PETEOGKAPHICAL CHAEACTEl! OF NEGAUNEE FORMATION. 365 



The reddish specidar ores pass <>-radually iuto tlie soft hematites. The 

 majority of the soft, ores have a distinct lamiuation. Many of tlieni on 

 freshly broken surfaces have a finely crystalline apjiearance. All give a 

 brilliant cherry-red streak. In hand specimen the pure hematites are bright- 

 red. The limonitic hematites differ from the red hematites in having a 

 brown color, due to the pi-esence of hydrated iron oxide. 



While a laminated or banded appearance of the ores is very general, 

 locally they are entirely without any such structure. Oftentimes the 

 massive varieties contain numerous cavities, varying from those of minute 

 size to those of considerable magnitude. These cavities are commonly 

 lined with crystals of hematite or magnetite, or by radiating needles of 

 hematite or the hydi-ated oxides of iron. Very often the interiors of these 

 cavities have a botryoidal appearance. In a few of the soft hematite mines 

 oxides of manganese occur in various forms, and in some places this 

 material is so concentrated as to furnish manganese ore. 



The magnetites and coarse specular hematites are confined to the 

 upper horizon of the Negaunee formation or to the basal horizon of 

 the overlying Ishpeming formation, and largely to the western part of the 

 district. The most common rock associated with these ores is jaspilite, 

 although in places it is a coarse, white, ferruginous chert. The fine-grained 

 specular ores are confined to the upper horizon of the iron formation, and 

 mainly to the eastern part of the district. The soft hematites are found at 

 middle or lower horizons of the Negaunee formation, associated with the 

 ferruginous slates or ferruginous cherts. 



It appears that the ferruginous slates, ferruginous cherts, jasper, and 

 ore form in the zone of weathering, and that the griinerite-magnetite-schists 

 develop iu the zone of deep-seated alteration. The difterent characters 

 are then due to original position within the formation and to subsequent 

 environment, rather than to difference in the original rock. 



In fullest section the Negaunee formation exhibits, therefore, the fol- 

 lowing stratigraphy: At the bottom are the sideritic slate and griinerite- 

 magnetite-slate; above these, ferruginous slate; above this, ferruginous 

 chert; and at the top of the formation, jaspilite. The iron ore may occur 

 at any horizon. While this is the common order, in a given localit}' one or 

 more of these members may be absent. 



