294 THE PENOKEE IRON BEARING SERIES. 



bodies, like those of the Gogebic district, are secondary concentrations 

 produced from carbonates by downwnrd flowing waters and resting npon 

 impervious formations.' These impervious formations, known as soap- 

 stones, are frequently altered basic eruptives, but in certain jjlaces they 

 are clearly sheared clayey phases of sedimentary rocks. It is an interest- 

 ing illustration of the uniformity of nature's processes that later investi- 

 gations have sliown tliat the iron-ore liodies in the other districts- of 

 the lake Superior country have an origin like those of the Penokee- 

 Gogebic series. 



Summary of more important conclusiovs. — Tlie Iron-])earing member is 

 separated from the Quartz-slate member below it and the Upper slate 

 member above it because it is nonfr^igmental, while they ai'e fragmental 

 sediments. 



It consists of three main types of rock: (1) cherty iron carbonate; (2) 

 feiTuginous slates and cherts, and (3) actinolitic and magnetitic slates. 



The cherty iron carbonates represent the original condition of the 

 whole member, the other types having reached their present condition by 

 a series of subsequent alterations. 



In the change of cherty iron carbonate to ferruginous slates and cherts 

 the siderite has been oxidized, and to some extent taken into solution 

 and redeposited in other places. The silica originally 2:)resent lias been 

 reaiTanged, and in many places additional silica has entered. 



In the alteration of tlie cherty iron carljonate to actinolitic slates the 

 oxidation of the protoxide of iron in the carbonate has not been complete, 

 and thus magnetite has been formed. At the time of the rearrangement 

 and introdi;ction of silica a portion of it has united with tlie bases present 

 and has formed actinolite. 



The iron ores are found in the lower horizons of the Iron-bearing mem- 

 ber, most of the deposits resting upon the upjjer quartzite of the quartz-slate 

 formation. Those deposits Avhich are not at the base of the mendjer have 

 also somewhat regular foot walls, which dip to the north like the quartzite 



' Villi Hise, C. R. : The Iron Ores of the MarqnettR District of Michigan ; Am. Jour. Sci., 3d 

 series, vol. 43, 1892, \t\t. 116-132. Also The Iron Ores of the Lake Superior Kegion ; Wis. Acad. Sci., 

 Arts, and Letters, voL 8, pp. 219-228. 



