5 68 



S. KOZU 



Microscopical characters. — The microscopic phenocrysts in this 

 type of rock are of olivine in great part, with subordinate andesine. 

 The groundmass is hypocrystalline and is filled with small and 

 round vesicles (Fig. 4), looking like the outline of leucite. 



Feldspar. — This mineral shows distinctly two different habits. 

 The phenocrysts are stout prismoid, sometimes tabular, and some- 





Sahxyo 



View from the north west 

 Fig. 2 



what rounded. They are andesine (Ab 3 An 2 ), with a mean index 

 of refraction slightly higher than n y = 1 -554. They contain abun- 

 dant small particles forming an outer zone, and round it usually, 

 thin and clean layers with different composition, but the difference 

 between each layer is not pronounced. Twinning is scarce, and in 

 rare instances undulatory extinction can be observed. Feldspars 

 forming the groundmass are slightly more sodic than the pheno- 

 crysts, and occur in elongated or rather slender shapes. They are 



