P RE-CAM BRIAN FORMATIONS OF GWINN IRON DISTRICT 573 



Middle Huronian appears in the absence from its basal conglom- 

 erate of jasper fragments from the Negaunee formation so strongly 

 developed in the adjacent Marquette district. 



Escape from the correlations suggested in this paper involves a 

 disregard or subordination of the importance of the unconformity 

 separating the Gwinn and the Princeton series. There is no certain 

 evidence in this synclinorium of great structural discordance 

 between these two series but it may be and probably is as great as 

 that separating the Upper Huronian and the Middle Huronian series 

 of the Marquette district. Great structural discordance could 

 hardly be expected inasmuch as the main deformation took place 

 after the deposition of the Princeton series. Some structural 

 discordance is implied in the consideration that although the upper 

 slate member of the Gwinn series was probably not cut through in 

 this district, there was sufficient erosion in adjacent territory to 

 uncover the different members of the entire Gwinn series prior to 

 the deposition of the basal conglomerate of the Princeton series. 



