10 ART. 3. — B. KOTO : 



ward the open Pacific. Through the sinuous point or middle wing 

 (Fig. 1) between tlie positive and negative curves, which is located 

 at the northeast point of Taiwan, a volcanic line passes from the 

 inner side of the Eyiikyû outcurve to that of the Taiwan incurve. 

 Essential ^a i^ sliouM, howcvor, bo bomo lu miud that the 



Chaeactee- ^ 



^"^RïûIïT^ volcanic chain of cantalitic hornblende-andesite of Tai- 



VOLCANIC r,, . . j_' i? 1 1 



Chain wau rcappcars, alter an mterruption oi seven degrees, at 



Unzen and Tara- daké (?7and T in Fig. 2), both near Nagasaki, and 

 then proceeds through the heart of Kyûsliû at Kibo-zan B, Kujii 

 K^, Tsurumi and Yufu-daké Y, and Futago-yama F, and finally 

 passes over to the contracted end of Honshu along the shore of the 

 Japan Sea (Fig. 1). TJic Ryuhfii volcanic chain, cliaractertzed hy 

 augitc- andésite or auganitc, on flic other hand, only starts froin Agnni 

 {A. in Fig. 1) off Okinawa, and, as is frequently mf^ntioned, runs 

 through tJie Togara group to soutliern Kyushu. 



We have, therefore, to distinguish two volcanic chains quite 

 different in the nature of magma, viz., the cantalitic hornblende- 

 andesite and the femic augite- andésite. To the latter group be- 

 longs the Kyûkyû volcanic chain ; and Sakura-jima, which is the 

 subject of the present paper, is one of the members of this chain. 



B) The Principal Formations and Main Geologic Structure 

 of Southwest Japan.— From a glance at the map of the southern, 

 portions (Figs. 1 and 2) of both Kyùshû and Shikoku — the two 

 main islands of " Old Japan," one can readily understand the 

 fundamental geologic structure. The principal geologic formations 

 appear in parallel zones, which cross them from the northeast to 

 the southwest, and the two islands are the //o/'sf-blocks in the 

 geological sense of the term, with the rias coast on the eastern 

 and western shores. 



