INTERESTING PHENOMENA ON THE ERUPTION OF USU 279 



From craters Nos. XXV and XLII great quantities of bombs and 

 sand were intermittently ejected to a height of 700 m. (Figs. 19, 20). 

 The ejected bombs and ashes frequently took the shape of serrate 

 peaks and pinnacles which rose alternately to great heights and 

 then sank back as another one shot up. It was noticed that 

 descending bombs, when struck by rising ones, produced loud 

 reports like the explosion of firecrackers. White, comet-like 

 tails followed the bombs into the air. The largest bomb measured 



WtT 6 "' *s„ * , ♦ ? 



Fig. 22. — Houses inclined 1 2° owing to the elevation of the left-hand side. Notice 

 a man standing straight. Taken September 4, 1910. 



was 25 cm. in diameter and was of the characteristic irregular 

 and rounded shape. The largest hole noted, formed by a falling 

 bomb, was 3 m. in diameter by 2 m. in depth. 



Petrography of the bombs {augite-hypersthene-andesite). — The 

 bombs ejected from the several craterlets are quite similar, though 

 the percentages of the constituent minerals are slightly different. 

 A brief description follows: 



Megascopically, the bombs are dark gray, porous, roundish in 

 shape, and less than 25 cm. across. The pores are very abundant 

 at the surface, slightly less numerous within, and range in diameter 



