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LAURENTIAN. 



The Laurentian formation in the Lake of the Woods 

 region is represented by large areas of granite and gneiss. 

 This group is almost entirely lacking on the shores of the 

 northern part of the lake, though there are several granite 

 outcrops which may belong to it but have been referred to 

 a later period by Dr. Lawson. If, however, the trap dykes, 

 which are elsewhere described, are to be assigned to the 

 Keweenawan it will probably be necessary to refer part 

 of this granite, to which a later origin has been assigned, 

 to the Laurentian. This would apply to the outcrop on 

 Micrometer island, where the trap cuts the granite, and it 

 would probably apply to all the granite in the northern 

 part of the lake. 



Typical Laurentian granites and gneisses are to be seen 

 from the train on the Canadian Pacific railway at Margach 

 (formerly Rossland) and west of Dailington bay near 

 Keewatin. In the present excursion no outcrop of un- 

 questioned Laurentian rock is visited, though probably 

 the granite at the Sultana mine is to be so classed. There 

 is an extensive development of rocks of this age north of 

 Kenora and in the region to the east of Route bay. The 

 most interesting area, however, from many points of view 

 is the Grande Presqu'ile, which is essentially a series of 

 domes of granite and gneiss with margins of highly altered 

 Keewatin trap, and may be compared with the granite 

 outcrops on the north side of Andrew bay and on the west 

 side of Bottle bay. In the Andrew bay outcrops the 

 granite protrudes through the surrounding traps in large 

 dome-like masses which, near the contact with the trap, 

 contain numerous fragments of re-crystallized trap, while 

 at Bottle bay some of the domes are overlain by arched 

 masses of the older trap, and others are like those to the 

 north of Andrew bay. 



The character of those granite masses can probably be 

 best studied near the Sultana and Ophir mines. There 

 the texture varies from that of a coarse granite porphyry 

 to a granitic and even microgranitic texture. Near the 

 contact with Keewatin traps there are places where it is 

 difficult to distinguish the two rocks, as both are fine 

 grained and have possibly undergone an interchange of 

 material which seems to furnish a gradation between them. 

 This however, is not the usual case ; ordinarily the contact 



