“Whilst our knowledge of the modes of formation of other gems is so rapidly advancing that the time does not seem to be very distant when the chemist in his laboratory will be able to produce them artificially if not in large at all events in microscopic crystals—the origin and mode of formation of the diamond is shrouded in apparently inexplicable mystery. It is even undecided whether the diamond is of igneous or vegetable origin, whether its nature is mineral or organic. Some diamonds appear to have been soft, as they are superficially impressed by sand and crystals; others contain crystals of other minerals, germs of plants, and fragments of vegetation. Professor Goppert has a diamond containing dendrites, such as occurs on minerals of aqueous origin, and there is at Berlin a diamond which contains bodies resembling _protococcus pluvialis_, and another containing green corpuscles linked together, closely resembling _polinogtœa macrococca_. (Palmoglœa Micrographic Dictionary.) Sir John Herschel quotes the case of a Bahia diamond mentioned by Harting, which contained well-formed filaments of iron pyrites. Messrs. Sorby and Baker have shown that the diamond may contain cavities entirely or partially filled with a liquid, probably condensed carbonic acid, and that the black specks in diamonds are really crystals which are sometimes surrounded by contraction cracks, a black cross appearing under polarised light. Sir David Brewster has likewise pointed out that the diamond possesses strata of different reflective powers. M. Damour states that diamonds sometimes contain spangles of gold in their cavities.... When shielded from contact with the air, the diamond may be exposed to the highest temperature of our furnaces without undergoing alteration, at least in the case of the colorless diamond; of colored diamonds more will be said hereafter.... A crystal of diamond, inclosed in a piece of dense coke and placed in a plumbago crucible packed with charcoal powder, was heated for half an hour in one of Siemens’ regenerative furnaces to the temperature at which cast-iron melts, without undergoing any change whatever. Another diamond, a cut (rose) diamond, which was inclosed in a crucible as before and heated for ten minutes in the furnace to a temperature at which wrought-iron melts, retained its form and the smoothness of its facets but became quite black and opaque, and exhibited a strong metallic lustre. The black portion formed a distinct layer of the thickness of a hair covering the unaltered substance within. These results confirm those of Schrötter, and appear to justify the view that diamond, though it undergoes no change when exposed to the greatest heat of a porcelain furnace or that at which cast-iron melts, is slowly converted at the temperature of molten wrought-iron into graphite. G. Rose states that some of the specimens of diamond in the