218 THE I'KNOKKI'; IIION-BKAHINH! skhiks. 



Fn»ti llir I'lnohrf (/dj) scclion. 



11. MiiK'nolKic actinolilic (niarlz-scliists, IVoiii middle horizons. Specimens 9550 

 (.slide .'{n^), from l!t(>(» N., \r>(n) VV.; itf)")? (.slide .JOOli), Irom ISfK) N., ir)(»» W.; 95r)8 

 (.slide ;}|!)1), IVoiii IS(»<I N., l.lOd NV., Sec. 14, T. 44 N., K. .'! W., Wisconsin. 



Tliesi' spcciiiiciis icpresciil tiic cuiiiiiosition of the west dill' :it I'eiiokee j;'ai>. 

 Tliis (dill' is made up of alleiiiiitiii^' hands ol' lii^lilci' and darker colors, individual 

 hands vai'vinji' V(My i;reatly in width and in tlie amount of distinctness (d' delinition. 

 'i'lic dai Uer hands, ot'ten in tluMUsehes thinly laminated, are veiy ri<'li in maf^netitc, 

 at limes so much so as lo present a dislinel inetallic luster. The lighter colored por- 

 tions are liii;hly (piarlzose and carry relatively little mannelite. The hands which 

 are rich(^sl in mai;'nelitc are usually found runninu' from a> fraction of an inch to 

 several inches in lhickn(^ss, lint lhickness(^s of a. iiund)er of I'cet are met with in which 

 tluire- is as much as 10 per cent of metallic, iron. The daiker colored, \ery hijihly 

 maignetitic phases ar(^ (piite aplianitic, hut the lijuliter coloifd portion.s, though still 

 very line gi'ained, show distinctly nnd(M' the magnifying glass a mixture of minute 

 actinolitic l)lades and (piart/.. Sp. gr. of OiMti, .'J-a?; of !».V.7, 4-:{l; of '.KWS, ;$-91. 



The thin sections are composed of magnetite, actinolitc, and (piartz, named iu 

 Older of time of crystalli/ation. Tlic only ilitferencc hetween the thin sections lies in 

 the varying coarseness of grain and the \aryiiig proportions of the three constituents, 

 each on(>()f which is in turn the pr(^ponderating ingrediiMit, and again iusignili(;ant 

 inipianlity. The (piart/, forms a grouudniass ol' closely titled or interlocked grains, 

 the smaller ones of which are often prosided with crystal outlines. Now here do these 

 giains show any traces of tniguiental cores, the wlnde appearance forhidding any 

 thought (if adetrital origin foi- any |)ortion of the section. The actinolitc is in color 

 less to pale gi'cen, fct'hly dichroic needles and l)lades, at times arranged in radiating 

 aggregations which vary very greatly in si/.e. Numliers of the more minute ne<'dles 

 occur often within single (piart/. grains, w Idle the laiger needles and hlades extend 

 tlirongii a numher of (pnirl/. individuals. Tlie arrangement of the actinolitc has plainly 

 been w ithoul an>- rcl'crtMicc what(^\•er lo the (piart/, which ai)pears therefore to he of 

 snhseipicnl origin. The magnetite occurs inmlimlc dust like |)art icies within both 

 ipiart/. and ac.tiuolite, and also in ((uite large aggregations of irrt^gular outline. At. 

 times thi^se aggregates ol' magnetite include particl(^s of actinolitc and (piartz, hut 

 such cases seem rather to be (explicable on the idea that the actinolitc and (piartz 

 lia\(' entered into ciivities within the magnet ile aggr(>gations subse(pieiit to their 

 .soliditication. No evidence is found that these two nun(Mals e\-er are included williin 

 or traver.se single in(li\i(luals of magnetite. (IM. XXIV, Fig. 1.) 



IL'. Magnelitic and actinolitic (piartz-.schists, from near the summit of the Iron 

 mcmlier. Specimens !».")."),'> (slide .tl'.IO). from (• N., \i'>'2'> \\ .. Sec. II; and 9.'>(>7 (slide 

 •JUto), fnun Kiir. N., 1100 W., Sec. 1 1, T. 11 N., II. :\ W., \\i.sconsiii. 



