PRE-CAM BRIAN LITERATURE OF NORTH AMERICA 567 



revision of the classification by Van Hise and Leith. The essentials 

 of the stratigraphic classification by Hotchkiss follow: 



Keweenawan sandstones and conglomerates overlain by basic flows 



Unconformity 



f Graywacke slates 

 Tyler gray^vacke slate J Iron carbonate slates 



0-2 miles thick 1 Pabst member-cherty and fragmental 



[ slate beds 



Unconformity 



Upper Ironwood /Anvil wavy-bedded ferruginous chert member 



formation \Pence even-bedded ferruginous slate member 



Slight unconformity 



Lower Ironwood 

 formation 



Norrie wavy-bedded ferruginous chert member 

 Yale roember — interbedded ferruginous cherts 



and ferruginous slates 

 Plymouth member — wavy-bedded ferruginous 



chert (most mines located on this member) 



Palms quartzite 400 feet to 800 feet 



Unconformity 



Bad River cherty dolomite with quartzite below in eastern part of district 



Unconformity 



Granite and green schist both of igneous origin 



The unconformities v^^ithin the Ironwood formation and between 

 the Tyler slate and the Ironwood formation have not been described 

 before. Their existence is inferred from basal conglomerates and 

 evidences of erosion of the members underlying the unconformity. 



Lane^ finds that the strata on the east side of the Copper range 

 were uplifted and the eastern sandstone deposited on them. The 

 Trap range subsequently overrode the sandstones in places several 

 hundred feet. 



Leonard^ states that pre-Cambrian granite struck in wells of the 

 Red River valley is the only known pre-Cambrian rock of North 

 Dakota. 



^A. C. Lane, "Abstract," Bull. Geol. Soc. of America, Vol. XXIV (1913), 

 p. 718. 



^A. G.Leonard, "The Geology of North Dakota," Jour. Geol, Vol. XXXVII 

 (1919), pp. 1-27. 



