210 PROCEEDINGS OF THE AMERICAN ACADEMY. 



diamonds were cut and polished in the same way. The last specimen 

 was a complex twin, and when a projecting angle was applied to the 

 wheel the cutting was naturally slow, but none the less effective, and 

 in all respects the residue from the Canon Diablo iron was found to 

 act exactly like any other diamond powder. 



Thus the combined evidence of the author's work with that of 

 Friedel * and Moissan f establishes the fact that the Canon Diablo 

 iron contains true diamonds, and not any new allotropic form of 

 carbon. It is surprising that crystals are so rare, but, as this paper 

 shows, they do occur. 



It has been suggested, since the Canon Diablo iron has been found 

 in such quantities, that it may have a terrestrial origin, but such an 

 idea is at once dispelled by an examination of the exterior surface of 

 the largest mass thus far obtained, apart from other considerations. 



The ma^s referred to was purchased by Professor J. P. Cooke from 

 Mr. W. W. Howell of Washington, D. C. It weighs 1087 pounds, and 

 is at present in the Harvard Museum. It is seldom that irons which 

 have not been seen to fall retain, at the time they are found, any of 

 the original features of their crust, but this specimen is a marked 

 exception. It is a roughly spherical mass somewhat flattened in one 

 plane. One of these flattened surfaces shows signs of fusion, but is 

 further characterized by deep pittings looking almost like bullet holes, 

 except that it frequently happens that they are larger on the interior 

 than at the orifice. Occasionally they are winding, but all preserve 

 the same general direction. They vary in size from one sixteenth of 

 an inch in diameter to two inches, and reach in some cases a depth of 

 from three to four inches. These cannot be explained by unequal 

 heating or by the erosive action of the air, owing to the fact just 

 mentioned, that they are larger in the interior than at the surface. 

 This character is shown in a reproduction of a small photograph, 

 (Plate I. Fig. 1). The other side of the mass (Plate I. Fig. 2) shows 

 large concave surfaces, as if pieces of six or seven inches in diameter 

 had flaked off, or the hollows had been scooped out by the action of 

 pneumatic drills. 



For some time these two utterly different surfaces were a puzzle, 

 but a closer examination disclosed troilite in the depths of some of 

 the small cavities (Plate I. Fig. 1) while on the side of the larger 

 pittings (Plate I. Fig. 2) the same mineral could be seen exposed and 



* Bulletin <le la Soc. Franoaise de Mine'ralogie, No. 9, Dec. 9, 1892, p. 258. 

 t Comptes Rendus, Tome CXVI. No. 7, Feb. 13, 1893, p. 288. 



