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not been observed in contact, and hence the presence or absence of a 

 normal erosion unconformity cannot be inferred. 



The Lower Menominee series. — The formations of the Lower 

 Menominee series are observed only in the center and on the northern 

 side of the Menominee trough. The Sturgeon formation is composed 

 mainly of a hard white vitreous quartzite forming a continuous border 

 of bare hills bordering the Archean complex. At its base is a coarse 

 conglomerate made up of debris from the underlying Archean com- 

 plex. The belt is in general a southward dipping monocline with 

 dips varying from 25" to perpendicularity, although there are many 

 reverse dips to the north. Its thickness is placed at from 1000 to 

 1250 feet. 



Above, the Sturgeon quartzite grades into the Randville formation 

 which is mainly a homogeneous dolomite interstratified with siliceous 

 or argillaceous layers. This formation appears in three belts. The 

 northern one is just south of the belt of the Sturgeon quartzite. The 

 central belt is on the north side of Lake Antoine for a portion of 

 its length, passes eastward between the Cuff and the Indiana mines, 

 and ends at the bluff known as Iron Hill in the east half of Sec. 32, T. 

 40 N., R. 29 W. The southern belt of dolomite extends all the way 

 from the western side of the sandstone bluff west of Iron Mountain to 

 the village of Waucedah, at the eastern end of the mapped area. 

 Structurally the northern belt of dolomite is a southward dipping 

 monocline, while the two southern belts are anticlines. The thickness 

 is not determined on satisfactory evidence, but is probably 1000 feet- 

 or more. The Randville formation is found, in a number of mines, 

 in contact with the basal formation of the Upper Menominee series 

 Here there is a coarse conglomerate in the basal part of the overlying 

 formation indicating unconformity. 



The Negaunee formation, overlying the Randville dolomite, is 

 represented in the district by so few and so small outcrops that it is 

 mapped with the Vulcan formation. Its presence is inferred mainly 

 from the occurrence of abundant iron formation debris in the basal 

 conglomerate of the Upper Menominee formation, showing that the 

 Lower Menominee iron-bearing series must have been present. In 

 the Marquette district an iron-bearing formation (the Negaunee) occu- 

 pies an exactly similar stratigraphical position. 



The Upper Menominee seines. — The formations between the uncon- 

 formity at the top of the Lower Menominee and the unconformity at 



