470 THE PENOKEE lEOJf-BEARING SEEIES. 



tlie lines of contacts between the iron-bearing- and the Keweenaw series 

 are followed for some distance, both with the Animiki6 and Penokee series, 

 this apparent conformity is found to be illusory ; that is, the Keweenaw 

 series is now in contact with one memlier of the underlying- series 

 and now with another, until in both districts at one or more ])laces the 

 entire iron-bearing series is entirely cut off, the Keweenaw rocks com- 

 ing directly in contact with the Basement Complex.' This means that 

 between the deposition of the Penokee and Animikie series and the outflows 

 of Keweenaw time there intervened a period of erosion which was sufficient 

 in places to entirely remove the two former ;nid to cut in some places deeply 

 into the older rocks themselves. There is, then, an inunense time gap 

 between these series and the overlying Keweenaw rocks, although this 

 unconformity does not approach in the length of time invohcd to tliat 

 separating- them from the underlying- schists and granites. 



The Aniiuikie series, in its most typical development, extends from 

 Gunflint lake, along the national boundary between Minnesota and Ontario, 

 to Tliunder bay, lake Superior. The Penokee series li^s npon the o])posite 

 side of lake Superior. The latter is a simple unfolded succession, di)ipiug- 

 to the northward under the lake. The Animikie is another sni-h succession, 

 dipping- to the southward under the same l)ody of water. There is, then, 

 little doubt, considering all the facts, that the two series represent a single 

 period in the history of the synclinal trough which forms the basin of lake 

 Superior.- The relations and likeness of the Penokee and the Animikie 

 series have been dwelt upon at length as sliowing the l>readth of the 

 geological basin in which the deposition of like rocks was taking place 

 simultaneously. The equivalency here shown is a long stej) in under- 

 standing the equivalency of other rocks in tlic lake Superior basin. 



Equivalency of Penokee and Marquette series. — A comparison of the 



' For full disciissioii of the pioof of the uiicoiifdriuitv between tlie Animikie ami Kewpeuaw 

 series see R. D. Irviuj^: Ou tlie ('las»iti<iitioii of the Karly Cambrian and pre-Cambrian Formations, 

 7th Annual Report IT. S. Ueol. Survey, jip. 417-423. if the Keweenaw series simjily were in contact 

 with the gneisses ami granites it might be held that we have only to do with an overlap, but its con- 

 tact — now with one horizon of the Animikie. now with another — can only be exjdained liy an uncou- 

 formity. 



'R. D. Irving: Copper-Bearing Rocks of Lake Superior, tJ. S. Geol. Survey, Monogra]di \ . 1883, 

 pp. 410-418. 



