72 THE MAKQITETTE IRON-BEARING DISTRICT. 



in the uppei- portion of th« Iluiouian series by Kimball, Brooks, and Wright, with 

 the ''(liorites" underlyiTig them. 



It will thus be seen that, while Foster and Wliitney regarded certain of the 

 rocks in the lluroniau as eruptive, Hubl)ard, Rivot, Kimball, Hunt, Creduer, Brooks, 

 and Wright regarded all, with a few slight exceptions, as sedimentary; and Hough- 

 ton, Hubbard, Locke, Kimball, Rivot, and Brooks teach that they pass by gradual 

 transition into one another. 



The most important points, then, about which there has been or is difference of 

 opinion, ai-e the age and relation of the granite and schists, the origin of the diorites 

 and iron ores, the passage of one rock into another, and the presence or absence of 

 eruptive rocks. These and other questions relating to this district admit in many 

 cases of no middle ground; one or the other party must be mistaken in their obser- 

 vations or conclusions, or both. 



After reviewing the literature on the Marquette area the author proceeds 

 at once to attempt tlie sokition of the prol)hnus tliat present themselves. 

 He studied the district miiuitely, and so compelled others who disagreed 

 with his conclusions to make a similar close study of it. Consequently, 

 "Wadsworth's paper may be regarded as the opening chapter of a new 

 volume on the geology of the district. As we shall see, several of the 

 author's conclusions were subsequently proved untenable, but the work 

 required to prove them wrong was necessary before a con-ect knowledge 

 of the geology of the district became possible. The article is especially 

 valuable for its detailed description of the relations existing lietween the 

 various rocks. 



The contat-ts of the jasper and ore with the schists associated with 

 them are shown to bt> like those of an eruptive with an older rock. At 

 the Lake Superior ]niiic, for instance, the jasper and ore were seen in contact 

 with the chlorite-schist. 



The junction of the two is very irregular, the banding of the jasper and ore 

 following the irregularities of this line, while the schist is indurated and its lamiute 

 bear no relation to the line of contact. Stringers of ore in-oject into the schist, which 

 near the jasper is filled with octahedrons of magnetite. The schist loses its green 

 color generally, and becomes apparently an indurated argillite. The contact and 

 relations of the two rocks are not such as are seen when one sedimentary rock is laid 

 down upon another, but rather that observed when one rock is intrusive through 

 another; and in this case the intrusive one is the jasper and its associated ore. (P. 30.) 



