); these are rapidly hoisted to the surface, where
their contents are automatically dumped into side-tipping trucks, and
these in turn are drawn away in a continual procession by an endless
wire rope along the tram lines leading to the vast "distributing
floors." These are open tracts upon which the blue ground is spread
out and left exposed to sun and rain until it crumbles and
disintegrates, the process being hastened by harrowing with steam
ploughs; this may require a period of three or six months, or even a
year. The stock of blue ground on the floors at one time in 1905 was
nearly 4,500,000 loads. The disintegrated ground is then brought back
in the trucks and fed through perforated cylinders into the washing
pans; the hard blue which has resisted disintegration on the floors,
and the lumps which are too big to pass the cylindrical sieves, are
crushed before going to the pans. These are shallow cylindrical
troughs containing muddy water in which the diamonds and other heavy
minerals (concentrates) are swept to the rim by revolving toothed
arms, while the lighter stuff escapes near the centre of the pan. The
concentrates are then passed over sloping tables (pulsator) and shaken
to and fro under a stream of water which effects a second
concentration of the heaviest material.

Until recently the final separation of the diamond from the
concentrates was made by hand picking, but even this has now been
replaced by machinery, owing to the remarkable discovery that a
greased surface will hold a diamond while allowing the other heavy
minerals to pass over it. The concentrates are washed down a sloping
table of corrugated iron which is smeared with grease, and it is found
that practically all the diamonds adhere to the table, and the other
minerals are washed away. At the large and important Premier mine in
the Transvaal the Elmore process, used in British Columbia and in
Wales for the separation of metallic ores, has been also introduced.
In the Elmore process oil is employed to float off the materials which
adhere to it, while the other materials remain in the water, the oil
being separated from the water by centrifugal action. The other
minerals found in the concentrates are pebbles and fragments of
pyrope, zircon, cyanite, chrome-diopside, enstatite, a green pyroxene,
mica, ilmenite, magnetite, chromite, hornblende, olivine, barytes,
calcite and pyr