GEOLO&IC STRUCTURE OF THE RIUKIU CURVE. 35 



sandstone, often with slate. Pyroxenite or amphibolite is rarely 

 found. These rocks show the same general dip as in Zamami-jima 

 with an angle of 25° — 45°. Geruma-jima and Moknraku-jima are 

 chiefly composed of sandstone and slate, showing the same dip as in 

 the two islands above mentioned. Indeed the islands of the Kerama 

 ■subgroup are nothing else than the mere continuation of the region of 

 PalsBOzoic rocks, excluding compact quartzite and limestone, in 

 Okinawa-jima, the evidence of which is assured by the kinds of rocks 

 iind the position of the islands on the map. 



The Iheiia Subgroup trending north and south, is composed of 

 four small islands, Iheya, Gushichfi, Izena and Yanaha. Mr. Kuroiwa 

 has found most of these islands to be of compact quartzite, except 

 Yanaha-jima and a part of Gushichfi-jima, which consist of raised 

 coral reefs. 



The very small islets on the west of Xaha, namely Kd-jima 

 Koisa-jiiiia and Kisu-jiina consist essentially of fragments of recent reef 

 corals. Only the western |)art of Kei-jima consists of undisturbed 

 old reefs. 



The three islands, Kinne, Aguni and Tori are the only volcanic 

 islands in the Okinawa group. Tori-shima, lying far to the north- 

 west of Tokuno-shima, has a length of three miles, and is still emitt- 

 ing a great quantity of sulphuretted hydrogen gas. Mr. Kuroiwa has 

 found Aguni-jima to be formed of neovolcanic rocks with raised coral 

 I'eefs; and Kume-jima* to be almost entirely augite-andesite. Only 

 between Janadö and Uemura on the eastern side of Kume-jima is 

 there a little exposure of Tertiary (?) sandstone, dipping 45° to the 

 northwest. A small mass of schalstein is found enclosed in the 

 volcanic rock. Thick raised coral reefs are found also in this island, 

 along its northern and on the middle of its western coast. 



* i^.Mëi (Kume-jima : in Japanese).— The Jouni. Geol. Sac. Tökijö, Vol. V, No. 59, 1898. 



