the original site to the pegmatite bands in those localities. In the Lapland instance the gem was not actually in situ, but
the surrounding rocks were of so similar an origin as to make the
presumption strong. Moreover, the pegmatite bands and the gneiss would
appear to be but an earlier and later stage of the same metamorphosis.
Gorceix concluded the San Joao Diamonds had also originated in
pegmatite " veins." The fact that in these bands Quartz, Anatase and
Haematite, seem to have been simultaneously formed with the Diamond,
recalls the changes described above concerning these oxides. Rodgers
(" Geology of Cape Colony ") points out that although the materials
filling the pipes of South Africa differ so, yet there are gradations
from one type to another; and Prof. Bonney (Geol. Mag., 1899,
p. 309) records the presence of Diamond in eclogite (an ultra-basic
rock without Olivine) from Newland's mine in Griqualand West. Rodgers
concluded that the Kimberley Diamonds probably originated in a
deep-seated ultra-basic rock-magma, explosions proceeding from this or
a lower horizon having filled the pipes with brecciated material
containing a large proportion of ferro-magnesian silicates; subsequent
hydration would convert the material into a serpentinous mass such as
is there seen.
Great
stress has been laid on the association with Olivine, but there are
many occurrences without this associate, and in any case, if Diamond
originates by this action of heated waters the same action could
affect, and apparently does affect, rocks containing no Olivine.
Although it has been allowed that the pegmatite bands might represent
the solidification of fused silicates saturated with water, the full
importance of the water does not seem to have been given
