PETEOGEAPHICAL CHAEACTEE OF NEGAUNEE EOEMATIOJS'. '631 



Analyses of cherty sideriteH. 



I The aliuve determinations of water were made on the original sample. 



It is unusual to find exposures of the cherty siderite-slates wliich have 

 not been more or less affected by deep-seated alteration or liy weathering 

 jn-ocesses. As a consequence, the iron carbonates pass by gradations, on 

 the one hand into griinerite-magnetite-schists, and on the other into ferrugi- 

 nous slates, ferruginous chert, jasper, or iron ore. 



The griinenfe-magnetite-schists consist of alternating bands composed 

 of varying proportions of the minerals griinerite and magnetite and 

 quartz (PI. XYIII). Where least modified they have a structure precisely 



MON XXVIII- 



