Geological researches in China, Mongolia, and Japan, during the years 1862-1865.

CHINA, MONGOLIA, AND JAPAN. 95
remains of a stratified deposit seen here and there, about the base, and fragments
of scoriae were found in the neighborhood.
There are several small crateriform depressions at different points near the
summit, filled to the level of the lip with sand and clay, and forming small plains
surrounded by rocky sides. In one of the walls a compact black rock, either a
dyke or the remnant of a lava flow, was observed.
The Iwaounobori is the central one of three volcanoes, which lie in a straight
line running about N. N. W., S. S. E., and this is also the trend of a broad belt,
within the limits of which the solfatara action is most developed, both across the
summit and on the outer walls.
Throughout this belt the rock, wherever not covered by the products of decomposition, is found to be traversed by countless fissures, more or less filled with
sulphur. Wherever the filling is incomplete, small jets of steam and gases are still
seen to issue forth. Several trials, made by inserting a long chemist's thermometer
as far as possible into different fissures, gave a constant temperature of 98~ C.
The steam has a strong odor of both sulphurous acid and sulphuretted hydrogen.
It has an acid reaction on litmus paper, which is especially strong when the condensed drops, that hang on the sulphur crystals in the cavities, are tested. Beautiful crystals of sulphur, a quarter of an inch long, were rapidly formed on the bulb
of the thermometer.
Excepting at the steam vents, which are not more than from one to five inches
in diameter, the fissures are closed up with sulphur at the surface, but by breaking
away a few inches deep, cavities are exposed lined with a bristling mass of most
beautiful straw-colored crystals of this mineral, made up of brilliant steep pyramids
connected in the line of the longer axis. Unfortunately, they were too delicate to
bear transportation.
On a precipitous part of the outer wall of the mountain, where a large mass of
rock seemed recently to have fallen off, I saw an interesting exhibition of the action
of the gases. The rock is seen to be
traversed by a perfect network of sulphur Fig. 16
veins (a) which seem to occupy the positions of the cracks common to all rock. >
The trachytic rock (b) is tolerably well
preserved in the centre of the blocks, but
toward the circumference it is more and
more disintegrated, and has assumed the
form of concentric layers, the outer shell'5,
being changed to a white earth. It seems 4 -
not improbable that this condition may
exist through a large part of the moun- V <J
tain, thus forming a great stockwerk of a. Sulplur. b. Rock.
sulphur.
The only way in which I can account for this structure is, by supposing that the
disintegration of the rock, which formerly occupied the spaces now filled with
sulphur, took place when the water, which now appears only as steam, stood at a