Volcixno übhima,, Llzn. 139' 



land, Fuji is most closely related to those of the Oshinia group in 

 all respects. These volcanoes appear to form one pétrographie 

 province, and their lavas are closely comagmatic. In the accom- 

 panying tables (Tables I & II), the pétrographie characters of the 

 lavas and the time d'stribution of the outbursts in historic times 

 of these and the related volcanoes are shown. 



As to the birth-timo of the volcanoes of the Oshima group, 

 the writer has been led, by correlating their lavas with the general 

 coarse of change iu the magma of andesitic hneage in the Idzu 

 peninsula (pp. 133-134), to think that they might have been 

 born at a late date, probably in lati- Diluvium, wdien the nature 

 of the magma regionally became strongly basic. Structural and 

 morphographic features of the.ie volcanoes also suggest that they 

 are very young. The injection of the basic magma appears to 

 have been the first step in the igneous activit}' of the basaltic 

 Idzu islands, and these insular volcanoes may have been formed on 

 the injection fissure at the locations where the lava extrusion was 

 specially favourable. 



The above is the writer's present assumption as to the geologic 

 position of Oshima but it must be subject to further study. 



In concluding this chapter the writer wishes briefly to 

 remark on the data so far known concerning the bathymétrie 

 conditions of the environs of Oshima (Fig. 42). The sea bottom 

 near the island slopes outwards from it in all directions, steeply 

 toward the north and east'\ and gently toward the south and 

 west. A sea over 800 fathoms (about 1,500 m.) deep separates 

 the island from the Bôsô'^ peninsula consisting chiefly of the 



1) How long the belt of this steep slope is prolonged is not known, but the bathymétrie 

 map suggests that it runs in the direction S. by E. nearly in a straight line. It may perhaps- 

 have some geotectonic meaning such as folding or fault. 



2) m&^^ 



