GEOLOGIC STRUCTURE OF THE RIUKIU CURVE. 55 



The formation of the Curve has been explained by Prof. Koto, as 

 due to the depressions of the Tung-hai ("East Sea" of China), which 

 took place mostly in the Tertiary period. Thus the greiiter part of 

 the Palaeozoic rocks in the above mentioned islands is inclined to the 

 west. Sometimes the strike of the beds, and sometimes the longer 

 axes of islands, are parallel to the direction of the Curve. The fissm*e 

 of volcanic eruptions, which is continued to tiie series of Kyùshù 

 volcanoes, such as Kiri-shima, Sakura-jima and Kaimon, is found on 

 the inner side of the sedimentary zones of the Riukiu Curve, and is 

 traceable through the islands, Take-shima, Iwö-jima, Kuro-shima^ 

 Kuchinoerabu-jima and tlie Tokara group, and further to Tori-shima 

 on the west of Tokuno-shima, Aguni-jima and Kume-jima in 

 Okinawa (PI. II). The probable south-western prolongation of this 

 o-reat fissure is throuo'h the uninhabited islands on the north-east of 

 Formosa, through Daitou-zan in the same island and the Hôko group 

 (Pescadores). The volcanic rocks in Ishigaki-jima have an aspect 

 diiferent from those in this line of eruption and may perhaps be 

 continuous with those in tlie s<juthern Pacific Ocean. There must be 

 some fissures, running from south to north, in the sea between For- 

 mosa and the Saki-shima group. The}' were probably caused by a 

 pressure independent ofthat which folded the Riukiu Curve; and the 

 volcanic rocks in the Yaeyama subgroup and those of the other islands 

 in the Curve may belong to ditferent periods, the former being older. 

 The thick beds of Iriomote-jima were probably raised by a volcanic 

 eruption in the Yaeyama subgroup. Limestone and sandstone, of the 

 same age as this eruption, have been deposited in Ishigaki-jima, alter- 

 nating with agglomerate-tuff. In Ishigaki-jima, the Tertiary as well 

 as the Palœozoic rocks have not been disturbed by volcanic action, 

 and remain equally inclined in the same direction with the strike 

 nearly E-W, the direction of which doen not coincide to the longer 



