10-2 



Vol. XLIil., Art. 6._S. Tsuboi : 



Names of rocks 



Phenocrysls 



Olivine 



Plagioclnse Pyroxenes 



Grouncl- 

 mass 



Kocks constitut- 

 ing the demol- 

 ished igneous 

 bodies along 

 the northwest- 

 ern coast 



Summa la\as 



Two-pyroxene-olivine- 

 anor thit e - basal t 



Olivine- by townite- 

 basalt (a and ß) 



(Fe,Si04)i3_i9 



(Mg;Si04)s7-81 



Comparntively 

 abundant 



Olivine-bytownite- 

 dolerite 



Basaltic bandaite 



(the commonest \ 

 somma lavas/ 



(Fe2Si04)25-TO 

 (Mg..SiO4)75-70 



Slight or absent 



Hyiersthene-basaltic 

 Ijandaite 



Absent 



Central cone 

 lavas 



Two-pyroxene- basaltic ' 

 bandaite 



Absent 



Hypersthene- bearing I „ . , 



augite-olivine- Comparatively 



bytownite-basa't 



abiiudant 



Sliharaite 



Absent 



Anorthite 

 AbjAnof) 



Hypersthene 

 and augite 



Comparatively 

 abundant 



Absent 



Augite 

 Slight 



Calcic 

 bytownite 



near 

 AbiôAnss 



Hypersthene 

 and angite 



Slight or 

 absent 



Hypersthene : 



moderate 



Augite : slight 



Hypersthene 

 and augite 



Moderate 



Hypersthene : 

 slight 



Augite: 

 moderate 



Hypersthene 

 and augite 



Slight 



Consisting 

 of plagio- 

 clase (from 

 sodic labra- 

 dorite to 

 sodic by- 

 townite), 

 augite, 

 magnetite, 

 and glass. 



The above table shows that the main difference between the 

 various rock-types exists in the amount and character of the pheno- 

 crysts of ohvine and pyroxenes, both of which are of comparative!}^ 

 high specific gravity. This fact suggests the importance of gravita- 

 tive effects on these heavy crystals. 



As to tlie effect of the separation and subsidence of crystals- 



