On the Norian or " Upper Laurentian" Formation. Vjl 



Speaking generally we may say that the southern limit 

 of this area extends from Lake Superior in a north-easterly 

 direction along the Lower St. Lawrence as far as Labrador, 

 and north-westerly to the mouth of the Mackenzie Eiveron 

 the Arctic Ocean. North of these limits, as far as the coast 

 of the Arctic Ocean, almost the whole area is composed of 

 the old crystalline rocks, and although subordinate areas of 

 Huronian rocks are found iti these enormous tracts of land 

 by far the greater part belongs to the lower Archaean or 

 the Laurentian system. 



This great rock complex consists principally of orthoclase 

 gneiss, of nearly every variety, both as regards structure 

 and composition. In many places these gneisses show only 

 the most obscure foliation and resemble granite, in other 

 areas, of great extent, they appear as perfectly stratified as 

 any Palaeozoic formation and they then lie over great areas 

 quite flat or in low indulations. A great part of the obscurely 

 laminated gneiss is probably eruptive, and in some instances 

 this has been established beyond doubt. On the other hand, 

 we have good reason to believe that many of the stratified 

 portions of the system are. of sedimentary origin. 



In certain areas, where the stratified gneiss occurs, we 

 find in it bedded layers of crystalline limestone, quartzite, 

 amphibolite and other rocks often of considerable extent. 

 In such cases, the gneiss itself is usually richer in varieties, 

 and certain of these varieties almost invariably accompany 

 the limestone beds. These are chiefly garnetiferons gneiss 

 and a peculiar sillimanite gneiss which weathers in a re- 

 markably rusty manner. These gneisses, together with 

 the accompanying granular limestones, quartzites, &c, 

 Logan regarded as a higher division of the Laurentian, 

 resting conformably upon a lower gneiss, which holds no 

 limestone or quartzite, and possesses a more uniform char- 

 acter. 1 



He called this upper division ' The Grenville Series " 

 after Grenville, 2 in the Province of Quebec, where it was 



1 Logan, Report of the Geol. Survey of Canada 1863, p. 45, and earlier reports of 

 the Geol. Survey of Canada from 1845-48. 



2 Logan, Rep. of the Geol. Survey of Canada 1863, page 839. 



