nerals which are common
accessory constituents of granite, gneiss and the crystalline schists.
Gold (also platinum) is a not infrequent associate, but this may only
mean that the sands in which the diamond is found have been searched
because they were known to be auriferous; also that both gold and
diamond are among the most durable of minerals and may have survived
from ancient rocks of which other traces have been lost.

The localities at which the diamond has been supposed to occur in its
original matrix are the following:--at Wajra Karur, in the Cuddapah
district, India, M. Chaper found diamond with corundum in a decomposed
red pegmatite vein in gneiss. At S[=a]o Joao da Chapada, in Minas
Geraes, diamonds occur in a clay interstratified with the itacolumite,
and are accompanied by sharp crystals of rutile and haematite in the
neighbourhood of decomposed quartz veins which intersect the
itacolumite. It has been suggested that these three minerals were
originally formed in the quartz veins. In both these occurrences the
evidence is certainly not sufficient to establish the presence of an
original matrix. At Inverell in New South Wales a diamond (1906) has
been found embedded in a hornblende diabase which is described as a
dyke intersecting the granite. Finally there is the remarkable
occurrence in the blue ground of the African pipes.

There has been much controversy concerning the nature and origin of
the blue ground itself; and even granted that (as is generally
believed) the blue ground is a much serpentinized volcanic breccia
consisting originally of an olivine-bronzite-biotite rock (the
so-called kimberlite), it contains so many rounded and angular
fragments of various rocks and minerals that it is difficult to say
which of them may have belonged to the original rock, and whether any
were formed _in situ_, or were brought up from below as inclusions.
Carvill Lewis believed the blue ground to be true eruptive rock, and
the carbon to have been derived from the bituminous shales of which it
contains fragments. The Kimberley shales, which are penetrated by the
De Beers group of pipes, were, however, certainly not the source of
the carbon at the Premier (Transvaal) mine, for at this locality the
shales do not exist. The view that the diamond may have crystallized
out from solution in its present matrix receives some support from the
experiments o