112 Vol. XLIII., Art. 6. — S. TsiiLoi : 



artificial plagioclases. The temperature at wliich the crystals 

 Abj^Angj are in equilibrium with the residual liquid in the binary- 

 system albite-anorthite (NaAlSi30, — CaAlSiA) is about 1470^'C., 

 the composition of the liquid being Ab^gAn^jo ; while in the ternary 

 system diopside-albite-anorthite (CaMgSi^Oo — Na AlSisO« — Ca Al-Si-Os), 

 it is about 1250^0., far lower than in the binary mixture, the com- 

 position of the residual liquid being then about 5i% of Ab,,;An.y 

 and 46% of diopside. The natural magma is a very complex 

 polycomponent mixture, so that tlie temperature at wliich the 

 crystals Ab,,An,- ai'e in equilibrium with the residual liquid must 

 be far lower than that in the binary mixture. From this it can be 

 asserted that iJic intratelluric temperature cf the magma of OsJu'ma 

 at the last stage icas decidedly knoer than 1470rC., and may possibly 

 have been as low as 1250rC. if not still loicer. 



Pyroxenes. — P^a^oxenes in the rocks of Osliima are liypersthene 

 (and clino-hypersthene) and augite. From studies on artihcial 

 melts'^ it is expected that pyroxenes may belong to a Liter crys- 

 tallization than olivine. In agreement with tliis, no close associa- 

 tion of olivine and pyroxene has been observed, in contrast to the 

 frequent association of olivine and plagioclase,'^ suggesting that the 

 durations of the crystallization of olivine and i)yroxene have not 

 overlapped. Accordingly, it is also inferred that i.lagioclase pro- 

 ceeded pyroxene in beginning the crystalhzation. 



Hypersthene occurs only as phenocrysts and never as the 

 constituents of the ground mass in the Ôshima rocks, indicating that 



1) BowEX anil Axdeksex, " The System MgO-SiO., " Am.. Jour. S'-i. (4), Vol. XXXVII., 

 p. 487, 1914. 



BowEN, "Tlie Ternary System Diopside-Forsferite Siliia," ihhJ., Vol. XXXVIII., p. 207, 

 1914. 



AND3RSEX, "The System Anorthite Forsterite-Silica," ibid.. Vol. XXXIX., !> 407, 1915. 



2) A close association of olivine and plagicclase is seen in the ChigasaLd lava (p. 90) and 

 in micro-allivalite (p. 98). 



