GEOLOGICAL EXPLORATIONS AND LITEEATURE 1873. 51 



Near the Repul)lir niiue outcrops of Iliirouiau and Laurcntiau rocks 

 were seen iu such relations to each other that, ah-hou<rli no contact of the 

 two series was observed, tlie author nevertheless concluded that the former 

 series is unconfornial)lv upon the latter. 



The Repuljlie and Kloinan mines are described in more detail than 

 most of the others. The author here discovered the relations of the differ- 

 ent formations to one another. He publishes a map of the area around 

 these mines, which is so accurate and comprehensive that the district has 

 served as a type district and a starting point for all geologists who, since 

 Brooks's time, have worked on the Marquette iron range. We quote the 

 author's description of Republic ^Mountain (formerly Smith's Mountain): 



The numerous outcrops of rock and ore at this uiouiitaiu, the strong magnetism 

 possessed by three of the beds, the remarkable uniformity in thickness of the several 

 formations, and the bold topographical features presented, all of which were carefully 

 surveyed and ai-e faithfully represented and explained on the accompanying * * * 

 maps and charts, * * * leave but little more to be said in this j)l;ice regarding 

 the general structure of Republic Mountain. 



* * * The ten formations, represented by colors on tlic map, * * * will 

 now be enumerated, commencing with the lowest, which reposes nouconformably on 

 the Lanrentiau granites and gneisses. 



The lowest bed of the series will be numbered V, for reasons which will hereafter 

 appear. (Pp. 125-126.) 



Then tollows tlie enuuKn-ation of the beds, which is given here In more 

 concentrated form than ap[)ears In the author's report. 



At the liottom of the series Is a quartzose rock (V), followed above "by 

 a magnetic, bright, banded, siliceous, and chlorltic schist" of various colors 

 (VI). "The greenish layers are apparently chlorltic, the wliltlsh and grayish 

 are quartz, and the ])rown and dark gray are siliceous layei-s of the red and 

 black oxides of Iron." Following the schists Is a diorlte (VII), and above 

 the diorlte another magnetic siliceous schist (VIII) like VI. A diorlte (IX) 

 again appears overlying VIII, and another schist (X) similar to VI and 

 VIII overlies the diorlte. This schist often contains enough iron to make 

 it a fairly rich flag ore. Formation XI Is a coarse diorlte, schistose in 

 places, and XII is a reddish quartz or jasper-schist. The Iron formation 



