384 THE MARQUETTE IllOX-BEARING DISTRICT. 



places they are folded into a series of minor isoeliual folds, the axes of which 

 pitch to the north with about the general dip of the formation. In horizontal 

 ])lan the beds of one of the folds are shown by fig. 23. On the north slope of 

 the ridge of the grunerite-maguetite-schists this material grades rapidly into 

 the ferruginous chert. A number of subordinate folds are observable at the 

 oj)en pits of the Saginaw mine. These have superimposed isoclinal folds of 

 the third order. As a result of the many nuuor foldings and crinklings, 

 the rocks are nmch broken. The strata of these minor folds were truncated 

 hv the inter- Marquette erosion, and consequently the Goodrich quartzite 

 cuts across the bedding of the Negaunee formation at various angles. For 

 instance, at the old Goodrich mine, at one place the strike of the jas])er is 

 almost parallel to that of the overlying Goodrich quartzite, but a little dis- 

 tance to the east abuts perpendicularly against it (figs. 20 and 21, p. 335). 



Fio. 23 Hoiiziuitul pliin of one of the minor pitchh 



irriinerite-ina^netite-scliist. 



Escanaba River area. WcSt of tllC Fitcll Uliue, SeC. 24, T. 47 X., R. 28 W., 



there are no exposures of the iron-bearing formation for more tlian 4 miles. 

 However, in sec. 20, just north of the Escanaba River, and in sec. 21,T.47 N., 

 R. 28 W. (Atlas Sheet XX), are exposures of griinei-ite- magnetite -schist, 

 which grade V)elow into a novaculitic rock or into a biotite-slate. These 

 are apjtarentlv transition varieties between the Negaunee formation and the 

 Ajibik quartzite. These biotite-slates are very similar to the transition rocks 

 between the Negaunee forinatiou and the Siamo slate at ^Michigamme. 



In thin section the griinerite-magnetite-schists are in all respects 

 similar to the far more extensive exposures of Mount Humboldt, described 

 innnediatelv lielow. The biotite-.slates are identical witli those near the top 

 of the Siamo formation at Michigannne, even in the matter of the develop- 

 ment of a certain amount of hornblende and garnet. The uovaculite, 

 which occurs at one place, has a fine-grained quartzose background, and 

 between the particles are innumerable minute flakes of sericite. Coarser 



