xxvn THE RIDGE-MOUNTAINS 375 



type. In its radiating valleys and gorges and in other characters 

 it recalls the description given by Dana of the island of Tahiti. 

 The peaks of acid andesites, represented in the isolated hills and 

 mountains of the Ndrandramea district, and in the solitary 

 mountains of Vatu Kaisia and Na Raro, are the necks and stumps 

 of submarine volcanoes dating back to the pre-basaltic period of 

 the island. It is, however, in the great mountain-ridges of the 

 central portion of the island, those of Va Lili, Korotini, Nawavi, 

 Thambeyu, Mbatini, Mariko, &c., that we find, as just remarked, 

 the most typical features of the internal topography of Vanua 

 Levu. 



Agglomerates overlying palagonite-tuffs and clays, that are 

 usually foraminiferous and sometimes inclose molluscan shells, clothe 

 the slopes of these mountain-ridges up to elevations of 2,500 feet and 

 over above the sea. Most of these great ridges, now more or less 

 covered over by these submarine deposits, represent lines of sub- 

 merged vents, of which only a few raised their summits above the 

 sea in the earliest stages in the history of the island. At this early 

 period there were no coral reefs. Some of the ridges present a 

 marked parallel arrangement, recalling the arrangement of the 

 mountain-ridges and lesser chains of hills as described by Dr. 

 Johnston-Lavis in the account of his visit to Iceland. 1 The 

 description of Hekla (as given by Thoroddsen) as "an oblong 

 ridge which has been fissured in the direction of its length and 

 bears a row of craters along the fissure," 2 comes very near to my 

 conception of the original condition of these great mountain-ridges 

 before the emergence. Dr. Johnston-Lavis sees in Hekla a type of 

 volcanic mountain very different from that of Vesuvius and Etna. 

 He regards it as a ridge marked by a number of parallel ridges and 

 furrows, and built up along a main fissure with a number of 

 subsidiary parallel fissures. 



The part taken by palagonite in the composition of the finer 

 deposits over the greater portion of Vanua Levu is another 

 prominent characteristic of the island. Palagonite, as I have 

 suggested in Chapter XXIV., is formed probably on the surface of 

 submarine flows of an ophitic basaltic rock. 



The age of the more recent of the deposits of this island, the 

 fossiliferous tuffs, the pteropod-ooze rocks, and the foraminiferous 

 muds, cannot be far different from that of the same deposits in 

 other parts of the group, since it is apparent that the same general 



1 Scott. Geogr. Mag. 1895. 



2 Ancient Volcanoes of Great Britain, by Sir A. Geikie, 1897, ii. 260. 



