Plate 70 



1. Seneca Township, Michigan; finest octahedrite; Ni-Co 11.67 percent. A superficial 

 invasion of intrusive magnetic oxide (with nickel-iron in solution) in the zone of alteration. 

 The dead black areas are oxide; the included area, slightly less dark, consists of nickel-iron 

 rejected during the cooling of the liquid oxide-iron solution. A crack filled with oxide 

 (below) runs some distance into the mass. The curving of the kamacite bands around the 

 oxide area suggests that a troilite nodule existed at that spot, which by reason of its fusi- 

 bility facilitated the invasion of the molten matter. Light picral; X 9, ordinary light. 



2. Seneca Township. Part of the area shown in figure 1. Droplets of iron rejected 

 in cooling, surrounded by the oxide, have crystallized with a dendritic structure. Light 

 picral; X 60. 



3. Seneca Township. A larger area of dendritic crystallization. Light picral; X 60. 



4. Seneca Township. Part of the area shown in figure 3 at higher magnification. 

 Light picral; X ISO. 



190 



