588 PETROLOGICAL ABSTRACTS AND REVIEWS 



solutions, corresponding to the monoclinic pyroxenes. The triangular 

 diagram, therefore, shows only three boundary curves and one ternary 

 invariant point. The writer shows that crystallization may proceed 

 according to two different methods, and the importance of distinguishing 

 between them is discussed. The optical properties of the pyroxenes 

 are discussed at some length; extinction angles, refractive indices, and 

 optic axial angles are measured and the orientation is determined. 



Bowen,N.L. "Crystallization-Differentiation in Silicate Liquids," 

 Amer. Jour. Sci., XXXIX (1915), 175-91. 

 Laboratory experiments showed that olivine and pyroxene crystals 

 sink and tridymite floats in artificial melts of diopside, forsterite, and 

 silica. From the rate of sinking, the viscosities of the melts were found 

 to increase with increase in silica. 



Collingbridge, Harvey. "The Determination of the Maximum 

 Extinction Angle, Optic Axial Angle, and Birefringence in 

 Twinned Crystals of Monoclinic Pyroxenes in Thin Section 

 by the Becke Method," Mineralog. Mag., XVII (1914), 

 147-49. 

 Gives a method for determining various optic properties by observa- 

 tions on twinned crystals which show the emergence of an optic axis 

 in one portion. 



Collins, W. H. The Huronian Formations of Timiskaming 

 Region, Canada. Museum Bull. No. VIII, Geol. Surv., 

 Dept. Mines, Canada. Ottawa, 1914. Pp. 27, figs. 3, pis. 1. 



Cross, Whitman. Lavas of Hawaii and Their Relations. U.S. 

 Geol. Surv., Prof. Paper 88, Washington, 1915. Pp. 97, 

 map 1, pis. 2, fig. 1, bibliography. 



The writer describes, with considerable space devoted to the norms, 

 various olivine-bearing and olivine-free-, bronzite-, picrolitic-, nephelite-, 

 and melilite-nephelite-basalts, limburgites, soda-trachytes, trachyande- 

 sites, a kauaiite or oligoclase-augite-diorite, some basalt tuffs, and a 



