30 



Vol. XLIir., Art. 6. — S. Tsuboi : 



Fig. 16. The centml homate, SIibaraya.mfi, viewed eastwards from (he south ol 

 Kagamibata ()c). The lava seen on the left si le (An) is that extruded in 1778 (An-ei 

 era). i£". . . .Kawajiri, the lowest point of tho crater margin. E ...Loisa éjecta of the 

 central cone. (Fig. 1, Ic) 



The homate is very simple in its building up, being composed 

 of siiperfluent lavas and éjecta the alternately accnmnlated layers 

 of which may be well observed on the inner wa'l of the summit 

 crater (Fig. 17). 



The lavas of the central cone do not differ much from those 

 of the somma, consisting mainly of basic plagioclase, augite, 

 hypersthene (including clino-hypersthene), and magnetite. But no 

 trace of olivine has ever been detected, in which point the central 

 cone lavas afford a contrast to the somma lavas, in most of which 

 olivine is meagrely present. Another distinguishing character of 

 the central cone lavas from the somma lavas is that the plagioclase 

 in the groundrtiass is more calcic in the former than in the latter. 

 Chemically, the central cone lavas are poorer in SiO.;, Fe^Oa, MgO, 

 and NajO, but are richer in ALO.!, FeO, and CaO. As described 

 in the petrography (p. 79), this rock is so peculiar in its com- 

 positi n as to deserve a new name, for which " MiJuiralts,'' derived 

 iTom Miharayama, is proposed. 



The volcanic products of tho central cone, both lavas and 

 €Jocta, not only lill the caldera, but are also spread down to the 



