Diamond Mines: Diamond Formation, Formation of the Diamond Page 164



	134 THE DIAMOND MINES OF SOUTH AFRICA were denuded before the formation of the diamond-bearing pipe. If such denudation had taken place after the filling of the pipe with a diamond-bearing matrix, the alluvial deposit of the country surrounding this mine must contain diamonds, but no such discovery of diamonds has been made. Jagersfontein is not the only diamond-bearing pipe that has produced diamonds without having bituminous shale as a country rock. Other pipes or veins have been found both in the Free State and the Transvaal, which are, however, of little commercial value, owing to the small quantities of diamonds found in them, but they are most useful in refuting existing theories, if not in the determination of the genesis of the diamond. An important contribution to this discussion was made by Professor Molengraaff, state geologist of the South African Republic, in a monograph on the diamonds at Rietfontein in the Transvaal. He stated that " the diamond-bearing breccia on the farm was of the same nature as the well-known blue ground of the Kimberley mines. The geological position of the volcanic chimney at Rietfontein was very different from that of the other diamond pipes in South Africa. The latter, of course, all occurred in a higher or lower horizon of the karroo formation, whereas the chimney at Rietfontein seemed to occur in the upper parts of the Pretoria beds in a system of strata overlying the Magaliesberg quartzite. If that position, which was almost certain to his mind, was proved to be correctly determined by a later and more careful geological survey of the surrounding country, this fact would be of high importance in the discussion of the genesis of diamonds. Of the different theories regarding this genesis he would only mention three principal ones. " He would take up first the theory agitated by Messrs. Stanislas Meunier,¹ M. Chaper,² and in a somewhat modified form ¹ " Composition et origine du sable diamantifere du Du Toits Pan, Afrique australe." Comptes rendus de I'Academie des Sciences de Paris. Vol. LXXXIV, No. VI, p. 250. " Examen mineralogique des roches qui accom-pagnent le diamant dans les mines du Cap de Bonne Esperance." Bulletins de I'Academie Royale de Belgique, 3d series, Vol. Ill, No. 4. ⁸ "Note sur la region diamantifere de 1'Afrique australe." Paris, 1880.