Volcixno Üshima, Wzu. 93 



(labradorito-bytüwnite) which is simply or polysynthetically 

 twinned, light gi-eenish anhedral augite occasionally twinned on 

 (100), and small isometric magnetite. Colom-less glass enclosing 

 a fine dusty substance is found very sparingly as the interstitial 

 matrix. 



8 Olivine-bytownite-dolerite. (PI- IV. Fig. 1.) 



31ofle of Occurrence. — To the east of Kazahaya (la), igne- 

 ous bodies are exposed on the sea cliff in the form of lavas and 

 intrusives (p. 41 ; PL YI. GA 10-11). The rock specimen here 

 described was taken from the westernmost intrusive mass which 

 appears to bo a congealed vent (PL YI. G A 11). 



Jlcffascopic Characters. — The rock is megascopically fine- 

 grained non-vesicular, and is gray in colour. Porphyritic com- 

 ponents recognizable with the naked eye are plagioclase, 5 vim. in 

 maximum diameter with nearly equant development, and olivine, 

 less abundant and smaller than the former. 



Microscojnc Characters. — Under the microscopo, the pheno- 

 crysts of calcic hytoicnite, Ab.öAn.g with the refractive indices «< 1.571 

 1.572</5< 1.575 1.577<r, show the usual characters. They are 

 generally subhedral, twinned, very faintly exhibit zonal structure, 

 and commonly cairy inclusions. 



Subhedral to anhedral diopsldic aucjife, occasionally twinned 

 on (100), and anhedral olUlnc, (Fe,Si04)u_i9(MguSiO,)87-Ki. (^/^^ 1.678 

 >/3/.1.601<r). with brown iron oxide deposited along the cracks 

 that traverse the mineral, are seen as microphenocrysts, letss than 

 1 mm. in diameter. 



The nearly holocrystalline groviidnmss consists of sodic 

 bytownite, light coloured diopsidic augite, and magnetite, with 

 only a trifling amount of brown glass clouded with fine dust. 



