286 ALCOCK AND BRUCE PRECAM BRIAN ROCKS OF MANITOBA 



Keewatin Anorthosite. 



Hornblende gabbro. 

 Limestone. 



Greenstone, greenstone schist, elilorite 

 schist, liornblende schist, felsite, seri- 

 cite scliist, asli beds, agglomerate, 

 siliceous slates and scliists, chert, mica 

 schist. 

 Couchiehing Mica schist, paragneiss, phyllite. 



The Couchiehing rocks consist of a group of mica schists, feldspathic 

 mica schists, and finely banded gneisses. According to Lawson, they 

 uniformly underlie the volcanic rocks termed Keewatin. The Keewatin 

 rocks comprise: "(1) fine-grained greenstones showing frequently ellip- 

 soidal or amygdaloidal structure, or both; (2) coarser-textured green- 

 stones showing neither ellipsoidal nor amygdaloidal structures; (3) 

 greenstone schists of varying degrees of schistosity; (4) rather massive 

 chlorite schists ; (5) evenly fissile chlorite schists ; (6) irregularly cleaved 

 chlorite schists; (7) black, glistening hornblende schists, usually on the 

 periphery of the Keewatin belts where they come in contact with granitic 

 intrusions; (8) gray felsites, sometimes amygdaloidal; (9) sericitic 

 schists; (10) various stratified grayish green schists, probably ash beds; 

 (11) agglomerates; (12) gray siliceous slates and schist; (13) banded 

 cherts; (14) mica schist; (15) limestone." 



The Keewatin rocks consist of altered volcanics, including flows, tuffs, 

 agglomerates with minor amounts of intrusives and sediments. A me- 

 dium to coarse grained biotite granite, which is termed "Laurentian," 

 intrudes both the Keewatin and Couchiehing rocks. 



The Seine series consists of a great thickness of conglomerate grading 

 upward into quartzite and slaty schists. It contains debris derived from 

 the waste of the Keewatin rocks, but most of its boulders are granite, 

 with lesser amounts of greenstone, quartz-porphyry, and chert. Near 

 Mine Center the Seine series rests unconformably on the granite. Where 

 it rests on the granite, it is composed of detritus which is nearly all de- 

 rived from the underlying granite, and where it rests on Keewatin it is 

 nearly entirely derived from rocks of that series. It is considered bv 

 Lawson to be a subaerial formation, representing a gravelly floodplain 

 rather than the beach of a transgressing sea. 



The Seine series is intruded by mica-syenite gneiss, to which the term 

 Algoman is applied. Other areas of massive granite and granite-gneiss 

 are believed to belong to the same general period of intrusion as the 

 syenite. 



