August 12, 1910] 



SCIENCE 



219 



lying between the Eagle and Fort Union forma- 

 tions, constitute on lithologic grounds a single 

 formation, but that on the north and east sides 

 of the Crazy Mountains these same tufaceous 

 beds are intercalated in the Colorado, Eagle, Clag- 

 gett, Judith River, Bearpaw, " Laramie " and 

 Fort Union formations. In other words, the 

 Livingston has no formational value and has no 

 deiinite age, for it represents volcanic activity 

 which recurred throughout late Cretaceous and 

 early Tertiary time. 



Geologic Thermometry: Fbed E. Weight, Wash- 

 ington, D. C. 



In ordinary thermometry, temperature is de- 

 fined by the expansion of a perfect gas, and is 

 expressed in terms of fixed units, determined by 

 the freezing and boiling points of water under 

 standard conditions. Temperatures are ascer- 

 tained practically by means of thermometers 

 which, altliougli they diflfer greatly in type, are 

 all based on some property which varies in a 

 definite way with the temperature. In geology 

 temperatures are of fundamental importance, par- 

 ticularly the temperature to which rocks were 

 heated in past geologic ages and under inacces- 

 sible conditions. Points on the geologic thermom- 

 eter scale must, therefore, be historical points, to 

 be determined primarily by the permanent effects 

 which such temperatures have produced on the 

 roclcs and rock components, and which are clearly 

 marked even at lower temperatures. The factors 

 which may serve to furnisli points of this nature 

 are, especially, melting temperatures of stable 

 minerals and of eutectics, inversion temperatures 

 of minerals, temperature limits beyond which 

 monotropic forms can not exist under different 

 conditions of pressure, also stability ranges of 

 enantiotropic forms and of minerals which disso- 

 ciate or decompose at higher temperatures, also 

 temperatures beyond which certaip optical or 

 physical properties are changed permanently. 

 These factors can be and are being determined by 

 modern laboratory methods, and are in turn 

 directly applicable to the study of rocks. The 

 data now available on the geologic thermometer 

 scale indicate that the establishment of such a 

 scale is feasible, and can be accomplished by a 

 sufficient number of proper laboratory determina- 

 tions. 



Di!;cussed by J. F. Kemp, E. A. Daly, A. C. 

 Lane and E. T. Wherry. 



Some Mineral Relations from the Laboratory 

 View-point : Arthur L. Day, Washington, D. C. 

 (Introduced by Fred E. Wright.) 



The remarkable contributions which have been 

 made to our knowledge of aqueous solutions since 

 the formulation of the science of physical chem- 

 istry leave little doubt but that its generalizations 

 can be applied with equal success to the study of 

 rock formation. But the efl'ort to make the appli- 

 cation has brought us face to face with the fact 

 that the problem of rock formation is of much 

 broader scope and its phenomena are far more 

 intricate than ever was imagined in the years 

 when the first plans for laboratory work in the 

 service of geology were made. This has had one 

 conspicuous consequence. Most of the work done 

 in the earlier years of laboratory experiment can 

 not now be used to aid in the application of the 

 new theories to mineral solutions. The first effect 

 of this conclusion is to emphasize the necessity 

 for widening our viewpoint to meet the increased 

 scope which physical chemistry has imposed upon 

 the study of mineral and rock formation from the 

 magma, and the second, to compel us to revise our 

 experimental methods so that the number of un- 

 known factors will not outweigh the known and 

 so prevent their intelligent interpretation and 

 eventual application to geology. It is also neces- 

 sary to recognize more explicitly the physical 

 conditions affecting the problem upon its quanti- 

 tative side. For example, we can not profitably 

 continue to determine melting and solidifying 

 points of natural minerals, and still less of com- 

 plicated rocks, knowing that the addition of a 

 small quantity of impurity almost always lowers 

 a mineral melting point considerably, and know- 

 ing also that no mineral type occurring in nature 

 is free from such impurities. We can not con- 

 tinue to observe melting temperatures by watch- 

 ing for the moment when the mineral begins to 

 sag and run, knowing that in many most impor- 

 tant minerals deformation does not occur until 

 long after melting is over. We can not continue 

 to ascribe individuality and characteristic proper- 

 ties to mineral glasses, knowing that they repre- 

 sent an unstable and undefined condition which 

 may persist for months or years, or even for geol- 

 ogic time, without reaching equilibrium. At best, 

 physical chemistry encounters this difficulty in 

 considering both the natural minerals and the 

 natural rocks — individual minerals do not occur 

 in nature in uniform types, but are somewhat 

 variable solid solutions with many minor ingredi- 

 ents; so too with the rocks we often find that 

 equilibrium is not reached during the entire 

 process of natural formation. It is difficult to 



