CHINA, MONGOLIA, AND JAPAN. 



95 



remains of a stratified deposit seen here and there, about the base, and fragments 

 of scoriae were found in the neighborhood. 



There are several small crateriform depressions at different points near the 

 summit, fiUed to the level of the lip with sand and clay, and fornyng •small plains 

 surrounded by rocky sides. In one of the walls a compact black rock, either a 

 dyke or the remnant of a lava flow, was observed. 



The Iwaounobori is the central one of three volcanoes, which lie in a straight 

 line running about N. N. W., S. S. E., and this is also the trend of a broad belt, 

 within the limits of which the solfatara action is most developed, both across the 

 summit and on the outer waUs. 



Throughout this belt the rock, wherever not covered by the products of decom- 

 position, is found to be traversed by countless fissures, more or less filled with 

 sulphur. Wherever the fiUing is incomplete, small jets of steam and gases are still 

 seen to issue forth. Several trials, made by inserting a long chemist's thermometer 

 as far as possible into difi'erent fissures, gave a constant temperature of 98° C. 



The steam has a strong odor of both sulphurous acid and sulphuretted hydrogen. 

 It has an acid reaction on litmus paper, which is especially strong when the con- 

 densed drops, that hang on the sulphur crystals in the cavities, are tested. Beau- 

 tiful crystals of sulphur, a quarter of an inch long, were rapidly formed on the bulb 

 of the thermometer. 



Excepting at the steam vents, which are not more than from one to five inches 

 in diameter, the fissures are closed up with sulphur at the surface, but by breaking 

 away a few inches deep, cavities are exposed lined with a bristling mass of most 

 beautiful straw-colored crystals of this mineral, made up of brilliant steep pyramids 

 connected in the line of the longer axis. Unfortmiately, they were too delicate to 

 bear transportation. 



On a precipitous part of the outer Avail of the mountain, where a large mass of 

 rock seemed recently to have fallen ofi", I saw an interesting exhibition of the action 

 of the gases. The rock is seen to be 

 traversed by a perfect network of sulphur 

 veins (a) which seem to occupy the posi- 

 tions of the cracks common to all rock. 

 The trachytic rock (6) is tolerably well 

 preserved in the centre of the blocks, but 

 toward the circumference it is more and 

 more disintegrated, and has assumed the 

 form of concentric layers, the outer shell 

 being changed to a white earth. It seems 

 not improbable that this condition may 

 exist through a large part of the moun- 

 tain, thus forming a great stoclcwerh of 

 sulphur. 



The only way in which I can account for this structure is, by supposing that the 

 disintegration of the rock, which formerly occupied the spaces now fiUed with 

 sulphur, took place when the water, which now appears only as steam, stood at a 



Fig. 16 



a. Sulpliur. 6. Rook. 



