454 DR. BUNDJIRO KOTO ON SOME JAPANESE ROCKS. 
an acute rhombic form which extinguishes light parallel to its 
diagonals. The square section becomes dark between crossed nicols, 
and remains so during rotation of the object-table. These minute 
crystals belong therefore to the tetragonal system. From the 
crystallographic form, the indifferent action of HF and other mineral 
acids, and the high specific gravity, they may be anatase. The 
crystal faces are not smooth, but possess a granulated appearance, and 
have a metallic adamantine lustre. 
The plagioclase in the granite from Tamadare, Hitatsi, is mostly 
decomposed, and is there in great part replaced by a pseudophitic 
decomposition-product. ‘This secondary mineral occurs in undulating 
scales, which have a fibrous structure. The scales are, as a rule, so 
arranged that they make an inclined angle with the traces of the 
twin lamelle of the plagioclase portions, which (traces) are still 
recognizable in some of the unaltered parts. The biotite is also not 
fresh, the margin from which the decomposition begins, becoming 
green in colour; and the final result is the production of colourless, 
non-pleochroic, wavy scales (sericite?). The latter could not be 
distinguished from the pseudophitic substance in the plagioclase. 
The extinction is parallel and at right angles to the folds of the 
scales. The altered biotite encloses tufts of yellow rutile needles, 
which show the sagenite arrangement. 
The rock from Konaka, Hitatsi, contains plagioclase of which the 
outer zone includes some quartz, which by its disposition gives rise 
to a micropegmatitic structure. 
Besides zircon and rutile, titanite is also present; the latter has 
brownish-yellow sections with a rather rough surface, feeble pellu- 
cidity, and generally sharp cuneiform outlines. It shows fine 
striations in the shorter diagonal, in the direction parallel to the 
orthopinacoid or one of the orthodomes. 
The quartz in the tourmaline-granite from Sai-Mura, Hitatsi, 
contains enclosures of liquid carbonic acid. Some inclusions havea 
hexagonal form, and are of a tolerably large size (0°015 millim.). 
The bubbles disappear by a slight application of heat. 
QvuaRtTz-miIcA D1oRITE. 
The rock from Kamagawa, Kai, is coarse-grained, having a 
granitic appearance and consisting essentially of quartz, plagioclase, 
hornblende, and biotite, all equally well developed and visible without 
a lens. The plagioclase is found in coarse grains, extremely well 
striated and fresh, poor in microscopic interpositions, rich in liquid 
lacunz. Besides the twin lamelle of the albite type, twinning also 
occurs in the direction of the macropinacoid, making with the first 
an angle of 86°-87°.. The maximum extinction makes 9°—13° with 
the twin lamelle parallel to o P ©. The hornblende forms large 
plates, and its pleochroism is very distinct. 
C=deep blackish-green. B=deep olive-green. A=oil-yellow. 
The hornblende and biotite have grown together in a peculiar 
manner, so that a section of the green hornblende shows layers of 
