270 VAN HISE—METAMORPHISM OF ROCKS AND ROCK FLOWAGE. 
Page 
Pemperabwve..< sts ch ee eee sea ask ees eo eee ee 2o5 owl 
Pressure and rapidity of deformation....................... 311 
Zone of combined fracture and flowage...................-..-----+- 312 
Comparative energy required for deformation in the three zones. .... 313 
Meaningof rock flowage, ace ua ce ne care ee ee eee 318 
Recrystallization and aqueo-igneous fusion....... Pe eee Re ares Ics S «5.6 326 
Suminairy, of conclusions: fees ead eae Oe eee een eee 328 
INTRODUCTION 
The following paper is adapted from a partly written treatise on the 
subject of metamorphism and the metamorphic rocks. In this article 
I shall summarize some of the more important physical and chemical 
principles which concern the alterations of rocks, and shall apply these 
principles 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 sat- 
urated, 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) dynamie action, (2) heat, and (3) 
chemical action. In all of the various kinds of metamorphism ordina- 
rily recognized in classifications, such as hydro-metamorphism, static 
metamorphism, pressure metamorphism, dynamic metamorphism, re- 
gional metamorphism, contact metamorphism, and thermo-metamor- 
phism, 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-metamorphism ; 
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 metamorphism is partly thermo-metamorphism ; there is no 
metamorphism of a rock in which chemical action does not enter, and 
