Plate 17 



1. CowRA, Australia; ataxite (or finest octahedrite); Ni-Co 14.25 percent. This iron, 

 hitherto classed as an octahedrite, is transitional between octahedrites and ataxites, and 

 more strongly resembles the latter class. It has no octahedral characteristics, except in 

 places a trace of octahedral orientation in the kamacite needles and spindles. Such orienta- 

 tion in several ataxites is more distinct — e. g., Illinois Gulch, Iquique, Shingle Springs, 

 San Cristobal (pis. 21, 22, 25, 29). General structure at moderate magnification, a thick 

 irregular dispersion of kamacite bodies in a dense groundmass. Many of them contain 

 droplike inclusions of phosphide-iron eutectic, as in numerous other ataxites. Picral 50 

 seconds; X 30. U. S. National Museum. 



2. CowRA. An area where the spindles are smaller and less numerous. Picral 45 

 seconds; X 60. 



3. CowRA. Part of the area shown in figure 2 at higher magnification. The groundmass 

 has a confused structure, resembling that in Monahans (pi. 18). Taenite borders around 

 the kamacite spindles are partly lacking. Picral 20 seconds; X 300. 



4. CowRA. Uniform dense plessite. Such areas are found around the larger kamacite 

 bodies; farther away small spindles like those shown in figure 2 begin to appear, and still 

 farther the regular structure shown in figure 1. Compare Wiley and Shingle Springs, plate 

 51. Picral 45 seconds; X 60. 



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