IMPORTANCE OF WATER IN RECRYSTALLIZATION. 741 



The identical character of the schists surrounding batholiths and those 

 produced in connection with regional mechanical action is explained by the 

 foregoing pages. The necessary conditions for the production of recrystal- 

 lized schists are movement under sufficient pressure, moderate temperature, 

 and presence of water. These conditions are produced in the two cases in 

 different ways. 



PRESSURE AND SAPIDITY OF DEFORMATION. 



The less the pressure the more likely is the deformation to be accom- 

 plished by granulation. The greater ■ the pressure the more likely is the 

 deformation to be accomplished by recrystallization. The pressure increases 

 with depth, with mechanical action, by igneous intrusions, and possibly 

 from other causes. 



To a certain point, the more rapid the deformation the more likely is 

 the adjustment to be by granulation. The limit beyond which this does 

 not apply is reached when the mechanical process develops such an amount 

 of heat that the readjustment is by recrystallization rather than by granu- 

 lation. The slower the deformation the more likely is the readjustment to 

 be by recrystallization. 



WATER CONTENT. 



Absence of water is favorable to granulation; presence of water is 

 favorable to recrystallization. If a series be so dense, or is of such origin, 

 that it contains comparatively little water, even if other conditions be favor- 

 able, deformation by granulation rather than by recrystallization may occur. 

 Another series, which is in every other respect under similar conditions, but 

 which contains a fair amount of combined water that may be liberated 

 bv dehydration to serve as a medium for the process, may be adjusted by 

 recrystallization and form coarse schists. This principle is believed to 

 explain the difference in the character of the deformation of the different 

 formations for many districts. It is a well-known fact that in the same 

 district different rock masses composed of similar minerals deformed in the 

 zone of anamorphism vary greatly in the character of the alteration, some 

 formations yielding by granulation, others by recrystallization. In general 

 the sedimentary rocks contain a considerable percentage of combined water, 

 and therefore when deformed are recrystallized. The same is true of the 

 porous igneous rocks, such as lavas and tuffs. In contrast with these are 



