DR. BUNDJIRO KOTO ON SOME JAPANESE ROCKS. 453 
character above mentioned, it is very probable that the chief mass 
of the felspar may be orthoclase or microcline, and the imbedded 
spindle-shaped bodies a lime-soda-felspar ; and the name microper- 
thite* may fitly be applied to the interlaminated growth of these 
two sorts of felspars. 
_ There are other sections of plagioclase in the thin slice, which do 
not contain these interpositions, and which frequently exhibit 
reticulated fissures parallel to 0 Pw, and 0 Po. These are pro- 
bably sections of microcline. Common orthoclase is also present, 
but requires no special mention. The quartz is the same as in 
common granites ; it contains liquid-enclosures with spontaneously 
moving bubbles; and since the latter never disappear by slight 
warming the fluid is probably water. 
The third essential ingredient is biotite. It is found in small 
laminz, of a dark brownish-red colour, and possesses a peculiar 
nacreous lustre. The transverse section exhibits energetic pleochroism 
varying from pale yellowish brown, through brownish red, to black. 
Mica is not found in great abundance, consequently the rock has a 
light colour. 
Tourmaline occurs in small prisms with indistinct terminations, 
and is intensely pleochroic, parallel to C, grass- or bluish green or ~ 
black, at right angles to the latter deep brownish red. Another 
accessory ingredient is zircon. It occurs in grains or in long 
columnar forms in combinations of P, oP, o Po, and very 
frequently in ditetragonal pyramids. It is rare to find terminated 
crystals, the majority of them being imperfect or broken at one end. 
Often zircon individuals grow together one upon the other, the 
contact-face being P o, or P. Some of the columnar crystals are 
broken and faulted. The zircon is light wine-yellow or colourless, 
and possesses an adamantine lustre. Under polarized light between 
crossed nicols it exhibits yellow, violet, and green colours. It ex- 
tinguishes the light parallel and at right angles to the chief axis. 
None of the zircon crystals are free from interpositions, the most 
common being transparent needles, which are arranged in a confused 
manner ; but few of them are turbid or opaque. The nature of these 
microliths is unknown; some are found to be negative crystals of 
zircon with two or more bubbles contained in them. 
Besides zircon, this granite contains another accessory ingredient, 
a peculiar kind of microliths, These occur in impellucid or, at the 
edge, slightly translucent or semitransparent pyramidal crystals, 
with sharply pointed extremities; the colour is deep brown. In 
order to isolate them, the granite powder was successively treated 
with HF and H,SO,, when the still undecomposed residue could be 
- separated by Thoulet’s solution. Eventually a minute quantity of 
these microliths together with zircon was obtained; but there was 
not sufficient material for a chemical analysis. The presence of 
zircon prevents even a qualitative test of these microliths. Viewed 
from above, the ovtline of these crystals is square, the side view is 
* Becke, loc. cit. 
