OF ARTS AND SCIENCES. 



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ured, as shown by an application goniometer, 145° with an adjacent 

 octahedral face, showing that it was the face of a dodecahedron 

 truncating the octahedral edge ; and when etched neither of these 

 faces showed any Widmanstattian figures, but only a mottled appear- 

 ance, as is usually the case with a surface consisting of a single plate. 

 The other oblique lines in the direction ce make an angle of 66° 19' 

 with c d, and are plates of the twin octahedron corresponding to the 

 twin cube before mentioned. 



Fig. 9. Robertson County. 



Figure 9 shows, of original size, two sections of the Robertson 

 County iron. The left-hand half of the figure is parallel to the octa- 

 hedral face, while the right-hand half is a face at right angles to the 

 first, and in the upper left-hand corner is shown an octahedral cleavage. 

 Here most of the plates are octahedral, and are at once recognized, 

 but the plates marked b and also the irregular cloudy-looking masses 

 bisect the octahedral angle, and these follow a dodecaliedral direction, 



