CHAPTER IV. 

 THE UPPER MARQUETTE SERIES. 



INTRODUCTION. 



Bv C. R. Van Hise. 



The g-eueral statement lias been made that tlie Upper ]\Iarqiiette series 

 ajjpears at Negauuee aud at Palmer in two detached areas, reappears at 

 Ishpeming, and from this place toward the west rapidly widens out into 

 a broad belt, occuppng the greater part of the area of Marquette rocks. 

 It has also been said that this general distribution is due to the great 

 north-south transverse anticline east of Negaunee. 



Broadly considered, the Upper Marquette series was predominantly a 

 gi-eat shale formation, which was subsequently modified to a greater or 

 less degree. The loAvest horizon of the series is, however, a conglomerate 

 and quartzite, which marks the transgression of the sea. Replacing this 

 in part in the west end of the area is a griiuerite-magnetite- schist horizon. 

 Following above this is the great slate formation, and in it is a horizon 

 whicli originally bore a considerable quantity of iron carbonate, from 

 which various ferruginous rocks have developed, and also small ore 

 bodies. Finally, during Upper Marquette time, in parts of the district 

 there was contemporaneous volcanic action, so that associated Avith the 

 modified shales of the series is a belt of volcanics a number of miles long. 

 As in the case of the Lower Marquette, later intrusives penetrated the 

 series at various jilaces. 



The Upper Marquette series is, then, structurally divisible into a lower 

 belt of conglomerate, quartzite, griinerite-maguetite-schist, and associated 

 rocks; a slate formation; and a belt of volcanics. The first will be called 

 the Ishpeming formation, the second the Michigamme formation, and the 

 last the Clarksburg- formation. 



