298 A NATURALIST IN THE PACIFIC chap. 



scopic pyroxene prisms, 2 mm. long, mostly rhombic but showing 

 also intergrowths with monoclinic pyroxene. The felspar- 

 lathes do not average more than -i mm., and there is a quantity of 

 small prisms of rhombic pyroxene in the groundmass, which also 

 contains a little residual glass.) 



Sub-Class Hornblende-Hypersthene-Andesites 



This is an extensive group which includes the rocks forming 

 several of the hills in the Ndrandramea district as well as the 

 isolated peaks of Na Raro, Vatu Kaisia, etc. It passes on the one 

 side into the Hypersthene-Andesites before described and on the 

 other into the Hornblende-Hypersthene-Quartz-Andesites, the 

 Dacites of this island. 



Of the four orders established in the Synopsis (page 236) 

 according to the general method there adopted, the first, where the 

 groundmass exhibits felspar-lathes not in flow-arrangement, is 

 not represented in my collection. 



Second Order of the Hornblende-Hypersthene-Ande- ' 



sites 



(Felspar-lathes in flow-arrangement) 



This order is only represented by three rocks, all of which belong 

 to the prismatic sub-order where the pyroxene of the groundmass 

 is prismatic and not granular. 



Two of these rocks are very similar in appearance and char- 

 acter, though coming from different localities on the opposite sides 

 of Savu-savu Bay, one from the agglomerate of Vatu-ndamu in the 

 Kumbulau peninsula (page 91), the other from an intrusive mass 

 in the vicinity of Urata (page 184). They are dark grey, with 

 specific gravity 2'6 to 27, and display macroscopic crystals of 

 hornblende and pyroxene. In the slide they exhibit in addition 

 numerous phenocrysts of plagioclase, i to 2 mm. in size, in a 

 groundmass showing small felspar-lathes (less than •! mm. in 

 length) in partial flow-arrangement and numerous pyroxene 

 prisms (-05 mm. long) giving straight extinctions, together with a 

 little residual glass. . . . The plagioclase phenocrysts, which 

 give extinctions of medium and basic andesine, are often tabular 

 and display zone-lines. They contain abundant pale inclusions 

 arranged zone-wise. . . . The hornblende phenocrysts are dark 

 brown, markedly pleochroic, and give extinctions up to 12 degrees. 



