592 PROCEEDINGS OF THE AMERICAN ACADEMY. 



Specimens of augite andesite were collected from the top and base of 

 the Kobu which show only a slight structural difference. The rock 

 from the top is dark gray and fine-grained. It shows under the micro- 

 scope a groundmass having a hyalopilitic structure. Feldspathic rods, 

 green augite microlites, and magnelite grains are thickly strewn in 

 a glass base. Some of the feldspars reach dimensions to be called plieno- 

 crysts, but iu general the porphyritic character of the rock is not marked. 

 The feldspar rods have a distinct parallel flow arrangement. 



The pyroxene constituent is only in microlitic form, no phenocrysts 

 occurring. 



The specimen from the base of the Kobu is of the same nnture as that 

 from the top, but it shows a distinct porphyritic structure, having numer- 

 ous large phenocrj'sts of feldspar. 



AUGITE-OLIVINE AnDKSITK FROM MoALO. 



Moalo is a triangular ^haped island seven miles long by five miles 

 wide, lying southeast of Viti Lcvu. The specimen was collected from 

 the Observatory llocks on the northern coast. 



The rock is dark gray, compact, and shows megascopic crystals of 

 augite and olivine in the base. 



IMicroscopically the groundmass has a pilotaxitic structure, and consists 

 of minute uniform-sized crystals of augite and feldspar in distinct flow 

 arrangement, sprinkled with grains of magnetite and some brown grains 

 of olivine. 



The uroundmass forms the larger part of the rock, and the phenocrysts 

 are mostly augite and olivine. 



The few plagioclase phenocrysts give labradoritic extinctions, averag- 

 ing 27° on sections normal to 010. 



The phenocrysts of augite and of olivine are large, the latter pre- 

 dominating in number. 



Augite is in good automorphic sections, and contains inclusions of the 

 older olivine. The olivine sections usually have a yellowish brown 

 border enclosing the colorless centres, and the iron oxide has also pene- 

 trated along the fractures. 



Olivine Basalt from Totoya. 



Totoya is a circular island about six miles in diameter, being an ex- 

 tinct volcano with a crater bowl three miles in diameter and a ridge 1,200 

 feet above the sea. It lies a few miles southeast of Moalo. Specimens 



