Speight. — Petrological Notes on Socks from the Kermadecs. 253 



Microscopic. — Groiindmass of numerous grains of magnetite, smaller 

 feldspar laths untwinned and twinned (labradorite), grains of olivine, and 

 occasional patches of glass. The phenocrysts are of basic labradorite, 

 augite crystals, and frequent grains of olivine stained with iron-oxides. 



No. 37. Basalt. — From lava-flow behind Denham Bay, Sunday Island. 

 Macroscopic. — A grey rock, vesicular, with numerous phenocrysts of 

 feldspar. Specific gravity, 2-82, 



Microscopic. — Groundmass of augite grains and plagioclase microlites, 

 showing well-marked fluxion structure. The phenocrysts are of labradorite, 

 olivine in rounded grains, partially serpentinised with seams of limonite. 

 Grains of magnetite are very common. A more basic rock than No. 36. 



No. 38. Andesitic Basalt. — From lava-flow, south end of Denham Bay, 

 Sunday Island. 



Macroscopic. — Greyish rock, with prominent feldspar phenocrysts. 

 Specific gravity, 2-86. 



Microscopic. — Groimdmass containing much augite, grains of olivine, 

 feldspar laths. Subophitic in texture. The phenocrysts are of basic labra- 

 dorite, irregular grains of olivine and augite. There are large grains of 

 titaniferous magnetite in irregular forms. The feldspar phenocrysts are 

 very numerous. 



No. 39. Andesitic Basalt. — From lava-flow, north end of Denham Bay, 



Sunday Island. 



Macroscopic. — Grey rock, with small phenocrysts of feldspar. Specific 

 gravity, 2-87. 



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

 of olivine, also occasional colourless glass. The phenocrysts are of basic 

 labradorite with numerous glass inclusions, clear grains of olivine, and small 

 augites. Very similar to No. 38. 



No. 41. Andesitic Basalt. — From lava -flow at sea-level. Scenery Bay, 

 Sunday Island. 



Macroscopic. — Dark-grey rock, very vesicular, with numerous feldspars 

 showing. Specific gravity, 2-81. 



Microscopic. — The groundmass is holocrystalline, of augite and magne- 

 tite grains, and feldspar microlites. There are numerous feldspar and 

 olivine phenocrysts, the latter fresh or but slightly stained with limonite ; 

 occasional augites are present. 



No. 42. Basalt. — From lava-flow under tuffs, Macauley Island. 



Macroscopic. — Dark-grey rock, vesicular, with numerous feldspars show- 

 ing. Specific gravity, 2-55. 



Microscopic. — Groundmass of feldspar laths, many grains of olivine, 

 augite, and magnetite. The phenocrysts are of basic labradorite, olivine 

 in irregular grains, seamed with limonite and occasional augite. 



No. 43. Andesitic Pumice. — From pumice tuffs, Macauley Island. 



This is evidently the scoriaceous equivalent of the andesite lavas, as it 

 contains numerous fragments of plagioclase feldspar and augite similar 

 to those occurring in the lavas. 



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