INTERESTING LOCALITIES OF NEGAUNEB FORMATION. 383 



lu the great exposures in sees. 2t), 30, 31, and 32, the t( tiding-, hreeciation, 

 and minor faulting of the formation are particularly well shown. At many 

 places between the Piatt mine and Cascade Brook are seen the transition 

 phases between the Negaunee jasper and the Ajibik qnartzite. 



In thin section the ferruginous chert and jasper of the Cascade area are 

 in no respect ditferent from those of the Ishpeming-Negaunee area except 

 that in the lower horizons fragmental quartz appears in the slides as dissemi- 

 nated grains and in minute laA'ers. 



Fostcr-Lowthian area. — Passiug to tlie west, there are again great exposures 

 of the ferruginous chert in sees. 21, 22, 23, 26, and 27, T. 47 N., R. 27 W. 

 (Atlas Sheets XXVI and XXIX). In the northeast part of sec. 20 is a 

 bluff consisting of massive greenstone, greenstone-schist, and greenstone- 

 conglomerate. On the south side of this knob the greenstone-schist and 

 griinerite-magnetite-slates appear to be interbanded, the layers varying 

 from a few inches to several feet across. There are also several exposures 

 of griinerite-magnetite-schist on top of the bluff. Whether the greenstone 

 is an intrusive Avliieh has caught fragments of the Negaunee formation, or 

 whether it was a contemporaneous volcanic, was not positively determined, 

 but the latter is perhaps the more probable. The occmTenees here again 

 strongly suggest that the igneous rock is the cause of the development of 

 the griineritic and magnetitic kinds of the Negaunee formation. Just to the 

 north of the greenstone, at the open pits of the Lowthian mine, ai'e typical 

 exposures of ferruginous chert. 



Saginaw-Goodrich area. — In tlie ueighborliood of the Saginaw and Goodrich 

 mines, in sec. 1!), T. 47 N., R. 27 W. (Atlas Sheet XXVI), are again nearly 

 continuous exposures from the Ajibik quartzite below to tlie Croodricli 

 quartzite above. This locality, however, differs from the Cascade range 

 in that the southern exposures of the Negaunee formation are the typical 

 griineritic and magnetitic slates. These are, however, cut through by 

 greenstones, which again suggests that the griineritic and magnetitic char- 

 acter is due to intrusive rocks. At the bottom of the formation are found 

 ferruginous quartzites, which stand as a transition horizon between the 

 Ajibik quartzite and the Negaunee formation. For the most part the 

 griinerite-magnetite-slates have a somewhat uniform strike and dip, but in 



