GEOLOGIC STRUCTURE OF THE RIUKIU CURVE. 63 



Astridi/peus integer \ osh., found with Ecliiiiodiscus in Formosa 

 and Iriomote-jima has been also found from the Miocene Tertiary near 

 Mizuho-mura, Prov. Kai in Honshu. Xear this place, there is found 

 a limestone filled with Orhitoides. Nearly similar Orbitoides were 

 collected by me in greater numbers from the limestone in Iriomote- 

 jima. R. Vi. N"ewton and R. Holland have mentionedf that the 

 Litliotliamniiim in the Tertiary of Formosa belongs to the same species 

 as those in the Miocene of Timor. Thus the Tertiary sediments of the 

 Saki-shima group and of the northern part of Formosa are of the same 

 horizon belonofin»' to the Miocene. 



According to earlier investigations by many geologists, the main 

 part of Formosa, consisting of slate, granite. Palaeozoic limestone and 

 Archean ( ?) rocks, is surrounded by Tertiary sediments mainly deve- 

 loped on the north, east and west coasts. The limestone and granite 

 are no doubt the same as those in the Riukiu Curve. I found also 

 many blocks of pyroxenite-like rocks from the neighborhood of Giran 

 in Formosa. The grenter part of Formosa is of clay slate, whose age 

 is still unknown, but may be regarded as Mesozoic and Palaeozoic. 

 No indisputably Mesozoic rocks have yet been discovered in the 

 island. 



PART v.— Conclusion. 



The Riukiu Curve consists of a number of islands, forming; a Ions: 

 arc between Kyûshù and Formosa. The difference in longitude of the 

 two extremities of this arc is about twice that measured in Kyushu, 

 while the difference of latitude is thrice that in Kyushu. The sedi- 

 mentary rocks in the Curve are never horizontal, showing usually a 



t Newton and Holland, Note on microscopic Sections of Limestones from Formosa, &c. — 

 Jour. Geol. Soc. Tokyo., Vol. VII., No. 81, 1900. 



