312 REVIEWS 



7. In a magma with the ratio of bases to alumina greater than 1, 

 melilite crystallizes after olivine and simultaneously with anorthite. 



8. Plagioclase begins to crystallize after olivine, and in many cases 

 after augite, according to the amount present. Nepheline is one of 

 the latest products of crystallization, forming usually a groundmass 

 product between plagioclase laths (mesostasis). 



10. The glassy groundmass represents an uncrystallized solid solu- 

 tion and frequently has the composition (Me0.2Si0 2 ) of Lagorio's 

 "normal glass." 



With respect to the question of magmatic differentiation, Moroze- 

 wicz favors rather the hypothesis of one primary magma, chemically 

 differentiated for a single region by means of processes determined in 

 the main by the laws which govern solutions. In many of the experi- 

 ments described a single crucible showed remarkable variations in 

 structure, coloring, and composition locally. This was especially true 

 of magmas rich in the alkaline earths. In a 100-pound mass, consist- 

 ing chiefly of alkaline augite, the lower portion showed throughout a 

 higher specific gravity than the upper, with much magnetite below and 

 none above. In common glass-melting, separation of layers of higher 

 specific gravity in the bottom of the crucible has been noticed, these 

 being especially rich in iron, lime, and magnesia. A mass of granite 

 weighing two pounds was melted in large pieces in the hottest part of 

 the furnace, and allowed to glow at the inner entrance of the chamber 

 for five days, producing a glassy mass below with quartz grains unmelted 

 and partially altered to tridymite above. These quartz grains had 

 apparently been floating in the glass ; the glassy portion appeared fully 

 homogeneous and was of uniform color ; in fact, however, careful sep- 

 arate analyses of the upper and lower portions of the glass showed not 

 only that the upper portion was richer in silica, but that the ratio .of 

 the bases was different. Thus Fe 2 3 showed in the lower layers an 

 increase of .8, MgO of .7, CaO of .4, and alumina of .2. The specific 

 gravity of the lower part was about .1 greater than the upper. The 

 silica percentage of the upper part was 73.65, of the lower part only 

 59.20. Thus the iron and alkaline earths settled to the bottom, and 

 the silica and alkalies remain in excess above. It is significant that 

 these substances (FeO, MgO and CaO) which form the lower stratum 

 of glass, are the ones which crystallize out earliest from silicate mag- 

 mas. 



In conclusion the reviewer would call the attention of geologists 



