R. VAN HISE — PRE-( IMBRIAN OF Nil. BLACK HILLS. 



have been believed in the past to be a pan of this complex have turned out 

 upon a closer examination to belong to a later series. I have no theory to 

 bring forward t" explain the origin of 1 1 1 « - fundamental complex, but Buppi 

 that different parts of ii will be found to have diverse histories. 



This basement compli - i great in mass and so unique in character 



thai Professor [rving li:i~ insisted that the term A.rchean Bhould be restrict* d 

 to it. and that another term Bhould be introduced to cover the clastic -■ ri< - 

 which are later than this and earlier than Cambrian. The great thickn 

 of undoubted elastics belonging here, the United States Geological Survey 

 has collected together under the general term "Algonkian."f This term, 

 thus used, certainly covers independent series of vast thicknesses separated 

 by great unconformities. Using ii in this sense, and restricting A.rchean as 

 above, the Blates and Bchists of the Black Hills of Dakota clearly belong to 

 the Algonkian period. 



While this is undoubtedly true, it i- to I"- said that the most crystalline 

 mica-schists and mica-gneisses locally associated with and caught in the 



nite present a suggestive resemblance on a small scale to the rocks of the 

 fundamental complex.} When the whole world is taken into account, ii is 



-ihle. perhaps probable, thai the AJgonkian and Archean will be found 

 to be divisible only by a somewhal arbitrary line, just as are all other lines 

 limiting the periods. Even it' thi> should turn out to be the case, the value 



the separation upon the basis mentioned i- not lessened. It is, bowevi i . 



-aid that there is apparently i <• chance that a very \\ idespread break 



will be Bhown to exist between these two periods than anywhere else in the 



•logical column, with the possible exception of the break at the base of 

 the < lambrian. 



D, liv; nth 



-, pp. ii- 



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