28o 



Y. OINOUYE 



from i mm. to 2 cm. The majority of the pores are filled with 

 ashes and sand. Phenocrysts of white plagioclase, which do not 

 exceed 3 mm. in size, produce a porphyritic texture. There are also 

 crystals of dark-colored pyroxene, but they are small and not 

 abundant. 



Microscopically, the rock has a hyalopilitic-porphyritic texture. 

 The groundmass consists of dark-brown glass with minute crystals 



Fig. 23. — New elevated mountain seen from the east. Taken December 23, 1910 



of plagioclase, augite, and hypersthene, and the phenocrysts of 

 colorless plagioclase and green pyroxenes. 



Plagioclase is the chief constituent. It is either tabular or 

 equidimensional, and polysynthetic twins and zonal structures are 

 remarkably well developed. Zonally or irregularly included in some 

 of the crystals are patches of brown glass and minute grains of 

 pyroxene. 



The extinction angle on the M face of the plagioclase is between 

 — 28 and — 30 , and the maximum extinction angle in the sym- 

 metrical zone is +32 , showing it to be labradorite. 



The hypersthene has a slender prismatic habit and strong 

 pleochroism, green to reddish brown. 



