388 THE DIAMOND
Vertical
rents in the plateau were made in the process, into which a magma of
ultra-basic rock exuded from the interior, and a mass of
hydrocarbonated material poured from the surface, forming an
agglomerate having the characteristic of an altered eruptive rock, yet
differing from any other lava known.
Owing
to the precipitation of carbonaceous surface; material into the magma
confined in the depths of the vertical fissures, processes ensued which
segregated the carbon in the mass and crystallized it as diamond.
The
cooling and cooled mass was raised in the chimneys by successive
uplifts, occasioned by the generation of gases within the mass and the
settlings of the earth's crust.
The
yield of diamond will decrease as the rock passes from an agglomerate
of igneous lava and surface material, into the underlying eruptive rock
which was not reached by the surface admixture.
Inasmuch
as it is the brecciated kimberlite only which contains the diamonds,
and the breccia though somewhat altered, has not been fully
amalgamated with the ground-mass, the kimberlite was not in a state of
ignition when the diamonds were crystallized.
The
chemical reactions whereby the carbon was crystallized, remains a
subject for speculation and the experiments of scientists, but it
appears probable that it was accomplished in the African diamond
chimneys by the passage of superheated steam through an agglomerate of
magma while being cooled by carbonaceous material and water poured into
it from above. That the crystallization of carbon as diamond does not
depend absolutely upon the geologic structure, during
