THE PROBLEMS OF GEOLOGY 609 



After it was appreciated that the gross deformation of rocks is 

 very different in an upper and a deeper zone, the question naturally 

 arose as to whether there are not differences in the rock alterations 

 in these zones. This idea, when followed up, resulted in astonish- 

 ingly fruitful results. It was found that in the upper zone, that of 

 fracture, the chief alterations which take place are those of oxidation, 

 carbonation, and hydration. These reactions occur with liberation 

 of heat and expansion of volume. In other words, the reactions are 

 controlled by chemical energy. In the lower zone the dominant 

 factor controlHng alterations is physical energy. Pressure diminishes 

 the volume. In order to accomphsh this, the chemical reactions of 

 the upper zone are reversed. Deoxidation, sihcation with decarbo- 

 nation, and dehydration occur with absorption of heat. The reac- 

 tions controlled by the force of gravitation are under the principles 

 of physics. It thus appears that the reactions of the two zones are 

 opposed throughout. It is plain that if the subject of metamorphism 

 is to be reduced to order, the alteration of the upper zone, that of 

 fracture, must be discriminated from that of the deep-seated zone, 

 that of rock-flowage. "■ 



The working out of the principles of metamorphism was a physical- 

 chemical problem. The handhng of the problems of rock alteration 

 with fairly satisfactory results was possible because of the rise of 

 physical-chemistry. Had this science not been developed within the 

 past score of years, it would not have been possible to have gone far 

 upon the problem of metamorphism. 



It is to be emphasized that gross deformation is not independent 

 of metamorphism, or metamorphism independent of gross deforma- 

 tion ; the two interlock. The general solution of the problem of gross 



I The necessarily narrow limits of this paper render it extremely difficult to show 

 the manner in which the subject of metamorphism has been treated under the system 

 advocated as a general method for geology. By referring to Monograph XLVII of 

 the Unifed States Geological Survey, a treatise on metamorphism now just appearing, 

 the reader will better appreciate the illustration. In this volume the forces of meta- 

 morphism, the agents of metamorphism, and the zones of metamorphism, are first 

 fully treated, the point of view being mainly physical-chemical. After the general 

 principles contained in these chapters are given, the alterations in each of the different 

 belts and zones are developed. The point of view of the latter chapters is mainly 

 geological, but the geology is interpreted in the terms of the principles earlier formu- 

 lated. 



