58o R. C. ALLEN AND L. P. BARRETT 



correlating the various exposures of the different members of this 

 series. The chief difhculties refer to the relation of the quartzite 

 on the west hill to that exposed on the east hill and to the deter- 

 mination of the stratigraphic position of the two outcrops of 

 quartzite north of the slate at the base of the east hill. The out- 

 crops of gray quartz slate and red-banded quartz slate on the 

 north slope of the west hill are apparently stratigraphically above 

 the exposures of quartzite in outcrops and pits on its northwest 

 and northeast sides. Whether the quartzite at the base of the 

 north slope of the east hill is stratigraphically above the quartz 

 slate or represents the underlying massive quartzite brought up 

 by faulting cannot be determined. * 



Extended description of the different phases of the quartz 

 rocks in the upper series has little interest for present purposes. 

 The dissimilarities of the different members refer mainly to texture 

 and bedding structures rather than to composition. The red 

 color of certain layers in the quartz slates is caused by the presence 

 of small particles of finely disseminated hematite. 



Notes on the correlation. — In a former paper the senior writer 

 discussed the importance of the unconformity separating the 

 Princeton (upper) and Gwinn (lower) series in the Gwinn syn- 

 clinorium and adduced evidence in support of the correlation of 

 these two series with the Upper and Middle Huronian. The 

 lithologic similarity of the arkose-conglomerate formation at Little 

 Lake to the basal member of the Gwinn series, only a few miles 

 distant, considered in connection with the unconformity separating 

 it from the overlying quartzites and quartz slates is a sufficient 

 basis for extending the arguments for the correlations in the Gwinn 

 district to cover the two unconformable series at Little Lake. 

 The geology of each area accounts for three unconformable series 

 of sedimentary rocks corresponding to the Lower, Middle, and 

 Upper Huronian of the adjacent Marquette district. The upper 

 two series are present while the lower one is represented in both 

 areas by fragments of some of its formations in the base of the 

 middle series. 



The absence in the lower series at Little Lake of the slate and 

 iron formation members developed in the Gwinn synclinorium 



