BASIS OF PRE-CAMBRIAN CORRELATION 2^ 



United States geologists in reference to the succession and relation of the pre- 

 Cambrian series of Canada. So far as there are differences they will appear 

 below. 



The elucidation of the pre-Cambrian succession for the Lake Superior region, 

 which term as here used includes the great tract extending from the Lake of the 

 Woods to north of Lake Huron and south to the Paleozoic rocks, has been the 

 work of many men extending through many years. In 1892, when Bulletin 86 

 of the United States Geological Survey, on the Archean and Algonkian, appeared, 

 the Lake Superior succession, as now recognized, had been fully worked out,' 

 with the exception that what was then called the Lower Huronian has since been 

 found lO comprise two series; also the series now called Keewatin was called 

 Mareniscan, but was properly defined. Some years after the publication of this 

 bulletin, Mr. A. E. Seaman discovered the unconformity mentioned in the lower 

 Huronian of the Marquette district. As soon as this discovery was made it was 

 appreciated that the two divisions of the Huronian in the original Huronian area 

 worked out by Pumpelly, Leith, and myself correspond with the two divisions 

 in the Marquette district. The classification of the pre-Cambrian as thus devel- 

 oped was fully accepted by the International Geological Committee in 1904, and 

 the table giving the succession was published by Leith in 1904, and by the com- 

 mittee in 1905, as follows:^ 



Cambrian 



Upper sandstones, etc., of Lake Supeiior 

 Unconformity 

 Pre-Cambrian 



Keweenawan (Nipigon) 

 Unconformity 

 Upper (Animikie) 

 Unconformity 

 Huronian ( Middle 



Unconformity 

 Lower 



Unconformity 



Keewatin 

 Laurentian 



Eruptive contact 



This succession is repeated by Dr. Adams in his communication, except that 

 the unconformities are omitted, and it is extended to the entire Canadian pre- 

 Cambrian region. 



It is indeed gratifying to have completely accepted for the great Canadian 

 pre-Cambrian area the succession which has been worked out for the Lake 

 Superior region, but Dr. Adams implies that his classification rests upon a sounder 

 basis than the same classification offered by others since "drawing evidence from 

 the area as a whole rather than from a few restricted areas on its southern border." 

 But unhappily for the contention of Dr. Adams, it is still true that the Lake 

 Superior region is the only very extensive area in which the detailed geology' has 



1 C. R. Van Hise, "Archean and Algonkian," Bull. 86, U. S. 0. S., p. 195. 



2 Journal 0} Geology, Vol. XIIL p. 104. 



