96 ^'ol XLIII., Art. 6. — S. Tsuboi : 



Microscopically, subhedral phenocrysts of calcic bi/townite (Abjß 

 An^j) with usual characters and a few anhedral ones of hyperdhene 

 are found. The groundmass consists of small plagioclase prisms, 

 augite anhedrons, and magnetite grains, with a small amount of 

 colourless glass as interstitial matter. Only one crystal of apatite 

 was found in a thin section. These component minerals of the 

 groundmass vary from 0.003 to 0.04 mm. in diameter and arrange 

 themselves in granular intersertal texture. 



{IE) IJJecta. 



12) Ashes, Sands, Lapilli, and Bombs. 



Ejecta are not less important than lavas in the building up of 

 the volcano Oshima. They are found in many layers alternated 

 with lavas. 



In size tliey are of four grades — (1) ashes, (2) sands, (3) 

 lapilli, and (4) bombs. 



Ashes mid Sands — -These are brown, black, or yellowish in 

 colour ; sometimes as red as rouge, having been scorched by 

 the intense heat of the molten lava. Ashes and sands treated 

 with HCl were observed under the microscope to consist mainly 

 of splinters of glass and fragments of calcic bytownite with 

 only a negligible amount of fine pieces of the minerals that 

 constitute the groundmass of the lavci. This fact indicates that 

 these ashes and sands originated in the magma itself before the 

 consolidation c>f the groundmass and did not come from the 

 disturbed and shattered portions of the rocky walls througli which 

 tlie vent was drilled. These form what Piksson'^ terms '• vitric 



1) "The Microsn'pic Characters of Volcanic liiflFs," .4???. Jour. Sd. (i). Vol. XL., p. 191, 

 1915. 



