(GEOLOGICAL EXJ'LOKATIOXS AND LITEKATURE. 69 



BioriUc group. — . . . The extension of tlie snrvey into the Gogebic (lis 

 trict showed to nie ;i ix-ircct ;inah>8y in the structure of tlic Ilnronian series with the 

 MiiHiuette or tlu' ^Menominee region. North of tlie granite range previously men 

 tioued, iu many, but not in all, localities a large body of schistose and massive dioritic 

 rocks overlies it, dipping to the north, and. forms the base on which the iron-bearing 

 roi'ks repose. More rarely the dioritic rock belt is found missing and the iron rocks 

 follow immediately above the granite. The dioritic rock group there amounts to a 

 considerable thickness. Most of the diorites are fine grained, and some of them very 

 light colored, almost totally composed of granular plagioclase. Itocks of this kind are 

 largely exposed along the north line of Sec. 2.3, T. 47, R. 44, associated with singular 

 compact rock belts of coarsely brecciated structure, composed of large and small 

 angular blocks of various kinds of diorite cemeuted by a seme iuterstitial mass very 

 similar in composition to the inclosed dioritic fragments. In this cement numerous 

 milky jjlagioclase crystals of large size, or also rounded concretionary needles of 

 feldspar, have segregated. Calcsi)ar likewise sometinu's enters freely into the composi- 

 tion. The cementing gToundmass exhibits a distinct fluidal structure, as if the rock 

 fragments had been stirred into it while it had the plasticity of dough. The fresh- 

 fractured rock resembles a compact porphyritic diorite, as the color of the rock frag- 

 ments and the cement does not differ much, but on the weathered faces of the rock 

 the brecciated coiaposition and the fluidal structure of the cement become very obvious. 



Large bluffs of the same kind of breccia are also exposed on the side of the trail 

 near Mr. Gillis's camp in T. 47, R. 4.'5, along the north line of Section 2.3; it forms there 

 the foot- wall of the galena- bearing quartzite formation, whose lowest beds are a coarse 

 conglomerate of quartz pebbles of various color. South of these outcrops a large 

 succession of massive and schistose dioritic beds follows, then granite follows in close 

 contact with them. 



Iron Ore f/roup. — . . . The eastern portion of the range, extending from 

 lake Gogebic to the Montreal river across the center part of the ranges 44, 45,' 4U, 

 and 47, of the Town tier 47, did not prove to be much charged with iron ore this side 

 of Sunday lake, but west of it so far as Montreal river it was found to be ricJier, and 

 in a number of localities iron ore of a very good quality and in paying quantities is 

 so far demonstrated to be i)resent; but no actual mine has yet been opened, as these 

 remote places must first be brought into communication with the outside world bj- 

 the construction of a railroad, which is surveyed but only partly built at this 

 time. . . . 



The ore-bearing strata displayed in the Menominee region, on the nortii side of 

 the Quinnesec ore range, are in all pmbability a perfect counterpart of those of the 

 Gogebic regioji. Here, as well as there, a large belt of limestone forms the base of 

 the series; the ore in both localities is to a great extent limonitic ore; in both i)laces 

 aie graphitic schists associated with the ore deposits; and in the Penokee region 



