424 THE MARQUETTE IKON-BEARINa DISTRICT. 



NE. J see. 31, in a course somewhat south of east, into the SW. ^ sec. 33, 

 a distance of about 2 miles. This ridoe for the most of the distance has an 

 abrupt soutliward-facing slope, which overlooks swampy land to the south. 

 The north side of the ridge is distinctly but not so sharply marked. For the 

 most part this ridge is composed of typical griinerite-magnetite-schists and 

 griiuerite-magnetite-rocks of the Bijiki horizon. However, where tlie ridge 

 breaks down upon its west end, in the SE. J sec. 31, adjacent to the road, at 

 the bottom and central parts of the exposure are conglomerates containing- 

 fragments of chert, coarse quartzites, and fine-grained novacnlites; and schis- 

 tose and dolomitic graywackes and shales intermediate between the fore- 

 going and the Bijiki schists. The change from the fragmental rocks to the 

 Bijiki schist takes place very quickly. The elastics are in most respects 

 like those at the bottom of the Bijiki schist at the Spurr and Michigamme 

 mines, and they doubtless mark the lowest stratum found in this anticlinal 

 ridge. The quartzites and novacnlites are much brecciated by the sharp 

 folding. To the south of the fragmental rocks are tj'pical griinerite- 

 magnetite-schists. To the north the Bijiki rocks are very quartzose, and 

 griinerite is subordinate. Both north and south they show extreme plica- 

 tion, and occasionally brecciation. In places the schistosity does not 

 correspond with the bedding. 



In thin section the rocks of this ridge are in almost every respect 

 identical with those of Spurr and Michigamme. The siliceous layers 

 between the griiuerite-magnetite layers are very often composed of crystal- 

 outlined grains similar to those of the Negaunee formation at the Spurr 

 and Michigamme mines. In coarseness of crystallization the quartz of the 

 two formations is identical. ( )n account of their crystal outlines the grains 

 do not intei-lock, and the rocks are therefore rather friable. In some sections 

 films of hematite occur everywhere between the grains, thus giving a con- 

 tinuous net-like area of translucent red hematite, the spaces between being 

 occupied by the pellucid quartz. This is best seen in the sections from the 

 north side of the ridge, where the griinerite is rather sparse and quartz is 

 the predominant constituent. 



Boston and Dexter area. In paSSlug tO tllC eaSt, tllC UCXt eXpOSUreS foUud 



are those in the neiffliborhood of the Boston and Dexter mines and at 



