THE GKEAT ERUPTION OF SAKUßA-JIMA IN 1914. 



2U 



Fig. 46. — Trass, a magma-soaked lapiUi aggregate, partially coated 

 with obsidian rind. Loc. : Koike. 



of plagioclase mixed with a subordinate quantity of those of augite. 

 It may perhaps have consoHdated from partially resorbed magmjt 

 from trass mass, i.e., chemically speaking, syntectic. 



The trass core contains fragments of the underlying Mesozoic 

 slate. The second component is dark brown augite-andesite. The 

 third is gray, hornblende -bearing biotite-hypersthone andésite or 

 ash-stone (hai-ishi). The grass-green hornblende and weakly 

 pleochroic prismatic light-colored hypersthene are the mafic ele- 

 ments, besides accessory biotite and diopsidic augite and abundant 

 plagioclase (andesine) phenocrysts. The groundmass is higlily 

 feldspathic and full of feldspar microlites in colorless glass. The 

 component rock is an ancient piperno andésite that built, up the base 

 of the volcano. The fourth and the last component is the pumice 

 derived from the preceding, and the pumiceous hollows are entirely 

 filled with calcite. The third and fourth together make up a large 

 bulk of the trass. 



The piperno^-" andésite and pumice, as already stated, built 

 up the extensive plateau of southern Kyûshii,^^ and constitute the 



1) See page 13 and footnote on hai-ishi 2) See page 19. 



