322 SMITH. 



feldspars not so prominent. In the rocks from Mounts Apo and Pinatubo 

 the reverse is the case. 



Basalts. — Of this great class of rocks Iddings saj's : 



There are transitions between olivine-bearing pyroxene andesites and basalts 

 rich in olivine, so there are basalts with the texture found in andesite, and others 

 with textures not developed in andesites. No line can be drawn between these 

 two groups of rocks and petrographers differ as to the classification of rocks 

 intermediate between basalts and andesites. It happens that the lavas of Mayon 

 and Taal Volcanoes belong in part to these intermediate varieties, which may be 

 called olivine-bearing pyroxene-andesites or andesitic basalts, while other varieties 

 of lava from these volcanoes are normal basalts, with abundant olivine. 



Basalts with andesitic habit occur in the Batanes. In two cases the rocks 

 have the composition of hypersthene-augite-andesite with small phenocrysts of 

 colorless olivine partly altered to iddingsite, the groundmass being holocrystalline, 

 with anhedral feldspars. These probably are best called olivine-bearing pyroxene- 

 andesites. 



Varieties with andesitic habit and much olivine occur at Mount Mariveles in 

 Bataan and in Mindanao. In both of these rocks the olivine is present as small 

 colorless crystals in part altered to red iddingsite. 



Basalt from the floor of the crater of Taal Volcano is dopatic (groundmass 

 dominant), mediophyric (moderately porphyritic), with phenocrysts of subhedral, 

 green augite, having inclusions in zones in some crystals, subhedral, equant to 

 tabular labradorite, Ab 2 An 3 — Ah, An 2 , zonally developed; and fewer colorless to 

 yellow olivines, altered on the surface of the crystals. The augite and labradorite 

 are anhedral toward each other when in clusters. The olivine in some instances 

 is partly inclosed in augite, with anhedral forms. The groundmass consists of 

 euhedral prismoid plagioclase, with central euhedral prismoid inclusion that has 

 much lower refraction and is isotropic, apparently glass. The plagioclase pris- 

 moids have diverse arrangement. There is also much equant anhedral augite, 

 less magnetite, and pi'obably intersertal glass, but ' the microlites are crowded 

 close together, and the rock may be holocrystalline. 



Basalt from Mayon Volcano, Albay, is dopatic and mediophyric, and highly ve- 

 sicular or porous. The euhedral, rectangular, prismoid phenocrysts of labradorite 

 contain many inclusions of brown glass ; the phenocrysts of green augite are 

 subhedral ; those of colorless olivine are subhedral to euhedral. The groundmass 

 is dark brown, globolitic glass with microlites of their needle-like prismoids of 

 plagioclase, and anhedrons of augite and magnetite. 



Basalts from Mindanao differ somewhat from thcfe already described from 

 Luzon, in being richer in ferromagnesian minerals and in having plagioclase 

 slightly less calcic. 



Basalt from the Lanao District, Mindanao, is dopatic mediophyric, and seriate, 

 with many phenocrysts of olivine, but slightly altered and with inclusions of 

 magnetite. The groundmass consists of much anhedral augite, some anhedral 

 olivine, less magnetite, and prismoid plagioclase about equal to the ferromagnesian 

 minerals in amount. The composition of the plagioclase is not readily determi- 

 nable, it is as calcic as andesine. There is a small amount of colorless matrix 

 with lower refraction, which may be glass. 



Leucitites. — A dark, fine-grained rock with small, almost circular white 

 areas, 2 or 3 millimeters in diameter, occurs near Aroroy, on the Island 

 of Masbate. This proves to be analcite, an alteration product of leucite, 







