Volcano Osliimn, I<lzu. 73 



2) Hypersthene -basaltic bandaite. (The second type of the 

 somma lava.) (PI. II. Fig. 1.) 



This type looks like the serapatic variety of the precediag 

 one in its megascopic appearance, but is characterized by the 

 presence of hypersthene phenocrysts in moderate quantity. 



Mode of Occurrence. — The rock of this type occurs only as 

 a small flow and is exposed on the sea cliff to the south of Moto- 

 mura'^ (V\. V. Ic 11; PI. VI. BC 2), As soen in PI. YL, it is 

 clear that lava of the present typo was poured out in the middle 

 of the outpouring of lavas of Ihe first type, and accordingly that 

 the pétrographie difference between this type and the preceding 

 one is not due to a difference in the time of its extrusion but 

 must be attributed to another cause. This point will be discussed 

 later (pp. 118-110). 



Megascopic Characters, — Megascopically, the rock is strongly 

 porphyritic, with numerous phenocrysts of plagioclase and moderate 

 ones of hypersthene. They are scattered with no trace of any 

 regular arrangement. The plagioclase is 2 mm. in average diameter 

 and the hypersthene is of about the same size being dark green 

 with resinous luster. The groundmass is grayish black and 

 aphanitic, and has many small pores of rather irregular shape, 

 averaging in diameter about 1.5 mm., uniformly distributed through 

 the whole parts of the rock, l^ut is not slaggy. 



Microscopic Characters. — Under the microscope, the rock is 

 porphyritic and sempatic. The conspicuous phenocrysts are short 

 prismatic, crystals of calcic bytownite (Abj5An,5). Its character is 

 quite the same as that of the mineral in the preceding type and 

 requires no spocial mention. 



1) TCft 



