172 



THE CKYSTAL FALLS IRON-BBARING DISTEICT, 



fectly crystalline scliists, as described bj- Van Hise in the Penokee and 

 ]\Iarquette districts.^ No rocks corresponding in content of carbon to the 

 carbonaceous slates which occur among the rocks around Crystal Falls and 

 south t)t' that town have been found among these crystalline schists. These 

 crystalline schists are throughout moderately fine grained, and consist of 

 cjuartz, feldspar, and mica, with associated epidote, rutile, tourmaline, and 

 iron oxides, and in a few exceptional cases crystals of staurolite and garnet. 

 In some of the rocks quartz and mica are preponderant and feldspar is prac- 

 tically wanting, and we have mica-schists. In others all three essential min- 

 erals are present, and we have mica-gneisses. The presence of the feldspar, 

 and to some extent the proportion of the mica and other minerals, depend 

 on the character of the original sediments. Conclusive evidence of the 

 sedimentary origin of these schists is furnished bj- their occurrence in the 

 field, where are found all gradations between them and rocks of unques- 

 tionably sedimentary character. 



In PL XV there is reproduced the part of Brooks's PI. IX in Vol. Ill 

 of the Geological Survey of Wisconsin which comes within the Crystal 

 Falls district and includes a pai-t of the area underlain by the Huronian 

 sediments. There is here given his macroscopical description- of the rocks 

 collected in his study of the area. 



Brooks's macroscopical description of rods collected in the Crystal Falls district. 



' Mon. U. S. Geo!. Survey, Vol. XIX, cit., pp. 332-34.'5; Mon. U. S. Geol. Survey, Vol. XXVIII, cit., 

 pp. 449-450. 



-Geology of the Menominee iron region, by T. B. Brooks: Geol. of Wis., Vol. Ill, 1880, Pt. VII, 

 p. 496. 



