84 PETROLOGICAL ABSTRACTS AND REVIEWS 



and half orthoclase and plagioclase. The components are held together by 

 their fine grain, by quartz, and by small amounts of ferritic and claylike 

 substances which originated from alteration of the constituents. An important 

 part of this study is the use made of pairs of alternating coarse and fine layers 

 for the determination of the conditions of sedimentation. 



Wright, Fred E. "The Petrographic Microscope," /owr. 0/?/zca/ 

 Soc. Amer., I (1917), 15-21, fig. i. 

 Gives a brief description of the petrographic microscope and describes its 

 use in the determination of various optical properties. 



Wright, Fred E. "The Petrographic Microscope in Analysis," 

 Jour. Amer. Chem. Soc, XXXVIII (1916), 1647-58. 



Discusses the applicability of the petrographic microscope to certain classes 

 of problems of a chemical nature. The differences between an ordinary and a 

 petrographic microscope are described, and the various optical properties used 

 for diagnosis are briefly stated. 



Wright, Fred E. "Recent Improvements in the Petrographic 

 Microscope," Jour. Washington Acad. Sci., VI (1916), 465-71, 

 fig. I. 

 Describes a sliding objective changer, the removal of astigmatism in the 



analyzer, the prism method for observing interference figures, and a device 



for use in the accurate measurement of extinction angles. 



Wright, Fred E, "Note on the Lithophysae in a Specimen of 



Obsidian from CaKfornia," Jour. Washington Acad. Sci., VI 



(1916), 367-69. 



The lithophysae in a specimen of obsidian from Little Lake, about 40 miles 



south of Owen's Lake, Inyo County, California, are thought to be due to 



hydrostatic tension resulting from the contraction of the magma during cooling 



and outward pressure of the gases set free during the crystallization of the 



spherulites. The minerals of the spherulites are potash-soda feldspar, tridy- 



mite, and magnetite, with some fayalite, and occasional jet black mica. 



Wright, Fred E. " A 'Precision 'Projection Vlot," Jour. Washing- 

 ton Acad. Sci., VI (1916), 521-24, fig. i. 



Describes a stand with a frosted glass top, illuminated beneath by an 

 electric lamp, upon which is placed a stereographic projection net 40 cm. in 



