1897.] on Diamonds. 497 



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 vapour 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 a 

 great pressure and high temperature, holding carbon in solution, 

 ready to crystallise 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 f 

 found its way. On 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 endeavour to find the quickest vent to the 

 surface. But steam in the presence of molten or even red-hot iron 

 rapidly attacks it, oxidises the metal and liberates large volumes of 

 hydrogen gas, together with less quantities of hydrocarbons J of 

 all kinds — liquid, gaseous and solid. Erosion commenced by steam 

 would be continued by the other gases, and it would be no difficult 

 task for pipes, large as any found in South Africa, to be scored out 

 in this manner. Sir Andrew Noble has shown that when the screw 

 stopper of his steel cylinders in which gunpowder explodes under 

 pressure is not absolutely perfect, gas finds its way out with a rush 

 so overpowering as to score a wide channel in the metal; some of 

 these stoppers and vents are on the table. To illustrate my argu- 

 ment Sir Andrew Noble has been kind enough to try a special 

 experiment. Through a cylinder of granite is drilled a hole • 2 inch 

 diameter, the size of a small vent. This is made the stopper of an 

 explosion chamber, in which a quantity of cordite is fired, the 

 gases escaping through the granite vent. The pressure is about 

 1500 atmospheres, and the whole time of escape is less than half a 

 second. Notice the erosion produced by the escaping gases and by 

 the heat of friction, which have scored out a channel over half an 

 inch diameter and melted the granite along their course. If steel and 

 granite are thus vulnerable at comparatively moderate gaseous pres- 

 sure, is it not easy to imagine the destructive upburst of hydrogen and 

 water gas grooving for itself a channel in the diabase and quartzite, 

 tearing fragments from resisting rocks, covering the country 

 with debris, and finally at the subsidence of the great rush, filling 

 the self-made pipe with a water-borne magma in which rocks, 



* The requisite pressure of fifteen tons on the square inch would exist not 

 many miles beneath the surface of the earth, 



t There are abundant signs that a considerable portion of tliis part of Africa 

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

 undisturbed blue ground at Kimberley. 



X The water sunk in wells close to the Kimberley mine is sometimes impreg- 

 nated with paraffin, and Sir H. Roscoe extracted a solid hydrocarbon from the 

 "blue ground." 



