PRE-CAMBRIAN LITERATURE OF NORTH AMERICA 647 



The major divisions are based on the position of the various 

 series with reference to a conspicuous unconformity and to certain 

 granite bathoHths. He recommends that this section be adopted 

 as a standard for the Lake Superior region. 



In 191 5 Coleman' classified the rocks of the Canadian Shield 

 to the northeast of Lake Huron as follows: 



Keweenawan (Mamainse and nickel eruptive) 

 Discordance 

 Late Proterozoic < Upper Huronian 1 



Small discordance > Typical Huronian 

 Lower Huronian J 



Great discordance 

 f (Laurentian granite and gneiss) 

 Early Proterozoic < Eruptive contact 



[ Sudburian — Timiskaming, Pontiac, etc. 



Great discordance 

 f (Granite eruptive through lower series) 

 Archaeozoic < Eruptive contact 



[ Keewatin and Grenville 



The important points of this classification are the recognition 

 of two major unconformities in the succession and the naming of 

 certain granites and gneisses which are intrusive into rocks younger 

 than the Keewatin, as Laurentian. In his discussion following 

 the classification, he substitutes the term Animikie for Upper 

 Huronian. The term Sudburian for a series is recent in the 

 general discussions of the stratigraphy of the Canadian Shield. 

 This series, Coleman states, is typically developed in the Sudbury 

 district, where it consists chiefly of quartzites, slates, and con- 

 glomerates, without limestones or dolomites, and with almost no 

 carbon. These rocks are severely folded, but not intensely altered 

 excepting near intrusives. Their deposition was followed by the 

 extrusion of lava Sudburite, the effusive equivalent of Norite. 

 Other probably Sudburian areas include portions of the region to 

 the northeast of the Wahnapitae River, and the Timiskaming, 

 Gowganda, Larder Lake districts, the area of the Pontiac series of 

 Quebec, the Dore formation of the east shore of Lake Superior, and 

 certain rocks of Heron Bay on the north shore of Lake Superior, 



'A. P. Coleman, "The Proterozoic of the Canadian Shield and Its Problems," 

 Problems of American Geology (1915), pp. 81-161. 



