148 S. SEKIYA AND Y. KIKUCHI 



or in other words, the fissure-line lay under the summit of Ko- 

 bandai. 



For ease of calculation the shape of the mountain was assumed 

 to be conical, a near enough approximation. Then, subtracting the 

 parts left undestroyed and making other allowances, we found the 

 total volume of the mountain blown away to be 1*213 cubic kilo- 

 metres or 1,587 millions cubic yards. This is equivalent to say that 

 if the devastated area extending over 70 square kilometres or 27 

 square miles had been evenly covered with a stratum of earth, rocks 

 and boulders, this stratum would have had an average thickness of 

 17 # 4 metres or 57 ft. The cubic content above given represents the 

 gross total of the volume of the mountain destroyed, including not 

 only the débris of earth and rock that descended the mountain -sides, 

 but also the dust, ashes and boulders which were hurled into 

 the air. 



To calculate the weight of the material corresponding to 

 this cubic content, we determined the specific gravity of different 

 kinds of rocks and earth obtained from Bandai-san. The specific 

 gravity of the pyroxene-andesite composing the mass of the 

 mountain differed more or less with the different varieties met 

 with, ranging from 2*58 to 2*71. On the average it may be 

 taken as 2*65. But as the mountain consisted of much looser 

 materials than these rocks such as pumice, scoriœ, &c, the density 

 of the mountain would be much lower than this value. The 

 mean specific gravity of the earthy materials thrown down 

 by the eruption, as determined by Prof. J. Sakurai, was 

 2*172. 



We may suppose without much error, that the mountain mass of 

 Bandai consisted of rock and earthy materials in the proportion 1 : 2, 

 and then we obtain from the foregoing numbers, as the density of 



