NOTES ON SOME IGNEOUS ROCKS OF JAPAN 



567 



tional forms in both texture and mineralogical characters, owing 

 to their crystallinity, but are closely alike in chemical properties. 

 They are represented by three types as described below. 



As the first type, a bomb ejected from the volcano Ondake-was 

 selected for the following description and chemical analysis: 



Eukae 



View from the northwest 

 Fig. 1 



Megascopic characters. — This rock type is aphanitic and black 

 in color. Scattered magnophyric feldspars are the only con- 

 stituents visible to the naked eye. The groundmass is vesicular, 

 and the vesicles are small and round. The phenocrysts are of 

 fresh aspect and show rather euhedral forms, short prismatic or 

 tabular, and in some instances are of considerable size, reaching 

 20 mm. in length (Fig. 3). Olivine, which is present as abun- 

 dant microscopical phenocrysts, is scarcely recognizable even by 

 the aid of a lens. 



