PETROLOGICAL ABSTRACTS AND REVIEWS 497 



subheads alone would require five or six pages of this Journal. After 

 a short discussion of homogeneous and heterogeneous equilibria, the 

 subject of magmatic rock-formation is taken up. Under this head the 

 author treats of the essential components of magmas and the melting- 

 points of minerals, and includes a discussion of various methods of 

 determining melting-points and of obtaining and measuring high tempera- 

 tures in the laboratory. He speaks of the alteration of melting-points 

 at different pressures, of uniform and non-uniform pressures, and of 

 overheating and undercooling. Under the properties of silicate melts 

 are included internal friction and diffusion, surface-tension, electrical 

 conductivity, influence of gravity and centrifugal force upon the com- 

 position of melts, measurements of density at high temperatures, etc. 

 Following a chapter on the inversion points of minerals, he discusses 

 the genetic significance of melting- and inversion-points in rock-forming 

 minerals. He describes two, three, four, etc., point systems, and then 

 devotes about seventy-five pages to the physico-chemical, especially 

 the thermal, properties of the more important rock-forming minerals. 



In the second division of the book the author takes up the gases 

 in magmas — their nature, their solubility in melts, and their equilibrium. 

 In the third division he treats of the pegmatitic, pyrohydatogenic, and 

 hydrothermal phases of the solidification of magmas. Here are included 

 the properties of water at high temperatures, and a general discussion 

 of the formation of minerals in systems with volatile components. 

 Then follows a chapter on the synthesis of pneumatolitic and hydato- 

 genic minerals; then hydrothermal synthesis, solubility of the common 

 products of hydrothermal mineral-formations, alteration with tempera- 

 ture and pressure of salts which are but slightly soluble, the relation- 

 ship of solubility and size of grain, succession and paragenesis of the 

 hydrothermal ores and vein-minerals, zeolites, etc. 



The fourth division is devoted to weathering or colloid mineralogy; 

 the fifth to sediments. Here is included a long discussion of salt deposits 

 (43 pp.) to which the author has devoted considerable study. The book 

 closes with a short chapter on metamorphism and a double column index 

 of 26 pages. 



