206 PROCEEDINGS OF THE AMERICAN ACADEMY. 



" Graphite is further found associated with the iron of the deep- 

 seated rocks. 



" Graphite, crystallizing iu the form of diamond, is found in meteoric 

 iron. Diamonds are also found iu meteoric iron. 



" The greatest deposits of native diamonds appear to have come 

 from great depths. 



" Does it not appear plain that the meteoric diamonds, which are 

 obviously in their original matrix, may explain the origin of the 

 terrestrial diamonds ? 



" My object has been merely to point out a possible relation, and not 

 to advocate a theory, but in this relation we have a clue which may 

 possibly lead to a solution of one of the most obscure problems of 

 mineralogy." 



It was further suggested that pressure might be a determining 

 factor in the crystallization of carbon. At the time this seemed a 

 somewhat large assumption to make from so small data, but since 

 then M. Moissan has followed up the same idea by most interesting 

 experiments, iu which he finds that carbon can be made to crystallize 

 out of melted wrought iron in the form of diamond if the iron is 

 allowed to cool under pressure ; as is the case when the melted metal 

 expands in setting against the crust formed by quenching the exterior 

 of the mass with water.* May it not be that, if we could reach thus 

 a pressure commensurate with that produced by the crust of the earth, 

 the resulting diamonds would attain the size and perfection of those 

 now found in the famous diamond fields of South Africa? 



In December, 1892, M. C. Friedel,f apparently not having seen the 

 papers published by the author seven months before, made a thorough 

 examination of some of the Canon Diablo iron. The diamonds that 

 he isolated were of the carbonado variety, and in order finally to 

 prove that the black grains were diamond he burnt a portion in 

 oxygen. Thus he proved chemically that the substance was carbon, 

 and since the hardness was beyond the ruby he considered it suffi- 

 ciently determined that it belonged to the variety diamond. The proof 

 of the hardness of the diamond, however, does not rest with the fact 

 that diamonds will scratch the sapphire or the ruby, since this may be 

 done by other substances, notably " carborundum," but diamond alone 

 will cut diamond, and this test had not been applied to the material 



* Comptes Rendus, Tome CXVI. No. 6, Feb. 6, 1893, p. 218. 

 t Bulletin de la Socie'te Francaise de Mineralogie, Tome XV. No. 9, Decem- 

 ber, 1892, p. 258. 



