436 DR. BUNDJIRO KOTO ON SOME JAPANESE ROCKS. 
subject again in support of the views of MM. Fouqué; and W. Cross 
has stated that the chief subdivision of the augite-andesites may 
more properly be called hypersthene-andesite. 
The augites in the Japanese andesites show analogous phenomena 
in thin slices. As already mentioned, some are pleochroic and some 
are not, or, at most, very feebly so, even if pleochroism be really 
present at all. 
The pleochroic sections extinguish the light parallel to the axis ¢, 
and at right angles to it, while the non-pleochroic ones haye the 
oblique direction of extinction. The question whether the pleo- 
chroic and non-pleochroic sections belong to two species of pyroxene, 
will be elucidated by the following explanations, which lead us to 
the logical conclusion that they are one and the same species. 
If a monoclinic augite-crystal be cut parallel to 0 P ow, then its 
optical properties are identical with those of rhombic pyroxenes, and 
the pleochroism is very strong, because C = deep green, and B= 
brown or sometimes reddish brown. In fact it is just like hyper- 
sthene. In the clinopinacoidal section the pleochroism is very weak 
or scarcely noticeable, because C== deep green and A = light green. 
These light and deep green colours appear in an approximately 
clinopinacoidal section as a mixed green; but the extinction-direc- 
tion determines at once whether the mineral belongs to the mono- 
clinic or the rhombic system. 
For the sake of experiment, an augite crystal was picked out ofa 
rock collected in Yawatano and immersed in soft balsam. The 
orthopinacoid showed an intense pleochroism and optically behaved 
just like the rhombic mineral hypersthene, for which it is often 
taken; but the clinopinacoid was non-pleochroic, the extinction- 
direction was oblique, c: C=43°. Relying upon these facts, this 
mineral, seemingly belonging to two species, appears to be one and 
the same substance, 2. ¢. normal augite. The property of pleochroism, 
which has been made of critical moment in distinguishing hypersthene 
from ordinary augite, is a very doubtful one, since the intensity 
depends upon the thickness of the section; and also because hyper- 
sthene, in a very thin section, no longer exhibits pleochroism, although 
a clinopinacoidal section of considerable thickness exhibits tolerably 
intense pleochroism. ‘The intensity of pleochroism depends some- 
times upon a certain stage of chemical change in augite. If hyper- 
sthene be really present, its basal section would probably show a 
trace of the brachypinacoidal cleavage, which I have never seen in 
my slices. The chemical analysis given in the sequel shows 10 per 
cent. of CaO, which is hard to reconcile with the assumption that 
this mineral is hypersthene. 
The never-failing accompaniments are the glass-enclosures with 
or without fixed bubbles, which are arranged parallel to the longitu- 
dinal axis. In some augites the enclosed glass is brown, although no 
such glass-basis is present in the ground-mass. Augites, poor in 
longitudinal fissures, are rich in glass-enclosures, and wice versd. 
This fact indicates that the presence of the one precludes the 
development of the other. Light reddish brown, grey or colourless 
