EXPOSUKES OF THE MICHIGAMME FOKMATION. 445 



of the formations both to thu north and south. This is i)articuhu-ly the 

 case from the eastern extremity of the area to Lake Michigamnu;. At 

 Lake Michigamme and to the south and west the formation was much more 

 metamorphosed, becoming a mica-skate, a mica-schist, or a mica-gneiss, and 

 here, on account of the increased resistant power, the exposures are 

 numerous and conspicuous, especially on the southern side of the west arm 

 of the lake and upon the islands to the east. In the Republic tongue the 

 schist, being softer than the lower formations, is followed by the Michigamme 

 River. 



FOLDING. 



Broadly considered, for most of the area the Michigamme formation is 

 in a great syncline. This syncline is, however, very complex, and there 

 are many subordinate anticlines and synclines. East of Lake Michigamme 

 one of these anticlines is of sufficient importance to bring the Bijiki schist 

 to the surface, and thus to divide the Michigamme formation into two 

 synclines, the southern one of which is the more important. Another 

 probable anticline is indicated by the iron -ore pits in sees. 29 and 35, 

 T. 48 N., R. 29 W., as it is thought that the ferruginous horizon belongs near 

 the base of the formation (Atlas Sheets XII and XV). The Republic and 

 Western tongues are both isoclinal synclines. If the exposures are exam- 

 ined in detail, it is found that many of the secondary anticlines and 

 synclines have upon them tertiary folds, and upon these are folds of the 

 fourth order, and so on to microscopic plications; so that in many places 

 the rocks are minutely implicated. This is particularly well seen in the 

 schist at Lake Michigamme. 



PETBOCtRAPHICAL oharacteb. 



Macroscopicai.— The rocks of tlie formation comprise two main varieties— 

 little-altered slates and graywackes, and mica-schists and mica-gneisses. 

 Each of these comprises both feiTUginous and uonferruginous kinds. The 

 first class occurs chiefly in the area east of Lake Michigamme and the sec- 

 ond in the Lake Michigamme area, although representatives of the first are 

 found along the northern side of the Michigamme formation to the western 

 limit of the district considered. The mica-schists are also found along 



