118 AET. 3.— B. KOTO : 



silt mixed with a little fine sand in the grade of the above cate- 

 gory. The particles above 2 mm. are scanty. 



A wash skeleton (PL XXIII. Figs. 6-7.) of the ash that fell on 

 January 12th on the roof of a house (p. 122) at Kokubu Station, 

 19 hn. away from the vent, was examined by the writer and seen to 

 be composed of rougMy-rectangular plagioclase, slender hyper sthene 

 and magnetite crystals, the first two being OA^ mm. in longest 

 extension, the last 0.2 mm. The skeletal portion may be taken 

 for fine crystal lapilli or crystal sand in contrast to slag lapilli, as 

 the components remarkably retain their idioraorphic shape. The 

 light major portion consists of finely pulverized colorless splinters 

 of strained pumiceous glass, mixed with small quantities of plagio- 

 clase powder, of a minimum size of 0.002 mm. As the locality is 

 not far away from the orifices, the heavy crystal components are 

 still found in large quantities among the ingredients of the ash. 



The ash dust, carried away by storm for a distance of 

 1,000 km., rained in Tokyo on January 14th, two days after the 

 eruption. It is light-gray and is uniform in size, being 0.007 to 

 0.008 mm. in diameter. It is composed of about ^% of plagioclase 

 fragments, w^hile the rest is glass splinters and textile fibers, with 

 a single piece of hypersthene (PI. XXIII. Fig. 8). The heavy com- 

 ponents — magnetite with sp. gr. 5, hypersthene, 3.3-3.5, and a 

 large portion of plagioclase, 2.5-2.75 — were precipitated during the 

 aerial voyage, and only particles of light friable colorless glass 

 remained in suspension in the air. The glass contains drawn-out 

 air pores, and is marked with striations produced by the stretching 

 of the magma ; thereby the substance became greatly strained and 

 easily pulverulent. 



It is no easy matter to decide whether the original rock is 

 resurgent or juvenile. From the idiomorphism of the crystal com- 



