296 A NATURALIST IN THE PACIFIC chap. 



cated mass when seen from the side. A similar change of form is 

 to be noticed in the illustrations of Ndrandramea. No traces of 

 crateral cavities came under my notice. The rocks are neither 

 vesicular nor scoriaceous, and are usually massive ; but exhibit at 

 times a rudely columnar structure. 



Each hill or mountain has its peculiar variety of these rocks. 

 This is well shown in the Ndrandramea district. Thus the rocks 

 of Ngaingai and of Wawa-levu in carrying porphyritic quartz 

 differ from those of all the other hills around. Those of Soloa 

 Levu are distinguished by the orthophyric groundmass and by the 

 absence of hornblende. Those of Mount Ndrandramea again have 

 no porphyritic quartz, but little hornblende, and possess a micro- 

 felsitic groundmass. The rocks of Na Raro and Vatu Kaisia differ 

 as regards specific gravity, the " grain " of the felsitic groundmass, 

 the presence of phenocrysts of rhombic pyroxene, etc. The 

 characters of these rocks from various localities are contrasted in 

 the table given on a later page, whilst the different sub-classes to 

 which they belong are described in detail below. 



Sub-Class Hypersthene-Andesites 



These are dark and light grey rocks, sometimes granitoid in 

 appearance. They pass on the one hand into the hypersthene- 

 augite-andesites before described and on the other into the horn- 

 blende hypersthene-andesites to be subsequently dealt with. 

 From the former they are distinguished by the great predominance 

 of rhombic pyroxene both as phenocrysts and in the groundmass ; 

 whilst from the latter they are separated by the absence of brown 

 hornblende or its pseudomorphs. These rocks are found in the 

 Ndrandramea, Valanga, and Vunimbua districts. They may form 

 isolated dome-shaped hills as in that of Soloa Levu, or they may 

 constitute the deeper-seated rocks of the region from which these 

 hills arise, as in the Ndrandramea district. In their general mode 

 of occurrence, however, they cannot be treated apart from the 

 allied hornblende-hypersthene-andesites and the dacites. 



This sub-class maybe divided like the hypersthene-augite-ande- 

 sites into four orders according to the character of the groundmass ; 

 and these are enumerated in the Synopsis. Only the orthophyric 

 and felsitic orders are represented in my collection. Of the former 

 the most typical rocks are those composing the hill of Soloa Levu 

 which is described on page 103. 



These Soloa Levu rocks are lightish grey and granitoid in aspect. 



