THE GREAT ERUPTION OF SAKURA-JIMA IN 1914. 157 



of an ophitic aggregate of plagioclase and pleochroic pyroxene ; 

 the brownish hornblende, which was only once seen in the 

 Saknra-jima shdes, occurs marginally'^ intergrown with the pyroxene. 

 Apatite was observed once or twice in slides. In the lavas of the 

 southern slope augite is represented in moderate quantity. 



The texture of the groundmass (PI. XVI. Figs. 5 and 6) is 

 pilotaxitic and hyalopilitic (if colorless glass is abundant) and fine, 

 and appears dirty gray under weak powers (Fig. 5). As already 

 stated, the color of the rock is solely influenced by different be- 

 haviors and a relative quantity of microlites of feldspar and augites 

 besides magnetite and glassy base in the groundmass. 



One exception to the general rule is the lava on the 

 northern shore at the Point Wari-ishi-Zakl near Kômen. It is 

 stuffed with light- colored, crystalline nodules of secretionary origin ; 

 but the lava itself is blackish, being built up of broivn, sometimes 

 colorless, glass in which only resorbed and dasted augite prismoids 

 are seen swimming. No feldspar was detected among microlites, 

 owing perhaps to rapid cooling under water, which did not allow 

 the crystallization of feldspars. 



The Atago-yama lava is gray with brownish flecks. Micro- 

 scopically, it is similar to that of Wari-ishi-Zaki, having networks 

 of chilhng cracks, appearing as if it were sohdified lava under 

 shore water. A noticeable feature is the colorless devitrified fibrous 

 glassy base with corroded and fibrillated augite microlite, which is 

 partially oxidized into hematite dust. Brownish flecks are solely 

 due to this dust, which is also strewn through the oxidized margin 

 of slaggy holes. 



1) Bowen says in his experiment ou the gravitative difiEerentiation of melts, that olivine 

 and pyroxene during their settling (olivine-nodiile) cause crystallization of amphibole upon their 

 cooling surface. Amer. Jour. ScL, Vol. XXXIX. 1915, p. 175. 



