428 W. G. Foye — Nephelite Syenites of Ontario. 



The close association of nephelite syenites with granite peg- 

 matites, in the Halibnrton area, indicates that they. originated 

 during the pnenmatolytic stage of the intrusion of the Lauren- 

 tian granite. The parent magma of the Gooderham nephelite 

 syenite laccolith must have been especially charged with pneu- 



Fig. 6. 



Fig. 6. Tracing of the sodalite areas of a polished slab of sodalite-syenite 

 from the Ice River district, British Columbia. 



matolytic gases since the amount of nephelite pegmatite associ- 

 ated with the body is unduly large. 



Many instances have been given in the discussion of the 

 Gooderham and Tory Hill laccoliths of the replacement of 

 microcline by albite, of albite by nephelite, and in certain cases 

 of nephelite by sodalite. The accompanying microphotographs 

 illustrate this point (fig. 7). It is believed that these replace- 

 ments show that a magma, from which microcline was first 

 capable of crystallizing, was gradually enriched in soda, until 

 first albite, then nephelite, and, finally in the extreme cases of 



