218 AET. 3. B. KOTO : 



remarkably changed into an aggregate of confused straiglitly 

 extinguisliing fibres, which may be an allotropie quartz, and the 

 normal portion is swarmed with liquid inclosures, which are ar- 

 ranged without relation to cracks. The orthoclase is entirely altered 

 into an aggregate of doubly refracting pseudophitic substance 

 presenting a blurred aspect in the figure. In short, the changes 

 which the granite suffered, are of a caustic nature and the result 

 of intense baking. 



Continuous regular long ci'acks in quartz intersecting at obtuse 

 angles may be traceable to the rhombohedral cleavage. The 

 sericitization of orthoclase started from twinning sutures and also 

 fi'om externally-bounding faces, and this alteration seems to have 

 taken place not in a low temperature, as it is usually assumed. 

 We find no tridymite which may be thought to have originated 

 from /3-quartz. It is stated^^ that above 870^C /^-quartz inverts to 

 tridymite ; but unless a flux is present this change does not occur until 

 a temperature of 1,400^C is attained. Our granite-block must have 

 been dropped into a bath of andésite- magma having a temperature 

 of above l,loO°C (p. 112), and yet tridymite was not formed. 



The friability of the granite éjecta may be attributable to the 

 molecular (cleavage and twinning) and physical (expansion) changes 

 which promote disintegration through great heat.'^ 



1) W. A. Tarr, ' Study of Heating-ïest.' Eco. Geol, 1915, p. 348. 



2) During the field work in the volcanic district of Kaimon at the entrance of Kagoshima 

 Bay in 1915, M. Nagabiichi made an interesting find of dull white subangtilar blocks of granite' 

 about 10 cm. in diameter. The granite is trirtle-backed, much cleft and friable, and easily 

 crumbles by hauimering. It is found scattered about between the northern slope of the konide 

 of Kaimon and the northerly lying Lake of Ikeda. a caldron-shaped crateral depression of 

 volcanic origin, nearly equal in dimensions and mass to the volcano of Kaimon. îno granitic 

 rocks are exposed on the surface within a distance of 19 km. (in Prov. Osumi). Therefore, it is 

 not unreasonable to conjecture that our fritted granite blocks were torn away and thrown out 

 from the subcrust by an intense volcanic explosion, as in the case of éjecta of Sakura-jima. 

 Here we have again the proof, that explosions of pent-up gases play a more important rôle in 

 volcanic eruptions than we have hitherto imagined. 



