Reviews — The Colour of Amethyst, etc. 521 



February, 1914. Sakura-jima is an island, one of a series of five 

 volcanoes situated along a N.N.E.-S.S. W. line on or near the southern 

 end of the island of Kyushu, which is the most southerly of the main 

 islands of the Japanese Empire. The activity of the Japanese 

 volcanoes is restricted to certain periods, separated by more or less 

 long periods of quiescence; and in this present active period 194 

 eruptions occurred from eleven volcanoes between 1909 and 1914. 

 The eruption was preceded by the usual premonitory warnings, the 

 significance of which was so completely understood by, the authorities 

 that the whole population of the island, some 23,000 in number, 

 were removed with the loss of only three lives. The paroxysmal 

 phase was one of extraordinary violence ; it began with the ejection 

 of stones and ashes from one of the main craters, which was followed 

 somewhat later by the outpouring of lava from two groups of 

 craterlets on the west and south-east sides of the island ; it was also 

 accompanied by a severe earthquake, which was recorded by European 

 observatories, and by a small earthquake wave, which was probably 

 caused by the subsidence of the bottom of the neighbouring 

 Kagoshima Bay. 



Detailed surveys of the district, before and after the eruption, show 

 considerable elevation (between 30 and 40 feet) of the mass of the 

 island itself and subsidence of from 4 to 20 inches over the sur- 

 rounding country. These displacements require the sinking of 

 a mass of the crust of at least half the volume of the material 

 ejected during the eruption. The sound phenomena were found to 

 behave in a normal manner, that is to say that there were two zones, 

 one near and one far from the volcano, in which the sounds were 

 separated by a silent zone, the middle line of which lay about 

 75 miles from the mountain. The chief eruption of Sakura-jima was 

 associated with eruptions from the other vents in the line. Three 

 out of four of these were active between January 8 and March 21, 

 beginning with the most northerly and ending with the most 

 southerly. 



W. H. W. 



Y. — The Colour op Amethyst, Rose, and Blue Varieties of 

 Quartz. By T. L. Watson and R. E. Beard. Proceedings of 

 the United States National Museum, Washington, 1917, 

 pp. 553-63. 



UP to the present time but little information is available as to the 

 cause of the disperse colours of minerals, as distinguished from 

 the colours due to the actual chemical constituents of the mineral 

 itself. The authors of this paper have made a careful investigation 

 of the chemical composition and physical structure of variously 

 coloured varieties of quartz with a view to discovering the reason of 

 the wide variations that exist in different types. The principal con- 

 stituents found which might give rise to colour are manganese, 

 titanium and iron, with traces of cobalt. On the average of thirteen 

 analyses it was found that amethyst contains the highest percentage 

 of manganese, while rose quartz has the highest percentage of 



