590 WILLET G. MILLER AND CYRIL W. KNIGHT 



studied his "Huronian" rocks on Lake Timiskaming, the name 

 Timiskamian is appropriate for a part of them. Further, the 

 name Sudburian is Hkely to be confused with sudburite, a name 

 applied to certain basic igneous rocks at Sudbury that intrude the 

 Timiskamian but are older than the Algoman granite and gneiss.^ 

 It may be added that basic rocks of the age of sudburite are wide- 

 spread and have frequently been mistaken for Keewatin. They 

 are represented by the peridotite and augite lamprophyre of the 

 Porcupine region, one hundred miles north of Sudbury, and by 

 the lamprophyres and other rocks of Cobalt, ninety miles to the 

 northeast of Sudbury. For economic purposes, at least, some age 

 name should probably be applied to these basic rocks. Sudburian 

 would be suitable had it not been used in another sense. 



While Coleman and the authors are agreed on the age relations 

 of the two great series of granites and gneisses, different nomen- 

 clatures are employed. The rocks that he calls "Granites Erup- 

 tive through the Keewatin," and to which he gives no distinctive 

 age name, we class as Laurentian. In his classification Laurentian 

 is applied to the granites and gneisses that we, following Lawson's 

 nomenclature, class as Algoman. 



The appellation Laurentian was first given to the rocks of the 

 district bordering the Lower Ottawa River, and the older granites 

 and gneisses here are different in age from the Algoman. The 

 fact that the rocks now called Algoman have frequently been 

 classed as Laurentian should not be given consideration. If the 

 name Laurentian is to be retained, it should be applied to the 

 oldest granites and gneisses. The following quotation shows that 

 Logan did not intend that the name should be applied to granites 

 that are intrusive into any part of his "Huronian." Further, it 

 will be seen that, in the classic area of Lake Huron, Logan recog- 

 nized both the Laurentian which, in his opinion, underlies all of 

 his Huronian sediments, including that part of them now known as 

 Timiskamian, and granites eruptive into the Huronian. Unfortu- 

 nately later work has shown that much, at least, of what he con- 

 sidered to be Laurentian is really the intrusive granite which he 

 called Huronian granite. 



^ Ont. Bur. Mines, XXl'lI, 215-17. 



