b AET. d. — B. KOTO : 



one of the members of the ' Eyûkyû volcanic chain,' it will be well 

 here to give a general outline on the geological significance and 

 the genesis of the Eyûkyû arc. 



There is a tectonic line of first magnitude in Eastern Asia 

 which, starting from the east coast of Korea, apparently terminates 

 at the south end of Taiwan, thus enclosing the entire region of 

 the shallow Tunghai or Eastern China Sea (Fig. 1). The writer 

 will hereafter call it the Peri-lhcughai tectonic line. This rupture 

 line assumes various phases on its long sweep. 



n) On the east coast of Korea it appears as step- 



East Ooast 



or KoEEA faults dropping eastward under the deep bottom of 

 the Japan Sea.^^ 



Faulting 



OP South h) Ou its soutliward course it cuts transversely 



Japan Axis 



right through the solid axis of the mountain fold'^ which 

 constitutes southern Japan, causing the west wing by this time 

 to sink down to the continental shelf of the Tunghai. The 

 shattered coast of western Kyûshû, the ' ^gean Sea of Japan,' 

 owes its formation to this cause. The large crooked indentation 

 of Ariaké, lying to the east of Nagasaki, is, geologically speaking, 

 a part of the easterly lying Inland Sea or Seto-iichi that lies 

 between the contracting end of Honshu and the island of Shikoku 

 (Fig. 1). 



In western Kyûshû we see a peculiar but highly important 

 crustal movement of the Peri-Tunghai rupture-line, which can be 

 adduced from the orientation of the Smnbagawa-Mikahn Series'^^ 



1) B. Koto, 'Journey tlirough Southern Korea.' This Journal, ^'ol. XXVI. Art. 2, 1909, 

 Tokyo, p. 3. The faults produced are of the nature of what the liussian geologists call the 

 disjunctive, and of the late von Kiehthofen's Zen-ungsver-werfung. 



2) It is what geotectonists call the Blatt, or heave-fault. 



3) The series is an old prasiuite complex of chlorite and graphite schists and overlying 

 limestone, amphibole-schists, and clasto-pyroxenite of gabbroic derivatives, associated with glau- 

 cophane and piedmontite schists. In the writer's opinion, the series rexire.sents a metamorphic 



