STRUCTURAL FEATURES OF THE PRE-CAM BRIAN 71 



invading the Grenville sediments. It is a volcanic or surface rock, 

 retaining in places an ellipsoidal or pillow structure, and a fine or 

 medium-grained texture. In the second place the greenstone does 

 not send dykes into the sediments, nor give other evidence of being 

 intrusive into these rocks. It is thus inferred that the quartzite, 

 greywacke, and limestone are younger than the pillow lavas." 

 Basing upon this evidence their conclusion that the "Keewatin" 

 is older than the Grenville, they determine the Grenville to consist, 

 from the base up, of gray gneisses and quartzites, some of which 

 are garnetiferous, iron formation, and crystalline limestones. 



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