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PROCEEDINGS OF THE AMERICAN ACADEMY 



the idea of a forcible explosion, and yet all the cracks, even the most 

 ragged, follow directions parallel to the octahedral faces. 



A second specimen of the same iron, measuring twelve and a half 

 inches in its longest dimension, and weighing 9,980 grammes, is a very 

 remarkable mass of cleavage octahedrons, loosely jiacked together and 

 piled on top of each other, not unlike crystals of alum, and almost as 

 sharply defined. The largest octahedral face measures five inches in 

 diameter, but is made up of numerous smaller crystals, in some places 

 jutting out and in others receding, forming numerous triangular pro- 

 jections and depressions. 



Another striking octahedral mass is a fragment of the well-known 

 De Kalb County meteorite. One specimen of this iron shows hollow 

 octahedral faces, two inches in diameter, like hopper crystals, con- 

 sisting of skeletons built up of a series of plates about half an inch 

 wide and one sixteenth of an inch thick. These plates, when cut 

 transversely, constitute the Widmanstattian figures. "When the section 

 is cut at random, the figures may differ somewhat in character, and 

 the plates appear to make various angles with each other ; but when 

 the etched surface is parallel to an octahedral face, the Widmanstattian 

 figures all make equilateral triangles, their sides being parallel to 

 the octahedral edses. 



Fig. 1. De Kalb County. 



Such a section is shown in Fig. 1, which is part of a surface cut 

 parallel to an octahedral face of the De Kalb specimen just referred 

 to. The figure is an exact sketch, representing the plates of their 

 natural size. The most noticeable character in the figure is the 

 system of broad bands which divide the mass into equilateral triangles. 

 These are cross-sections of the crystal plates, which, in another part 

 of the specimen, stand out so markedly in forming the hollow-feced 

 octahedrons. These plates consist of the purer iron to which Rei- 

 chenbach gave the name of Balkeneisen, or Kamacite, and they are 



