GENERAL GEOLOGY OF THE DISTRICT. 471 



Penokee ami Mai'([uette successions shows that between the Iwo there is a 

 very close correspondence. 



Unconforinably below the elastics of" those districts is a crystalline 

 Basement Ooinplox coni[)osed of schists, gneisses and gTanites. Within the 

 pre-Keweenawan elastics [n each district is a second physical break. In 

 the Penokee district the series below the bi'eak is known to be represented 

 only by a single formation, the Cherty limestone. That other higher 

 formations once here existed is indicated l)y the presence of fragments of 

 jasper and quartzite in the lowest horizon of the Quartz-slate. These jasper 

 fragments occur in the basal conglomerate of the Quartz-slate at Potato 

 river, at two localities near the Palms mine, and at one place in the Eastern 

 area. Usually the pebbles are not of large size, but occasionally they are 

 several inches in diameter. Quartzite pebbles are even more abundant 

 than those of jasper. It is, therefore, probable that the three sedimentary 

 formations of the Lower Marquette series were once represented b}' eqiiiva- 

 lent members in the Penokee district. 



The correspondence of the members of the penokee series jiroper 

 with those of the Upper Marquette is complete. The Upper Marquette and 

 Penokee series, looked at broadly, are great slate formations, l)oth of which 

 contain, near the base, an iron-bearing horizon. In the Penokee series 

 that portion of the slate ovei'lying the ore formation has been called the 

 Upper slate member, and that below it the Quartz-slate member. The 

 lower part of the Quartz-slate is a quartzite and conglomerate which cor- 

 responds to the quartzite and conglomerate forming the base of the upper 

 Marquette series. The upper most horizon of the Penokee Quartz-slate is a 

 narrow layer of 'persistent quartzite which does not appear to be repre- 

 sented in the Marquette district. The character of the ore-bearing me'm- 

 ber is identical in both districts, being unquestionably derived from a lean 

 cherty carbonate of iron. The characteristic rocks of l)()th are now the 

 iron carbonates, cherts containing bands and shots of ore, and the iron ores. 

 The chief differences between the two are that in the Penokee district the 

 actinolite-magnetite-schists are more prevalent, that the iron-bearing for- 

 mation is more persistent, and that its ore bodies are more abundant. Con- 

 nected with these facts is perhajjs the presence of the upper horizon of 



