190 A NATURALIST IN THE PACIFIC chap. 



in the stratified sedimentary clay-tuffs which are exposed on the 

 shore-flat of the south side of the neighbouring Sava-reka-reka 

 Bay. These beds, which within a distance of fifty paces are 

 inclined 10 — 15 to the south-west and the same amount to the 

 north-west, have apparently a quaquaversal dip. In places they 

 exhibit a spheroidal and concentric structure, and are penetrated 

 by cracks containing some calcite, but mostly filled with a white 

 zeolitic mineral. 1 One of these rocks is a bright green, hard and 

 compact deposit, containing but little lime, and evidently an altered 

 palagonitic clay-tuff. It contains a few minute tests of the 

 " Globigerina " type ; and on account of the small size of its 

 fragments of minerals, which range from *oi to "04 mm., it may be 

 regarded as a relatively deep-water sediment. 2 It is interstratified 

 with a coarser, somewhat altered palagonite-tuff, which shows but 

 little lime and only a suspicion of tests of foraminifera. The size 

 of the larger included fragments does not exceed half a millimetre. 



The low hill, near Yaroi, on which the magistrate's house 



is built, is composed of fine and coarse tuffs, probably submarine. 

 It is doubtful whether any but sedimentary tuffs occur in this 

 peninsula. 



In the hills of the western part of the peninsula, that is, west 

 of Na Kama and Naithekoro, a particular type of basaltic andesite 

 prevails, characterised by rhombic pyroxene as well as augite 

 phenocrysts, and referred for the most part to genus 13 of the 

 hypersthene-augite andesites. Their specific gravity ranges from 

 276 to 2-83, and the interstitial glass may be fair or scanty in 

 amount. The average length of the felspar-lathes is unusually 

 small, '04 — -06 mm. In these respects the basaltic andesites of 

 the Savu-savu Peninsula differ from the basaltic andesites found in 

 most other parts of the island, where, as exemplified by those of 

 the Wainunu, Solevu, and Seatura regions, the felspar-lathes 

 average between *i and '2 mm. in length, and there is practically 

 no rhombic pyroxene. A somewhat scoriaceous semi-vitreous 

 form of pyroxene andesite is exposed on the south slopes above 

 Nukumbalavu, where it is covered by basic agglomerates. The 

 pyroxene in the groundmass is here prismatic, and not granular, 

 and for the most part rhombic ; and the rock is referred to the 

 prismatic sub-order of the hypersthene-augite andesites described 

 on p. 287. 



1 It is granular, but fuses in the blowpipe flame into a clear glass and 

 gelatinises in HC1. Probably a form of natrolite. 



2 It is described under Sample D on p. 326. 



