542 GEOLOGY 



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 controlling alterations is physical energy. Pressure diminishes 

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

 the upper zone are reversed. Deoxidation, silication with decarbon- 

 ation, 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 

 largely opposed. 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. 1 



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

 chemical problem. The handling 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 

 deformation made it possible to formulate the principles controlling 

 the interior transformations of rocks. In a similar manner these 

 problems interlock with the other problems of physical geology, and 

 physical geology interlocks with the other sides of the subject. The 

 whole science is one interlocking system, a part of which cannot be 

 satisfactorily developed independently of the other parts. For 

 instance, weathering can be placed in order only when considered in 

 connection with general metamorphism, erosion, and sedimentation. 

 Ore-deposits can be explained only by combining the principles of 

 volcanism, deformation, metamorphism, etc. 



In attempting to reduce a small part of the subject of geology 



1 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 United States Geological Survey, a treatise on metamorphism now 

 just appearing, the reader will better appreciate the illustration In this volume 

 the forces of metamorphism, the agents of metamorphism, and the zones of meta- 



jped. The point of view of the latter 



chapters is mainly geological, but the geology is interpreted in the terms of the 

 principles earlier formulated. 



