84 Van IRse — Metamorphism of Hocks and Rock Flowage. 



sliced, piled up, or brecciated, and in each block or slice the 

 alterations are metasomatic, or those of molecular dynamic 

 action. 



Zone of combined fracture and flowage. — In the middle 

 zone of combined fracture and flowage the alterations may 

 combine those of fracture and of flowage. 



Zone of flowage. — At the outset it may be said that the pro- 

 cess of rock flowage is very different from the flowage of a 

 liquid. 



It has been explained in another place that in the deep- 

 seated zone of rock flowage the process of deformation is 

 similar to that of mashing or kneading. There every particle, 

 small or great, takes part in the deformation. 



As soon as interior movements begin, the destruction of the 

 original textures and structures begins and goes on very rapidly, 

 so that with comparatively little motion the original textures 

 may be wholly destroyed. For instance, such rocks as 

 quartzose sandstones, which retain their textures for indefi- 

 nite periods if there be no mass action, even when buried 

 under thousands of feet of other rocks, when deformed by 

 mashing rapidly lose all clastic textures. In the same way the 

 textures which are characteristic of igneous rocks rapidly dis- 

 appear by mashing. In the place of the original textures, 

 whether those of sedimentary or igneous rocks, there appear 

 peculiar textures and structures referred to subsequently as 

 characteristic of mass dynamic metamorphism. 



During the interior mass movements of rocks water makes its 

 way between the particles much more readily than under 

 conditions of quiescence.' This follows partly from the move- 

 ments and partly from the heat developed by the movements. 

 The increased temperature results in decreasing the viscosity of 

 the water, and it has been seen that low viscosity is of great 

 importance in the penetration of water through minute spaces. 



Consequent upon interior mass movements two kinds of de- 

 formation occur, granulation and recrystallization. Between 

 the two are all gradations. Where the movements result in 

 granulation this exposes large surfaces to the action of the 

 contained water. The dissolving power of water when not 

 nearly saturated is almost directly in proportion to the area 

 upon which it can act. One perhaps might expect that the 

 more profound the kneading the finer would be the granula- 

 tion of the altered rock, but this is not the case. Many of the 

 most profoundly altered rocks, instead of being extremely fine 

 grained, are somewhat coarsely crystalline. 



It is generally agreed that the crystalline schists of this 

 character have been recrystallized throughout, and therefore 

 strongly contrast with those rocks which have been granu- 



