374 A NATURALIST IN THE PACIFIC chap. 



to place the limit of these basaltic flows at the water's edge ; and 

 as is indicated in the sections, they probably extend for miles under 

 the sea. 



If we look for an island which in its extensive palagonite- 

 formations, in its basaltic table-lands and later basaltic flows, in its 

 huge mountain-ridges, and in its evidence of submergence, most 

 resembles Vanua Levu, we seem to find it in Iceland. It is in 

 Iceland, I think, that we must expect an explanation of many of 

 the puzzling features in the structure of Vanua Levu. 



I pass on now to refer to some of the general points in the 

 geology of this island, which have been dealt with in detail in the 

 earlier chapters of this work. With regard first to the distribution 

 of the volcanic rocks, it may be remarked that my materials do not 

 lend themselves to making a geological map. The most compre- 

 hensive idea of the principal points in the geological structure 

 will be obtained by reading the description of the profile given in 

 Chapter I. There is, however, a method in the distribution of the 

 rocks that may be again noticed here. The plutonic rocks are 

 very scantily exposed, as is shown on page 249 ; and they are not 

 displayed at all in the western half of the island. The more basic 

 eruptive rocks, the olivine-basalts and basaltic andesites, are mainly 

 confined to the western half, that is, west of Nanduri on the 

 north and of the Ndreke-ni-wai River on the south. Ordinary 

 augite-andesites occur also in the western half; and together with 

 the hypersthene-augite-andesites they are found over most of the 

 rest of the island, excluding the north-east portion, east of Lambasa 

 and Tawaki, where quartz-porphyries, oligoclase-trachytes, and 

 acid pumice tuffs prevail. The acid andesites, including the horn- 

 blende-andesites and the dacites or felsitic andesites, are best repre- 

 sented in the Ndrandramea district in the midst of the basic rocks. 

 They occur in the isolated peaks of Na Raro and Vatu Kaisia and 

 in one or two other localities, as in the Valanga Range and on the 

 shores of Natewa Bay in the vicinity of the Salt Lake. These 

 peaks of acid andesites, as in the instances of Vatu Kaisia and 

 Soloa Levu, are at times in part overwhelmed or surrounded by 

 the basaltic flows. This singular feature of bosses of acid rocks in 

 the midst of basaltic fields offers another point of resemblance 

 between Iceland and Vanua Levu. 



The mountain-types vary considerably, the ridge-mountains, 

 however, being most characteristic of the island. The basaltic 

 mountain of Seatura, though its lava-flows were evidently in the 

 main submarine, belongs as before observed to the Mauna Loa 



