132 Van Hise — Attempt to harmonize some apparently 



of the Penokee district mica-schists have developed from these 

 slates, but the original condition of these rocks was essentially 

 like that of the unaltered phases.* 



Underlying both the Animikie and the Penokee Series is a 

 complex of granites and schists, the unconformity between 

 which and these series is of the most pronounced character. 

 That the Animikie Series is thus separated from the underly- 

 ing rocks has been seen by all who have studied it. Above 

 both series follow the Keweenaw rocks. In both regions, in 

 passing at any place from the underlying rocks to the Kewee- 

 naw Series in section, the two are in apparent conformity ; but, 

 when the lines of contacts between the iron- bearing and the 

 Keweenaw series are followed for some distance, both with the 

 Animikie and Penokee series, this apparent conformity is found 

 to be illusory. That is, the same member of the Keweenaw 

 Series is now found to come in contact with one member of the 

 underlying series and now with another, until in both regions at 

 one or more places the entire Iron-Bearing Series is cut off, the 

 Keweenaw rocks coming 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 remove the whole of the inferior series and to 

 cut in some places quite deeply into the Fundamental Com- 

 plex. There is then an immense time-gap between these series 

 and the overlying Keweenaw rocks, although this unconform- 

 ity does not approach in the length of time involved to that 

 separating them from the underlying schists and granites. 



The Animikie Series in its most typical development extend 

 from Gunflint Lake, on the National Boundary between 

 Minnesota and Ontario, to Thunder Bay, Lake Superior. The 

 Penokee Series lies upon the opposite side of Lake Superior. 

 The latter is a simple unfolded succession dipping to the north- 

 ward under the lake ; the Animikie is another such succession 

 dipping to the southward under the same body of water. 

 There is then little doubt, considering all the facts, that the 

 two series represent a single period in the geological history of 

 Lake Superior. The relations and likeness of the Penokee 

 and the Animikie Series have been dwelt upon at length as 

 showing the breadth of the geological basin in which the 

 deposition of like rocks was taking place simultaneously. 



*Upon the Origin of the Mica-Schists and Black Mica-Slates of the Penokee- 

 Gogebic Iron-Bearing Series, C. R. Van Hise: this Journal, III, xxxi, 453-459, 

 1886. 



f For full discussion of the proof of the unconformity between the Animikie and 

 Keweenaw Series, see On the Classification of the Early Cambrian and Pre-Cam- 

 brian Formations, R. D. Irving: 7th Ann. Kept., U. S. Geol. Survey, pp. 4L7-423. 



