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

98 GEOLOGICAL RESEARCHES IN
Retracing our steps to Ousubetz we embarked in a boat propelled by eight oars.
men, four scullers, and a large sail, and soon reached Iwanai.
August 25th. Leaving Iwanai we went by boat to Isoya, passing close under the
rocky cliffs of the Raiden. The northern part of this mountain is formed of the
volcanic tufa-conglomerate covered by a great bed, or perhaps several flows, of lava,
often exhibiting columnar structure. In places beds of lava seemed to be interstratified with the conglomerate.
At about half the distance between the northern and southern sides of this highland, a large amphitheatre or crateriform valley opens towards the sea. South of
this the cliffs, less high, consist of the conglomerate, and in the perpendicular walls
are visible many small but regular dykes with transverse columnar structure, and
in places dislocated by faults. The conglomerate strata have a considerable southwesterly dip, and as we approach the southern flank of the Raiden, near the village
of Hamajime, they disappear under the sea. Overlying this formation and forming
the mountain above, is a gray volcanic rock, possessing a tabular structure, which
gives it often a stratiform appearance near the bottom, but in the upper half of its
thickness the plates curve irregularly upwards, presenting their edges towards the
upper surface of the bed.
This mountain is a high, flat ridge, running nearly east and west, between the
valleys of the Shiribetz and the Shiribuka rivers, and on it is the Iwaou nobori,
and at least one more volcano.
August 27th. Leaving Isoya, we rode around the head of Odaszu bay to Sutzu.
On this side of the bay we met again terraces of conglomerate, covered with loose
sand and gravel, corresponding to those mentioned as occurring on the opposite
side.
Before reaching Sutzu the conglomerate formation was found to be succeeded,
for a short distance, by a gray eruptive rock, apparently a trachytic porphyry. The
conglomerate in this region consists, almost entirely, of rounded fragments of a compact black rock, almost a pitchstone, containing crystals of white triclinic felspar.
August 28th. Leaving Sutzu we rode westward, over the lower of the two terraces
that rise between the sea and the hills. The highlands are wooded with small
trees, but on the terraces there is generally only a heavy growth of weeds and jointgrass, often from six to ten feet high. Leaving the sea-shore, we crossed the promontory to its western flank, travelling over the conglomerate, upon which was
seen a loose deposit of sand and gravel closely resembling the auriferous deposit of
Kunnui. In one place 1 observed an outcrop of the argillaceous rock, with the
peculiar vermiform fossil, seen at Kunnui, Washinoki, etc.
At Achase the tufa-conglomerate dips inland, and beneath it there is an apparently conformable bed of fine-grained, brown sandstone, easily scratched with the
knife, and seemingly of the same origin as the conglomerate.
A few miles further southward we reached Shimakomlaki. Here the semi-vitreous
character of the pebbles that compose the conglomerate is better developed
than usual, although a black amorphous base was found to be generally prevalent,
in these fragments, in the tufa-conglomerates of the west coast. Here the base of
the rock is jet black, opaque, with the lustre of pitch, and imperfect conchoidal