64 THE MARQUETTE IRONBEARING DISTRICT. 



that tlic Iluroiiiaii of ]\Ilclii<i;iiu, inehidiug- of course the Mar(|uette Huronian, 

 is a distinct and older series than that to which the copper-bearing- rocks 

 belong. 



The (jnestion of the age of the Keweenawan was contested long and 

 l)itterly, and it was tinallv decided to the satisfaction of most geologists 

 that the view snggested by Hunt and Brooks is the correct one. The 

 copper-l)earing rock.s are younger than the iron-bearing series of the Upper 

 Peninsula and entirelv distinct from them. The literature of this subject 

 need not be referred to again. The subject is mentioned here merely to 

 simplify and make clearer the geology of the Marquette rocks, which in 

 this district had l)een included with the eopper-l)earing series as forming- a 

 portion of Foster and AMiitney's Azoic. 



Brooks, T. I>. Classitied list of rocks observed in tlie Hurouiau series south 

 of Lake Superior, with remarks ou their abuudance, trausitious, aud geographical 

 distribution; also a tabular preseutatiou of the sequence of the beds, with au 

 hypothesis of equivalency. Am. Jour. Sci. (3), Vol. XII, 1876, pages 194-204. 



In another article in the same year Brooks g-ives a revised classilication 

 of Huronian rocks, based on microscopic examinations of thin sections 

 made by A. Wichmaim, Charles E. Wright, and Frank RutleA'. The clas- 

 sification includes Huronian rocks from tlie then known iron-bearing 

 areas of this age in Michigan and Wisconsin. We are concerned only with 

 the Marquette series. This, exclusive of the youngest observed member 

 (the granite bed), according- to the author, has a thickness of not more 

 than 6,000 feet. The sequence of the beds is shown in the following- table, 

 in which the italicized names are those of the rocks possessing greatest 

 lithological interest : 



Lower Silurian. 

 Copper series (wanting). 



nURONIAX. 



XIX. Grayish black miea-schiKt, often xtoiirolitic, and holding andahtsite and 

 garnets; rarely chloritic schist. Quartz in bunches aud veins, aud hornblende seams, 

 rare. Quartzyte. (?) 



Probably soft slate. 



XVII. Anthophyllitic (?) schist, usually magnetic, and coutaining manganese. 



