OEE DEPOSITS OF UPPER HURONIAN. 175 



region have been traced into igneous rocks.'' These gneisses are beheved to 

 be igneous rocks, either intrusives which were injected parallel to tlie bed- 

 ding of the Upper Huronian sediments prior to the folding, or contempo- 

 raneous volcanics. They haA^e been metamorphosed and rendered schistose 

 by the same forces which metamorphosed the sediments. This explains the 

 perfect agreement of their schistosity with that of the adjacent sediments. 



ORE DEPOSITS. 



HISTORY OF OPENING OF THE DISTRICT. 



For a number of years after the opening of the mines of the Menomi- 

 nee range, j)rospectors worked in various places, among others in the vicinity 

 of Crystal Falls, seeking to follow the iron range west of the Menominee 

 River. As a result of this endeavor, the deposits at Florence, Wisconsin, 

 and then those farther north and west at Crystal Falls, Michigan, were in 

 turn located. It was not until 1881 that sufficient exploratory work had 

 been done at Crystal Falls to warrant a belief in the future of this iron- 

 beai'ing area. In April, 1882, the Chicago and Northwestern Railway com- 

 pleted its branch to Crystal Falls, and the shipment of ore began. The 

 Amasa deposits were not exploited to any great extent until the year 1888, 

 when the Chicago and Northwestern Railway built a branch from Crystal 

 Falls to Amasa. The Chicago, Milwaukee and St. Paul Railway, in 1893, 

 completed a line from Channing to Sidnaw, which runs throug-h Amasa. 



DISTRIBUTION. 



The iron-bearing rocks trend northwest and southeast from Crystal 

 Falls. East of Crystal Falls some of the ore deposits are found in prox- 

 imity to the Hemlock volcanics, and follow along a line located a short 

 distance from them. Other deposits are those at Amasa, about 12 miles 

 northwest of Crystal Falls. These are near the contact between the Upper 

 Huronian and Lower Huronian, and above the Hemlock volcanics, like 

 the deposits east of Crystal Falls. Four mile's north of Amasa are the 

 explorations in sec. 20, T. 45 N., R. 33 W., in which the iron-bearing beds 

 are exposed. Another exposure of the iron-bearing formation is in sec. 34, 

 T. 46 N., R. 33 W., about 4 miles still farther north. 



These are the northernmost known exposures of the iron-bearing rocks 

 of the Upper Huronian in the Crystal Falls district. However, dial- 

 compass and dip-needle work has located a line of magnetic attraction for 



