THE DIAMOND MINES OF SOUTH AFRICA. 153 
been slightly higher than the surrounding country, but now it 
has been excavated for a depth of 300 feet or more. The walls 
of the mine consist entirely of yellowish shales lying on dark 
_carbonaceous shales, with thin streaks of coal, and much pyrites. 
The shales are horizontal, but their edges are turned up where 
they are in contact with the eruptive rock of the mine itself. 
This eruptive rock is a breccia of very peculiar character. The 
matrix is a green, or yellowish-green rock, composed of serpen- 
tine and hydrated bronzite, and may be considered as an altered 
olivine-enstatite-rock. It contains angular fragments of shale, 
and more rounded “ pebbles” of various eruptive rocks, such as 
olivine-enstatite-rock, gabbro, dolerite, and augite-andesite, as 
well as grits and small fragments of gneiss. The diamonds are 
found only in the serpentinous rock, and are absent from all the 
included fragments. They are usually imperfect, portions ap- 
parently having been broken off. Along with them occur other 
minerals, such as garnet, magnetite, ilmenite, and bronzite. It 
will be noticed that this diamond-rock differs altogether from the 
diamond-rock of Brazil, which is a crystalline schist called Itaco- 
lumite, formed of quartz-grains and talc. 
The walls of De Beere’s mine are dolerite, except the north 
side, which is shale overlaid by about 50 feet of gabbro. In Du 
Troit’s pan mine the south wall is shale, the rest is formed of 
dolerite. Both are volcanic pipes, and the diamond rock in each 
is the same as at Kimberley mine. Many other undoubted pipes 
have.been opened and prospected near Kimberley, but they have 
been abandoned as unremunerative, although some diamonds 
were obtained. 
The rock is blasted at the bottom of the mine, and broken 
into small pieces. It is brought to the surface in buckets run- 
ning on wire ropes that stretch from the brink of the mine to 
each claim. It is then spread out on the ground, watered, and 
and exposed to atmospheric action. When disintegrated it is 
washed, and the diamonds are picked out. 
We now come to the important question, What is the origin 
of the diamonds? 
That the whole mass of rock in the pipe has flowed upwards 
from below is proved by the upturned edges of the shales in con- 
tact with it; but as the edges of the fragments forming the 
breccia are not fused, we cannot suppose that the temperature of 
the rock was very intense. This, together with the altered and 
hydrated condition of the rock itself, make it probable that it 
was largely mixed with water, and that it flowed upward from 
the expansive force of super-heated steam at a great pressure. 
The occurrence of pieces of gneiss, as well as many minerals, 
with the diamonds, suggests the idea that all of them may have 
been derived from metamorphic rocks lying at great depths below 
the surface, and the broken character of the diamonds has also 
been mentioned in support of this hypothesis. But, however 
good this latter point may be to prove that the diamonds were 
