STRUCTURAL FEATURES OF THE PRE-CAMBRTAN i8i 



south shore of Opawika Lake. The west end of the lake breaks 

 across into the next anticline to the north. 



The rocks in the southern anticline are andesites, fairly massive 

 and without pillow structures. Dips vary from 65° to 90°. On the 

 north side of this anticline, in the long east bay of Tush Lake, coarse 



Longitude V^est 76 /rpm Greent^ich 



Fig. 3. — Key map of the part of northern Quebec dealt with in this paper, and 

 the positions of the small areas particularly described. 



andesitic tuffs lie conformably on the andesites. They are not 

 bedded. 



Along the axis of the syncline, on the south shore of the western 

 end of Opawika Lake, a flow of highly acid quartz porphyry, a 

 translucent, greenish-white rock, conformably overlies the andesite. 

 In the anticline to the north, lavas of acidity intermediate between 

 the quartz porphyry and the andesite outcrop until the normal 

 andesite is again reached. The latter continues to outcrop as far 

 as Sturgeon fall. 



