334 



THE MARQUETTE IKOX BEARING DISTRICT. 



forinatious. In j)as.sini;' upward within the fragmental t'onnatiou noiitVag- 

 meiital material begins to a])pear and the shite or quartzite becomes more 

 or less feiTug'inoiis, and by an increase of the ferruginous constituent it 

 grades up into the iron-bearing forniation. This gradation may occur within 

 a comparatively few feet, or it may require a thickness of 100 or more feet. 

 More often than not the gradation is not a reg-ular transition, liut is accom- 

 plished by interlamiiiations of material which is mainly fragmental and 



Fig. 19. — Folded ferruginous ihert of Starwest mine. 



material which is mainly nonfragmental. These interstratiiicati(ins are 

 particularly well shown at the top of the Ajibik quartzite south of Palmer 

 and at the top of the 8ianio slate east of Negaunee. In different places 

 the lowest horizon of the Negaunee formation mav be the sideritic slate, 

 the griinerite-magnetic-schist, the ferruginous chert, or the jasper. 



The overlying fonnation is the Ishpeming formation of the Upper 

 Marquette series. The relations between the two are those of uuconfonnity, 

 there having been considerable orogenic movement and deep erosion after 



