314 PROCEEDINGS OF THE AMERICAN ACADEMY 



members of the regular octahedron cube and dodecahedron appear on 

 the surface of fracture, still the cube gives character to the iron, and, 

 together with the etched surface, serves to connect it closely with the 

 Brauuau (Hauptmannsdorf) and other so called cubic irons. 



In seeking to explain this apparent variation in the structure of the 

 Butcher specimens, a number of large masses were polished and 

 etched. The most striking result was obtained on a specimen which 

 formed one end of a large mass originally cut up by Ward and Howell 

 for the late J. Lawrence Smith. This surface as it appeared after 

 etching is shown, one third the natural size, in Plate I., which was 

 made directly from a photographic negative. The figure, although so 

 much reduced, shows clearly a zone passing through the thickest part 

 of the mass characterized by a very different crystallization from the 

 rest of the piece. The greater portion of the etched surface is cov- 

 ered only with Neumann lines so characteristic of the Coahuila irons. 

 These lines, although not well shown in the photograph, are plainly 

 exhibited by the print from an etched plate previously published.* 

 This last feature is characteristic of the outside of the mass, where the 

 cooling must have been quicker and the crystallization more rapid and 

 disturbed, though following, nevertheless, the fundamental forms of 

 the regular system. In the central zone, however, corresponding to 

 the thickest part of the specimen, the iron appears to have crystallized 

 more slowly, and exhibits all the characters of Widmanstattian figures 

 resulting from well marked crystal plates ; and here the octahedron 

 appears to predominate, though the presence or absence of the cube 

 and dodecahedron cannot be established by the examination of only a 

 single etched surface cut at random. 



The etched surface of another portion of the same mass seemed to 

 explain this contrast of coarse and fine grained crystallization. There 

 is in the Harvard collection the largest slab ever cut from the Coa- 

 huila specimens, being a full section of the large mass which we have 

 been discussing. The etched surface of this slab was fully as striking 

 as that shown in Plate L, but exhibited more uniformity in the. distri- 

 bution of the figures. Unfortunately, the slab was too large to allow 

 of its reproduction on paper within the limits of this publication, but 

 the figures can be best described by their resemblance to the mark- 

 ings of frost on a large window-pane. Around the edge the crystals 

 were so compact as to show no details, but these compact masses 

 joined the inner portion on a curved outline, looking like cloud masses 



* Proceedings of the American Academy, vol. xxiii., Plate I. 



