196 THE TENOKEE IKON-BEAEING SEEIES. 



predominating one in all this class of rocks, nevertheless analyses show 

 that some of the sesquioxide is usually mingled with it, the presence 

 of which oxide indeed is not infrequently evident to the naked eye in 

 the more ferruginous varieties, the luster of specular iron and a red- 

 dish or purplish tint in the powder both testifying- to its presence In 

 the less ferruginous portions of these phases the sesquioxide is less 

 plentiful, but at times the siliceous seams present a dull reddish or jasjiery 

 appearance froyi the presence of hematite. In one vicinity in the eastern 

 portion of the district a bright red jasper is thinly laminated with a typical 

 actinolitic niagnetitic slate, but this is unusual. The ordinary occurrence 

 in the lake Superior region of the bright red phase of nonfragmental 

 silica, commonly -spoken of as jasper, is in direct association with the 

 more brilliantly lustered, steely, specular iron ores. Such bright cglored 

 jaspers only rarely occur in immediate association with the actinolitic and 

 magnetitic slates." The following analyses of the rocks of this type are 

 taken from the Geology of Wisconsin.^ They are of samples selected by 

 the senior author with direct reference to the richness of the rock in 

 metallic iron ; they therefore represent in the main the more ferruginous 

 poi-tions of the belt, or rather the more ferruginous ])ortions having 

 any considerable thickness. The original samples, having been selected 

 for an economic pvirpose, were made by breaking small pieces from all 

 across the thickness sampled. Had the analyses been made more especially 



^The more highly siliceous phases of this class of rocks are sjiokeu of by Irving iu the Wis- 

 consin Reports as quartzites (Geol. of Wis., 1880, vol. iii, jip. 118, 119, 120, etseq.), the adjectives 

 magnetitic, heniatitic, etc., being prefixed to the word qiiartzite to indicate the special phases. The 

 name quartzite was thus u.sed iu ignorance of the fundamental distinction which we now know 

 holds between these rocks and the genuine (jnartzites, the latter having )>een shown to be always in 

 the main composed of original fragmental material, while the siliceous constituent of the rock 

 now especially under consideration is always of a nonfragmental nature, having been solidified iu 

 situ. The term ([uartzite is used, then, throughout this volume and all other later writings ol' thu 

 authors to designate only a genuine fragmental rock indurated by means of interstitial deposition. 

 On PI. .XXII of the Atlas of the Geology of Wisconsin, and on page 119 of vol. lit of that work, the 

 Iron-bearing member is represented as made uj) of three subdivisions, a basement inuirtzite M fe(^t 

 thick, a series of magnetitic schists and quartzites 800 feet thick, and a garnetiferous actinolitic schist 

 10 feet thick. The quartz at tlie base of the series, although highly vitreous, wo now know to be of 

 a completely fragmental character, and to belong to the underlying Quartz-slate member rather 

 than to the Iron-bearing member, the so-called quartzites of which prove to be wholly nonfrag- 

 mental rocks. 



3 Vol. Ill, pp. 156-160. 



