on
the farm of Du Toit's Pan led to the opening up of the mine now known
by that name, and soon there was a rush. This discovery was followed by
another close by, on the site now occupied by Kimberley; this was the
famous De Beers' mine. In all there are now four large deposits close
to the town. Two other deposits were also found south-south-east of
Kimberley, namely, the Koffyfontein and Jagers-fontein mines, in what
is now the Orange Eiver Colony. A very important deposit has more
recently been found at the New Premier mine, near Pretoria, from which
the famous Cullinan Diamond was obtained.
There
was little on the surface to mark the position of these deposits around
Kimberly; some of them were slightly raised above the surrounding
country, some showed a slight depression. When they came to be worked,
however, it was soon seen they were anything but surface deposits, as
at first supposed, for the material in which the Diamonds were found
was utterly unlike the neighbouring rock, from which, moreover, it was
separated by a sharp line of demarcation. This surrounding rock
consists of beds of the Karoo formation. Under a layer of reddish
earth is a bed of calcareous tufa which has evidently been deposited
long subsequent to the formation of the material in which the Diamonds
are found, and therefore, too, later tban the Karoo beds, which are
themselves of comparatively recent geological age, belonging as they do
to the time of the New Bed Series. The Karoo beds, as seen in the
Kimberley mine, consist of a layer of shale, varying in colour from a
greenish tint above to yellowish below ; an intrusive sheet of dolerite
of late Karoo age follows, and with the shales makes up a thickness of
50 feet. Below this comes a bed of black shales
