738 A TREATISE ON METAMORPHISM. 



Whether granulation or reciystallization is preponderant in a given 

 place in the zone of anamorphism depends upon many factors. Some of 

 these factors are, the character of the material and water content, tempera- 

 ture, pressure, and rapidity of deformation. 



CHARACTER OF MATERIAL. 



The degree to which granulation and reciystallization takes place 

 depends to a considerable extent upon the character of the material. The 

 character of the material involves both mineral composition and coarseness. 



In the same rock mass certain minerals may be mainly recrystallized 

 and others mainly granulated or even retain their integrity. For instance, 

 it is well known that quartz suffers granulation and reciystallization much 

 more readily than feldspar. This is illustrated by the reciystallization of 

 the flat individuals of quartz in the quartz-porphyry described by Futterer" 

 (PL III, B), in which the feldspars have been little affected. 



I shall make no attempt to compare the various minerals with one 

 another with reference to ease of reciystallization. There are all gradations, 

 from calcite, which can be easily recrystallized in the laboratory by the 

 passage of water through finely powdered material under very moderate 

 pressure, to the more refractory minerals, such as feldspar. 



Since some minerals when strained recrystallize much more readily than 

 other minerals, it follows that a formation composed chiefly of one class of 

 minerals maybe deformed mainly by granulation, and an adjacent formation 

 composed of another set of minerals may be deformed mainly by reciys- 

 tallization. One formation may thus show complete granulation or other 

 important strain effects, while the reciystallization of the adjacent formation, 

 because of the greater mobility of its mineral particles, nearly keeps pace 

 with the deformation. One rock may recrystallize so as to show the tex- 

 tures and structures of the schists and gneisses with more or less residual 

 strain effects, while an interlaminated rock recrystallizes so readily as to 

 take on a granolitic texture after movement has ceased. As an illustration 

 of this are the closely associated gneisses and marbles of the Adirondacks 

 and of the Hastings series of Canada. The gneisses, besides having their 

 characteristic textures and structures, show marked residual strain, while at 



"Futterer, Karl, Die " Ganggranite " von Grosssachsen, und die Quartzporphyre von Thai im 

 Thiiringer Wald, Heidelberg, 1890, pp. 27-47. 



