726 C. K. LEITH AND R. C. ALLEN 



judgment, the proposed change runs squarely across certain funda- 

 mental facts which will not give way to the new hypothesis, however 

 attractive it may be. Allen's argument is based (i) on the sup- 

 posed equivalence of the Iron River slates (and iron formation) 

 with the Animikie in the Gogebic district, (2) on the supposed 

 equivalence of the Iron River slates with the Middle Huronian of 

 the Marquette district. 



1. That the slates and iron formation of the Iron River district 

 are to be correlated with the Animikie of the Gogebic district is the 

 conclusion that has been reached by nearly all investigators, and in 

 the absence of definite proof to the contrary must stand. I would 

 suggest, however, that the recent discovery of the Copps series 

 opens up an alternative, that the Iron River series is equivalent 

 to the new Copps series and both equivalent to the Upper Huronian 

 of the Marquette district. This would have the effect of throwing 

 the Animikie down a step in the scale, but would not disturb the 

 local correlation between the Marquette and Crystal Falls-Iron 

 River districts. This is only a possibihty, for outcrops are few in 

 the connecting areas, metamorphism due to intrusion has been 

 intense, and I see no likelihood for some years of sufficient informa- 

 tion being available to develop the evidence necessary for this 

 possible conclusion. 



2. That the slates and iron formation of the Iron River-Crystal 

 Falls district are equivalent to the Negaunee (Middle Huronian) of 

 the Marquette district is a possibility which has been often con- 

 sidered discarded. Practically no new evidence has been brought 

 up in the crucial area between the Iron River-Crystal Falls district 

 and the Marquette district, and such additional evidence as there 

 is, is damaging to the conception of the new hypothesis. 



The great essential fact of the situation, which cannot be 

 ignored, is that in the Marquette district the Negaunee iron forma- 

 tion (Middle Huronian) is unconformably below a great slate series 

 (Michigamme slates. Upper Huronian) which contains lenses of iron 

 formation identically like those in the Crystal Falls and Iron River 

 districts, and contrasting with the Negaunee iron formation of the 

 Negaunee. The Michigamme slate of the Marquette district is all 

 but proved to be the same as that in the Iron River and Crystal 



