Plate lo 



A. Supposed Grenville gneiss resembling sj^enite. Micro- 

 perthite is the pale gray mineral with numerous inclusions. 

 The clear white or gray mineral with cleavage cracks is 

 orthoclase. The very dark mineral is chieflj^ hornblende, 

 except where the rectangular cleavage reveals pyroxene. 

 Crossed nicols, actual field o.i inch or 2.5 mm. 



B. Syenitic gneiss from north side of Pitchoff moun- 

 tain, containing garnet (G), associated with pyroxene 

 (Px), uralitic hornblende (Hb), feldspar (Fs), and a 

 little quartz (Q). White light, actual field 0.08 inch or 

 2.0 mm. 



