158 IDDINGS. 



prismoid and equant, mostly indistinct bounded anhedrons, seriate in size, with 

 some subparallel arrangement, or flow-structure. The feldspar is not notably 

 birefringent except in prismoid sections, and is probably more alkalic than labra- 

 dorite, possibly andesine. There are minute prismoids, or needles, of pyroxene, 

 seriate in size, in places diverse in arrangement;- also in clusters of subparallel 

 prisms, crowded together closely by the side of the feldspar prisms or plates; 

 also in slightly radiate bundles. Magnetite occurs in prominent and numerous 

 euhedral and subhedral crystals. 



An exceptional rock related in fabric to that just described is found 

 in gravel at Montalban, Eizal Province. . 



It is a dense, greenish-gray, nonporphyritic rock, showing small megascopic 

 crystals of feldspar and fewer of pyroxene. In thin section it consists of dendritic 

 radiating clusters of nearly colorless monoclinic pyroxene, augite, and prismoids 

 of feldspar. Also prismoid plagioclase in diverse arrangement and in many cases 

 curved. The feldspar is probably oligoclase, as indicated by its optical properties. 

 There is much green spherulitic serpentine or chlorite. There are small crystals 

 of magnetite, and clusters of brown anhedrons, probably epidote. There is some 

 secondary quartz. 



Hornblende-pyroxene-andesites are very similar to pyroxene-andesites 

 in composition except for the px - esence of variable amounts of hornblende, 

 and' generally smaller amounts of hypersthene. They resemble them also 

 in texture, having similar habits and like variations in the fabric of the 

 groundmass. There are varieties with little hornblende which grade by 

 increasing amounts of this mineral and decreasing amounts of pyroxene 

 into hornblende-andesites. A few rocks of this group contain small 

 amounts of olivine. They are not so abundant in the Islands as pyroxene- 

 andesite, judging from the collections already made, and occur intimately 

 associated with them in various localities. 



Hornblende-pyroxene-andesite from Cabcaban, Bataan Province is dosemic 

 seriate, and mediophyric; that is, it is richer in phenocrysts than in groundmass, 

 and they vary in size from something less than 5 millimeters to microscopic 

 crystals that may be considered as constituents of the groundmass. The phenocrysts 

 are mostly labradorite, euhedral to subhedral. There are fewer of augite and 

 hypersthene, and still less of hornblende, which is in relatively large crystals, 

 greenish-brown, with dark borders. There are small phenocrysts of magnetite, and 

 long thin prisms of apatite. The groundmass consists of microlites of plagioclase, 

 pyroxene and magnetite, probably with a small amount of glass as matrix. There 

 are some secondary minerals in the rock. 



Another variety from Dinalupihan, Bataan Province, is similar to that just 

 'described, but the phenocrysts of plagioclase carry fine glass' inclusions; some of 

 them brown, and in some crystals in zones. Brown hornblende without any dark 

 border is abundant, and occurs also in small crystals in the groundmass. 



A hornblende-pyroxene-andesite from Subic contains euhedral crystals of 

 labradorite (Ab 3 An 7 ), red-brown hornblende, with strong absorption and a narrow 

 dark border, and an equal amount of pyroxene, mostly augite, besides magnetite. 

 The groundmass consists of euhedral microlites of prismoid plagioclase and 

 pyroxene, with a little hornblende and magnetite, with, probably, a small amount of 

 colorless glass matrix. 



