DIAMOND MINES OF SOUTH AFRICA 273
Christiana.
There are a few companies, but a majority of the miners are independent
diggers. The work is done by Kaffirs, and the white men oversee them.
The terraces and river gravels vary in depth from a few inches to 40 or 50 feet. In Smith's Gully at Wal-deck's
Plant, the diamondiferous material was found, on reopening it after the
Boer war, to be 75 feet deep. In some cases these deposits extend
laterally three or four miles from the river, and in places there
appears to have been more than one period of sedimentation; the pebbles
in the last have a matrix of stiff siliceous clay. In the gravels are
large greenstone bowlders filled between with sand and pebbles, the
whole resting on a floor of amygdaloidal greenstone. The pebbles are
principally siliceous; jasper, chalcedony, agate, and with them,
greenstone, ironstone, ilmenite, garnet, topaz and diamond. The
diamonds are usually dodecahedral crystals, free from flaws. All
colors are found, though a yellowish tint predominates. Mr. T. E. Coe
says that the deep places are the result of a period of great erosion,
as the steep channels were worn through hard diabase and were filled
with sand, pebbles, and bowlders much rolled and smooth. In some cases
this deposit was overlain with red sand, the " rooi-grond " of the
early Dutch digger. The bed rock of these deep places consists of Karoo
shale on a bed of amygdaloidal diabase. The diamonds are not
distributed uniformly through the deposit, but are found in " bantam"
layers; beds of smooth pebbles of moderate size.
The Zaud deposit near the Wedburg placers has an
unusually thick layer of the surface sand in which most
of the early wet diggings was done. Now, where open 18
