very moderate thickness upon the under- 

 lying base. This base may be either a flat of an eroded ele- 

 vated reef or of a similar substructure of volcanic rocks, the 

 nature of that base depending absolutely upon its character 

 when elevated in a former period to a greater height than it 

 now occupies. 



Denudation and erosion act of course more rapidly upon the 

 elevated reef rocks than upon those of a volcanic character. 

 It is therefore natural to find that the larger islands like 

 Kandavu, Taviuni and Ovalau are of volcanic origin, while the 



