696 A TREATISE ON METAMORPHISM. 



recrystallization is the dominant or preponderant process, gliding may not 

 occur as a subordinate simultaneous process, especially with such minerals 

 as calcite, which, as Adams" has shown, is especially likely to be deformed 

 by movement along gliding planes. 



In the theory of recrystallization we have an explanation of the 

 general uniformity in size of the particles of any definite mineral in a rock 

 metamorphosed at depth during mass-mechanical action: The larger grains 

 of any mineral have smaller areas of contact for the solutions to work on, 

 and therefore granulation plays a large part; the smaller particles have, 

 larger areas of contact for the solutions to work on, and consequently 

 recrvstallization merges them, producing larger particles. Therefore, the 

 tendency of granulation and recrystallization together is to produce 

 uniform-textured rocks. 



Recrystallization lags behind deformation. — In the deep-seated zone adjustment may 

 not lag far behind the disturbing forces. However, in all cases there is 

 apparently some lag. In the most regularly laminated of the schists, close 

 examination usually reveals a slight undulatory extinction, and therefore a 

 state of unequal strain in the minerals, showing that recrystallization has 

 not exactly kept pace with deformation, or else that the schists have been 

 somewhat deformed since recrystallization. 



Where such subsequent deformation has not taken place, the amount 

 of strain shadows and granulation is thought in many cases to be a measure 

 of the amount that molecular readjustment lags behind the disturbing 

 movement. In the typical schists strain is in many cases scarcely percep- 

 tible. In other cases all of the mineral particles show marked strain 

 shadows. In still other cases the strain shadows are accompanied by more 

 or less of granulation, and this phase of the rocks grades into the ordinary 

 granulated rocks. Thus there are all gradations between molecular read- 

 justment or recrystallization almost pari passu with deformation, and 

 readjustment almost wholly by granulation. 



Evidence that recrystallization does nearly keep pace with deformation 

 in the case of the schists consists partly in the absence of marked strain 

 structures, for it is to be supposed that if recrystallization did not nearly 

 keep pace with deformation the result would be that the mineral particles 



a Adams, F. D., and Nicolson, J. T., An experimental investigation into the flow of marble: 

 Philos. Trans. Royal Soc. London, ser. a, vol. 195, 1901, pp. 363-101. 



