PRE-CAM BRIAN FORMATIONS— ONTARIO AND MANITOBA 461 



schists, garnetiferous mica schists, hornblende schists, and phylHte/ 

 In some of the mica schist, quartz makes up three-fifths of the 

 rock mass, biotite one-fifth, with zoisite the other important 

 mineral present. It seems evident from Lawson's descriptions of 

 the field occurrences and from the results of petrographical examina- 

 tions and chemical analyses as given in his report, that the rocks 

 are sediments, possibly of somewhat abnormal types. They are 

 entirely clastic; no limestones have been found in association with 

 them. A striking and peculiar circumstance is the lack of coarse 

 sediments or conglomeratic beds in this supposedly thick series. It 

 seems possible that these rocks were formed along the seaward margin 

 of a delta which supplied large quantities of fairly fine debris, 

 the site of deposition for the Coutchiching being so far from shore 

 that no gravels were suppHed, but not far enough out to allow 

 the formation of limestones, assuming that conditions were suitable 

 for the deposition of lime rocks at that early period. 



The Keewatin series consists of: "(i) fine-grained greenstones 

 showing frequently ellipsoidal or amygdaloidal structures or both; 

 (2) coarser-textured greenstones 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 felsite 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 schists; (15) limestone."^ 



This group is clearly made up for the most part of lava flows 

 and their derivatives with minor amounts of sediments inter- 

 banded with the igneous rocks. In summary, then, it may be 

 said that the Coutchiching consists chiefly of sediments, with 

 possibly some beds, such as the hornblende schists, of igneous 

 origin; the Keewatin series is chiefly igneous, with minor sedi- 

 mentary beds intercalated with the lava flows. There seems 



^ Lawson, Memoir 40, Geol. Survey of Canada, p. 28. 

 == Ibid., p. 35. 



