34 ART. 2- S. YOSHIWARA: 



They are uU entirely capped with horizontal reefs. Only in Miya- 

 gusuku-jima and Hianja-jima, the foundation rock, raised above the 

 sea-level, is loose brownish sandstone with intervening marly layers; 

 bluish sandy shale also occurs. In Miyagusuku-jima they are inclined 

 to SE on the south-eastern side; and to SW 10 degrees with the strike 

 of S60°E, in the southern part. Fossils found from the Tertiary of 

 this island are mostly small forms of shallow sea deposits. They are 

 Natica, Trochm^ Guililfonlia, Fecfunculus, Liniopsis, Pecten, Anomia and 

 Dentalium. There are also well preserved specimens of Rhynchonella 

 lucida Gld., Mcr<ielia sanguinea Chemn., TerehratcUa mariae A. Ad., 

 Terehratula japonica Sow., Dosinia cxolela Linn'e and Nucida mirahilis 

 Hinds. Besides these, I have collected unpetrified wood, fossil bones, 

 corals and echinoids. The Tertiary rocks on the northern side of 

 Hianja-jima, when traced from the western end of the island to the 

 east, show a gradual change of dips, namely from an eastward to a 

 southward and finally to a southwestward. Thus the structure, 

 arrangement and kinds of the Tertiary rocks of the islands on the east 

 of Okinawa-jima are just the same as those in the southern part of the 

 large island itself, witli which they are similar in origin. 



Almost all of the Kerania Subgroup which contains the islands of 

 Zamami, Aka, Geruma, Mokaraku, Yakashi, Kuba, Tokashiki, Kuro, 

 Mae and others, as well as Tonahi-jima seems to consist of I^alaeozoic 

 rocks. So far as I know, there is no tnice of raised coral reefs; and 

 the islands are mosth^ mountainous like the northern part of Okinawa- 

 jima. Zamami-jima is especially mountainous and has the best 

 anchorage of any of the lliukiu islands. Palœozoic slate, with a less 

 extensive sandstone, generally dips toward the south, southwest or 

 west, with an angle of 20°-45°, but never to the east, as in the other 

 islands in Riukiu. A dyke of porphyrite is found in Akamura. Aka- 

 jima, lying on the south of Zamami-jima. consists chiefly of greywacke 



