668 GEOLOGY OP SAMOA AND THE ERUPTIONS IN SAVAII, 



augite and serpentine after olivine are present. The augite is 

 light brownish and titaniferous. 



Name : Hyalopilitic and Porphyritic Olivine Basalt. 



Sp. S.4. Hyalopilitic and Porphyritic Olivine Basalt. Loc : 



Patamea: old lava flow. (Plate lxiv., figs.5-6). 



Handspecimen grey, porphyritic in olivine phenocrysts studded 

 in an aphanitic base. 



Microscopically it is like Sp. S.3. The felspar consists of basic 

 labradorite, and the augite is a slightly titaniferous diopside. 

 The iron ore is titaniferous magnetite, decomposing to leucoxene. 

 The olivine is decomposing at the edges to serpentine, with a 

 structure resembling bastite structure under the high power. 



Name : Hyalopilitic and Porphyritic Olivine Basalt. 



Sp. S.5. Pilotaxitic Olivine-Enstatite Basalt. Loc: Vaipuli, near 

 Matauto, Savaii. (Plate lxiv., fig. 4). 



Handspecimen greyish-black, porphyritic in olivine, and vesi- 

 cular; the vesicles large and egg-shaped, amounting to less than 

 10 % of the bulk of the rock. 



This rock is holocrystalline, with a very tine-grained pilotaxitic 

 base consisting of augite in small grains, and labradorite felspar 

 in acicular microlites. The phenocrysts comprise olivine, greenish- 

 yellow augite, bronzite, and colourless enstatite. 



Name : Pilotaxitic Olivine-Enstatite Basalt. 



Sp. S. 6. Olivine Basalt. Loc: Vailima Plantation, near Apia, 

 Upolo. 



Handspecimen a compact, miarolitic, greyish-black rock, fine 

 and even-grained in appearance. 



Under the microscope it is seen to have a holocrystalline 

 texture, with pilotaxitic fabric. It is porphyritic in olivine under 

 the microscope. The felspar exists in the form of acicular 

 microlites and crystallites, and the augite in minute grains in the 

 base. These three constituents occur in about equal amounts. 

 The magnetite is less in amount. 



Name : Olivine Basalt. 



