248 E. B. Baileij—The New Mountain o/'1910— 



lime also, derived from calcareous rocks, also powerfully attacked by 

 f^round-water, even under a triick covering of argillaceous and 

 arenaceous rocks. Given a tropical country, liowevei', in which the 

 ground-water acted on siliceous rocks only, a not impossible state of 

 affairs, then it might be that the sea-water would become so charged 

 with silica that siliceous organisms would flourish, while calcareous 

 organisms would diminish. 



The most favourable conditions for accumulations of such siliceous 

 organisms to form cherts would be found near or beyond the limit of 

 the finest detritus brought down by the rivers. Within the area of 

 sedimentation we could expect rocks with some Radiolaria to be 

 formed, such as the Sarawak indurated shales and the shales of the 

 Upper Gondwanas near Madras, described by Mr. Coomaraswamy.^ 



This suggestion of the necessary supply of silica having been 

 afforded by tropical weathering is, of course, no less speculative than 

 the other suggestions, but, as a third possible cause of the formation 

 of Radiolarian cherts in shallow seas, it may be of interest. In 

 conclusion I would put forward the two following propositions : — 



1. The presence of abundant carbon in Radiolarian cherts appears 

 to be an indication that such cherts are not of deep-sea origin. 



2. Large quantities of silica in solution, supplied by tropical 

 weathering of siliceous rocks, may have promoted, or helped to 

 promote, the abundant growth of Radiolaria in shallow seas. 



II. — The New Mountain of thk Yeak 1910, TIsct-sak, Japan. 



By E. B. Bailey, B.A., F.G.S. 



(PLATES XII AND XIII.) 



TMHE writer's attention was directed to Dr. Omori's^ description of 



J_ the 1910 eruption of Usu-san through a review which appeared 



in Nature (1911, p. 221) from the pen of Professor Milne, F.R.S. 



The following pages constitute a resume, rather than an additional 



review, and are justified on account of the interest of Omori's 



observations to many geologists who may not find it convenient to 



consult his original paper. All three figures here published have 



been redrawn for the purpose. Plate XII is based on a coloured map, 



and Plate XIII on photographs which have already been reproduced 



by Professor Milne in his review. 



Usu-san is one of a group of volcanoes situated in the south-western 

 peninsula of the island of Yezo, Japan. It is bounded on the south 

 by the sea, and on the north by the Lake of Toya — a circular lake 

 some 10 km. in diameter and 187 m. in depth. The distance of the 

 centre of the volcano from the nearest point of the sea is 4'7 km., and 

 from the lake 2*2 km. ; in fact, the situation could not be more con- 

 venient than it is for dealing with questions involving measurement 

 of changes of level. 



] Geol. Mag., 1902, pp. 305, 306. 



- F. Omori, " The Usu-san Eruption and Earthquake and Elevation 

 Phenomena" : Bulletin of the Imperial Earthquake Investigation Committee, 

 Tokyo, vol. V, No. 1, pp. 1-88, pis. i-xiii. 



