DEPOSITION OF THE UrPEE MARQUETTE SEPJES. 565 



The area over wliicli the voh-auic material wa.s deposited j^i-adually grew, 

 reaching east as tar as Stoueville and west as far as Champion. These 

 more remote deposits are comparatively thin, and show evidence of water 

 arrangement. As the lavas and tuifs were jnled up, subsidence, possibly 

 due to the burdening of the crust, went on, so that there resulted a gxeat 

 bend of the adjacent formations to the southward. How far to the south 

 and to the north these volcanoes were felt we do not know, but the slates 

 to the north indicate that their ashes reached to the extreme northern part 

 of the district. This volcanic activity lasted for some time ; for, beginning- 

 in the time of the Goodrich quartzite, it did not cease until a considerable 

 thickness of the Michigamme .slate had been deposited. Contemporaneously 

 with the extrusives, it is probable that intrusives penetrated the Basement 

 Complex and the Lower Marquette series. 



In the western part of the district the Goodrich quartzite grades upward 

 into a g-riinei'ite-magnetite-schist (the Bijiki schist), and this into a ferriferous 

 slate, often sideritic. In the eastern jjai't of the district the Bijiki schist 

 may exist, but exposures have not been found. As the schist is regarded 

 as developing from a sideritic slate, it apjjears that following the deposition 

 of the sandstone there were waters favorable to the deposition of a non- 

 fragmental sideritic formation — that is, the conditions for the production 

 of the Negaunee formation of the Lower Marquette were repeated, but 

 not Avitli perfection, for the ferruginous slates in much of the district were 

 mingled with greater or less quantities of mechanical sediments. These 

 are more abundant in the eastern end of the area than in the western, 

 where a considerable belt of griinerite-magnetite-schist is comparatively 

 free from mechanical sediments and might be maj^ped as a narrow separate 

 formation. 



The zone of ferruginous shales was a})parenth' of variable thickness. 

 It was followed above by ordinary shales, which, however, are locally 

 feiTuginous. Also with the shales was deposited much organic matter, 

 as is shown by the fact that the resultant slates and schists are anthra- 

 citic or graphitic. These carbonaceous rocks are particularly abundant 

 at the horizons which are heavily ferruginous, and thus confirm the sugges- 

 tion made in considering the Negaunee formation, that organic matter 



