726 PETROLOGICAL ABSTRACTS AND REVIEWS 



chlorite, albite, sericite, quartz, and calcite. In most of the rocks the 

 amount of soda is greater than potash. Of these rocks, two, prasinite 

 and epidote glaucophane schist, are derived from igneous rocks. 



A.J. 



Wright, Fred. Eugene. " Mikroskopische Petrographie vom 

 quantitativen Gesichtspunkte aus," Neues Jahrb., XXV (1913), 



753-75- 

 A translation of an article by the same writer in the Journal of 

 Geology, XX (191 2), 481-501. 



Wright, Fred. Eugene. "A New Thermal Microscope for the 

 Measurement of the Optical Constants of Minerals at High 

 Temperatures," Jour. Wash. Acad. Sci., Ill (1913), 232-36. 



Describes and illustrates a new thermal microscope for the determi- 

 nation of the birefringences, extinction angles, and optic axial angles of 

 minerals at temperatures between 10° C. and 1200° C. 



A.J. 



Wright, Fred. E., and Van Orstrand, C. E. "The Determina- 

 tion of the Order of Agreement between Observation and 

 Theory in Mineral Analyses," Jour. Wash. Acad. Sci., Ill 

 (1913), 223-31. 

 The authors discuss the principles underlying the calculation of 

 mineral formulas. 



A. J. 



Wright, Fred. Eugene. The Methods of Petrographic-Microscopic 

 Research. Carnegie Institution, Publication No. 158. Wash- 

 ington, 191 1. Pp. 204, pis. II. 

 The author found, in his work on silicate preparations in the Geo- 

 physical Laboratory, that the ordinary methods of determining minerals 

 microscopically were not always sufficient in working with artificial fine- 

 grained products, and it was necessary to devise new methods or modify 

 old ones. While many of the results of the author's comparative studies 

 on the relative merits and accuracy of a number of these methods have 

 been published at different times in the American Journal of Science, 

 they are here brought together in proper relations to other available 

 methods. As stated by the author, the different methods best adapted 



