THE GKEAT ERUPTION OF SAKURA-JIMA IN 1916. 31 



the Plateau Formation (Fig. 3), which are supposed to make the 

 foundation are not actually observed. The calcareous trass bombs 

 among the éjecta, coated with black rind, may represent sandy 

 tuffite B?^ 



From the cores of many stumped mountains it is ascertained 

 that the depth of the local reservoir or lava-macula may be estimat- 

 ed at 1,000 )iiP below the vents, and consequently, the thickness 

 of the direct volcanic foundation may be assumed to be 1,000 ??i. 

 Both the YuNO-HiEA and Xabe-yama vents of the recent eruption 

 are located at 300 m. above sea-level, and the bottom of Kago- 

 shima Bay is 100 fathoms or approximately 200 m. deep. fSetting 

 apart 250-400 m. for the thickness of the Plateau Formation 

 (Fig. 3), there still remains about 100 ??2. to make 1,000 vy^. for the 

 subterranean location of the Mesozoic slatc'^'' formation, which is, as 

 already stated, often intruded by granite (Fig. 2). 



It follows from the above that the lava reservoir of Sakura- 

 jima probably lies within the terrane of the Mesozoic formation, 

 for which the above-mentioned granitic projectile may be taken 

 as a proof, and 500 m. below the bottom of the bay. 



Part II. The Volcano of Sakura-jima.'^ 



§ I. Morphogeography. 

 A) General.— The volcanic island of Sakura-jima is situated 



1) See 'Ejecta of Trass' in retrographical Fart. 



2) F. V. Wolff, ' Der Vulkanismus.' IM I., S. 331. 



3) After a comparison of average compositions of igneous rocks and slate or shale, 

 W.H. Hobbs arrived at the conclusion that lava, especially the Pacific type, originates through 

 fusion of slate, the most easily-fusilde of sedimentaries. It is to be remarked that the lava- 

 macula of Sakura-jima is probably located in the slate formation. ' Some Considerations con- 

 cerning the Place and Origin of ^Macul;«.' Beiträge zur Geophysik, XU. Bd., l.)13, S. 330. 



4) a. K. Nakashima, 'Explanatory Text to Sheet Kagoshima.' Geol. Surv. Japan, 1897. 



