ANDENDIORITE IN JAPAN. 
In the northern fringe of the Kwanto plain, the environs of 
Tokyo, there is a series of volcanoes, including Asama, Haruna, 
Akaki, Niko, and Nasu, some of which are active, while the 
others are totally extinct. One of the oldest rocks erupted from 
these volcanoes is exposed at Usui Pass, in the form of propy- 
lite. The pass makes several trends along the steep, rocky 
slope of propylite mountains, and the railway of the Abt system 
passes through the rock by means of twenty-six tunnels. The 
propylite directly overlies the Miocene beds. 
The propylite seems to have been derived from augite-ande- 
site ; the normal variety has a homogeneous aspect, looking like 
a common andesite. The usual forms are altered. They are 
white or pale greenish, with scattered granular or sometimes 
cubical crystals of pyrite. Yellowish epidote grains and calcite 
crystals are also distinctly observed. 
Midway between the telegraphic posts No. 367 and No. 368, 
on the same pass, I have seen, piercing through the above men- 
tioned propylite, an interesting diorite dike, extending in an east 
and west direction. The eastern part of the dike is coarse-crystal- 
line, while the other end is fine-granular or somewhat porphyritic. 
The diorite, which is manifestly younger than the Miocene 
beds, is a hypidiomorphic aggregate of plagioclase and horn- 
blende, with quartz, magnetite, iron pyrite, and remains of 
augite, sometimes mixed with hornblende. Epidote and chlorite, 
besides secondary pyrite, are also very common as secondary 
products. The plagioclase is distinguished with the naked eye 
as milky white grains, while the hornblende is greenish black, 
with a resinous luster on the newly cleaved surfaces. Iron 
pyrite and epidote grains are always found on the fresh surface 
of the rock, with their characteristic colors. 
The plagioclase, which is the most important essential 
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