252 Transactions. 



in others the rock is abnost holocrystalline. The phenocrysts are of large 

 fresh olivines, augite, basic labradorite, with grains of magnetite. The 

 groiindmass of this rock is distinctly basaltic in character, but the numerous 

 feldspar phenocrysts give it an andesitic character. The same remark 

 applies to other specimens. 



Lava-flows. 



No. 2. Andesitic Pitchstone. — From a boulder at base of cliffs, Fleet- 

 wood Bluff, Sunday Island. 



Macroscopic. — A rock dark in colour with pitchy lustre. 



Microscopic. — The groundmass consists of glass, fairly clear in some 

 parts, crystallitic in others, perlitic, with well-marked flow structure. The 

 phenocrysts are of sanidine, plagioclase (acid labradorite), strongly pleo- 

 chroic hypersthene, and occasional augites. 



No. 9. Andesite. — From lava-stream on Moumoukai, Sunday Island. 



Macroscopic. — A dark-grey rock, vesicular with small phenocrysts of 

 feldspar. Specific gravity, 2-44. 



Microscopic. — Groundmass of feldspar laths (labradorite), augite grains, 

 a good deal of glass in patches. The phenocrysts are of medium labra- 

 dorite ; no others were observed. 



No. 21. Andesite. — From lava-stream, Denham Bay, Sunday Island. 



Macroscopic. — A very dark compact rock, with very occasional small 

 phenocrysts of feldspar showing. Specific gravity, 2-89. 



Microscopic. — Groundmass composed of feldspar microlites, augite and 

 magnetite grains, with patches of clear coloured glass. Very occasional 

 small phenocrysts of feldspar and augite are visible. 



No. 26. Augite Olivine Andesite. — From lava-flow, south end of Den- 

 ham Bay, Sunday Island. 



Macroscopic. — Dark-coloured fairly compact rock. Specific gravity, 2-80. 



Microscopic. — Groundmass composed of feldspar laths and augite grains, 

 ophitic in places, with a good deal of glass, and numerous grains of magne- 

 tite. The phenocrysts are of feldspar (basic labradorite), occasional augites, 

 and rare olivines. 



No. 34. Olivine Andesite. — From lava-stream west of Blue Lake, Sun- 

 day Island. 



Macroscopic. — A grey rock, vesicular, with numerous feldspar pheno- 

 crysts. Specific gravity, 2-76. 



Microscopic. — Groundmass consists of numerous augite feldspar micro- 

 lites, simple and twinned grains of augite and olivine, and occasional patches 

 of glass, with grains of magnetite. The phenocrysts are of basic labradorite, 

 with numerous gas-inclusions, small phenocrysts of partly serpentinised 

 olivines, and occasional slightly pleochroic augites. This rock resembles 

 somewhat the olivine andesite of Banks Peninsula. 



No. 36. Basalt. — From lava-stream, east coast of Sunday Island, over- 

 lying tuffs. 



Macroscopic. — A dark-grey rock full of small vesicles. Specific gravity, 

 2-84. 



