120 "^'ßl- X^'III., Art. 6. — S. Tsuboi : 



they are scarce can be explained on the above supposition. 



(3) Central Cone Lavas (miharaite).— The central cone lavas 

 are entirely free from olivine. These must represent the upper 

 portion of the magma basin in later stages when the subsidence 

 of the ohvine crystals in the remaining liquid had progressed so 

 far that they were remote from the extruded lavas. 



Pyroxene crystals occur sparingly since they are of later 

 separation than olivine crystals and accordingly their subsidence 

 was less extensive. 



In connection with the above proposition that the somma lavas 

 of the common typo as well as the central cone lavas originated 

 from the up)per portion of the magma basin from which the olivine 

 •crystals had subsided, it is a noteworthy fact that chemical analyses 

 made of the rocks of the somma and the central cone (pp. 71 & 

 85) gave an excess of silica with respect to other oxides, as 

 shown in the followino^ table : — 



A ... A typical soumia lava exposed ou the south shore at the east end 



of Sashikiji'^ (2e ; PL VI. DE 4). 

 B . . , Central cone lava in April, 1912. 

 C . . . . Central cone lava in October, 1912. 

 I) . . . .Scoria of the central cone in Octol)er, 1912. 

 E . . . Central cone lava in December, 1912. 

 F . . . . The average of the four B — E. 



1) mAcm 



