THE GREAT ERUPTION OF SAKURA-JIMA IN 1914. 113 



No. 3. 1000°, 1 hour. The groundmass-augite is reduced to grains, 

 but minute magnetite ciystals are newly formed. 



No. 4. 1000°, 2 hours. Phenocrystic plagioclase is resorbed on 

 edges and secondare' black glass-inclosures become abundant. In the 

 groundmass are seen the new augite prismoids and larger magnetite 

 crystals in brown glass. 



No. 5. 1050°, 1 hour. Phenocrystic hypersthene is rounded a Kttle 

 on edges. Newly formed are roundish rectangular augite and larger 

 magnetite clumps, with colorless glass full of globulites. 



No. 6. 1050°, 2 hours. Phenocrystic plagioclase is full of negative 

 crystals filled with black glass. A few large grains of magnetite and 

 abundant glpbulitic glass. 



No. 7. 1100°, 1 hour. The groundmass becomes cr3'staUine, being 

 an admixture of subangular augite and magnetite crystals, with inter- 

 stitial brown globulitic glass. 



No. 8. 1100, 2 hours. Apparently like the original rock with 

 dentritic skeletal magnetite in glassy groundmass. 



The test chips are not sufficiently raised to 1130°, which is the 

 complete melting point of the rock. 



To summarize the feature of changes : the long-prismatic hypers- 

 thene (not amblystegite), which is the only phenocryst of the 

 pyroxene group, remains almost unchanged. The bytownite is 

 left nearly fresh, the only changes noticeable being the increase 

 in size and quantity of black glass inclosures, showing that they 

 are the products of temporary retrogressive resorption phenomena 

 in bytownite rather than the progressive crystal development, as 

 they are usually supposed to he. Feldspar microlites in the ground- 

 mass seem not to have suffered any changes. Feldspar phenocrysts 

 and microlites are usually assumed to crystallize in several genera- 

 tions. To the writer it seems probable that they belong to the 

 same generation, the difference in crystal development being simply 

 due to dissimilarity in their chemical composition. 



