working
is not practicable, shafts are sunk to the lower layers of gravel,
which are richest in diamonds, and it is taken out by tunneling.
From
the nature of it, the yield of an alluvial deposit is uncertain and
irregular. Mr. T. E. Coe stated that 116 carats of diamonds were taken
at the Zaud Kopje in the first two months of 1903, from 1,340 loads of
gravel. This would equal only 0.087 of a carat per load, but they sold
for 94s. 6d. per carat. The alluvial diamonds of the Transvaal in 1898
amounted to 12,283 carats, and brought £35,228, or a fraction over 57s.
4d. per carat. The diggings at Christiana on the Vaal in the Transvaal
in 1907, yielded 2,562 carats and sold for £13,579, or 106s. per carat.
The output of the Vaal river diggings for 1905 is given as 81,7493/2
carats, at an average value of 77s. 7d., and for 1906 as 101,-60734
carats at 77s. 3d. The alluvial diggings of the Orange River Colony for
1907 yielded 7,102 carats valued at £36,895, or 103s. 8d. per carat.
It
is doubtful if all the wet diggings of Africa have exceeded an average
of 100,000 carats per annum since the discovery of the Kimberley pipes.
The diamonds, however, have probably brought an average of fifty per
cent, more than the average for the dry diggings.
The
territory in which diamondiferous deposits and chimneys in Africa are
known to exist, is spreading constantly. Alluvial deposits containing
diamonds have been found east as far as longitude 280 E. in
the Orange River Colony and the Transvaal; west to German South West
Africa; north to the watershed of the Limpopo and Zambesi rivers in
Matabeleland at about 190 S., and south to about 310 S. in the Orange River Colony,
