PETRCXJKAPHICAL CHAltACTER OF NEGAUNEE FORMATION. 375 



hence at the edges and various places through the centers of the shdes is a 

 brilHant red cohir. The slate ores in reflected light show tlie laminated 

 character of the rock, while the massive ores give the peculiar s])otty 

 reflections, exactly the same as magnetite. 



Tlie mottled red and black specular ores in reflected light present a 

 peculiar appearance, the true specular material giving the usual brilliant, 

 spotty reflections, while the soft hematite has a brownish-red color. 



The soft hematites in transmitted light, in many slides, show the char- 

 acteristic blood-red color of hematite, although for the most part the sections 

 are so thick as to give a brownish appearance or are opaque. In the softest 

 ores in reflected light a dark brownish-red color is everywhere seen, which 

 is much less brilliant than that presented by the same mineral in trans- 

 mitted light. In some of the soft hematites, however, within the mass of 

 red material are many small areas which reflect the light in the same 

 manner as the specular ores. The limouitic hematites diff'er from the j^ure 

 hematites only in that, in l)oth transmitted and reflected light, in many 

 places, the reddish colors are not so bright. 



The foregoing description shows that there are gradations from the 

 coarsest magnetite to the softest limonitic hematite. 



INTERESTING LOf!ALITIES. 



The localities where tlie Negaunee formation is exjjosed are so numerous 

 that onlv more important areas of exposures Avill be here mentioned. 



Michigammc and spurr. — At Miclugamme aud SpuH" mines (Atlas Sheet V), 

 and in the area connecting them, are very good exposures of the Negaunee 

 formation of a somewhat exceptional character. At the lowest horizon, 

 adjacent to or underlying a great greenstone ridge, are typical exposures 

 of magnetite-griinerite-rock and magnetite-griinerite-schist. Locally the 

 schist mantles areas of intrusive greenstone (PI. XI), and the latter in other 

 places includes many fragments of the schist (PI. XII). The griinerite- 

 magnetite-schists are overlain by coarse typical red jaspilite, which at sev- 

 eral places is just above the greenstone.' The jaspilite of this locality ditfers 

 from that of most of the district in that the pure jasper bands are of unusual 

 width, sometimes reaching a thickness of 6 to 8 inches. Between these 



