186 



THE MAKQUETTE IlJONBEAltlNG DISTRICT. 



origiual structure of the peridotite may still be detected, while in others 

 nothing can be seen but fibrous masses of ser])entine, irregular areas and 

 tiny veins of dolomite, and some magnetite and earthy products. When 

 the serpentine predominates, the rocks are well-characterized calcareous 

 serpentines; when the dolomite prevails, they become almost pure dolo- 

 mites. These latter rocks are not so abundant in quantit^'^ as the serpen- 

 tines are. They are found usually as veins cutting the latter rocks, and as 

 indefinitelv defined l)ands bordering cracks and joint planes in them. 



Analysis of the perUlotile from the Opin area. 



SiOi 



TiO, 



Al;03 



Cr.Ci 



Fe;03 



P'eO 



MnO 



NiO 



CaO 



SrO 



BaO 



WgO 



KoO 



Na,0 



H.O below 110- 

 HjO above 110 J 

 CO, 



P.Os 



39.37 



.66 



4.47 



.68 



4.96 



9.13 



.12 



.21 



3.70 



Trace. 



Trace. 



26.53 



.26 



.50 



.87 



7.08 



1.23 



.17 



Total 



No. 17972 ; from 1220 paces N., 500 paces W., of the soutlieast corner of sec. 27, T. 48 N., R. 27 W. 



FERRUGINOUS VEINS IN THE NORTHERN COMPLEX. 



At various places within the schist areas of the Northern Complex 

 there are small masses of ferruginous slate, ferruginous chert, and inaguetite- 

 griinerite-schist which are identical in hand specimen and in microscopical 

 character with similar rocks of the Negaunee iron formation. The best- 



