366 THE MARQUETTE IRON-BEAEING DISTRICT. 



For instance, at Republic (Atlas Sheet XI) only the griinerite- 

 magnetite-scliists, the ferruginous chert, and the jaspilite are found. South 

 of the Saginaw mine (Atlas Sheet XXVI), at the base, is the griinerite- 

 magnetite-schist; at the intermediate horizons, the ferruginous chert; and at 

 the top, the jaspilite. South of Palmer (Atlas Sheet XXXII) the jaspilite 

 occupies the whole breadth of the formation between the Goodrich quartz- 

 ite and the Ajibik quartzite. Farther to the east, however, where the 

 formation has a greater thickness, the ferruginous chert occurs below the 

 jaspilite. At and south of Negaunee (Atlas Sheets XXVIII and XXXI) 

 the full succession is found. Beginning at the Jackson mine and passing 

 southward, we find at the top of the formation magnificent exposures of 

 iaspilite; below this are numerous open pits, which give typical exposures 

 of the ferruginous chert. This grades down into the ferruginous slate of 

 the Grrand Rapids mine, and continuing southward, we find within the 

 valleys between the greenstones the griinerite-magnetite-schists and the 

 very little altered sideritic slate. 



Microscopical. — Tlie kiuds of rocks found in the iron-bearing member of 

 the Lower Marquette series and their relations to one another are very 

 similar to those of the iron-bearing member of the Penokee and Animikie 

 series, Avhich have been described in great detail. Also, the microscopical 

 characters of the different phases of rocks are similar to those of the Peno- 

 kee series. In fact, so remarkable is the likeness that, with a restatement of 

 localities, what has been written in reference to the Penokee and Animikie 

 iron formations might be applied almost verbatim to the Marquette iron- 

 bearing formation. Therefore, for a detailed description of the different 

 phases of the iron-bearing formation and the manner in which the original 

 rock grades into the other phases, reference is made to Mon. U. S. Geol. 

 Survey, Vol. XIX, Chapter V, pages 182-268. 



A very brief description will, however, be given of the general char- 

 acter of the different phases of the iron-bearing formation, and a more 

 detailed statement will be made in reference to those points in which there 

 are differences between the Lower Marquette and the Penokee iron-bearing 

 formations. 



In the purest phases of chert y sidcrife-sJate (PI. XVII) there is a contin- 

 uous mass of siderite, which contains separate granules or irregular, complex 



