90 THE ROYAL SOCIETY OF CANADA 



cerned, we may define them as the crystalHne, sub-crystalline or 

 metajnorphosed rocks which constitute the great Eocontinental 

 Crescent that extends around the basin of Hudson Bay through the 

 Provinces of Quebec, Ontario, Manitoba, Saskatchewan, and Alberta, 

 and into the unorganized portion of Canada north of the last of these 

 three Provinces. Wherever they are in contact with rocks of 

 Palaeozoic age they lie unconformably below them. 



In 1905 an international Committee of six geologists was appointed 

 to decide on a workable classification for these rocks, and the following 

 classification was unanimously adopted. 



^Pre-Cambrian 

 Keweenawan 



Unconformity 



Huronian 



Upper 



Unconformity 

 Middle 



Unconformity 

 Lower 



Unconformity 

 Keewatin 



Eruptive contact 

 Laurentian 



Since this classification was proposed a very large amount of work 

 has been done in Canada on these rocks by Drs. Adams, Barlow, Cole- 

 man, Lawson, Miller, and other Canadian geologists. 



Of these ^Dr. Lawson has proposed the following classification: 



I Keweenawan 

 Algonkian \ Unconformity 

 \ Animikie 



Eparchaean Interval 



' Report of International Committee on Lake Superior Geology. Jour, of Geol. 

 Feb.-Mar., 1905. 



!2 A. C. Lawson. A Standard Scale for the Pre-Cambrian Rocks of North America. 

 Compte Rendu Congres. Geol. Inter. 12 Session, Canada, 1913. 



