GEOLOGIC STRUCTURE OF THE RIUKIÜ CURVE. 



51 



only the large Echinoids, Echinodiscus and Astrichjpeus in the sandstone 

 of Hoka-(Soto-)banare. The former has a diameter of 9 cm. and greatly 

 resembles E, placenta Duncan and Sladen in the form of its lunules. 

 It is interesting to note, that I found the same species in the Tertiary 

 of northern Formosa, which contains numerous coal-seams and con- 

 sists of rocks which are the same as those in Iriomoto-jima. The 

 latter genus is now represented by one living species A. manni A'erill. 

 In 1899, I studied the Astriclijpeus from the Tertiary of Mizuhomura, 

 Prov. Kai (probably Miocene), and named them A. integer. The 

 specimens from Iriomote-jima are rather ill-preserved, yet showing 

 sufficient characters to identify them with the same species. Moreover 

 the Tertiary near Mizuhomura incloses a thin limestone with Orhitoides 

 very closely resembling that in Iriomote-jima. 



The Tertiary of Yonaguni-jima. This island consisting of Tertiary 

 rocks, is disposed in two hilly regions separated by raised reefs 

 (Fig. 8.). The eastern half is called Urabu, and the western Kobura. 



Tomozatt 



Aczakl 



OJshizaM 



Fine grained Alternation of Compact quartzose Coral reef. Coal, 

 sandstone- shale and sandstone- sandstone. 



Scale 1:100000. 

 Fig. 8.— Geological Map of Yonaguni-jima. 



Raised reefs are also observed along the margin of the hills, especially 

 on the western and northern sides (PL Y.). The Urabu region is 

 elongated from N to S, but Kobura is broad in shape. Between them, 



