GEOLOGIC STEUCTÜRE OF THE EIUKIU CURVE. 



23 



The ;ibove list shows that, the general dip is NW and the strike 

 NE to SAY, as in Oshima, 



In the plutonics, there are various granites in ditlerent places, 

 t'.(/., I found biotite-granite at San-mura and hornblende-granite 

 on tlie road from Mikyö to Kamezu. Diorite is exposed over 

 large areas, together with granite in the vicinity of J>uma. Serpen- 

 tines are found in some places, e.g. near Mikyö. Dyke rocks are not 

 uncommon; quartz-porphyry is found on the west of Buma, at 

 iShimokushi and Inokawa, and between Inokawa and Shoda, Yaezao 

 and Shirai, Mikyö and Setaki. On the north of Ketoku, there is a 

 porpliyrite dyke with a strike X4o°E. These pre- tertiary igneous 

 rocks have disturbed, only at the line of direct contact, the Palaeozoic 

 strata which usually show regular dips. Thus the last tectonic 

 disturbances in Tokuno-shima, Oshima and other islands seem to have 

 taken place long after their eruption, and certainly before the elevation 

 of the reefs which are quite horizontal. 



Okinoembu-jima. This island is a table-land of Diluvial coral 

 reefs with two peaks of Palaeozoic rocks in the interior. The highest 

 peak Oyama has a height of only 687ft. above the sea-level. The 

 island extends from NE to SW, which is also the direction of the 

 axis of folding of the Palieozoic rocks. In the bluish quartzose sand- 

 stone of Oyama, I have found the following stratifications: — 



N30°E NW20° N45°E N\V30° N— S W30° 



