DR. BUNDJIRO KOTO ON SOME JAPANESE ROCKS. 455 
the intercalated brown biotite, and inversely, the brown-mica 
lamellae contain hornblende individuals, indicating that they have 
erystallized at the same time. 
Quartz is found in grains which are as well developed as those of 
the plagioclase. They are rich in foreign enclosures and full of 
liquid-lacune. The quartz also contains hornblende microliths, 
apatite needles, and numerous black “hairs,” like the quartz in 
some tonalites of Southern Tyrol. These “hairs” in the quartz 
appear, under low powers, to be totally opaque; but high powers 
resolve them into light bluish-green pellucid thin plates. The 
extinction-direction of these plates is parallel to the longest side, and 
is 17°-20°. They probably belong to the amphibole group, and 
certainly cannot be identified with rutile, to which mineral these 
microliths have often been referred. Analogous interpositions are 
said to occur in the quartzite from Humboldt Mountain, Nevada *. 
The biotite is found in large lobes having a peculiar pearly lustre. 
Apatite and the colourless microliths are found as interpositions 
init. Zircon forms an accessory ingredient. It occurs in grains 
or in four-sided prisms with pyramids; the colour is yellow, the 
refraction is very strong. Sections display brilliant chromatic 
polarization. Tourmaline occurs in long needles, the pleochroism 
being very intense, w dark green, e deep brown. 
DioRITE-PORPHYRITE. 
Morisawa, Kozuke province. 
This is a dirty-green rock. Viewed under the microscope, it 
bears a striking resemblance to that of Potschapel, near Dresden. 
Plagioclase and orthoclase are present in nearly equal quantity ; 
the extinction-direction in the plagioclase makes an angle of 5°-8° 
with the twin lamelle. Both of these felspars contain numerous 
empty cavities arranged in zones,in which the process of decomposi- 
tion first begins. When the alteration is far advanced, the interior 
is entirely filled with colourless, somewhat fibrous scales, which, 
between crossed nicols, display intense aggregate polarization-colours. 
This substance is very like the pseudophite from Plaben, near Bud- 
weis, Bohemia‘. 
The hornblende is decomposed into viridite or, in other instances, 
filled with minerals of the carbonate group. The borders of the 
hornblende crystals consist of opacite together with epidote grains ; 
and these are so arranged as to preserve the original contours of 
the hornblende crystals. The basal sections show the characteristic 
four- or six-sided figures. The longitudinal section is accompanied 
by linear aggregates of opacite. Large magnetite octahedra or 
grains are sporadically distributed in the rock. The rest of the 
rock mass is apparently a grey homogeneous ground-mass, which, 
between crossed nicols, transmits a feeble light and consists of 
* Zirkel, ‘Microscopical Petrography of the 40th Parallel,’ p. 25. 
+ Described by R. v. Drasche, ‘Min. Mittheilungen,’ 1878, p. 25. 
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