170 AKT. 3. — B. KOTO : 



areas on diametrically opposite shores, and in point of time both 

 are only separated by an interval of five (?) years, dnring which 

 no magmatic differentiation seems to have taken place in the lava 

 reservoir, which is presumably common to the two lava-flows, as 

 in the recent lavas. 



The common feature of both the Urano-mayé and the Byôbn- 

 hira lavas is the development of varietal modifications in different 

 parts of the lava streams. All the lavas are, however, dopatic or 

 sempatic, dotted with abundant phenocrysts of plagioclase (1-3 mm.), 

 while pyroxenes (hypersthene>augite) are only sparsely re- 

 presented. 



The land lavas (PI. XVII. Figs. G-7) are pitch-black and 

 vitreous, while those at the water's edge (PI. XVII. Fig. 8, 

 PL XVIII. Fig. 1) are dull with shades of gray. The first is caused 

 by the abundancy and chocolate -brown color of glass and also 

 dusted augite-needles, while skeletal microlites are few. The sJiore 

 lavas present the same feature as the land lavas in regard to 

 phenocrysts ; but the groundmass is rich in feldspar -microlites, 

 which lend to the rock its dullness and gray tinge. Moreover, the 

 shore rock is cloddy, owing to quencliing fractures, and is stained 

 with limonitic films. Under the microscope circular minute flecks 

 are also seen, which are decolorized in its glassy base with the 

 simultaneous separation of fibrous augite (enstatite-augite ?) and 

 globulitic substance. These features are characteristic to shore Icwas 

 irrespectiüc of age and chemical composition of the magma. 



C. The Öhira-yama Lava-flow of 1749 (Westeen Slope). 

 PI. XVIII. Figs. 4 and 5. 

 a) Mode of Occurrence.— As a precursor of the gi'eat eruption 

 of the An-ei era (1779-1799), ' Mt. Ôhira-yama (spoken Uhira-yama) 



