APPENDIX. 45 



resembling Fahnoglcea macrococca. To these supposed algse the 

 names hare been given of P. adamantiniis and JBalmogleites 

 adamantimis. As illustrating the views he takes of these diamonds, 

 he says, the metamorphic rocks in ^yhich they occur also contain 

 evidences of vegetable fossils, such as JHozoon canadense; and that 

 even in some topazes there are traces of organic substances. 



A very interesting lecture was delivered by Dr. Percy, on 

 Chemical Geology, on 12th Decembei', 1863, before the School of 

 Mines, in which he treats of the foiTnation of Silica ;— of " tliat 

 glorious mineral Corundum ;'^ of Spinel, and of other gem-stones ; 

 showing the influence of water, moderate heat, and salts of 

 chromium, and he then adds: "The diamond will come ultimately, 

 no doubt." There is nothing to show that an igneous origin is 

 attributed to them. 



As an item in this inquiry, we may refer to a notice in Sillimmi''s 

 American Journal (VI., 110), 1848, by Professors E. and W. B. 

 ^Rogers, referring to a previous paper, on " A nev/ method of 

 determining the Carbon in Graphite" (V. 392), in which the 

 authors show that " the diamond may be converted into carbonic 

 acid in the liquid way, and at a moderate heat, by the re-action 

 of a mixture of bi-chromate of potassa and sulphuric acid ; in 

 other words, by the oxydating power of chromic acid." The 

 method is much the same as in the process of oxydating graphite. 

 By this method they obtained from half a grain of diamond an 

 evolution of as much carbon as was nearly equal to what was 

 due to the entire weight of the diamond. 



On the other hand, Sir J. Herschel (Phj^sical G-eography) 

 quotes the case of a Bahia diamond, mentioned by Harting, which 

 contained well-formed Jfilaments of iron pyrites, and he infers 

 from the combination of iron and carbon at high temperatures 

 the possibility of an igneous origin for diamond. 



A paper by Messrs. Sorby and Baker was read in 1869, before 

 the Eoyal Society of Londou, on the structure of certain minerals, 

 among them ruby, sapphire, and diamond, showing that these 

 gems contain cavities entirely or partially filled with a liquid, 

 probably condensed carbonic acid, as well as with crystals — that 

 some emeralds contain a strong saline solution with cubic crystals, 

 probably of chloride of potassium, and that the black specks in 

 diamonds (such e.g., as those seen in our Cudgegong mineral) 

 are really crystals, which are sometimes surrounded by contrac- 

 tion cracks, a black cross appearing under polarized light. The 

 authors conclude that the diamond does not afford positive 

 evidence of a high temperature, though not opposed to it. 



That its structure has great peculiarities has been shown by 

 the changes produced in a yellow diamond by heat. This stone 

 was exhibited by M. Premy to the Academic des Sciences at 



