GEOLOGY OF THE PARADOX LAKE QUADRANGLE 493 



proach each other. They also approach very closely to the fourth 

 intrusive type, namely, the gabbro. It was possible, however, to 

 trace these basic developments into masses typical of the classes to 

 which they belonged, and with microscopic work the distinctions 

 became clearer. On the map the areas were colored according to 

 their genetic relationship and they were named according to the 

 most prominent type of a single formation. The map is therefore 

 not lithologically accurate, since rocks that could properly be named 

 gabbro, or diorite, are included within both syenitic and granitic 

 areas. Only those were mapped as gabbro which could be recog- 

 nized as distinct in age from the other three intrusions. 



The relationships are further complicated by the intense meta- 

 morphism, all four types frequently being gneissic. The granitic 

 gneiss approaches the syenitic gneiss on the one hand, the sedi- 

 mentary hornblende gneiss on the other, while anorthosite gneiss 

 often resembles syenite gneiss or gabbro gneiss. Hence the only 

 possibility of unraveling their relationships is by studying them over 

 wide areas. 



The difficulty is further increased in that preglacial valleys were 

 usually established along the contacts, these contacts now being 

 masked by drift and swamp. 



The boundaries on the map are therefore subject to some doubt; 

 in some cases several miles of swamp occupy the contact, in others 

 gneisses appear to belong with almost equal accuracy to either of 

 two types. But although the boundaries may be a matter of dispute, 

 it is confidently believed that the high mountains in the northwest 

 consist of anorthosite ; that these are bordered on the east and south 

 by a sedimentary belt; that Pharaoh mountain marks the central 

 part of a granite intrusion, and that the mountains of the southwest 

 consist of the syenite. 



Petrography of sedimentary rocks 



Hornblende gneiss. As before stated, this rock is extremely vari- 

 able in mineral composition. Streaks of biotite schist are inter- 

 bedded with it; granite, syenite, anorthosite, pegmatites and trap 

 ^ cut it. The country rock itself is variable in composition, and has 



