REVIEWS 745 



from textbooks of physical chemistry, but discusses the applications of the 

 principles to the phenomena of metamorphism. 



Chap. 4, upon the zones and belts of metamorphism, discusses these 

 zones and belts from the physical-chemical point of view. It is shown 

 that the alterations of the zone of katamorphism occur with liberation of 

 heat and expansion of volume, the chief reactions being oxidation, carbon- 

 ation, and hydration. The alterations of the zone of anamorphism occur 

 with absorption of heat and diminution of volume, the chief reactions being 

 deoxidation, silication with decarbonation, and dehydration. Thus the 

 alterations in the two oppose each other. The zone of katamorphism is 

 divided into two belts — that above the level of ground water, the belt of 

 weathering, and that below the level of ground water, called the belt of 

 cementation. While the physical-chemical principles of alteration are the 

 same in each of these belts, the geological processes are very different. The 

 belt of weathering is characterized by solution, decrease of volume, and 

 softening, resulting in physical degeneration. The belt of cementation is 

 characterized by deposition, increase of volume, and induration, resulting 

 in physical coherence. 



Chap. 5 treats of minerals. Each of the rock-making minerals is dis- 

 cussed with reference to its occurrence and alterations. The alterations 

 are considered from the physical-chemical point of view. An attempt is 

 made to write chemical equations which represent the transformations, 

 and to calculate the volume relations resulting. It is found that a great 

 number of rock-making minerals undergo two classes of changes, one of 

 which is characteristic of the zone of katamorphism, and the other of which 

 is characteristic of the zone of anamorphism. Perhaps the most important 

 generalization of this chapter is as to the reversibility of reactions in the two 

 opposing zones. This generalization is as follows: The equations which 

 represent the reactions in the zone of katamorphism are reversible in the 

 zone of anamorphism; and, so far as there is expansion of volume and 

 liberation of heat in the upper zone, just so far is there condensation of 

 volume and absorption of heat in the lower zone. 



Chap. 6 considers the belt of weathering. The belt of weathering, 

 being the one which is most readily observed, has been treated by many 

 authors. The chapter in this volume on weathering differs from previous 

 discussions in that the phenomena are not considered mainly from the 

 descriptive point of view, the emphasis being given to the classification of 

 the phenomena and their explanation under physical and chemical princi- 

 ples. Also an important feature of this chapter is the consideration of the 

 phenomena of the belt of weathering in relation to the alterations of the 

 other belts of metamorphism. 



