Tilt: ERUPTIOX OF BASDAÏ-SAN. 



149 



the mountain, 2'33.* From this number and from the already es- 

 timated volume, the weight of the mountain destroyed was found to 

 be 2,826,290 million kilogrammes or 2J8'2 million tons. 



Volcanic products of Bandai-san. 



The volcanic rocks that compose the mass of Bandai-san, are Volcanic rocks, 

 comparatively of uniform character, and belong to that class of an- 

 désite which is of wide occurrence in Japan, viz., the Pyroxene- 

 andesite which is now to be briefly described. This rock under its 

 various modifications, may be seen piled up in layers in the side-wall 

 of the newly opened crater, alternating with accumulations of loose 

 products ejected from the volcanic vent in former times, such as 

 pumice, scoria\ fragments of obsidian, Occ. Prof. B. Kotô considers 

 tha£ there are six of these principal layers. The rock-layers which 

 doubtless consolidated from lava-flows, are divisible into two main 

 types; the one being lighter coloured, and the other darker coloured, 

 evidently more basic than the former. The first kind is well ob- 

 served as a great band on the eastern side- wall down Kushiini-mine, 

 more than 10 metres thick, overlaid by reddish coloured loose layers. 

 Lower in position and separated by layers of agglomerate, is found the 

 darker variety. The fragments that compose the agglomerate are 

 also usually of the latter kind. These rocks have, however, essentially 

 of identical mineral composition, and are probably to be considered 



* Prof. J. Milne in calculating the weight of Japanese volcanoes has assumed the average 

 density to be 2-5. (The Volcanoes of Japan — Trans: Seisin. Soc: Japan Vol. IX, part II 

 1886). Prof. T. C. Mendenhall, formerly of the University of Tokyo, in determining the 

 force of gravity at the summit of Fujiyama, took the density of that mountain as 2 - 12, which 

 was the mean of the densities of pulverized and porous rocks. (On pendulum experiments 

 mi i he summit of Fujiyama for the purpose of ascertaining the force of gravity at that point — 

 Trans: Seism. Soc. Vol. II, 1880). In the authors' Preliminary Report of the Bandai-san 

 Eruption published in the Official Gazette of September 27th, 18S8, the value of the density 

 was taken a little higher, but it was since altered to the present figure. 



