246 THE ROYAL SOCIETY OF CANADA 



definitely proved to be later in age than the Timiskamian sediments 

 but they appear to be so. If this is their age, they correspond chrono- 

 logically with the lamprophyre dykes of Cobalt and elsewhere and 

 with the sudburite of Sudbury. Basic rocks genetically connected with 

 titaniferous and certain non-titaniferous magnetites appear to be of 

 the same age. 



As in the case of arsenic, there are thus two epochs of nickel 

 deposition in Ontario, the Keweenawan and that described in the 

 preceding paragraph. 



Basic rocks contemporaneous with sudburite are more widespread 

 in the Province than they are generally recognized to be, as they 

 have frequently been classed as of Keewatin age. No age name has 

 been applied to these rocks. 



The Timiskamian — No ore deposits are known to have been 

 formed during Timiskamian times in Ontario. It may be added 

 that on the United States side of Lake Superior, rocks that appear 

 to be of Timiskamian age contain extensive deposits of iron formation 

 with which are associated ore bodies of commercial importance. 



Erosion has removed by far the greater cart of the Timiskamian 

 rocks that once were widespread in Ontario, and it is possible that ore 

 deposits of this epoch have also been destroyed. 



The Laurentian — No ore bodies that are genetically connected 

 with Laurentian granite and gneiss are known to occur in the Province; 

 but as rocks of this epoch that are now exposed at the surface represent 

 originally deep-seated material, from above which thousands of feet 

 have been eroded, it is impossible to say that ore bodies of Laurentian 

 age have not been destroyed. 



The Grenville and Keewatin — Iron formation representing 

 chiefly chemical deposits laid down during Keewatin-Grenville times 

 is widely distributed. In fact, it may be said that there is scarcely 

 a locality in the Province where Keewatin rocks are found from which 

 iron formation is absent. The iron formation usually consists of 

 interbanded silica and iron ore, magnetite or hematite, but at times 

 there is considerable siderite or iron carbonate. Through the action 

 of aqueous solutions on the iron formation, workable deposits of ore 

 have been produced at various localities. 



Erosion of Ore Deposits 



Nearly all the ore deposits of the Province have been subjected 

 to excessive erosion. The few exceptions that are known are repre- 

 sented by so-called "blind" veins or those that do not come to the 

 present surface, such as a small number of silver veins at Cobalt. 



