704 C. K. LEITH AND R. C. ALLEN 



correlation than that heretofore used. Two main possibihties 

 present themselves: (i) that the Copps represents a fourth Huro- 

 nian series between the Animikie and Keweenawan; (2) that there 

 are three Huronian series, and that the Copps formation may be 

 equivalent to certain series elsewhere in Michigan, now otherwise 

 correlated. 



1. CORRELATION ON THE ASSUMPTION THAT THE COPPS FORMATION 

 REPRESENTS A FOURTH HURONIAN SERIES BETWEEN THE 

 ANIMIKIE AND KEWEENAWAN 



If the Copps series be regarded as the remnant of a much larger 

 series that has everywhere else been removed by erosion, it may 

 be necessary to give it a position of the same general order as that 

 of the Animikie or Upper Huronian, with the result that the 

 Huronian series of Lake Superior become relatively lowered 

 throughout the column, which would involve some changes in 

 names. There would then be four Huronian series instead of 

 three. The evidence, as it is, seems to afford too sHght a basis for 

 moving downward all the rest of the formations and introducing 

 sweeping changes in nomenclature. The names now used have 

 come to have well-understood significance, and well express the 

 principal similarities and relationships of the pre-Cambrian series. 

 When the extent and relationships of the Copps series can be more 

 fully demonstrated it may be desirable to introduce such sweeping 

 changes. To do so now would be premature and would almost 

 inevitably require further changes when the significance of the 

 Copps formation becomes more fully understood. 



2. CORRELATION ON THE ASSUMPTION THAT THERE ARE THREE 

 HURONIAN SERIES AND THAT THE COPPS FORMATION MAY BE 

 EQUIVALENT TO CERTAIN SERIES NOW OTHERWISE CORRELATED 



Allen and Barrett regard the Copps formation as the equivalent 

 of the Upper Marquette series, the Princeton series,^ and certain 

 formations in other districts above the Animikie which are believed 

 to be, as in the Gogebic district, below the Keweenawan. Leith 



'^ R. C. Allen, "Correlation and Structure of the Pre-Cambrian Formations of the 

 Gwinn Iron-bearing District of Michigan," Jour. Geol., XXII (1914), 560-73. 



