432 TOE MARQUETTE IR02>-BEA1I1NG DISTEICT. 



In tJiiu secticni the conglomerates of the Saginaw range <\o not differ 

 from those oi the Ishpeniing area. In the varieties which are most mashed, 

 and therefore most ch)selv resemble the original jasper, the presence of 

 small, distincth' j-muided, and often enlarged fragmental grains of quartz 

 and secondar}' sericite shows the recomposed character of the rock. It 

 tlierefore apj)ears that while nearl}' all of the detritus came from the sub- 

 jacent Negaunee formation, the sea brought in fragmental material from a 

 more distant source. In the fine-grained quartz-conglomerates and the 

 coarser quartzites much chert and jasper are seen, and a large amount of 

 secondary iron oxide is in the matrix. Certain nonferruginous quartzites 

 are strongly feldspathic. Tliese grains and those of the quartz are of large 

 size, some of them almost pebble-like. It therefore appears that in the 

 shallow sea of this time, after the Negaunee formation was Ijuried to a 

 depth of a few hundred feet, most of the detritus came from the gneis- 

 soid granites of the Archean. The slides of the slate ores and hematitic 

 schists of the Goodrich mine show the silky, tibrous appearance of the 

 mashed hematite and the crystals of secondary magnetite. The recom- 

 posed character of the ore is indicated b}' occasional small grains of plainly 

 fragmental (juartz and by flakes of secondary sericite. The latter mineral 

 is rarely, if ever, present in the ore belonging to the Negaunee formation. 



Mount Humboldt area. — Wcst of tlic Fitcli miuc there are no known exposures 

 of the Ishpeming' formation until north of the Mount Humboldt ridge, in 

 sec. IS, T. 47 N., R. 28 W. From this place outcrops of the formation 

 are found at frequent intervals to some distance west of the Barron mine 

 (Atlas Sheets XVI and XIX). The oval Humboldt ridge is therefore sur- 

 rounded, except on the souths by concentric layers of the Goodrich quartzite. 

 The lowest horizon of the quartzite is represented by a quartz, jasper, 

 and ore conglomerate similar to that at the Goodrich mine. This ma>' be 

 seen in a cut on and adjacent to the Republic branch of the Duluth, South 

 Shore and Atlantic Railway, and at the various open pits. This conglom- 

 erate, in common with that at the Goodrich and at Palmer, differs from that 

 of the Ishj)eming area in containing more material derived from the 

 Archean, and particularly large ])el)l)les of white, coarsely cr}'stalline quartz. 

 The mashing phenomena spoken of as occurring at the Goodrich are even 



