732 SUBANTARCTIC ISLANDS OF NEW ZEALAND. [Physiography, Geology. 



No. 3. Dolerite. 



Macroscopic. — A black rock, with numerous coarse pale-green crystals of olivine. 

 Microscopic. — The groundmass is fine, and composed of feldspar laths, granular 

 augite, and magnetite grains. The phenocrysts are augite in pleochroic crystals, 

 often with a violet border, a little highly serpentinized olivine, and andesine-labradorite 

 feldspars. The term " dolerite " is applied in this report to a coarse-grained basalt 

 (fig. 14, ii). 



No. 4. Dolerite. 



Practically the same as No. 3, except that the augite crystals are very coarse 

 and the olivine in smaller grains with limonite border, and the feldspar is consider- 

 ably weathered with the formation of secondary calcite. 



No. 5. Augite-olivine Andesite. 



Macroscopic. — A fine-grained dense rock ; the phenocrysts are small, chiefly 

 of feldspar. 



Microscopic. — The groundmass is of medium grain, composed of feldspar laths 

 showing flow structure, fine magnetite, and granular augite. The phenocrysts are 

 oligoclase-andesine feldspars, highly weathered olivine, and a few pale augites. 



No. 6. Dolerite. 



Macroscopic. — A black rock, with numerous phenocrysts of augite and olivine 

 of varying size. Smaller feldspars also occur. 



Microscopic. — The groundmass is fine, and made up of feldspar laths, augite, 

 olivine, and magnetite, the last in both coarse and fine crystals ; the granules of 

 olivine are somewhat altered. The phenocrysts are coarse, and consist of olivine 

 in various stages of alteration, slightly pleochroic augite with characteristic dark 

 border frequently developed, and tolerably fresh labradorite. 



No. 7. Dolerite. 



Macroscopic. — The rock is black, with a good few phenocrysts of medium- 

 sized olivine, augite, and feldspar. 



Microscopic, — The groundmass is fine, composed of feldspar laths, grains of 

 magnetite and violet augite, plates and irregular patches of chlorite. There are 

 a few small pieces of pleochroic brown hornblende with included grains of magnetite. 

 The phenocrysts are of fairly coarse pleochroic augite with violet border, labradorite 

 often finely zoned with strings of secondary chloritic products, and olivine generally 

 fresh but sometimes serpentinized. 



No. 8. Dolerite. 



Macroscopic. — This rock is decomposed, and full of vesicles. 

 Microscopic. — Similar to No. 7, except that chlorite has completely replaced 

 some original ferro-magnesian constituent. 



No. 9. Dolerite. 



Macroscopic. — A coarse-grained rock, full of large augite and olivine crystals. 

 It is much weathered. 



