Van Hise — Metamorphism of Bocks and Rock Flowage. 89 



place of escape, where the pressure is least, the material is de- 

 posited from solution, and the grains increase in size or grow. 



During the deformation of the rocks this process of solution 

 and deposition of a mineral particle is continuous. In this rear- 

 rangement it is not supposed that the identical molecules 

 which are taken from the more severely stressed parts of a 

 grain are necessarily deposited at the places of less stress upon 

 the grain. Undoubtedly there is great interchange of material 

 between the particles by means of the solutions. It is, how- 

 ever, thought probable that in many cases of deep-seated de- 

 formation, where the passage of solutions is difficult and slow, 

 that much of the identical material which is taken from a 

 grain at one place is added to it at another place. 



When new individuals are produced in any way, as by 

 granulation or by the deposition of new mineral particles, per- 

 haps as different species from any originally in the rock, they 

 are subject to the same laws as the original mineral particles. 

 Many have a tendency to form with similar crystallographic 

 orientation. However, it is only rarely that the orientation of 

 the particles of a given mineral approximates exactness. One 

 mineral — for instance, mica — may be well oriented, whereas 

 such minerals as quartz or calcite may not be oriented. 



In proportion as the minerals readily respond to the forces 

 of recrystallization or are mobile, they do not gain or retain reg- 

 ularity of arrangement. After mass movement has ceased 

 the temperature may be sufficiently high and the heat be held 

 for a sufficient time, so that the solutions may completely re- 

 crystallize the minerals under mass static conditions, and there- 

 fore orientation may be lost. In proportion as minerals do 

 not readily recrystallize or stubbornly resist the force of recrys- 

 tallization, the minerals once oriented retain their regularity of 

 arrangement. 



It is concluded from the foregoing that rock flowage, as 

 deep as observation extends, is plastic deformation through 

 continuous solution and deposition, or, in other words, recrys- 

 tallization. During the adjustment ail or only a part of 

 the material may have passed through this change. However, 

 if a matrix, plastic by recrystallization, be filled with rigid 

 granules which are not recrystallized, the whole mass may be 

 deformed by true flowage of the matrix and by slipping or 

 shearing readjustment of the granules. So far as the average 

 mass deformation is concerned, the result is substantially the 

 same as though each rigid granule had not acted as a unit. 

 Indeed, the same average mass deformation may be accom- 

 plished wholly by granulation and welding, as in Adams' ex- 

 periments ; but it may, perhaps, be doubted whether this is 

 ever strictly the case with rocks in nature, for some small 

 amount of water is present, and probably, even in the case of 



