540 I'ni' :\iAi;(>>ui:Tri'; ikon hkaimnc; distkict. 



tlijin ihc thiiUncss nl' thai toiinatidii (Alias Sheet XI, sees. AA smd BB). 

 Field study shows clearly that the neutral suri'aee' of the eolunni ot" folded 

 material hiv Itelow the base of the (Joodrich (|uartyate, and iueluded a con- 

 sidcial)le |)orlion ol' the Ne^;aunee I'oi'inatiou. Tliis is |)rove(l by tlie severely 

 |ilieated condition of the thin-l>eddeil jaspers, and by the same structure on 

 a laru'er scale in th(> mor»> heaxilv bedded ([uartzite. The crowding' of the 

 rocks above the neutral surface into a very constricted s[iace has resulted in 

 the formation of thri'c s\-ut'lint's of the second order seiKirated by two anti- 

 clines, all subordinate to the main fidd. The most eastern of the synclines 

 occurs at the L;reat open pit of tlu' Kepuiilic mine; the middle, in the 

 UTouud openeil 1)V the Mor<iai\, I'aseoe, and Kly shafts, and the western- 

 most at the Swamp shaft. Tpon these folds of the second order are 

 suiterimposed a muilitude of smaller anticlines and synclines of various 

 dimensions. 'i1ie\ are more numerous ;ind more I'losely compressed iu 

 the iron-beariui;- member than iu the Cioodrich (piartzite. 



In the iron-beariuL;- meuiber, which is a thinly beddi'd rock, these 

 little folds are espi'cially luimerous in the Morgan- Pascoe- Ely syncHne 

 and in the anticline iuuuediately west of it. The effect of tins preva- 

 lent ( liukliuL;' :nid close compri'ssiou is to giv(» a gern'ral northwesterly 

 direction to the individual bauds, which in the narrow spaces open to 

 observation und(>rgronud, or in small outcrops on the surface, may lead 

 to erroiu'ous conclusions as to the real direction of the strike and dip 

 of the rocks, 'i'liis i\orthwestei-Iy structure is really at right ang'les to 

 the direction ol' contiunit\- ot" the rock. The true strike is determined 

 b\ the pliuie tangent to the little folds, and the true dii) by the angle 

 (if pilch ot' iheii- axes. l']\cu on the surface in the larger outcrops 

 the oliscrver ma\ sometimes be misled. The larger sul)ordinati' anticline 

 between the Swamp shaft and tiie Morgan is toi)ogTapliically indicated 

 bv a high sjuu-, ou whicli the specular jasper outcrops. The jasper 

 is thrown ii\Io innumeralile lillle I'.-lds, the axes of which pitch to the 

 northwest at an angle of less than 1;")"". The northern slope of the spur 

 is nearly as steep as the angle of pitch, and so the surtace cuts the 



' Priiiri)iU>s ol" North Aiiioviciiii iiro-eaiuliriiiu goolo^.v, by C. K. Vau Hiso: Sisteeuth Auu. Kept. 



U. S. Ciool.Survov, I'iiit 1, ISlUi. pp. 5!Ui-5!tS. 



