90 Van Ilise — MetcmorpA ism of Rocks and Rock Flowage. 



apparent perfect granulation, some degree of solution and re- 

 crystallization from solution has occurred. In the case of the 

 imperfect crystalline schists, which are very widespread rocks, 

 the adjustment to the new form is accomplished in part by the 

 process of differential movement of rigid granules and in part 

 by solution and redeposition. It is only in the case of the 

 typical granulated rocks that we can suppose that the process 

 of deformation is mainly accomplished by the movement of 

 the solid particles over one another, and it is only in the per- 

 fect crystalline schists that we can suppose that the deforma- 

 tion is accomplished almost wholly by recrystallization. 



Nothing is said by the foregoing conclusions as to the 

 condition of the material below the zone of the crystalline 

 schists or the meaning of the flowage of such material. 



The conclusions of the foregoing pages show clearly the 

 meaning of rock cleavage. I have already held that this 

 structure is largely due to the similar crystallographic orienta- 

 tion of numerous mineral particles, and especially those which 

 are authigenic, and therefore that rock cleavage is a capacity 

 to part largely due to the actual cleavage of the similarly 

 oriented mineral particles. As the cleavage of mineral parti- 

 cles has long been known to be a molecular structure, it fol- 

 lows that the cleavage of rocks is also largely a molecular 

 structure.. I have also explained that the similar crystal- 

 lographic orientation is frequently, perhaps usually, accom- 

 panied by an arrangement of the mineral particles with their 

 longer diameters in the same plane as the cleavage, and that 

 this dimensional arrangement is a factor in rock cleavage, 

 although one of probably less importance in most cases than 

 that of the crystallographic orientation of the mineral particles. 



Recrystallization and Aqueo-igneous Fusion. 



It is apparent that the conclusions of the foregoing paper 

 have an important bearing upon the hypothesis of aqueo- 

 igneous fusion. It appears that if water is present when the 

 material, as a result of the mechanical subdivision or for any 

 other cause, reaches the very moderate temperature of 180° C, 

 the adjustment is accomplished mainly by recrystallization, and 

 that fusion is not necessary to account for the plasticity of 

 the rocks. 



So far as the typical crystalline schists themselves are con- 

 cerned, it is certain that they are not the products of aqueo- 

 igneous fusion. They have peculiar textures characteristic of 

 themselves, which are wholly unlike textures of unmodified 

 sedimentary rocks, and unlike those which are known invari- 

 ably to appear in rocks which have crystallized from a magma, 

 however the magma has been produced. Every magma crys- 



