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.
