Februaey 5, 1909] 



SCIENCE 



203 



fusion, crystallization, and transformation 

 points of silicate compounds corresponding 

 to rock minerals, and of the behavior of 

 mixtures of pairs of such compounds in 

 producing mixed crystals, new compounds 

 or eutectic mixtures, are of the first impor- 

 tance. The accuracy of the methods em- 

 ployed and the thoroughness of the work 

 guarantee the value of the results and their 

 permanency. In addition to the establish- 

 ment of improved, or entirely new, methods 

 of operation of a purely physical character 

 tributary to the study of petrological prob- 

 lems, they have determined the isomorph- 

 ism and physical behavior of the lime-soda- 

 feldspar series ; the relations of the various 

 lime-silica compounds to one another ; those 

 of the lime-magnesia-metasilicate series; 

 the melting and transition points of quartz 

 and tridymite, and the character of still 

 other compounds, and they have materially 

 extended our knowledge of solid solutions. 



Doelter and his pupils have studied the 

 fusibility of the rock minerals and their 

 solubility in one another, but the methods 

 employed are less accurate than those just 

 mentioned and involve a large element of 

 subjectivity. They are approximations to 

 the facts desired, often of much value quali- 

 tatively, but sometimes misleading. Other 

 recent and valuable qualitative work in this 

 field has been done by Morozewicz, while 

 earlier work is represented by the classic 

 researches of Daubree, Fouque, Michel- 

 Levy and others. 



The most obvious result of the earlier 

 efforts was the demonstration of the ade- 

 quacy of fusion and gradual cooling, at 

 ordinary atmospheric pressures, to bring 

 about the crystallization of many minerals 

 found in igneous rocks; and the necessity 

 of some catalytic agency to promote the 

 crystallization of other minerals common to 

 these rocks. Such actions were ascribed to 

 "mineralizing agents," or " crystallizers, " 

 assumed to be in most instances dissolved 



gases, chiefly 11,0. One of the most sig- 

 nificant facts brought to light by the re- 

 searches of Day and his colleagues is the 

 new conception of high viscosity found in 

 alkali-feldspars and quartz. Viscosities so 

 great at temperatures near the transition 

 point of liquid to crystal phase as to be 

 indistinguishable within the two phases. 

 That is, the viscosities of the amorphous 

 glass and of the crystallized mineral are so 

 nearly identical that the two phases of the 

 substance react alike toward mechanical 

 stress. Molecular mobility is so slight that 

 readjustment'from crystalline arrangement 

 to the homogeneous chaos of liquid mole- 

 cules is accomplished with such extreme 

 slowness that the time of ordinary labora- 

 tory observation is not sufficient for its 

 detection. However, the time available for 

 ordinary "geological" processes, so called, 

 is sufficient, as shown by the devitrification 

 of volcanic glasses composed of these con- 

 stituents — ancient rhyolitic obsidians. The 

 function of a catalytic agent, as a gas dis- 

 solved in such a viscous liquid, is obvious — 

 the viscosity is reduced and molecular mo- 

 bility increased. If the transition is toward 

 the liquid phase, solubility of the crystal is 

 increased. If it is toward the crystal phase, 

 the rate at which crystallographic molec- 

 ular arrangement is accomplished is in- 

 creased. The dissolved gas becomes a 

 " erystallizer, " or "mineralizing agent." 

 Other substances, such as mineral com- 

 pounds, yielding less viscous liquids than 

 those of the alkali-feldspars and quartz, 

 when dissolved in the more viscous liquids, 

 reduce their viscosity in the same manner, 

 though not to the same extent, as dissolved 

 gases. They must behave catalytically 

 toward crystallization, as gases do. Their 

 behavior in this i,.^ it has not been gen- 

 erally recognized, though the function of 

 certain liquid compounds, as fluxes, or as 

 "mineralizing agents," is well known. 

 Thus the improvement in methods of 



