﻿294 Huntington — Crystalline Structure of Iron Meteorites. 



there are also diagonals of this rectangle. The plate a b and 

 those parallel to it make an angle of 45° with c d, and when 

 traced on to an adjacent face, cut at right angles to the one 

 in the figure, they follow the direction 

 of a dodecahedral plane, and on the 

 under side of the specimen there ap- 

 peared a large natural face, an inch 

 in diameter, exactly parallel to this 

 same plate. This face measured, as 

 shown by an application goniometer, 

 145°, with an adjacent octahedral face, 

 showing that it was the face of a dode- 

 cahedron truncating the octahedral 

 edge ; and when etched neither of 

 these faces showed any Widmanstat- 

 tian figures, but only a mottled ap- 

 pearance, as is usually the case with 

 a surface consisting of a single plate. 

 The other oblique lines in the direc- 

 tion c e make an angle of 66° 19' with 

 the twin octahedron corresponding to 



La Caille. 



c d and are plates of 



the twin cube before mentioned. 



Figure 9 shows, of original size, two sections of the Eobert- 

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

 to the octahedral 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 octa- 

 hedral angle, and these follow a dodecahedral direction while 

 the plates marked a on the octahedral face are parallel to a 

 lateral edge, and, on following the plates on to the face at right 

 angles to the first, it will be seen that they continue to be par- 

 allel to the lateral edge. Hence they cannot be octahedral 

 plates, and, since they are parallel to a principal section of the 

 octahedron, they must be cubic. In order to see whether the 

 Robertson County iron was an unusual case of cubic plates, 

 other well-marked Widmanstattian irons were examined, and 

 in the same way the cube was found, together with the dode- 

 cahedron, in the De Kalb iron before mentioned, and also in 

 the Obenkirchen or Oldenburg iron. Undoubtedly, many 

 other examples could be found, provided the proper faces 

 could be distinguished and etched. 



Thus it is evident that, in the first place, there is a regular 

 unbroken gradation between the coarsest Widmanstattian fig- 

 ures and the finest Neumann lines ; so that, beginning with the 

 Nelson Co. iron, we can arrange a series consisting of the irons 



