PRE-KEWEENAWAN FORMATIONS 701 



Relations of the Copps group to the Upper Huronian {Animikie) .— 

 It has been stated that the unconformity separating the Copps 

 and Animikie groups is one of the first order of magnitude. This 

 conclusion rests on the following evidence : 



1. The bottom horizon of the Copps group is a true basal con- 

 glomerate. 



2. The Presque Isle granite intrudes the Animikie but yields 

 bowlders and matrix to the basal conglomerate of the Copps. 



3. The Copps group is in great structural discordance with the 

 Animikie. 



4. The areal relationships are those of unconformity. 



5. Volcanic rocks are characteristic of the Animikie and are not 

 known to occur in the Copps formation. 



The only one of these evidences remaining to be discussed refers 

 to the great structural discordance between the Upper and Middle 

 Huronian groups. At this point the reader is referred to the 

 accompanying map and sections which exhibit the areal and 

 structural relationships much more satisfactorily than any amount 

 of written description could possibly do. It should be stated in 

 this connection that the structural sections are based to a great 

 extent on drill records, as are also the areal relationships of the 

 Ironwood and Palms formations in sections 20, 21, and 22, T. 47 N., 

 R. 43 W. It is not held that other interpretations of structure as 

 far as concerns merely the details are not possible, but that those 

 interpretations which have due regard to the facts of occurrence 

 must coincide in major outline and cannot fail to estabhsh the 

 main fact of great structural discordance between the Upper and 

 Middle Huronian groups. The data for structural sections are 

 unusually ample because of the large amount of drilHng and test- 

 pitting which has been executed, fortunately in the most critical 

 area, from the geologic point of view, on the east end of the range. 



The dominant structure of the Animikie group of the Gogebic 

 Range is that of a simple monocline in approximate structural 

 parallelism with the Keweenawan series. Pre-Keweenawan defor- 

 mation by folding is conspicuous only in the vicinity of Wakefield 

 and on the east end of the range. Without venturing an opinion 

 as to the vicinity of Wakefield, to which locaKty our field studies 



