4it DR. BUNDJIRO KOTO ON SOME JAPANESE ROCKS. 
around the porphyritic constituents. Traces of the brown glass 
basis are present in patches here and there. 
The augite-andesite from Yagisawa is essentially similar. 
The felspar is rich in rectangular glass-enclosures, and a basal 
section extinguishes the light at from 17° to 19° with P/M. The 
discoliths are typically developed in this rock. TIron-glance and 
hydrated iron-oxides are found in the porphyritic erystals and in the 
ground-mass. 
The augite possesses well-developed pinacoids. The porphyritic 
augite as well as that of the ground-mass crystallizes out after the 
felspar. Apatite is rare, and there is no glass-basis. 
Closely allied to the preceding is the rock from Toda. It deserves 
our special attention on account of the presence of tridymite, which 
is found in vacant spaces in the ground-mass, and consists of small 
hexagonal or rounded scales lapping one over the other like roofing- 
tiles. Another modification (page 441) also occurs associated with 
the former. Grey or brown apatite occurs in the augite and in the 
ground-mass. JIron-glance is plentiful in the augite and in the 
felspar. No glass-basis. The microfluctuation-structure is very 
distinct. 
Another tridymite-bearing andesite is from the Izu-San. The 
external appearance is light grey. It is somewhat porous, and it 
has a striking resemblance to the ground-mass of the trachyte of 
the Drachenfels, on the Rhine. O. Kuntze has mentioned the oceur- 
rence of a trachyte between Odawara and Atami. It is very 
likely identical with that of the Izu-San; and ifso, Kuntze’s* trachyte 
would prove to be a true augite-andesite, for the Izu-San rock is 
made up of augite and plagioclase. The felspar looks glassy, is 
well striated, and poor in microscopic enclosures, but contains large 
isolated steam-pores. Sanidine is also present. Large porphyritic 
augite crystals are scarce and show a weak pleochroism. The colour 
of the augite differs in different parts of the same crystal. The one 
portion may be yellowish brown, while the other is deep brown ; the 
latter has a glassy appearance. Light bluish apatiteis notrare. A 
few hornblende sections are occasionally found with the character- 
istic opacite margins filled internally with yellowish-brown augite 
grains, which result from the alteration of the hornblende +. 
The peculiarity of this rock is the abundance of its tridymite, 
which is found everywhere in empty spaces in the ground-mass, 
presenting a peculiar form of twinning. The well-known 
tion of hexagonal scales of tridymite suggestive of roofing-tiles, is 
here entirely absent. The tridymite is colourless, with a bluish 
tinge by reflected light. The augites crystallize after the felspars. 
Patches of brown globular granulated glass-basis are found in the 
interstices between the lath-shaped felspars. The ground-mass is 
mostly made up of felspar microliths, and a few augite grains and 
* ¢WMitth. d.d. Ges. fiir Natur- u. Volkerkunde Ostasiens,’ 7** Heft, 
Yokohama, 1875, p. 30. 
+t Vide page 440. 
+ Vide page 441. 
