CHAPTER V. 



By E, D. Ikvino and O. R. Van Hise. 



THE IRON-BEARING MEMBER. 



Section I. Details. 



Applicability (if the name. Abruptness of transition from the underlying Quartz-slate member. 

 GecifiTapliieal extent. Topojiiapliical features. Thiekuess. General petrograpbical eliaraeter. 

 Distribution of tbe tlner types of roik. Xliiniscopical eliaraeter of the cherty iron earbouates. 

 Microscopical clnuMiter of the ferruginous slates and ferrugimuis cherts. Mi<rosr(i|ii(:i] eliar- 

 aeter of the actiuolitic slates. Tabulation of petroj;ra))hical observatious. 

 Seetion II. Origin of the Roeks of the Iron-bearing Member. 



Tbe original rock. The ferruginous stales. The ferruginous cherts. The .ai'tinolitic slates. 

 Section III. The Aniniikie Iron-bearing .Series. 



The cherty iron carbonates. The ferruginous slates. Tlie ferruginous cherts. The aetinolitic 

 slates. (Jeneral. 

 Section IV. The Iron Ores. 



Position of the ores in the Iron-bearing nii'iubcr. Dikes in Iron-bearing member. Position of ore 

 in referenei- to tbe dikes. Kock aliove the ore. Practieal deilnetions to be applied in prospeiting 

 and mining. Nature of the roeks of the Iroii-be iring nn^jiiber adjacent to the ore bodies. The 

 character of the ore. A particular occurrence of iron ore. Chemislry of tbe process of concen- 

 tratiou. Time at which concentration of the main ore bodies occurred. Process of concentra- 

 tion. Exceptional localities. Probable extent in depth of ore bodies. Emmons on ore deposits. 

 Iron ores in other parts of lakr .'>u[ierior country. Summary of more imjiortant conclusions. 



SECTION I. DETAILS. 



AppVivahUUji (if the )iiinic. — The name given to this meiiiber is jnstified 

 by its large content of iron. Certain pliases of the belt contain little or no 

 iron, being wholly made nj) of silica in one tunn or another, l)nt such 

 phases have no ver\' great extent, thei-e being nearly always present at 

 least a little iron oxiile, while throughout the gceater jxtrtion of the belt 

 tlie content of metallic iron certainl}' exceeils 10 ])cr cent. Very consiiler- 

 able thicknesses are met with in which the amount of iron reaches 20, 30, 



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