724 C. K. LEITH AND R. C. ALLEN 



fourth Huronian series of which the Copps formation of the Gogebic 

 Range would be the sole representative. The practical identity of 

 the Huronian succession of the Gogebic and Marquette ranges, 

 together with the marked similarity of the Copps formation and 

 the Upper Huronian of the Marquette and Gwinn districts, is 

 beheved to be an adequate basis for moving the Animikie of the 

 Michigan and other Huronian districts downward into the Middle 

 Huronian, particularly as this correlation, as we have seen, elimi- 

 nates what would otherwise be a further necessity of including the 

 uppermost series of metamorphic sediments in the Felch, Calumet, 

 and Florence districts in the Keweenawan or the Paleozoic, where 

 they obviously do not belong. 



The anomalous position in the correlations of the great Negaunee 

 iron-bearing series has been unsatisfactory to many students of the 

 pre-Cambrian for many years.' We now have a firm basis for the 

 correlation of the Negaunee series with the great productive iron- 

 bearing series of the Animikie of all of the other districts of the 

 Lake Superior region and are able to recognize the consideration 

 that the unique conditions which resulted in the deposition of the 

 great Huronian iron formations were regional rather than local 

 and should be correlated in time. While it is true that the names 

 now used have come to have well-understood significance because 

 of long usage, it cannot be held that this is a valid argument for the 

 retention of a classification which no longer fairly interprets the 

 facts of present knowledge. 



ARGUMENTS FOR RETAINING THE PRESENT CORRELATION 



C. K. LEITH 



Doubts as to the present correlation of the Michigan formations 

 center in the great slate area (Michigamme slate) carrying the iron 

 formation of the Iron River, Crystal Falls, Florence, and con- 



' See A. C. Lane and A. E. Seaman, Mich. Geol. Survey, Annual Report, 1908, 

 pp. 23-30. In presenting their mature conclusions on Michigan pre-Cambrian suces- 

 sions, Lane and Seamen correlate the Animikie iron-bearing series throughout with 

 Negaunee (Middle Huronian) of the Marquette Range. 



