BY H. I. JENSEN. 669 



Note : At Stevenson's grave, on the top of Vai Mountain, n< j ar 

 Apia, a basalt of similar appearance was obtained. It proved to 

 be even more fine-grained, richer in magnetite and wanting in 

 olivine. A little glass is probably present. It would therefore 

 be a Hyalopilitic Basalt, or Augite Andesite 



Sp. S.7. Olivine Basalt Porphyrite. Loc: near Papasee Falls, 

 near Apia. 



i. Handspecimen dark grey, porphyritic in olivine and augite. 



ii. Microscopic examination. —(1) Texture: Holocrystalline 

 with variable grain-size: average gi^ain-size fine; fabric porphy- 

 ritic, with pilotaxitic base 



(2) Felspar, augite, and olivine form the essential constituents; 

 magnetite is a minor constituent; whilst serpentine, calcite, 

 sericite, and kaoline exist as decomposition products. 



(3) The olivine occurs wholly as phenocrysts. Augite occurs 

 as idiomorphic, corroded, phenocrysts, often twinned; and also in 

 idiomorphic grains in the base. The felspar consists of basic 

 bytownite (maximum extinction angle 30°-40° in symmetrical 

 sections), and is represented both as corroded phenocrysts, and as 

 microlites in the base. It is frequently zoned in the phenocrysts, 

 and exhibits Carlsbad, albite, and pericline twinning. Serpentine 

 is abundant, secondary after augite and olivine. 



This is a rock of two generations. 

 Name : Olivine Basalt Porphyrite. 



Note: A fine-grained, even-grained, pilotaxitic lava, containing 

 no olivine, was also obtained at the Papasee Falls. 



Sp. S.8. . Loc. : Tofua, Tonga. 



The specimen examined was a pebble obtained from the heap 

 of rock at Nukualofa, brought from Tofua to construct a jetty. 



Under the microscope it was found to be a hypohyaline, very 

 fine-grained, hyalopilitic rock, showing flow structure. It 

 consists of a felted mass of acicular felspar microlites and 

 crystallites and brownish glass. Some small tabular felspar 

 crystals also exist There is no olivine. It is, therefore, probably 

 a basic andesite in composition. 



