_'l" i;. VAN HISE — PRE-CAMBRIAN OF THE BLACK EULLS. 



Beparate areas in the Bame geological basin, as the Penokee series on the 

 south shore and the A.nimikie series on the north Bhore of Lake Superior, it 

 can safely be asserted thai these groups of formations Btand as equivalent 

 with each other, at least iii a broad way. It cannot l>c said to be proven 

 that all the Lake Superior iron-bearing series represent the same geological 

 period. All have, however, been placed by most writers as a part of the 

 Huronian, and were believed to be equivalent in a general way by Professor 

 [rving. The Minnesota geologists maintain that the Vermilion iron-bearing 

 series is older than the A.nimikie. When there is as yet difference of opinion 

 as to correlation of the iron-bearing series in the Lake Superior region 

 itself, no definite statemenl can be made as to the equivalence to them of bo 

 distant a series of rock- as the Black Hills pre-Cambrian. When the 

 structure of the Black Hills rocks is made out it may be ascertained that we 

 have tlnr.- a set of formations which are not only lithologically alike, but 

 occur in the same order a> certain or all of the iron-bearing series in the 

 Lake Superior country. If this proves to be the case, the evidence for 

 placing such groups of rock opposite each other will be very strong indeed. 

 Iii the meantime, until it i- more definitely decided how far lithological cor- 

 relations can be trusted; it can only he said that the pre-Cambrian rocks of 

 the Black Hills probably are the equivalent of a part or all of theHuronian 

 iron-bearing si ries of Lake Superior. 



Summary of < !on< lusions. 



The Black Hills -dates and schists cannot be divided into two series with 

 the surface distribution and upon the lithological differences given by New- 

 ton. These two classes of rock- grade into each other. 



The sedimentary rocks have all been so metamorphosed thai the most 

 marked structures are secondary phenomena, which are entirely independent 

 of original sedimentation. The true bedding is in many places yel discov- 

 ble by an alternation of hand- which differ in degrees of coarseness and in 

 composition. These bands are cut by the cleavage and foliation. It follows 

 thai the thickness of the serii - is yel to be ascertained. 



The largesl area of crystalline schists is a broad zone about the granite, 

 striking parallel to and dipping at a high angle away from it. A Becond 



important area i- aboul I >eadwood. 



tive evidence was found of the truth of Newton's conclusion that 

 the main n ranite in the Bediraentaries of pre-Cambrian age is 



l is every reason to believe thai the basic eruptive rock-. 



hornblende-schists and diorites, are even more ancient. They 



partake to some extent of the structure of the quartzites, Blates, and Bchists 



in which ihej in tained, and were regarded bj Newton as au integral 



part of these rocks. The} are never found in the granite. 



