PLATE VII. 



PHOTOMICROGRAPHS OF IRON-BEARING ROOKS. 



A. Sideritic rock from Penokee-Gogebic district of Michigan and Wisconsin. 



B. Greenalite or ferrous silicate rock from Mesabi district of Minnesota. After Leith. 



C. Concretionary chert resulting from the alteration of iron carbonate. From Penokee-Gogebic 



district of Michigan and Wisconsin. 

 I). Actinolite-magnetite-quartz rock resulting from the alteration of iron carbonate. From Penokee- 

 Gogebic district of Michigan and Wisconsin. 



83S 



