726 A TREATISE ON METAMORPHISM. 



cementation-injection bands of lighter color. These bands vary from those 

 as thin as leaflets, being perhaps but a single row of crystals, to those of 

 considerable width. There may be many such bands within the space of 

 a centimeter, or a single one may be many meters across. Frequently 

 parts of the injected material are in dike-like masses of varying size, which 

 cut the schistosity at various angles. At numberless places the leaf-like 

 bands of pegmatitic-looking material parallel to the schistosity are found 

 to be connected directly with the dike-like masses cutting the schistosity. 



The dark schistose bands are found to show exomorphism in various 

 degrees by the injecting material. Besides recrystallization, the modifica- 

 tion consists in the development of various new minerals, the material of 

 which is derived in part at least from the intrusive. Clear evidence of 

 this is the frequent addition of minerals, or a large increase in the amount 

 of minerals, in the pegmatized rock of the kinds found in the adjacent 

 intrusive. Not only may the main mass of unpegmatized schist show a 

 deficiency of certain minerals as compared with the pegmatized areas, but 

 if within the pegmatized area there be any considerable belt of schist not 

 affected by the pegmatite masses it may exhibit a similar deficiency. The 

 endomorphic effect upon the injection bands follows the same rule. The 

 more intimate the intrusion and pegmatization the greater the endomor- 

 phism. The smaller bands of injection material gain proportionally more 

 material from the schist than do the larger ones. 



The intrusive rock, which is the final inciting cause of the third phase 

 of pegmatization may vary from acid to basic, but pegmatization in connec- 

 tion with granite and other acid intrusives has been most closely studied. 

 The process of grauitization described by Michel LeVy" comprises the par- 

 ticular form of pegmatization produced by this rock. The pegmatization 

 known as grauitization has been studied more closely than other forms 

 because of its prevalence, because the light color of the granite renders 

 it easily distinguishable, and perhaps because acid magmas supply more 

 water and heat than basic ones. 



It seems to me that the third phase of pegmatization described above 

 can be conceived of only as an aqueo-igneous process. In many instances 

 the larger masses of cutting material are truly igneous dikes containing a 



a L6vy, A. Michel, Sur l'origine des terrains cristallins primitifs: Congres geologique international, 

 4th sess., London, 1888, pp. 117-129. 



