DIAMONDS. 231 



cavities which the same test proves to contain gas at considerable 

 pressure. 



The ash left after burniug a diamond invariably coutaiiis iron as its 

 chief constituent; and the most common colors of diamonds, when not 

 perfectly pellucid, show various shades of brown and yellow, from the 

 palest "off" color" to almost black. These variations accord with the 

 theory that the diamond has separated from molten iron, and also 

 explains how it happens that stones ^om different mines, and even 

 from different parts of the same mine, differ from each other. Along 

 with carbon, molten iron dissolves other bodies which possess tinctorial 

 powers. One batch of iron might contain an impurity coloring the 

 stones blue, another lot would tend toward the formation of pink 

 stones, another of green, and so on. Traces of cobalt, nickel, chromium, 

 and manganese — all metals present in the blue ground — might produce 

 all these colors. 



An hypothesis, however, is of little valne if it only elucidates one- 

 half of a problem. Let us see how far we can follow out the ferric 

 hypothesis to explain the volcanic pipes. In the first place we must 

 remember these so-called volcanic vents are admittedly not filled with 

 eruptive rocks, scoriaceous fragments, etc., constituting the ordinary 

 contents of volcanic dncts. At Kimberley the pipes are filled with a 

 geological plum pudding of heterogenous character— agreeing, how- 

 ever, in one particular. The appearance of shale and fragments of 

 other rocks shows that the melange has suffered no great heat in its 

 present condition, and that it has been erupted from great depths by 

 the agency of water vapor or some similar gas. How is this to be 

 accounted for *? 



It must be borne in mind I start with the reasonable supposition that 

 at a sufficient depth ^ there were masses of molten iron at great pressure 

 and high temperature, holding carbon in solution, ready to crystallize 

 out on cooling. In illustration, I may cite the masses of erupted iron 

 in Greenland. Far back in time the cooling from above caused cracks 

 in superjacent strata through which water ^ found its ways. Before 

 reaching the iron the water would be converted into gas, and this gas 

 would rapidly disintegrate and erode the channels through which it 

 passed, grooving a passage more and more vertical in the endeavor 

 to find the quickest vent to the surface. But steam in the presence of 

 molten or even red-hot iron rapidly attacks it, oxidizes the metal and 

 liberates large volumes of hydrogen gas, together with less quantities 

 of hydrocarbons^ of all kinds — liquids, gaseous, and solid. Erosion 



'The requisite pressure of 15 tons on the square inch would exist not many miles 

 beneath the surface of the earth. 



^There are abundant signs that a considerable portion of this part of Africa was 

 once under water, and a fresh-water shell has been found in apparently undisturbed 

 blue ground at Kimberley. 



=The water sunk in wells close to the Kimberley mine is somtimea impregnated 

 with paraffin, and Sir H. Eoscoe extracted a solid hydrocarbon from the " blue 

 ground." 



