EXPLANATION OF PLATE 12 



Fig. L Polished surface of olivine gabbro. X 27.5. 



A typical sulphide grain. Shows pentlandite, white, and chalcopyrite, inclosed 

 in pyrrhotite. 



Fig. 2. Enlarged view of portion of grain shown in figure 1. X 108. 

 Fig. 3. Polished surface of norite. X 108. 



A typical sulphide grain, showing both pentlandite and chalcopyrite in the 

 pyrrhotite. 



Fig. 4. Another grain from same rock as that of figure 3, plate 12. X 108. 

 Fig. 5. Polished surface of olivine gabbro. X 108. 



A grain of pentlandite and wedges of chalcopyrite, inclosed in a pyrrhotite 

 grain. Note the minute tufts of pentlandite along a calcite veinlet which cuts 

 the pyrrhotite. These tufts are believed to be secondary pentlandite derived from 

 the substance of the primary grains and deposited by the same agency that formed 

 the calcite veinlet. 



Fig. 6. Copper matte. 



The light portion of the field is substance " D, " the dark portion is metallic 

 copper. (Figure 100, Fulton's Metallurgy.) 



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