748 A TREATISE ON METAMORPHISM. 



continued was but a minute- fraction of the time of the action of water 

 under natural conditions, the experiment seems to me to furnish the 

 strongest possible confirmation of the conclusion already expressed as to 

 the importance of the presence of water during the recrystallization of 

 rocks. 



ROCK FLOWAGE. 

 MEANING OF ROCK FLOWAGE. 



If the conclusions of the foregoing' pages be true, the real meaning of 

 rock flowage, at least as deep as observation extends within the earth, 

 follows as a corollary. It is apparent that the process of rock flowage is 

 very different from the flowage of a liquid or that of a malleable solid, 

 although it involves elements which occur in these processes. 



In discussing the subject of rock flowage it will be necessary to repeat 

 the substance of certain things which have already been said. This is nec- 

 essary in order to bring the different elements which enter into rock flowage 

 into juxtaposition in proper relations to one another. I have previously 

 maintained that deformation at considerable depth is accomplished by rock 

 flowage." However, I made no attempt to explain in detail the nature of 

 the interior movements. 



All of the different processes which have been described are involved 

 in rock flowage. That is to say, the mechanical processes of strain within 

 the elastic limit, gliding, granulation, and welding, and the chemical proc- 

 esses of cementation and metasomatism resulting' in recrystallization, all 

 enter into the result. In the foregoing pages each of these processes has 

 been separately discussed and their relations have been pointed out. Vari- 

 ous combinations of the foregoing mechanical and chemical processes 

 explain rock flowag-e. Commonly in rock flowage the chemical process of 

 recrystallization is dominant; but this, as has been explained (pp. 690-692), 

 is promoted by the simultaneous mechanical strains. But in many cases of 

 rock flowage the evidences of chemical and mechanical processes are about 

 equally marked, and in some instances of considerable importance mechan- 

 ical processes have been dominant. 



I shall first consider the slates, schists, and gneisses, which are typical 

 examples of rocks that have been deformed by rock flowage, and are also 



"Van Hise, 0. R., Principles of North American pre-Carnbrian geology: Sixteenth Ann. Rept. 

 U. S. Geol. Survey, pt. 1, 1896, pp. 593-595, 636-643. 



