42 Vol. XLIII., Art. 6. — S. Tsuboi : 



to bo the centre of the igneous action is exposed on the cliff, tlie 

 layers of lavas and éjecta incUning outwards (Fig. 28). The whole 

 mass is highly disturbed, being traversed by many fissm^es, cracks, 

 fractures and johits. Faultings, small in scale (vertical downthrows 

 being ^ m. in /i, 1 m. m f, and /•„ and 5 m. in f^), are also seen 

 on this cliff, always with downthrows on the side of the igneous 

 centre. The formation of these faultins's seems to be attributable 



:i - 



f^fw.ï^KrT 



Kig. 28. Diagrammatic sketch showing the exposure on the sea cliff to tbe west of Okata. 



a Lavas of the rained igneous bjcly. 



5 Ejecta o£ the same. 



c Ejecta of the sommn . 



f^ -f^ . .Faultä. (/ ) Fits ire. 



to the depre3sion of the layers, due to their own weights, after 

 the igneous agitations were over.^^ An éjecta bed of the som- 

 ma body (c in Fig. 28) discordantly covers this demolished 

 igneous mass. 



From what has been stated in the foregoing pages, it may be 

 claimed that the small demolished igneous bodies along the western 

 half of the northern coast have no direct structural relation to the 

 main body of the volcano Oshima, and that the] materials con- 

 stituting them were supplied by local vents. 



These igneous bodies must have existed, as their structure 

 shows, before the skirt of the main body had developed to its 

 present state, constituting at some time or other islets separated 

 from the main body by the sea. It was not until marine abrasion 



1) Depression of lava laye s due to their own weight is a phenomenon actnally obseived 

 in some active volcanoe3 as Mil ara (p. 32], Asama (Omoet, Bull. Earthq.llnvest. Com , Vol. VU., 

 No. 1; Eeport Earthq. Invest. Coin., No. 81), etc. 



