THE IJEPUBLKJ TKOUGH. 537 



Republic I\rouiitiuu. Ill g'oiui^' north from llepublio ]\Iountaiu on the east 

 side of the fold the lower series is progressively and rather slowly cut out, 

 so that at the old Chippewa exploration, in sec. 22, T. 47 N., R. 30 W., the 

 Goodrich (piartzite rests directly upon tlw Arcliean. Thence northward, 

 and eastward almost to the C-hanipion mine, the lower series probul)l\' does 

 not again emerge. 



On the west side of the fold the lower series is entirely gone on 

 the west side of the river, opposite the Republic mine, and the Good- 

 rich quartzite rests directly on the granite. It reappears to the north 

 oiih' ill patches, once at the Standard location, possibly again at the Metro- 

 politan, and again at the Erie. Beyond the Erie it appears again and 

 continues beyond the Magnetic mine and the limits of the area now 

 descril)c<l. 



The evidence, which it is not thought necessary to present here in 

 greater detail, is thus conclusive, and settles beyond the pos.sibility of ques- 

 tion that between the deposition of the Lower ]\Iarquette series and that of 

 the Upper Marquette series an interval of time elapsed during which the 

 lower series was elevated, folded, probably metamorphosed, and deeply 

 denuded. This break in continuity of deposition between the two series 

 lasted sufficiently long- to permit the removal in many places of the entire 

 Lower Marquette series and a deep gnawing into the Arcliean. The 

 present uneroded thickness of the Lower ]\Iarquette series on Republic 

 Mountain is at least 1,500 feet. How much in all was removed by erosion 

 before Upper Marquette time there is no means of knowing. Fifteen 

 hundred feet of Lower Marcpiette strata, with an unknown thickness of 

 Arcliean, is the minimum amount taken away in the Republic area. The 

 time-break in the Marquette district is far less impressive than that below 

 the upper series on the north shore of Lake Superior (with which, indeed, 

 we do not know that it was conterminous), because the earlier folding on 

 the south shore was less severe, while the later folding, which followed 

 Upper Marquette time, was far more severe than on the north shore; and 

 hence the structural discordances and the differences in degree of metamor- 

 phism between the two series are less pronounced. But the conviction 

 remains that this is one of the i-reat breaks in the ffeoloo-ical record. 



