gQ Vol. XLin, Art. 6. — S. Tsuboi : 



crystallinity, and the texture is accordingly from nearly hyalopilitic 

 to granular intersertal. 



An-ei Lava (1778) (PL IT. Fig. 6).— The lava of 1778 

 is the most conspicuous now seen in Osliima. As is shown in the 

 geologic map (Pi. V.), extensive lava fields stretch from the top 

 crater eastwards and southwards to the sea shores in almost 

 uncovered condition. The field feature of tliis lava shows that it 

 belongs to the " Pahoehoe " type. The vesiculation of the mass 

 of the lava is rather evenly developed and uniformly disseminated 

 as Daly^^ says, but the size of the pores is not always very small. 



Megascopically, plagioclase phenoerysts, 0.5 — 3 mm. across, are 

 sparsely scattered through the compact, aphanitic groundmass with 

 abundant vesicles varying in diameter from a few mm. to 1 cm. 

 They are mostly spherical, but some are elongated in one direction, 

 even to such an extent that the length is ten times the breadth. 



Microscopically, plagioclase phenoerysts are always seen. The 

 groundmass consists of plagioclase, augite, magnetite, and lirown 

 glass. Its texture varies in different parts owing to the different 

 conditions of consolidation. A specimen from the lava field on the 

 northern flank of the central cone shows microporphyritic ground- 

 mass (PI. II. Fig. 6) with microphenocrysts (0.05-0.3 mm. across) 

 of plagioclase, augite, and a few of hypersthene scattered in dopatic 

 fabric through the black base which even in thin section is opaque 

 owing to the fine dissemination of magnetite. Another specimen 

 collected near the eastern end of the flow has its groundmass quite 

 like that of «-type (p. 70) of the somma lava. 



Meiji-Taisho Lava {1912 1914) (PI. III. Figs. 1-4).— During 

 the eruption in 19 12-' 14, the extrusion of lavas took place in five 



1} Ljneous Bocks and Their Orljin, pp. 290-231, 1914. 



'•The Nature of Vulcanic Action,' Proceedings of the American Academy of Arts aiicl 

 Hciences, Vol. XLVII, No. 3, 1911. 



