52 -^ï^T. 2,-S. YOSHIWAHA : 



there probably existed a fault line on both «ides of which we observe 

 a difference in petrography and tectonics. The western half is com- 

 posed entirely of brownish sandstone dipping to SE l(f — 30° with 

 the strike N 30° E. I]ut in the other part, brownish sandstone is seen 

 only on a high level, and under it .are found a hard Ijluish sandstone, 

 compact quartzose sandstone and shale witli a thin coal-seam. Fossil 

 plants and Echinoids are found just al)ove the coal-seam. The bedding 

 of these rocks is X — 8, E 20^. TliouMi the island is elono'ated from 

 east to west, yet the strike of rocks is not ])arallel to the longer axis of 

 the island, but is really perpendicular to it. 



Igneous Roch in the IWi/ania Suhijroup. Among the plutonics, gra- 

 nite, of which biotite-and hornblende-granite are the chief varieties, oc- 

 cupies large areas in Ishigaki-jima, forming elevation of ICxSO ft. It 

 has pierced compact quartzite on the south ;ind west, and other 

 Palœozoic sediment on the east. Olivine-diorite is found in the 

 granitic region on the south of Omoto-dake, their mutual relations 

 being still unknown, besides, in Uchino-mura in the northern part 

 of the part D, there are small exposures of diabase and quartz-por- 

 phyry. In the part C, a liparite dyke is found in the north-east, and 

 a liparite stock in the south-east, 1)otli of wliich i-un fnjm XE to SAV. 

 Andésite is predominant in Ishigaki-jima. Pyroxene-andesite is the 

 principal lava from the Xosoko volcano, and extends even to the 

 north-west and north-east of Ibaruma. Around the volcano wc find 

 agglomerate-tuft' with angidar blocks (jf andésite. The volcano is 

 much eroded, showing no trace of its original form. Its highest part, 

 Xosoko-màhë, has an elevation of i)51 ft., and foi-ms a sharp point 

 standing out prominently from the surrounding hills (the remains of 

 the Xosoko volcano), which again descend by perpendicular clift's to 

 the plateau on their northern side (Fig. !)). The two independent vol- 

 canic masses in the wx\st of Xobara-zaki as well as in the ])art B con- 



