CONTRASTING REACTIONS OF DIFFERENT ZONES, 181 



even be reversed in the lower part of the zone of katamorphism. It is 

 therefore apparent that the two zones are not sharply delimited. In 

 general, however, it may be said that the outer zone to a depth in which 

 oxidation, carbonation, and hydration preponderate is that of katamor- 

 phism, and that the deeper-lying zone, in which the reverse of these 

 processes preponderate, is that of anamorphism. But carbonation and its 

 opposite, desilication, are the most fundamental reactions of the zone of 

 katamorphism. Silication and decarbonation are the most fundamental 

 reactions of the zone of anamorphism. By these reactions more than by 

 airy others, these zones are delimited. The three sets of reversing reac- 

 tions, oxidation and deoxidation, carbonation and silication. hydration and 

 dehydration, constitute three cycles in metamorphism. The second of 

 these cycles was recognized many years ago by Bischof (see pp. 176-177), 

 and was called the carbono-silicic cycle. 



From the foregoing statement it is clear that the work of the zones of 

 katamorphism and anamorphism are opposed to each other. What the one 

 is doing the other is undoing. At the present time it is therefore possible 

 that in the case of any one of the pairs of opposed reactions, consider- 

 ing both the zones, either one of them preponderates, or that they are 

 approximately balanced. For instance, the amount of water being fixed 

 in the zone of katamorphism may be greater or less than the amount of 

 water being freed by dehydration in the zone of anamorphism, or the 

 two may be nearly balanced. The same statement may be made in refer- 

 ence to the other reversing reactions. Upon the preponderance of these 

 opposing sets of reactions in the opposite zones depends the answer to 

 the question whether, on the whole, oxygen, carbon dioxide, and water 

 from the atmosphere and hydrosphere are being fixed or freed by meta- 

 morphism. This question is considered in Chapter XL 



While the zones of katamorphism and anamorphism are separated 

 from each other by contrasting reactions, all reactions do not reverse in the 

 two physical-chemical zones. The first part of van't Hoff's law of heat 

 and the law of pressure may work together — that is, in both zones reactions 

 may occur which, simultaneously with the liberation of heat by chemical 

 action, also result in liberation of heat by condensation. In so far as 

 there are cases of this kind it is to be presumed that such reactions are 

 common to both zones. As an instance in which heat is probably evolved 



