COKRELATIO:^ OV THE MAllQUETTE SEKIES. 579 



series, in the Sijinio slate — that is, toward the higlier part of tliis great fra"-- 

 inental formation. Tlie Fence liiver volcanics, in the Menominee district, 

 occupy a similar horizon. 



(2) The pure, nonfragmental iron formation of the ^rai-cjuette district 

 is equated with slates, cherts, jaspers, and the rich ores of the Menominee 

 district. The only substantial difference, however, is that in the Menominee 

 district the i-ocks liear, with the nonfragmental, a considerable amount of 

 fragmental material. In other words, the conditions in that district were 

 not favorable to ])ure nonclastic sediments, as they were in the Marquette 

 district. 



As there thus seem to be closely parallel successions in the two dis- 

 tricts in early Marquette time, it seems highly probable that the western 

 part of the Marquette district, where the lower members of the series do 

 not appear, must have been a high area largely or completely surrounded 

 by water, since the lower members of the series were deposited to the south- 

 east and northeast. This elevated tract included the area west of Ishpeming 

 and Negauuee to Lake Michigamme and thence south to Republic. How 

 much farther it extended to the west, and whether it was an island or a 

 peninsula, it is yet too early to venture an opinion. 



Until more detailed studies are made of the Upper Huronian rocks in 

 the Menominee district it is unsafe to attempt a detailed correlation of the 

 formations of the Upper Marquette series with the formations there found. 

 In both districts there are certain general likenesses. The basal formation 

 in each district is frequently an ore and jasper conglomerate, which passes 

 iqj into a quartzite. In both the Marquette and Menominee districts, not 

 far above this quartzite, near to or associated with the slates, is an iron- 

 bearing formation. The upper predominant formation was a shale, which 

 has been metamorphosed to a mica-slate or mica-schist. 



