INTERESTING LOCALITIES OF THE ISnPEMING FORMATION. 427 



this were not the case the quartz would be irregaihu-ly dissolved and the 

 magnetite take the vacant space. It is in the rocks which are half way 

 between ore and feriiiginous quartzite or conglomerate that this process of 

 replacement is best seen. 



For most of the Ishpeming area only the belt of ore and ore and jasper 

 conglomerate is exposed. However, in the center of the city of Islqie- 

 ming typical quartzite is seen. Also in sec. 16 the exposures are found at 

 intervals from the basal conglomerate to the top of the formation. The 

 cong'lomerate, by a disappearance of the ore and jasper fragments varies 

 up into ferruginous quartzite and ferruginous slate, and this into ordinary 

 quartzite, which is, however, interstratified with graywacke. In thin section, 

 taken in the same order there is a steady lessening of the chert and jasper 

 fragments, and in the feiTuginous quartzite there is a very considerable 

 amount of complex material derived from the Negaunee formation. Above 

 the lower 200 feet the material was derived mainlj- from some other than 

 the Negaunee formation. 



Negaunee area. — Wcst of Negauuec aud uorth of the Jackson mine is a 

 basin of the Goodrich quartzite (Atlas Sheet XXVIII). As explained in 

 another place, the Negaunee formation and the Goodrich quartzite at the 

 main Jackson pits are infolded. As a consequence of this, both have appar- 

 ently the same dijj, nearly vertical, and at the west end of the open pit the 

 two are infolded several times, so that a horizontal section from the south 

 toward the north passes from the Negaunee formation to the Goodidch quartz- 

 ite, thence to the Negaunee formation, thence to the Goodrich quartzite, 

 thence to the Negaunee, and tinally to the Goodrich quartzite; that is, 

 there are two tongues of the Negamiee formation between the exposures of 

 the Goodrich quartzite. The basal horizon of the Goodrich quartzite here, 

 as at Ishpeming, was composed almost wholly of the fine and coai'se detri- 

 tus of the Negaunee formation. As a consequence of the close infolding, 

 the detrital rock was so closely mashed that it is difficult to discriminate it 

 from the original Negaunee formation. Especially where the detritus was 

 fine, the rock simulates to a remarkable degree the typical jaspilite, and 

 even where fragments of jasper were present these have been mashed until 

 they resemble jasper lamina;, or, where not so much altered, they have an 



