THE ORIGIN' AND FORMATION' OF THE DIAMOND. 179 



lieen produced in common, such as mica, garnet, tourmaline, 

 .graphite, and so on. though owing to the very special conditions 

 prevailing in the diamond mines the number and variety of 

 the minerals is much in excess of what is usually found in ordinary 

 metamorphic areas. 



Third — The entire absence of diamonds from unaltered volcanic 

 rock and their presence only in such rocks after they had under- 

 gone metamorphisra, together with the presence in the diamonds 

 occasionally of water, or of minerals containing water, tells strongly 

 in favour of the diamonds having been formed in the mines 

 after the latter had reached the mud volcano stage. Did time 

 permit many other facts, tlian those already mentioned, might 

 be put forward in sup})ort of this view. I will give only one 

 more. In the various experiments undertaken to prove the 

 nature of the diamond it was sometimes found that the ash re- 

 maining behind retained the exact form of the diamond, if 

 the combustion was carried out carefully. As that ash is com- 

 posed of various oxides it is a fair assumption that those oxides 

 were present in the mud-like surroundings and became, by 

 contact, entangled in the diamond during its growth. Such 

 perfect interspersing of those foreign enclosures could hardly 

 occur if the surroundings were not quite mobile, that is, liquid. 

 Such a liquid could scarcely be other than water, or some 

 hydrocarbon, excluding, of course, the molten iron idea. If 

 the temperature were anywhere near a moderate red heat the oxides 

 of iron, at least, would be almost certainly decomposed by 

 prolonged contact with a hydrocarbon. So that by a kind of 

 O.E.D., we are bound to fall back on water or water vapour 

 as practically the only other fluid present. I am not forgetting 

 of course, that above a temperature of some 365° C. water is 

 necessarily a vapour, but it has been shown by Daubree and 

 -others in their experiments that supposing the pressure is suf- 

 ficiently great, the dense water vapour acts in many respects 

 more or less as a liquid. Moreover, in the presence of water 

 vapour, at temperatures above the critical point, and under great 

 pressure, many substances act differently to what they do under 

 ordinary conditions. Thus, I find that hydrocarbons belonging" 

 to both the paraffin and the aromatic series may be heated 

 in closed vessels in presence of water to temperatures m^uch 

 higher than they would endure under ordinary conditions 

 without undergoing decomposition. Other substances such, for 

 instance, as ferrous oxalate, which in the dry condition decomposes 

 under 200° C, can, I find, be heated in a closed vessel with 

 water up to a low red heat and not undergo the slightest decom- 

 position. 



Fourth — There can be no doubt that a high pressure is one 

 of the necessary conditions under which diamonds have been 

 formed in nature. This is shown, inter alia, by their action on 

 polarised light, and by the presence of liquified carbon dioxide 

 in their cavities ; and it is further borne out by experiments 

 with molten cast iron. How much such pressure may have 

 amounted to it is v^ery difficult to say. In the case of diamonds 



