THE ERUPTION OF BAN DAT-SAX. 153 



characteristic twins. When taken out of the cavity and examined closely the 

 crystals were found in hexagonal plates, in combination with the faces (when re- 

 ferred to the hexagonal axes) oP, ocP, P, œP? , flattened along the basé. Under 

 crossed niçois, however, the plate was seen to consist of innumerable patches 

 crossing at an angle of nearly 120°, and showing oblique directions of extinction. 

 The specific gravity of the mineral determined by swimming it in the Thoulet's 

 solution was 2272. 



For the chemical analyses, given below, of the Bandai rocks and 

 ashes we are indebted to Prof. T. Wada, the Director of the (Geo- 

 logical Survey. They are the result of a very careful analysis by 

 Mr. T. Shimizu. 



I. II. Ill 



SiOo 59-66 % .... 



ALO, 15-51 



Fe 2 0, 3-76 



FeO 5-40 



Mn, 0, 1-40 



CaO 6*56 



MgO 3-67 



Xa 2 U 2-50 



K,(> 1-08 



S -59 



WA)-, -IS 



Loss bv ignition — -44 1'35 



L00-31 L00-67 99-77 



Insoluble portion in HCl. Insoluble portion in HCl. 



= 75-34 % = 85-34 % 



