Plate XXIII.— MAGNETITIC CHERT FROM THE MICHIGAMME MINE. 



The liluish-gray bands are rather coarsely crystalline quartz. This kind of quartz is characteristic of 

 the west end of the district. The dark material is hematite, and the lustrous material is mag- 

 netite. The hematite was present before the last folding, and is in brilliant ilecks, due to 

 accommodations along the beds. The magnetite entered after the last folding. In fig. 1 the 

 abundance of the magnetite is seen to be in direct ratio to the fracturing. On the left-hand 

 side of the figure, -where the rock is much broken, there is little quartz. The peculiar magnetitic 

 chert represented by this plate is found closely associated with the ore at the Michigamme and 

 Spurr mines. 

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