THE GREAT ERUPTION OF SAKURA-.TIMA IN 1914. 7 



(Si', ill Fig. 2). The series, shaded black in Fig. 1, conforms to 

 the curvature of South Japan in detached bands. In northern 

 Kyiishû it widens and suddenly deflects southward near Nagasaki, 

 continuing farther southward along the west coast of the islands 

 of Amakusa. After an interruption of four degrees it reappears 

 unexpectedly in Oshima, whence it follows the curviforni structure 

 of the Eyûkyû arc {><('e Fig. 1). 

 cMN^ ^) ^^^^^ Ryûkyû arc is monoclinar^ in structure, 



^Ïrc^ dipping westward, and facing its tilted edge toward the 

 fore-deep of the Eyûkyû Graben (7,000 m.) on the open Pacific (Fig. 1). 

 The overthrusting movement of crust-wave upon the fore-deep, 

 accompanied perhaps contrariwise with underthrust, seems to the 

 writer to be the cause of the curvilinear alignment of the sub- 

 marine Cordillera, whose crests appear as the serial islands of 

 Eyûkyû. A reactionary regressive movement on the continental 

 side caused depression (500-1,000 />?.) and loosened the crust within 

 the continental shelf — the Asiatic bank, giving occasion later 

 to the outburst of magma. It is the inner zone and at the same 

 time the Volcanic Chain of Eyûkyû. (Fig. 1) 



The Peri-Tunghai tectonic movement happened between the 

 Cretaceous and pre-Lepidocyclina Tertiary times.'^ From the main 

 distribution of typical marine Tertiary beds which fringe the outer 

 side of the cordillera and also Taiwan, it seems probable that the 



faciès of the whole Lower Paleozoiciim, especially of the Devonian. As it is the oldest complex in 

 our islands, excepting the basement gneiss which is of limited occurrence, the writer has chosen 

 that as the exponent of the stratified bed. 



1) It is usually spoken of as a portion of folded mountains which constitute the axis of 

 the southern wing of the main Ja^janese islands. So far as the writer knows at present, there 

 are no folded mountains in existence, biit that of isoclinal flexure-xsmQes which simulate the 

 folded structure. 



2) Prof, l'abé informs me on a siiecimen which I sent him that a Niimmulite, Pellastispira, 

 occurs in the limestone from Motobu in Okinawa Island. He assigned the age of the rock to 

 be either the Ohgocene or the Eocene. 



