INTERESTING LOCALITIES OP MICIIIGAMJIE FORMATION. 457 



staurolite ami garnet. Just west of the west end of the hike the rock is so 

 coarse and quartzose as to become a micaceous quartzite. 



Along the southwest arm of the lake, in sees. 5, 7, 8, 17, and 20, 

 T. 47 N., R. 30 W., at various places mica-schists are found. The rocks of 

 this area are very similar to those on the islands and tliose to the west on the 

 mainland, but upon the whole they ai'e more strongl}- foliated and coarsely 

 crystalline, being- rather coarse-grained, typical, foliated mica-schists. The 

 crystals of garnet and staunilite are very al)undiint, and are of larger size 

 than in the area to the nortli. At one place in sec. 17 the rock has a strongly 

 feldspathic appearance, and is apparently a garnetiferous mica-gneiss. 



Tlie mica-schists of the Lake Michigamme area are very similar to 

 those of the Penokee district.' The most important diflfei'ence between the 

 two areas is that mashing has played a more important role in the ]\Iar- 

 quette than in the Penokee district. There has evidently been movement 

 throughout the rock, each particle having been rearranged with reference 

 to the surrounding- particles, and where the rock becomes strong-ly foliated 

 the slickensided surfaces between the folia sliow that tliese had differential 

 movements with respect to one another. Accompanying this more strongly 

 crystalline character are abundant garnet and staurolite, and a less quantity 

 of chloritoid. 



In thin section, by using the gradation varieties, the proccKSses of trans- 

 formatif)n of the fragmental rocks to the completely crystalline schists is 

 made out with great clearness. The processes are almost identical with 

 those which have been described as taking- place in the mica-schists which 

 occupy a similar horizon in the Upper Huronian series of the Penokee 

 district and in the Black Hills. A full description of these processes will 

 therefore not be here given, but a few supplementary notes may be made. 



The ordinary mica-schists of the area have a quartzose background, in 

 which biotite is very abundant. F'requently a large amount of chlorite is 

 associated with the biotite, and very often also muscovite is present. In 



' The Penokee iron-bearing series of Michigan and Wisconsin, by R. D. Irving and C. R. Van 

 Hise: Mon. U. S. Geol. Survey, Vol. XIX, 1892, pp. 332-343. 



The pre-Cambrian rocks of the Black Hills, by C. R. Van Hise: Bull. Geol. Soc. America, Vol. I, 

 1890, pp. 222-229. 



