1898.] Funafuti, Rotuma and Fiji. 467 



3. Volcanic Islands. 



The rock of these islands is usually a dense, coarse, and heavy 

 volcanic conglomerate with no vesicular lava and no remains of 

 craters. Most of them have well-defined water-courses, broad 

 fringing reefs and often distant barrier reefs as well. There 

 are no signs of recent activity or movement. 



Mothe, to the south, rises to a single peak of 590 feet, and has 

 a considerable barrier reef round it with a long extension south- 

 wards. In the same lagoon is a small island, Karoni, 120 feet 

 high, the formation of which is doubtful ; as seen from the ship 

 it appeared to be of limestone. 



Thithia, 540 feet high, is a larger and rounder island with 

 several peaks of about the same height, fringed by a broad reef. 

 Kanathea has several peaks up to 330 feet, with an extensive 

 barrier reef. Yathata has a single conical hill of 840 feet, with a 

 broad fringing reef. 



SECTION III. 



Summary and Conclusions. 



Considering the peculiar forms that these islands of limestone 

 and of mixed rock in the Lau Group take, it is impossible to 

 conceive that they can have had any origin different to that 

 of many of the atolls, barrier and fringing reefs of the present 

 day. They differ however in the great hardness and dense nature 

 of their limestone, and that it shows little or no signs of organic 

 structure. I have already given my reasons for considering that 

 the soft limestone of the eastern half of Viti Levu had its origin 

 in coral reefs, which, although some may have been inner reefs, 

 cannot have differed essentially from the reefs, which formed the 

 Lau Group. The surface of these soft limestone reefs where it is 

 exposed to the atmosphere is no doubt harder than the interior, 

 but metamorphosis has only taken place in the small fissures, where 

 the carbonate of lime has obviously been dissolved by the carbonic 

 acid gas in solution in the rain water and been redeposited. 



The raised reefs of Tonga 1 , the Solomon Islands 2 , and Cuba 3 , 

 seem to be formed of absolutely similar limestone. From the 

 character of these reefs, together with those of Fiji, I can scarcely 



1 The Geology of the Tonga Islands, by J. J. Lister. Quar. Jour. Geo. Soc. 1891. 



2 The Geology of the Solomon Islands, by H. B. Guppy. 



3 On the elevated Coral Reefs of Cuba, by W. O. Crosby. Proc. Boston Soc. of 

 Nat. Hist. xxn. 1882—3. 



