THE GREAT ERUPTION OF SAKURA-JTMA IN 1914. 



171 



above Nojiri erupted violently in the second year of Kwan-yen era 

 (1749) ' after remaining dormant for four centuries.'^ On the 

 southwestern slope just on the south of the mamelon-like knob 

 (553 m.) of Hikino-hira (Hiyoku-oka),'^ the writer found a doubtful 

 bocca at an elevation of 500 m., and another, but fresh and small 

 one, at a spot 100 m. lower than the preceding. See PL XI. Fig. 3. 

 This lower nameless shallow vent, which here may be con- 

 veniently called the Hikino-taki (cataract) bocca, lies at the head of a 

 lava stream which flowed down for a distance of 2.5 km. in a tongue- 

 shaped strip without reaching the shore, and is partially overflooded 

 in its northern skirt by the recent lava. See Geologic Map. 



b) Pétrographie Characters of Pyroxene-andesite (PL XVIII. Figs. 

 4-5). — The white-spotted (2-3 mm.) dopatic lava bears the stamp 

 of historic type in its dark color ; but it is I'ather compact, break- 

 ing in conchoidal masses 

 with cloddy texture. 

 Moreover, the groundmass 

 of this black rock has a 

 dull, lustreless gray shade, 

 due to the large amount 

 of rectangular and lath- 

 shaped feldspar swimming 

 in a light-brown glass. 

 Microscopic flecks in the 

 groundmass are caused by 

 local globulitization and 

 decoloration of brown 

 glass. Pyroxene pheno- 



Fig. 36. — Micronoritic segregation in the 

 (Jhira lava of 1749. 



1) See page 43. 



2) Hiyoku-oka ib ^ [ü^], an old name of Hikino-liira ^| y ^. 



