THE mON-BEAlilXG ME.MKEK'. 185 



of the Iron-hearing- member and immediatelv upnu tlic vitrei ms (piartzite 

 whicli tonns the uppermost layer of the Quartz-slate memlx'r. In these 

 mines the eontact is between this (juartzite on the one side and eithei' the 

 lire or a hematitic cherty material of an entirely nonfra;>'mental ciiaracteron 

 the other. But the contact between the two formations is also visible at a 

 nundjer of natural exposures, as, for instance, at the jjassage of Tylers fork, 

 in T. 45 N., R. 1 W., Wisconsin (Fig. i<), and the passage of Bad river at 

 Penokee gap, in T. 44 N., \l. 3 W., Wisconsin. (See PI. xxxvi.) In these 

 cases on one side is the magnetitic cherty and slat^- rock, and on the other 

 the vitreous quartzite: and, as usual, the two cla.sses of materials come 

 directly against each other without transition phases. West of Penokee 

 gaj) but few contacts were seen. In a number of places, however, the 

 exposures of the two formations were found in ver\- close proximit}- to 

 one another. (Pis. v, vi.) As already stated, the uppernatst portion of 

 the Quartz-slate is everywhere a vitreous quartzite, i. e., a sandstone in 

 which the interstices of the quartz fragments have been filled with a 

 secondarv silica, which has in the main coordinated itself with the oriuinal 

 fragments. However, as is usually the case in such (piartzites, some of 

 the silica has deposited in a more or less minute mosaic in the interstices. 

 This mosaic, itself of direct chemical origin, in a few sections is not tar 

 ditierent from the coarser grained phase of the noidVagmontal silica, which 

 forms the groundwork of most of the rock of the Iron-bearing mendier. 

 But in any case the chemically de})Osited silica is of a secondary- nature, 

 and can not be taken as indicating a transition between the modes of 

 deposition of the two formations. 



Geographical pxtnif. — Longitudinalh- the Iron-bearing mend)er is co- 

 extensive in di.stribution with the underlying Quartz-.slate; that is to sav, is 

 continuous from the western end of the Penokee range in the nortli half of 

 Sec. 24, T. 44 N., R. 4 W., Wisconsin, to the NE. ] of Sec. "Jl, T. 47 N., 

 R. 44 W., Michigan, a distance of more than '»() miles. To the west of 

 the western end of the Penokee range, as indicated heretofore, the entire 

 succession of the Penokee series is lost for a distance of C miles, in which 

 distance exposures of the underlying granitic and gneissic rocks on the one 

 hand and of gabbros on the other, come in close proximitv to each other 



