PRE-CAMBRIAN OF NORTHERN ONTARIO AND QUEBEC 331 



where careful detailed geologic work was being done following the 

 discovery of the great copper and iron deposits, it was applied 

 more rigidly only to granites unconformably below the Lower 

 Huronian. In 1905, the International Committee on pre-Cambrian 

 nomenclature defined the term Lauren tian as applicable to "the 

 granites and gneissoid granites which antedate or protrude through 

 the Keewatin, and which are pre-Huronian." They added, "In 

 certain cases this term may also be employed, preferably with an 

 explanatory phrase, for associated granite of large extent which 

 cut the Huronian or whose relations to the Huronian cannot be 

 determined." 



From 1905 to the present time the term Laurentian has 

 gradually fallen into disuse in Canada. Careful detailed geologic 

 work has been carried on in this period by the Geological Survey, 

 with the use of local names to designate formations, and without 

 any attempt at general correlation until all the necessary evidence 

 has been obtained. In general, no names whatever have been 

 applied to the granite masses, although Miller has called the 

 granite around Cobalt the Lorrain granite. But with the writer's 

 work of last summer, which completed the mapping of a large 

 n'uclear area in Ontario and Quebec, and brought in the evidence 

 necessary for correlation and age determination, it appears possible 

 to apply the term Laurentian correctly and rigorously. 



The writer suggests that the term Laurentian be defined, in 

 the more rigorous sense intended by the International Committee, 

 to apply only to those granites and granite gneisses which intrude 

 all rocks below the peneplain at the base of the Lower Huronian. 

 Older granites, which will undoubtedly be found some day since 

 the Timiskaming series contains granite pebbles in places and 

 granite pebbles are found in Keewatin tuff beds occasionally, must 

 receive other names when found. Laurentian will therefore apply 

 to all granitoid masses intrusive into the Timiskaming series, and 

 cut off by the peneplain which bevels it. This use of the term for 

 northern Ontario corresponds to the usage in the Marquette 

 district, the nearest pre-Cambrian on the south shore of Lake 

 Superior; where the Laurentian granite is that which underlies 

 the Lower Huronian. 



