THE GREAT ERUPTION OF SAKURA-JIMA IN 1914. 159 



downward course. Tlio northwestern rim of the Kita-daké is 

 built up of this black glassy lava. Geologic Map, and Text-figs. 

 33 (1) and 37 (1). 



The relative age of this rather weak lava cannot be stated 

 with certainty. It solely rests upon the Kita-daké lava, and is 

 not in anyway related to other flows, so that it is still an open 

 question whether its eruption happened soon after the building-up 

 of Kita-daké, or later in historic periods. The writer puts it on 

 record here merely fi'om a geographic point. 



As stated elsewhere (p. 153), the eruption began with the 

 ejection of ash and pumice, followed by and covered with the 

 later flow. Exposures are seen in the gulches of Matsura-gawara. 

 Text-fig. 33 (2). From a pétrographie point the lava belongs rather 

 to historic types. In contrast to the light- colored rock of the north 

 cone, it is black and vitreous, dotted white with crystals of feldspar 

 (from 1 J mm. downwards). The rock is hyalopilitic pyroxene 

 (hyp>aug) andésite. 



h) Pétrographie Characters.— Under the microscope, this dohyal- 

 ine and dopatic rock is seen to be largely made up of colored 

 glass (often colorless), with shades of purplish-brown, dark- 

 brown and red -brown, variously kneaded and streaked after a 

 pattern of damask (Fig. 1). Abundant augite in the form of fibrous 

 and also minute stiff needles in tufts and axiolites (Fig. 8), and 

 relatively few skeletal plagioclase are present in the brown glassy 

 base. Phenocrysts of zonal- structured plagioclase are abundant ; 

 but pyroxenes are few, of which the prismatic hypersthene 

 {h in Fig. 8) predominates over anhedral augite {h in Fig. 1). 

 IMagnetite is present in small quantity. The lava is a black 

 vitrohypevsthene- andésite with augite -microlite or brown glass in the 

 groundmass. 



