1898.] Funafuti, Rotuma and Fiji 499 



windward side would do the same, and, where the wind and current 

 are in opposition, the reef would be growing equally vigorously on 

 all sides, as is found to be the case in the Marshall Islands. 



It is not, of course, necessary that all barrier reefs should have 

 gone through the fringing stage to the barrier condition. They 

 might equally well grow up on any bank off an island, which is 

 within the requisite depth for the reef-building organisms. I 

 believe that the Great Barrier Reef of Fiji and the reef, which 

 bounds the deep pool between Viti Levu and Vanua Levi, has been 

 thus formed. The reef round this pool is by no means complete, 

 and if it grew out from a fringing reef, there is no reason why it 

 should not be moderately so. There are, also, off the north of 

 Vanua Levu a large number of islands, and the line of mountains, 

 of which the Yasawas are the emerged peaks, appears as if it 

 extended round nearly in the line of the Great Barrier Reef. 

 Should such be the case, the double nature of this reef would be at 

 once explained. Indeed incrusting nullipores seemed to cover 

 most of the surface of the inner part. These only grow where the 

 water is constantly in motion, and to their protection outside from 

 solution the reef, I think, owes its existence. This talus theory 

 serves also to explain why terraces due to sudden subsidences are 

 not found outside the reef off islands, in the same way as terraces 

 are found in the raised reefs of the Solomon Islands, Cuba and 

 other lands. 



It is inconceivable that with the elevations which formed 

 the Lau Group of Fiji there have not been other upheavals, 

 which have brought areas within the depths, required by the 

 reef-building organisms, but many of its atoll-reefs are probably 

 due to different causes. After the reefs were first upheaved, it 

 would take a long time, owing to the loose nature of the rock 

 on the outside, for the organisms to get a firm hold. The 

 result has been that solution has gone on outside to such an 

 extent, that the whole thickness of the reef almost from its 

 highest point to the sea level has been exposed as a cliff in 

 many of the islands. After the reef was formed, the base of 

 the island would be protected by it and its solution would then 

 be very small. As the reef, however, spreads outwards on its 

 own talus a lagoon would be formed and the solution of the 

 limestone would at once recommence with renewed activity. 

 The final result would be that the whole island would be washed 

 away and an atoll-reef left. It is quite probable that the atoll- 

 reefs of the Lau Group, particularly the larger ones, owe their 

 origin to this. The Mbukatatanoa atoll-reef, east of Lakemba, 

 with a depth of 35 fathoms has probably been formed in this 

 way, and every intermediate stage from such an atoll-reef to high 

 coral islands with narrow fringing reefs can be found in the Lau 



