Vanllise — Metamorphism of Rocks and Rock Flowage. 75 



Art. VIII. — Metamorphism of Rocks and Rock Flowage ; 

 by C. E. Van Hise. 



[Condensed by the author from the Bull. Geol. Soc. Am., vol. ix, 1898, pp. 269-328.] 



The paper of which this is condensed is adapted from a 

 partly written treatise on the subject of metamorphism and 

 the metamorphic rocks. 



In the article some of the more important physical and 

 chemical principles which concern the alterations of rocks are 

 summarized, and these principles are applied to the alterations 

 which occur in connection with dynamic action. 



Summary of Physico-Chemical Principles. 



The agents through which the alterations of rocks take place 

 are water solutions and mineralizers. In the present discussion 

 mineralizers will not be considered. 



Below the level of the free surface of underground water 

 the rocks are practically saturated ; above that level the rocks 

 are not ordinarily saturated, but upon the average contain a 

 considerable amount of water held by adhesion between the 

 liquid and the solid mineral particles. Both below and above 

 the free surface, water is the all-prevailing agent through which 

 the chief alterations of rocks are accomplished. 



The forces of metamorphism are (1) dynamic action, (2) 

 heat, and (3) chemical action. In all of the various kinds of 

 metamorphism ordinarily recognized in classification, such as 

 hydro-metamorphism, static metamorphism, pressure meta- 

 morphism, dynamic metamorphism, regional metamorphism, 

 contact metamorphism, and thermo-metamorphism, all of the 

 forces above mentioned are required, and also the agent, water. 

 There is no metamorphism of a rock without the presence of 

 water, and hence all metamorphism is partly hydro-meta- 

 morphism ; there is no metamorphism of a rock without 

 motion, either molecular or mass, and hence all metamorphism 

 in an exact sense is partly dynamic ; there is no metamorphism 

 of a rock without the presence of heat, and hence all meta- 

 morphism is partly thermo-metamorphism ; there is no meta- 

 morphism of a rock in which chemical action does not enter, 

 and hence all metamorphism is partly chemical metamorphism. 

 When it is realized that in all the varieties of metamorphism 

 mentioned, chemical action, heat, and dynamic action enter as 

 factors, only in different degrees, and when it is remembered 

 that water is the universal agent which is present and active 

 wherever metamorphism occurs, it is self-evident that the clas- 

 sifications of metamorphism ordinarily given are not satisfac- 

 tory- 



