THE GKEAT ERUPTION OF S.VKURA-JIMA IN 1914. 195 



cessoiy mass of rock deserves the new name of micro-allivalite, 

 since it is mainly composed of anorthite and olivine, corresponding 

 to micronorite-patches in andésites first described and named by 

 Laceoix in his well-known Martinique work. 



A similar eucritic intergrowtli or rather enclosure of anhedral 

 olivines in a basic plagioclase is to be seen in the feldspar-pheno- 

 cryst of the recent lava near Yébino-tsuka hill in the eastern lava- 

 field, as in Text-fig. 44. 



The whitish masses dealt with under the present heading are 

 usually interpreted as formed under p 1 u t o n i c condition, and 

 caught up by magma and brought to the surface. From the mortar 

 texture with glass cement, pumiceous texture and pseudophenocrystic 

 (cumuloporphyric) occurrences of masses, it seems they may not 

 necessarily be formed in a deep horizon, and especially the noritic 

 patches are likely formed even during subaërial flows.^^ Anyway 

 they are products of relatively early separation, and composed of 

 minerals of high melting point among andesitic components. 

 Selective crystalhzation and resistance toward resorption of the 

 components caused magmatic differentiation, and concentrated the 

 minerals in certain spots. The segregated portions were then 

 conveyed through upward current to the surface. They are not, 

 however, necessarily buoyed up in viscous magma from a deeper 

 horizon, where the minerals gather owing to their comparatively 

 high specific gravity. 



It is to be noted that the enclaves of diopside-gabbro are 



1) The macroscopic banding, e.r/., as in the ß type (p. 191), is due to special aggregation of 

 diopside and tremolite in one plane. To the writer this si^ecial texture seems to suggest the 

 formation of the mass near the surface or on the surface of the lava-vent. Under plutonic 

 conditions the same mass will crystalhze in homogeneous mixture, or else the banding must be 

 attributed to primary flow of segregation — a fact which is not observalile in microscopic analysis 

 in this granular aggregate. 



