248 THE ROYAL SOCIETY OF CANADA 



associated with them, and the deposits of whatever age enclosed in 

 the Keewatin and Grenville would also have largely disappeared. 

 Faulting and folding have preserved parts of ore bodies that 

 otherwise would have been completely destroyed by erosion. This 

 is well illustrated by the Cobalt Lake fault, where silver veins have 

 been protected on the down-throw side of the fault. Had it not been 

 for this fault and others associated with it, practically all the ore that 

 has been mined in the vicinity of the fault and to the west of it 

 would have been removed. Folding at Kjrkland lake and Porcupine 

 has preserved comparatively narrow synclinal belts of Timiskamian 

 sediments and the weathered Keewatin rocks that immediately 

 underlie them, and at one time formed the surface of the earth. 

 There is no reason for believing that erosion has been less in the two 

 localities mentioned than elsewhere in the pre-Cambrian; but prob- 

 ably the character of the rocks, all of which were at one time, before 

 folding took place, subjected to surface influences, has a bearing on 

 the formation of openings and the deposition of ores. The gold 

 deposits are found both in the Timiskamian sediments and in the 

 Keewatin, the more schistose and more highly altered varieties of the 

 latter group appearing to be the more important from the economic 

 point of view. 



Relative Economic Importance of Various Epochs. 



The following table gives the value of the metallic production 

 of Ontario for the year 1913, classified according to age and origin. 

 Considerable nickel, cobalt and arsenic in the Cobalt ores are not 

 represented in the table, nothing being received for them by the mines. 

 A comparatively small quantity of the nickel and copper in the 

 table should be credited to the deposit in Dundonald township that 

 is associated with the basic eruptives of pre-Algoman and probably 

 post-Timiskamian age. 



It should be understood that the ages given for the deposits 

 do not refer to secondary concentration, as, for instance, in the case 

 of iron ores, but to the epoch in which the metals were first deposited. 



