have
been worked to the edge of the morass and then abandoned for lack of
machinery to drain, and it is thought that in addition to the deposits
lying under them, the swamps contain large quantities of carbonado that
have been washed into them with the tailings and lost during the years
when the value of carbons was unknown.
The
output was said to average about 2,500 carats per month in 1902, but
must be very much larger now and probably was at that time also. There
is a steady and increasing demand for carbons owing to the constant
increase of drilling, pumping, and other machinery requiring a very
hard substance. The average weight of the stones found is about six
carats. The most desirable sizes are those weighing from one to six
carats, those being the sizes used generally for higher mechanical
purposes. Larger stones are broken up and the pieces have the advantage
over the natural stones that they show the inner quality of the stone.
Nevertheless, selected natural stones are preferred by expert
engineers, because the natural formation renders them less liable to
wear and breakage than the square corners and sharp edges of the broken
up stones. Some enormous pieces have been found. The first very large
one, discovered on the ledge of a mountain in the Len-coes district in
1895 weighed 3,078 carats. It measured about 3 inches x 3 inches x
3-1/2 inches. I. K. Gulland of London bought it September 15, 1895, of
Kahn & Co. of Bahia for £6,400. He broke it up into pieces suitable
for diamond drills and sold it for ten per cent, profit. Seven years
later it would have brought four times as much. A piece of 975 carats
was found the year
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