DISCUSSION OF CORRELATION 709 



Huronian (Animikie) of these districts the situation is reversed, 

 i.e., the thick Tyler slate formation above the Ironwood series is to 

 be considered with the evidence of deep erosion of the Negaunee 

 series and the development of iron ores on the exposed surface of the 

 iron formation (now represented by the hard ores of the upper part 

 of the Negaunee formation) prior to the deposition of the Upper 

 Huronian. If the correlative of the Tyler slate was ever deposited 

 on the Negaunee formation, it had been removed prior to the 

 deposition of the Goodrich quartzite. The Middle Huronian 

 (Animikie) of both districts is characterized by volcanic activity 

 which continued on into and culminated in the Upper Huronian 

 in the Marquette Range but terminated prior to the deposition of 

 the Copps formation in the Gogebic Range. 



There is a strong resemblance of the Copps formation of the 

 Gogebic to the Upper Huronian of the Marquette Range in respect 

 to lithology and order of succession. At the base of these series 

 is a great conglomerate which is overlain by slate and graywacke. 

 Neither series carries a great productive iron-bearing member, but 

 both contain jasper and ferruginous beds near the base, which in 

 the Marquette district are locally iron ore-bearing. 



It can hardly be doubted that if Van Hise and Irving had 

 discovered in 1892 the great unconformity at the base of the 

 Copps formation on the Gogebic Range, and Van Hise and Bayley 

 in 1896 the great unconformity at the base of the Ajibik quartzite 

 on the Marquette Range, the correlation of the Huronian group 

 of the Lake Superior region would have been tripartite from 

 the beginning and not dual, for the correlations have been built 

 up on these two type districts which were earliest studied by the 

 United States Geological Survey. The Ironwood (middle) series 

 would then have been correlated with the Negaunee (middle) series 

 because, as above stated, they occupy identical positions in the 

 Huronian succession, are essentially similar, are overlain and 

 underlain by essentially similar series, and are in practically 

 adjacent territory. The character of the reasoning which was 

 employed in correlating the formations in these districts and which 

 resulted in a separation of the similar iron-bearing series in the 

 correlation would have united them if the facts of present information 



