DR. BUNDJIRO KOTO ON SOME JAPANESE ROCKS. 449+ 
primitive constituent of this rock. Hexagonal colourless apatite is 
pretty abundant, especially in the augite sections. The ground-mass 
consists wholly of a light-brown glass-basis with multitudes of 
microliths. 
The rock from Sitaru contains quartz with hexagonal glass- 
enclosures, and glassy-looking plagioclase, both having abundant 
liquid-enclosures with movable bubbles. With a few exceptions, 
the augite is decomposed into viridite, and the felspar has also 
suffered a decomposition. Epidote grains and needles are plentiful 
in the decomposed augite. They have usually an intense yellow 
colour and are distinctly pleochroic. The ground-mass is holo- 
erystalline, Thirdly the rock from Kamifunabara also belongs to 
this group. Here the quartz grains are somewhat large (2 millim.) 
and rich in glass-enclosures. The latter show the hexagonal form of 
quartz and contain fixed bubbles and an amorphous opaque substance 
in the centre. The quartz is irregularly indented, forming bays and 
inlets ; and the ground-mass is pressed into these spaces as in the 
quartz of quartz-porphyries and rhyolites. The rock-texture is 
coarsely porphyritic. The rock from Tsiogigahara is a dark grey 
porphyritic variety. The quartz occurs in grains and is rare. No 
glass-basis is present. 
HorNBLENDE-ANDESITE. 
Kamagawa, Kat province. 
This is a dark-grey rock. The porphyritic ingredients are not so 
distinctly developed as in the augite-andesites. The microscope 
shows the mineral components to be hornblende, plagioclase, and — 
magnetite, but neither augite nor apatite is present. The felspar 
is twinned and well developed, and contains liquid-enclosures. The 
pericline type of twinning also makes its appearance in this 
plagioclase. In the basal sections of the hornblende the charac- 
teristic cleavage is very distinct. The longitudinal columnar 
sections are seen to be made up entirely of fine fibres, which run 
parallel to the vertical axis, and biack rods (or opacite) are 
interposed between them, causing the crystal to resemble enstatite ; 
the oblique extinction on 0 Po=17°. Itis pleochroic, ranging 
from sea-green to reddish brown, or light brown. ‘The hornblende 
is partly altered into epidote grains of a greenish-yellow colour. 
The ground-mass consists of lath-shaped felspar, hornblende needles, 
and magnetite octahedra, together with brown plates of hornblende 
showing a microfluctuation-structure. No glass-basis. Colourless 
apatite is plentiful. 
PLAGIOCLASE BASALTS, 
Plagioclase basalts cannot be distinguished from augite-andesite 
except through the presence of olivine as an essential ingredient, 
and as these rocks occur closely connected with each other 
geologically, I was confronted with considerable difficulty in 
assigning a name to either, especially when the olivine is present 
