492 



THE MARQUETTE IRON BEARING DISTRICT. 



(Atlas Sheet XXVIII), southeastward to a httle beyond the east quarter post 

 of sec. 13 in the same township. Only tliat ])(trtion of the knob that lies 

 in sec. 12 has been sectioned, although the entire knob has been carefully 

 sampled (fig. 27). Of the eleven sections made from this portion of the 

 knob, three contain remnants of augite. The Vtalance of the specimens 

 are amphibole rocks. 



Fig. 27. — Poaition of specimens of greenstone from eoiith h.ilf of sec. 12, T. 47 N., R. 27 "W. 



The commonest phase of the greenstone is a dense granular rock 

 showing compact hornblende. Under the microscope this latter mineral is 

 typical uralite. It is strongly pleochroic in light yellowish-green and dark 

 bluish-green tints, and is often bordered by dirty-brown biotite. The horn- 

 blende is often twinned, and often it possesses idiomorphic outlines. The 

 plagioclase is not ^'er3' abundant. The crystals are shattered. Fibrous 

 hornblende of the same nature as the larger, more compact grains, together 

 with chlorite, has filled the fissures thus produced. Some biotite occurs in 



