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small amount of hematite, together with glass in an amount com- 

 parable with that of the feldspar. Cone No. XVIII ejected the mud 

 periodically in a geyser-like fashion. The mud contained a large 

 amount of gas which came to the surface of the mud-flow after it had 

 almost solidified, making "puff cones" 1 in great numbers (Fig. 18). 

 The materials of the mud-flows, the sand of the seashore, and 

 the substance in the mud cones mentioned above, when compared 



Fig. 21.— Heavily burdened trees near the craters. Taken October 16, 1910 



under the microscope, were found to be identical in composition. 

 The fineness, however, is variable; the size of grains in the beach 

 sand being the largest, that in the mud cones intermediate, and 

 that in the mud-flow the finest. The base of the volcano Usu is 

 composed of brown pumice, uniform in constitution throughout 

 the whole region, and the fact that the mud-flows, the cones, and 

 the sand of the beach are alike in composition suggests that they all 

 came from some common source, which in all probability lies 

 horizontally and extends not much below the level of the sea. 

 'Jour. Geo/., XXIV, No. 6. 



