INTERESTING PHENOMENA ON THE ERUPTION OF USU 281 



Augite is usually small in size, mostly in the groundmass. 

 The rock may be formulated as follows: 



P 40= . Lab. 28 +Hyp.8+Aug. 4 



G60 Glass 36 +Lab. l8 +Hyp. 3 +Aug. 3 

 P 40 , 40 per cent of phenocryst. 

 G60, 60 per cent of groundmass. 

 Lab., labradorite. 

 Hyp., hypersthene. 

 Aug., augite. 



Chemical composition. — The rock is rather basic, low in Si0 2 , 

 high in A1 2 3 , CaO, and iron, so that some might call it basalt. The 

 writer found a great similarity in mineralogical and chemical 

 composition between the bomb and the lava which forms the old 

 crater ring of the main volcano, as shown by Table III, which gives 

 an analysis of the bombs, with other similar rocks for reference. 



TABLE III 



11 



III 



IV 



VI 



VII 



VIII 



M203 



Fe 2 3 

 FeO. 

 MgO 

 MnO 

 CaO. 

 K 2 0. 

 Na 2 



H 2 0. 



Ti0 2 . 

 P*O s . 



52.40 



17-59 



3-51 



7.07 



3-73 

 0.16 

 936 

 1.77 

 2-93 

 o.57 

 1 .06 

 0.14 



51.86 



21.69 



4.46 



5-39 

 2.87 

 o. 29 

 10.37 

 1.08 

 2.02 

 0.26 



51.88 

 21-53 

 2-45' 

 6.36 

 2.08 

 o. 20 

 II .09 



1.56 



3.12 



o. 17 



5132 

 17.84 



4-34 

 6.70 

 4.18 



9-51 



1-52 



3.01 



50.16 



17.97 

 2.23 

 6.25 

 4.70 

 0.30 



11.85 

 2.80 



3-5"° 



52.02 

 17.14 

 7.96 

 3-52 

 3-*3 

 tr. 



n-57 

 0.60 



2.38 

 0.28 



52.86 



18.25 



6.61 



3-39 

 4.27 

 o. 16 

 9-58 

 0.69 



3-24 

 0.69 



51.12 



19-59 

 2.86 



6-53 

 4-47 

 0.65 



9-54 

 o-57 

 3-ii 

 o. 11 

 0.86 

 0.14 



I. A bomb from Usu, analyzed by Bulletin of the Imperial Geological Survey of Japan, XXIII, No. i. 

 II. Mean value of three bombs, analyzed in the laboratory of geology in the Agricultural College, 

 Sapporo. 



III. Lava of old crater ring on Mount Usu, analyzed in the same laboratory. 



IV. Luciite, Luciberg, Odenwald Hesse. 

 V. Augite-andesite, Kilauea, Hawaii. 



VI. Basalt ? Yate Volcano, Patagonia. 

 VII. Pyroxene-andesite, Choa-shen, Kamchatka. 

 VIII. Basalt, Goentoer lava, Java. 



Ill to VIII taken from J. P. Iddings, Igneous Rocks. 



IV. DAMAGE 



By the fracturing of the earth and the explosions, the deep, 

 beautiful forest on the slopes of the mountain was destroyed. 

 The leaves were all stripped from the trees, the greater number of 



