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 tinder 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 inter- 

 stratified with the conglomerate. 



At about half the distance between the northern and southern sides of this high- 

 land, 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 south- 

 westerly 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 irregxilarly upwards, presenting their edges towards the 

 upper surface of the bed. 



This moimtain 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 conglomer«,te, 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 com- 

 pact 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 joint- 

 grass, often from six to ten feet high. Leaving the sea-shore, we crossed the pro- 

 montory 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 I 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 appa- 

 rently 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 Shimakomaki. 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 



