472 THE PENOKEE IRON BEARING SERIES. 



qiiartzite in tlie Quartz-slate, which shows that a clearing up of the waters 

 occurred before the beginning of deposition of the iron-bearing sediments. 

 A still further analogy between the Penokee and Upper Marquette series 

 is the presence in both of abundant surface volcanics. We have, then, in 

 the two districts the following parallel descending pre-Keweeuawan suc- 

 cession : 



Penokee. Marquette. 



Upper slate, rather extensively mica-schist. 



Iron-beariug (brmation. 



Lower sl.ite; lower part qiiartzite or 

 qnartziti' conglomerate, bearing frag- 

 ments of lower series, either lower Mar- 

 quette or Basement Complex. 



Upper slate, locally mica-schist. 



Iron-bearing formation. 



Qnartz-slate ; upper horizon persistent 

 quartzite; central mass a slate; lower 

 part often conglomeratic, Ijearing frag- 

 ments of lower series, either Cherty 

 limestone or Basement Complex, and 

 locally a quartzite. 



Unconformity. 



Eroded away. 



Limestone. 



Unconformity. 



Basement complex. 



Unconformity. 

 Iron-be.'iring forui:iti<m. 

 Limestone ami lower i|uartzite. 

 TTni'.onformity. 

 Bnseiiient e(iiiii)lex. 



Comparison, with oilier series. — As is well known, in the region about 

 lake Superior are other areas containing liitiestone, quartzites, graywacke, 

 graywacke-slates, mica-slates, mica-schists, volcanic elastics, and the peculiar 

 phases of rock of the iron-bearing formations. The positions of these various 

 areas as shown upon PI. i, are designated, respectively, by H, Ho, H„ H4, 

 etc. These have been kno\fn in the past as the original Huronian district, 

 the Marquette, Felch Mountain, Menominee iron-l)earing districts, tlie 8t. 

 Louis slates, the Chippewa valley quartzites, the Black river Iron-bearing 

 schists, the Baraboo quartzites, the Sioux quartzites, and the folded schists 

 of "Canada, including the Vermilion series. 



The relations of these series to one another and to the Penokee series, 

 less closely related with the Penokee district than are the Animikie and the 

 Marquette, are fully considered in a bulletin of the United States Geologi- 

 cal Survey on the Algonkian and Archean.' As a result of the discussion 

 there given, the relations of the series of these different districts are talni- 

 lated as follows : 



'C. K. Van Hiser Correlation papers, Algonkian and Archean. Bull. 86, U. S. Geol. Survey. 



