BY H. I. JENSEN. 667 



(4) Order of consolidation — 



Magnetite 



Olivine 



Ilmenite 



Augite 



Felspar 



Glass ^- 



The augite and felspar evidently cooled together most of the 

 time. 



(5) Name : Typical Hyalopilitic Olivine Basalt. 



(6) Remark. — This specimen consolidated at a depth of 5 or 6 

 feet under the crust of the lava flow, and was obtained from a 

 broad fissure in the lava flow. The surface rock consisted here, 

 as everywhere else on the flow, of glassy or hypohyaline scoria. 



Sp. S.2. Hypohyaline Olivine Basalt, or Tachylite. Loc: Lava 

 surface, near sea, Malaiola. (Plate lxiv., fig.3). 



i. Handspecimen black, glassy-looking, light through great 

 porosity, being almost pumiceous, showing a few small pheno- 

 crysts of olivine and fragments of augite 



Microscopically the cells are seen to be round or oval, and 

 separated by more or less thin partitions of glassy lava containing 

 a few small corroded crystals of olivine and microlites of felspar 

 (labradorite). The olivine occludes minute magnetite grains. 



Name : Hypophyaline Olivine Basalt or Tachylite. 



Sp- S3, Hyalopilitic and Porphyritic Olivine Basalt. Loc: 

 Manase near Safotu. 



Handspecimen a compact dark grey porphyritic rock, with 

 phenocrysts of yellowish-green olivine in an aphanitic base. 

 Microscopically it is seen to be a hypocrystalline, fine-grained, 

 microcrystalline and uneven-grained basalt, with large olivine 

 phenocrysts in a hyalopilitic base. 



The olivine forms about 20 % of the area of the slide. Mag- 

 netite forms about 5 %. The rest of the rock is made up of 

 augite, in idiomorphic grains; felspar in microlites and crystallites; 

 and brownish glass. A little chlorite from decomposition o£ 



