324 THE MARQUETTE lllO:sr-BEARlNG DISTRICT. 



numerous g-ranules of quartz. Large crystals of" chlorite, includiug- gi'aius 

 of quartz, with folia transverse to the schistosity, are plentiful in the 

 coarser schists. These and the hornljlende crystals appear to be the latest 

 minerals of the rock. Probably they developed under static conditions 

 after the folding and after the intrusion of the greenstone. It appears 

 highly probable that the unusuallv crystalline character of the Siamo slate 

 in this neighborhood is partly due to the later intrusives. 



The garnetiferous gruuerite-magnetite-schists near the base of the 

 Siamo formation at Michigamme are identical witli similar transition rocks 

 near the base of the Negaunee, and are described in connection with that 

 formation. 



Nonpareil mine. — Tlic uext cxposures of lutercst are at and south of the 

 Nonj^areil mine, west of Lake Cooper (Atlas Sheet XXV). Here the I'ock 

 is a regularly laminated ferruginous slate, which contains layers of fer- 

 ruginous chert and graywacke. In the less ferruginous layers is seen 

 a tissility which dips to the south 70° or 75°, but the more ferruginous 

 layers on the south or hanging wall of an open pit dip south about 45°, 

 and these probably follow the true bedding. Farther south the exposures 

 of the formation are ordinary ferruginous slate. When examined in thin 

 section the ferruginous chert differs from that of the Negaunee formation 

 only in that it contains scattered, distinctly fragmental grains of quartz 

 and layers which contain a great deal of fragmental material. In some of 

 these cherty phases there is present a small amount of siderite. This occiu'- 

 rence, taken in connection with the known origin of the similar rocks in 

 the iron formation, suggests that at the Nonpareil mine the lowest horizon 

 of the Siamo slate contained interlaminated sideritic jjhases. 



Siamo Hills. — Tlic uext Importaut set of exposures is southwest of Teal 

 Lake, on the Siamo Hills (Atlas Sheet XXVII), and these are taken as the 

 type outcrops of the formation. The exposures, besides being numerous 

 and large, give a nearh' comidete section from the Ajibik quartzite below 

 to the Negaunee formation above. At the base of the formation, as at 

 the Nonpareil mine, as shown by test-pitting, there is ferruginous chert. 

 The central larg-e exposures of the formation comprise all varieties of slate 



