46 Vol. XLIEL, Art. 6. — s. Tsaboi: 



It is the writer's, belief that the steep slope near tlie east 

 coast is the remnant of a fault escarpment, as has already been 

 stated (p. 17). 



With regard to the cause of the abnormally gentle slope of 

 the eastern flank of the mountain, the present writer differs from 

 previous writers, considering it to be due mainly to an ununiform 

 distribution of the volcanic materials. That this is not improbable 

 may be illustrated thus : — 



(a) In the first place, it is a fact often recognized that in 

 some volcanoes^\ during their eruption, flue clasmatic éjecta fall 

 more abundantly on the east than on tlie west, being transported 

 by tlie ui)per atmospheric current (at least 4-5 km.) which is 

 always travelhng eastwards owing to the efiect of the rotation of 

 the earth ; accordingly it is to be expected that in such volcanoes 



A 



as Oshima, where fine clasmatic éjecta take an important part in 

 the building up of the volcano, the asymmetric form of the moun- 

 tain was originally developed, though the writer has not yet found 

 any direct evidence for this in Oshima. 



(b) As already stated (p. 27), the caldera is considered to 

 liave been formed with its centre somewhat to tlie west of the 

 very top of the somma. The more extensive development of the 

 slope on the east than on the west may be partly attributable to 

 this eccentric depression. 



(c) The ring-wall of the somma that surrounds the caldera 

 must liave checked the lavas of the central cone from flowing out 

 of the caldera, but there is a great gap in the wall on the east, 



1) B. Koto, " The Great Eruption of Sakura-jima in 1914," Jour. Sei Coll. Imp. Uniu, 

 Tokyo, Vol. XXXVIIT., Art. 3, p. 125, 1916. 



F. Omoki, "The 8iikur:i-jiina Ernpti)ns aocl Earthquakes IL," Ball. Imp. Earthq. InvesL 

 Com., Vul. VUL, No. 2, p. ll.'j, 191«. 



It is said tb.it dnring the erujition of Asama in May 1911, ashes fell maiuly on the east 

 ■although the surface winds at the time were east or south. 



