162 IDDINGS. 



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

 andesites. 



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

 Bataan Province and on Mindanao. In both of these rocks the olivine is present 

 as small colorless crystals, in part altered to red iddingsite. In the Batanes 

 Islands and Binangonan, Rizal Province, similar rocks have a groundmass with 

 brown globulitic glass base. In the first case it is filled with microlites of feldspar, 

 pyroxene and magnetite. 



In the rock from Binangonan the groundmass is intersertal between the 

 phenocrysts, and consists of the same kinds of minerals in smaller crystals with 

 intersertal brown globulitic glass as a matrix. Somewhat similar basalts occur 

 at Mount Arayat. Pampanga Province. 



In Lepanto there is a basalt which is dopatic and hyatal magnophyric, having 

 a few large phenocrysts of olivine surrounded by small crystals of hypersthene. 

 The groundmass is itself porphyritic, dopatic, seriate; that is, porphyritic with 

 variously sized, small phenocrysts, which are plagioclase and some olivine. The 

 groundmass for these phenocrysts is holocrystalline, and consists of prismoid 

 feldspars, in part with subparallel arrangement (flow structure), also smaller 

 prismoid hypersthene and augite, rounded in form, and partly altered, together 

 with much magnetite. The small ferromagnesian minerals occur between the 

 crystals of plagioclase. There are also still smaller rounded pyroxenes scattered 

 as inclusions through the feldspar. 



Basalt from Pagsanjan, Laguna Province, is dopatic, mediophyric, with few 

 rather large clusters of labradorite (AfrAn-) containing many microscopic inclu- 

 sions. There are smaller phenocrysts of red altered olivine. The groundmass 

 consists of prismoid plagioclase, with smaller equant anhedrons of augite, 

 subhedrons of altered olivine and others of magnetite, for the most part intersertal 

 between the plagioclase, besides intersertal globulitic glass, the globulites appearing 

 to be minute equant anhedrons of augite, together with minute prismoids of the 

 same mineral. 



Somewhat similar basalts occur at San Pablo, Laguna Province, and on Min- 

 danao. The first is minophyric, with small phenocrysts of augite, fewer of plagio- 

 clase, and euhedral olivine with partial borders of minute magnetite crystals. 

 The second is perpatic and minophyric. 



Basalt from the floor of the crater of Taal volcano is dopatic, mediophyric, 

 with phenocrysts of subhedral, green augite, having inclusions in zones in some 

 crystals ; subhedral equant to tabular labradorite ( Ab»An 3 to Ab t An 2 ) , zonally 

 developed; and fewer colorless to yellow olivines, altered on the surface of the 

 crystals. The augite and labrodorite 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 prismoids have diverse arrangement. There 

 is also much equant anhedral augite, less magnetite, and probably intersertal 

 colorless glass, but the microlites are crowded close together, and the rock may be 

 holocrystalline. Another variety of basalt from Taal Volcano is dopatic, medio- 

 to minophyric, and hyatal. The phenocrysts of plagioclase are euhedral and 

 anhedral fragments, with many minute inclusions, and pockets and cracks 

 filled with groundmass. In one crystal a narrow crack is filled with brown glass 

 containing no microlites, whereas the glass of the surrounding groundmass is 

 crowded with them, illustrating differential flow in a partly crystallized magma, 

 and the probable origin of differential contemporaneous veins. There are few 



