NOTES ON SOME IGNEOUS ROCKS OF JAPAN 63 
crysts are quartz and feldspar, the latter being more abundant. 
Besides these, there are present bluish-green and deep reddish- 
brown ferromagnesian minerals belonging to the pyroxene and 
amphibole groups. These are fewer and smaller than the colorless 
phenocrysts. The groundmass is strongly marked with flow 
structure, due to both the diversity of crystallinity and the 
arrangement of constituent minerals. The greater part shows a 
microfelsitic texture, essentially composed of quartz and feldspar, 
through which are scattered numerous small ragged shreds or 
mosslike patches of aegirite and aegirite-augite, associated with 
minute grains of magnetite. A microspherulitic intergrowth is 
also seen. Through this fine groundmass are coarser crystalline 
bands, mainly composed of feldspar and quartz with subordinate 
green pyroxene, developed in a lenticular form. The mode of 
development of these minerals exhibits some peculiarities. The 
minerals occurring in the marginal part of the lenticular area are 
arranged perpendicular to its outline, but those in the inner part 
show a microgranitic or micropegmatitic arrangement. 
The quartz phenocrysts are mostly subhedral, sometimes 
anhedral, with diameters varying from 0.05 mm. to 3 mm., but 
euhedral forms are also seen. The mineral contains several kinds 
of inclusions. Glass inclusion with or without a gas bubble is not 
rare. They are commonly bounded by crystal planes. There are 
abundant inclusions of groundmass material, showing irregular 
forms. Aegirite groups are also inclosed. 
The feldspars are wholly alkalic, and almost all of them are 
possibly soda-bearing potash varieties, though a few crystals appear 
to be sanidine. The phenocrysts occur in two shapes, tabular or 
columnar, and are commonly subhedral. In some instances, the 
outline is strongly rounded and curved, and is deeply invaded by 
the groundmass. Some crystals have a regular shape, fairly well 
inclosed by crystallographic faces. The twinning observed is 
wholly Carlsbad, and no microcline structure is noticeable. The 
feldspar material is entirely fresh and is plainly marked by the 
cracks characteristic of sanidine. The plane of the optic axes 
appears to be perpendicular to (o10). The acute optic angle 
(2E), measured on three thin sections, is 56° 34’, 50° 16’, and nearly 
