338 



THE MAEQUETTE IKON-BEAEING DISTEICT. 



like the sideritic slates from which they grade, the gi'iinerite-mag-netite belts 

 having taken the place of the carbonate bands. In some places the griinerite- 

 inagnetite-schists are minutely banded, the alternate bands consisting of 

 dense, green griiuerite and of white or gi'ay chert, with but a small quan- 

 tity of magnetite. Certain important kinds appear to be composed almost 

 altogether of griinerite, with a little magnetite. In general, the griinerite- 

 magnetite-schists are found at low horizons, below the ferruginous chert and 

 jaspilite, i. e., at or near the same horizon as the sideritic slates. Frequently, 

 also, they are below intnxsive masses of greenstone. 



Analyses of four of the typical griinerite-magnetite-schists were made 

 in the chemical laboratory of the Greological Survey, the first by George 

 Steiger, the second and third by W. H. Melville, and the fourth by H. M. 

 Stokes. The material for the first analysis (specimen 21146, 1,200 steps N., 

 985 W., sec. 12, T. 47 N., R. 27 W.) was from the broad area of iron formation 

 southeast of Ishpeming; that for the second (specimen 16149, 1,475 steps 

 N., 150 W., sec. 11, T. 47 N., R. 27 W.), from Humboldt; that for the third 

 (specimen 16566, 1,555 steps N., 1,375 W., sec. 18, T. 47 N., R. 28 W.), 

 from a mile or two east of Humboldt Mountain ; and that for the fourth 

 (specimen 18938, 900 steps N., 50 W., sec. 20, T. 46 N., R. 30 W.), from 

 the Magnetic mine, at the northwest end of the Republic trough. 



Analyses of griinerile-magnetite-schisis. 



Loss 



SiOj 



AUG, 



FesOa 



FeO 



MnO 



CaO 



MgO 



CuO 



Na^iO 



P,05 



COj 



H2O (above 110°) , 



(1) 



2.42 

 26.49 



5.03 

 2.17 



(2) 



(3) 



0.67 

 46.94 

 .66 

 4.51 

 33.72 

 .31 

 3.22 

 6.64 



.16 



.07 



2.79 



1.40 

 49.70 

 1.35 

 3.10 

 37.19 

 .93 



Trace. 

 .12 



W 



46.25 

 .92 

 30.62 

 16.92 

 1.01 

 1.69 

 2.13 

 Trace. 



.07 

 .42 



