668 GEORGE W. BAIN 



of the granite have brought about fracturing in the garnet and its 

 alteration to biotite mica. In the mica much of the lime is retained 

 and magnesia increases; both soda and potash have been added. 



In the garnet rock fractures traverse the equidimensional 

 almandite grains. Folding has extended the fractures and elongated 

 the grains; magmatic waters have brought about their alteration 

 to chlorite. Recrystallization of the chlorite in the presence of 

 alkaline waters containing fluorine had produced biotite. The 

 increase in volume has aided the lateral thrust of mountain folding 

 and developed a schistosity in the biotite gneiss. 



In the contact zones the rule seems to be "Each succeeding 

 zone is enriched in those constituents in which the preceding one 

 is impoverished. There is no indication of the reverse being true; 

 that is, no reverse reaction is taking place." The changes after the 

 formation of a zone are due to the extension of the contact effects 

 farther into the limestone and a burial of the old zone in a new one. 



Pegmatitization and replacement were the agents that changed 

 the rock. Replacement is important in the garnet zones, recrystal- 

 lization in the biotite gneiss zone, and pegmatitization in the gran- 

 ite gneiss zone. All the processes more or less overlap. 



If metamorphic rocks can be spoken of in terms of youth, 

 maturity, and old age, the crystalline limestone might be considered 

 as representing youth, the skarn rocks maturity, and the granite 

 gneiss the extreme old age of the Grenville limestone. 



