THE GREAT ERUPTION OF SAKURA-JIMA IN 1914. 209 



up undoubtedly a largo portion of éjecta, besides gray lapilli, and 

 the size differs within wide limits from 2 m. to 2 cm., depending on 

 the distance from vents and the fury of eruptions, those of later 

 phases being smaller in size and compact. They are all black 

 and porphyritic with plagioclase phenocrysts. Textures vary from 

 compact to vesicular and even slaggy, lustres also from pitch-black 

 to dull. Pétrographie characters are the same as the main flows, 

 of which qualitative microscopic analyses and descriptions were 

 already given (pp. 176-181, 184-187). 



As has been pointed out already, the lavas of the acidic, 

 western, and the basic, eastern flow differ only in slight degrees. 

 The éjecta of the east side are, however, rich in basic plagioclase 

 (labradorite, symmetric extinction 30^-33°), and in hypersthene, 

 augite being present only in subordinate quantity, and the glass of 

 the groundmass white. 



Those of the ice stern side contain a large quantity of higlily 

 biréfringent non-pleochroic augite. The nature of plagioclase is 

 apparently the same. The prevailing type of the groundmass con- 

 tains brown glass and augite microlites in large quantities, in 

 contrast to the eastern flows. 



5) Bread-crust Bombs.^^— The bread-crust bombs or turtle-back 

 bombs are the characteristic projectiles of the west, varying in size 

 fi'om 10 cm. to 1 m., and always angular in form. They are a 

 common type all over the globe, frequently depicted and described 

 among the projectiles of recent volcanoes. Larger ones make 

 hollows in dashing against the ground, whereby the projectiles 

 themselves break open, exposing the gray spongy interior, the 

 color being solely caused by fine inclusions of gas. The exterior 

 is black and compact, passing by degrees to the brown and gray 



1) On the formation of bread-crt;st bombs see p. 114. 



