Jj^^ Vol. XLHI., Art. 6. _ S. Tsuboi : 



sively lower than 1470^C. and possibly as low as 1200^-1300^0. 

 At this stage, bytownite crystals AbijAn^j were suspended in the 

 residual liquid. 



In the loicer portion of the magma basin heavy mafic minerals - 

 accumulated and also some of the early separated plagioclaso 

 crystals which had sunk in company with the olivine crystals. 

 There these minerals remained rich in higher-melting components 

 owing to the small amount of the available liquid. 



In the upper portion only a few crystals of mafic minerals of 

 later separation, comparatively rich in the lower-melting components, 

 were in the act of sinking. 



All the observed lavas of Osliima belong to extrusions after 

 this last state of the magma was reached. The residual liquid in 

 the magma reservoir consolidated after extrusion as the ground- 

 mass, consisting of plagioclase, augite, magnetite, and a small 

 amount of glass. 



Development of the Various Rock-Types. 



The development of the features seen in every rock-type can 

 he e^xplained by supposing that the rocks of different types 

 were extruded from various portions of the magma basin, where 

 differences in amount and character of the heavy intratelluric 

 crystals were effected by gravitative action. 



(1) Rock-Types Comparatively Rich in Phenocrysts of Mafic 

 Minerals. — Rocks of these types are : — 



(a) Tvvo-pyroxeue-oliviiie-auortliite-hasalt (p. S9). 



(h) (^livinf-hytowiiite-basalt a (p. 92) aucl [i (p. 94). 



(c) Oliviiie-bytownite-dolen'te (p. 98). 



(<0 Hvperstlieue-basaltic haudaito (p. 73). 



( e ) Tw< )-pyroxeue-l)asalti(' l)audaite ( ]). 74). 



(/) Hyjierstlieui-boarin.u; :niiA-ito-oliviiie-l)ytowiiitr-bas:ilt (p. 7n\ 



