[miller-knight] 



PRE-CAMBRIAN OF ONTARIO 



243 



volume of acidic varieties.^ The pre-Algoman basic rocks are of 

 greater volume and wider extent than they are usually recognized 

 to be since they are frequently wrongly classed as Keewatin. These 

 basic rocks are represented by the sudburite of the Sudbury area, by 

 the lamprophyres of Cobalt and elsewhere, and apparently by the 

 basic rocks of the townships of Dundonald, Reaume and others where 

 associated with them are nickeliferous pyrrhotite and chromite. 



Area of Ontario -407,262 sq. mis 

 _ LEGEND 



( ES3 Devonian 

 PALEOZOIC 1 l^'SHurian 



( ^Hordoviclan 



PRE-CAMBRIAN fVVl 



100 50 



Scale 



QTJE 



;^C 



3<''^*»« 



K^ 



I) ^ J 



w lit ^~ïû 



'VbjM^^ sItatbs 



Owing to erosion, the sequence of metal deposition shown in the 

 table is doubtless incomplete. Iron formation occurs in three epochs, 

 the Grenville-Keewatin, Animikean and Timiskamian, but is of 

 economic importance only in the former two. Certain deposits of 



^Granites later in age than the Keweenawan are known in the Sudbury area 

 and elsewhere, and their volume is greater than it is usually considered to be. 



