GEOLOGY 41 



known in history. The bulk of the material ejected in the form 

 of pumice, glass fragments, and other material, is estimated at 

 five cubic miles. C. N. Fenner has presented the preliminary- 

 results of a new study (Journ. GeoL, 1920, 28, 569-606). The 

 enormous number of fumaroles in the famous Valley of Ten 

 Thousand Smokes is believed to be due to the injection of a 

 sill in the underlying strata, and the continued evolution of 

 volatile matter through the shattered cover. The Katmai 

 eruption is believed to have been due to the development of an 

 explosive condition after some interval had elapsed subsequent 

 to the ascent of the magma from the depths. It is suggested 

 that current theories of volcanism may have to be revised from 

 this new standpoint. 



Mr. J. W. Shipley has made chemical observation on the 

 emanations and incrustations in the Valley of Ten Thousand 

 Smokes (Amer. Journ. Sci., 1920, 50, 141-53). The majority 

 of the incrustants are secondary products arising from the 

 decomposition of the ash by the volcanic gases, but the greater 

 part of the escaping vapours have a magmatic origin. Water 

 vapour is the major constituent of the emanations. 



S. Tsuboi presents the results of a geological study of the 

 insular volcano of Oshima, off the Idzu Peninsula of Japan 

 (Journ. Coll. Sci. Tokyo Univ., 1920, 43, Art. 6, 146 pp.). 

 Oshima is a basaltic volcano, consisting of a somma ring and 

 a central cone built up of alternating lava and fragmental beds. 

 Between a.d. 684 and 191 5 it has erupted sixteen times, and 

 shows no signs of diminution of activity. The lavas are all 

 basic, consisting of bandaite, miharaite (basaltic lava with 

 normative quartz and bytownite), and olivine basalt, the 

 differentiation being ascribed to the gravitative separation of 

 crystals. 



MINEBrALOGY. By Alexander Scott, M.A., D.Sc. 



The problem of the coloration of minerals is considered in a 

 paper by J. Jakob {Zeit. Kryst., 56, 194, 1921), who differen- 

 tiates two types of coloured minerals, one in which the so-called 

 " chromogene," or group of colouring atoms, is a prominent 

 constituent and another in which the colouring agent is present 

 in small quantity in the form of a finely divided foreign sub- 

 stance. The latter type is discussed with reference to the 

 author's constitutional formulae for the silicates [Helv. Chim. 

 Acta, 3, 669, 1920), and the colour of such minerals as the fels- 

 pathoids explained by the presence of unsaturated valencies 

 through which the chromogene can unite with the silicate 

 molecule. The coloration of substances by a and yS rays 

 is explained in a similar fashion, the finely divided chromogene 



