56o 



EDWARD STEIDTMANN 



the Iron River and Crystal Falls districts. The granite intrusive 

 into them, they believe, is of the same age as their Presque Isle 

 granite of the Gogebic district. Wolf lake is situated between 

 the Iron River and Gogebic districts. 



Quaternary — Pleistocene glacial deposits 

 Ordovician and Cambrian — limestone and sandstone 



Algonkian — Keweenawan, probably represented by certain basic dikes which 

 cut all formations 



Upper Huronian 

 Princeton Series 



Slate, ferruginous slate, 

 chert and quartzite, quartz- 



ite 

 ^ Conglomerate graywacke 



\ Equivalent of Michi- 

 / gamme slate 



[Equivalent of Goodrich 

 < quartzite of Mar- 

 [ quette district 



Unconformity 



Middle Huronian 

 Gwtnn series 



Gray slate 

 Black slate 

 Iron formation 

 Gray slate 

 Black slate 



Equivalent of Negaunee 

 iron formation and Siamo 

 slate 



[Equivalent of Ajibik slate 



Arkose 

 Conglomerate 

 Unconformity 

 Archean system 

 Laurentian — Granite and greenstone, mainly granite 

 Keewatin 



Allen and Barrett^ find that the pre-Cambrian rocks at the 

 Little Lake Hills about seven miles east of the Gwinn district of 

 Michigan consist from the base upward of conglomerate, arkose, 

 and quartzite separated by an unconformity from a conglomerate 

 quartz slate and quartzite respectively. The strata appear to 

 be concordant, but the conglomerate near the middle of the column 

 is clearly basal. The lower series is correlated with the Middle 

 Huronian Gwinn series of the Gwinn district; the upper series with 

 the Upper Huronian-Princeton series of the aforementioned dis- 

 trict. The absence of iron formation in the Little Lake Hills, 

 Middle Huronian is thought by the writers to indicate the depth of 

 erosion of the Gwinn series before the Princeton series were laid 

 down. 



^ R. C. Allen and L. P. Barrett, "Evidence of the Middle-Upper Huronian Uncon- 

 formity in the Quartzite Hills at Little Lake, Michigan," Mich. Geol. Surv. Pub. i8 

 (1915), Geol. Ser. 15, pp. iS3-S9- 



