DISCUSSION OF CORRELATION 719 



series of the Marquette Range and the Ironwood series of the 

 Gogebic Range, the age of this great granite bathoHth and its 

 outhers may be considered as late Middle Huronian. 



CONSIDERATION OF ARGUMENTS WHICH MAY BE ADVANCED FOR 

 THE RETENTION OF THE CORRELATION OF THE ANIMIKIE AS 

 UPPER HURONIAN 



We have seen that the correlation of the Animikie as Upper 

 Huronian dates from the earliest work of the United States Geo- 

 logical Survey in the Lake Superior region. It seems reasonable 

 to believe that if the early workers in the Gogebic and Marquette 

 ranges had recognized that the Huronian of both exhibits a tri- 

 partite rather than a dual division, the Animikie would have been 

 considered by them as Middle Huronian rather than Upper 

 Huronian. We have referred to some of the difficulties which were 

 encountered in the application of the dual classification to some 

 of the other Michigan ranges and have shown how these difficulties 

 largely disappear in the correlation of the Animikie series as 

 Middle Huronian. Having established the basis of the proposed 

 correlation, we may turn to a consideration of some of the objections 

 which may be offered to it. 



Dr. Leith has emphasized the general similarity of the slate in 

 the great Iron River-Crystal Falls area and the Animikie slates 

 of the Cuyuna and Mesabi districts of Minnesota, and beheves that 

 "there is probably but one great slate formation of this type in the 

 Lake Superior region." Although this observation has little 

 bearing on the question of whether the Animikie is Middle or is 

 Upper Huronian, it may be observed that this similarity is marked 

 so far as concerns the slates which occur in areal association with 

 the iron formation, but does not extend to the great mass of slate 

 which occupies a large area of indefinite boundaries north and west 

 of the Crystal Falls-Iron River iron-bearing area. These rocks are 

 mainly gra5rwacke of uniform composition and appearance and are 

 not at all similar to the fine-grained gray and black pelites of the 

 Animikie series which are associated with the iron formation (Vul- 

 can) in the Iron River, Crystal Falls, Florence, and Menominee 

 districts and the Negaunee iron formation of the Marquette Range. 



