666 GEORGE W. BAIN 



ferrous iron in the garnet would seem to indicate that some reaction 

 similar to that given below had taken place : 



2(H.O+2F)=4HF+02 



: — Nascent oxygen. 

 4FeO+02=2FeA 

 From garnet-: : In biotite containing F. 



Some reaction giving this final result does take place, and since 

 the entire oxidation that is transpiring in the rock accompanies 

 this change which involves the fluorine, it would seem that the 

 above condition represents the instability in this zone. If this is 

 correct the reaction represents the critical point above which water 

 and fluorine can exist together as definite and distinct components. 

 The increase in volume caused by this reaction (the change of 

 almandite to biotite) must have developed a pressure normal to 

 the fractures in the garnet so that where the chlorite recrystaUized 

 to biotite the mica flakes are elongated along a certain plane to 

 produce schistosity in the rock. Two directions of fracture are 

 present in the garnet, one parallel to the schistosity and another at 

 right angles to it. The chlorite along the fractures parallel to the 

 schistosity seems to have recrystaUized more readily than along 

 the fractures at right angles to it. Fracturing in the garnet seems to 

 have been caused by folding of the Grenville series; thus the planes 

 of schistosity and the banding of the gneisses produced by lit-par-lit 

 injection are controlled by the direction of the axes of the folds 

 of the Grenville series. Migration of the biotite along the planes 

 of schistosity, for short distances, has taken place in some cases, 

 owing to the strong tendency of the biotite to crystallize along 

 these planes. 



CONCLUSIONS 



The Grenville crystalline limestones have been subjected to 

 intense contact action by the intrusion of the Laurentian granite. 

 Garnet zones were developed in the limestones. 



The garnet is of an unusual type containing almandite, 

 grossularite, and pyrope in the molecular ratio 20-2-7. Kemp has 

 collected as complete a Hst as possible of the analyses of garnets 



