DR. BUNDJIRO KOTO ON SOME JAPANESE ROCKS. 443 
has a crater 200 metres in depth. All are well-shaped conical 
peaks. This district contains eleven thermal springs (41°-103°C.), 
one of which is the geyser of Atami. 
The fundamental rock of this district is exposed only in one 
locality (Nasimoto), where beds of limestone are observed under- 
lying the later eruptive rock, and these contain some remains of 
Foraminifera. These beds reappear at Simoda. 
Voleanic tuffs of submarine origin fringe the coast and, occasion- 
ally, contain sharks’ teeth, corals, and shells of Mollusea. This fossil- 
iferous layer is found in the interior of the district at a considerable 
height (400 metres above the sea-level). The country has cer- 
tainly undergone an upheaval at a comparatively recent date, as 
stated by Hahn in his work *. 
The typical augite-andesite of the district is that from Thama 7‘. 
It is a dark grey and somewhat porous rock. Felspar (3 millim.) is 
the dominant porphyritic component. Augite ranks next to it and 
then magnetite. The composition is normal. The general pro- 
perties of the mineral components have already been described ; 
hence in the following pages only particular cases will be noted. 
The felspar is fresh and hyaline (Tschermak’s mikrotine), but 
variously bent and cracked, and the crystals are mostly rounded. 
Tt contains abundant glass-enclosures, steam-pores, colourless micro- 
liths, magnetite-grains, and trichites. Under high powers the 
oval or round glass-enclosures in the felspar are seen to contain 
very minute flat colourless bodies (K. v. Chrustschoff’s discoliths) ¢. 
These are absent from the large felspar fragments enclosed in the 
augites, but abound in the liquid-enclosures with spontaneously 
moving bubbles. In a thin slice of the rock from the same locality 
T observed a felspar section which is twinned on the Baveno type. 
Its form is square and the trace of the twinning plane runs diago- 
nally across that section. That this felspar is asymmetric, is evident, 
since the planes of the optic axis do not stand at right angles to one 
another in two halves of the resolved crystals, but make an included 
angle of 12°. 
Augite is found in well-developed crystals in the combination 
(oP om, Pwo Po) with rudimentary faces of the prism and also 
pyramids. Itis pleochroic and contains numerous glass-enclosures. 
Negative crystals with fixed bubbles occur, as well as liquid-en-clo 
sures. Biotite is present in small flakes of a brown colour, and 
displays strong absorption. This is the only one of these augite- 
andesites which contains biotite. 
The augite is brown or grey. 
The ground-mass consists of a mixture of the lath-shaped felspar, 
small augite prisms and needles, and also magnetite grains. A 
peculiar arrangement of these produces the microfluctuation-structure 
* «Untersuchung tiber das Aufsteigen und Sinken der Kiister,’ Leipzig, 1879. 
+ Unless otherwise mentioned, all the localities of augite-andesites are situ- 
ated in the Izu province. j 
+ oo ‘Mineralogische und petrographische Mittheilungen,’ Band iv. 
p. 481. 
