132 CARNEGIE INSTITUTION OF WASHINGTON. 



(9) The significance of glass-making processes to the petrologist. N. L. Bowen. J. Wash. 



Acad. Sci., 8, 88-93 (1918). 



Contrary to certain claims that have been made, glass-making processes 

 offer no support to the belief in liquid immiscibility among silicates nor to 

 the belief in a significant density stratification in a mass wholly liquid. They 

 do, however, suggest the importance of gravity acting on a mass partly solid 

 and partly liquid and emphasize two stages: (1) that at which there is much 

 liquid and little solid, and (2) that at which there is little liquid and much 

 solid. In magmas these two stages are probably those during which the 

 most significant results in the way of differentiation are accomplished. 



(10) The ternary system MgO-Al!!03-Si02. G. A. Rankin and H. E. Merwin. Am. J. 



Sci., 45, 301-325 (1918). 



The temperature-concentration relations of the various crystalline phases 

 in equilibrium with liquid in the ternary system MgO-Al203-Si02 have been 

 investigated, and are represented by diagrams and a model. A ternary com- 

 pound, 2MgO'2Al203-5Si02, unstable at its melting-point and considerably 

 affected by solid solution, has been observed in two forms. The /i-form 

 (unstable) crystallizes from glass at temperatures below about 950°, and 

 transforms at somewhat higher temperatures into the a-form (stable). The 

 properties of both forms, but especially the a-form, are close to those of the 

 mineral cordierite. The effects of solid solution in flattening two of the 

 boundary curves of the field of this compound are discussed. The prepara- 

 tion and properties of crystalline aggregates of substances which dissociate 

 when melting are considered. 



Crystals of natural cordierite dissociate when melting. Brief considera- 

 tion is given to the effects of FeO in magnesian rocks and minerals. 



(11) Chemical analyses of igneous rocks, published from 1884 to 1913, inclusive, with a 



critical discussion of the character and use of analyses. Henry S. Washington. 

 Prof. Paper 99, U. S. Geol. Survey (1917). 



Reviewed under No. 29 of the annual report for 1916 (Year Book No. 15, 

 p. 156). 



(12) Crystals of barium disiUcate in optical glass. N. L. Bowen. J. Wash. Acad. Sci., 



8, 265-268 (1918). 



In some types of barium crown glass, crystals which ruin the glass for 

 optical purposes may be formed at certain stages of its manufacture. While 

 attempting to discover a means of eliminating the formation of these crystals 

 it was found desirable to determine their nature. They proved to be the 

 compound BaSi205, hitherto unknown. Crystals of BaSi205 have the follow- 

 ing properties: orthorhombic crystaUization in six-sided plates with negative 

 elongation. 2V = 70°, 7 = 1.617, and a = 1.598. 



(13) Augite from Stromboli. S. Kozu and H. S. Washington. Am. J. Sci., 45, 463-469 



(1918). 



This paper records the optical characters and chemical composition of the 

 augite crystals that were being thrown out of the volcano of StromboH during 

 the visit of A. L. Day and the authors in August 1914. Analyses of the lavas 

 are also given. The augite is shown to be of a commonly occurring type. 

 The paper is part of an investigation on the augites and other pyroxenes of 

 Italian and other localities. 



