488 



PROCEEDINGS OP THE AMERICAN ACADEMY 



-b'if 



7. HauptniiinnsJorf 

 (Braunau). 



peareJ, as shown in Fig. 7, some of the lines being parallel to the 

 cube edges and others forming diagonals of the cube face. These 

 diagonals might be octahedral lines or dodeca- 

 hedral lines, or they might be lines of cleavage 

 parallel to the face of the other individual of a 

 tvrin, and as the face show^n in section replacing 

 the cube angle at a was the face of a twin 

 cube, the lines parallel to that edge would prob- 

 ably be due to the same plane; and this was 

 proved to be the case, as on an adjacent face the 

 same lines followed the direction of twinning. 

 These lines of twinning are not represented in 

 Fig. 7, to prevent confusion. 



Thus the Hauptmannsdorf iron appears to be purely cubic in struc- 

 ture, while the Tazewell appears to be purely octahedral. However, 

 as the octahedron was observed in the Coahuila iron, and the dodeca- 

 hedron appeared in the Butler iron, it became a question whether the 

 cube and dodecahedron could not be found in the typical octahedral 

 irons. A veiy large number of irons were studied with this end in 

 view, but nothing could be determined with specimens where only one 

 face could be examined. It was necessary to have two known crystal 

 faces, and to be able to follow the plates over an edge. For on a 

 cube face the octahedral plates give rectangular intersections, while on 

 an octahedral face the cube plates would give intersections parallel to 

 the octahedral edges. 



Figure 8 shows of original size a section of the well-known La Caille 

 meteorite, cut parallel to an assumed cube 

 face, the direction being determined by 

 external well-developed octahedral faces. 

 Here the rectangular intersections a c and 

 c d result from octahedral plates intersect- 

 ing the cube face, but there are also diago- 

 nals 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 do- 

 decahedral plane, and on the under side 

 of the specimen there appeared a large 

 natural face, an inch in diameter, exactly 



Fig. 8. La Caille. 



parallel to this same plate. This face meas- 



