he rocks of
the African mines and in the diamonds themselves, imparting yellow or
brownish tints to the material. The "River" stones seem to have lost
this color to a considerable extent, if they ever had it. Possibly long
extraction with water has removed the very slightly soluble coloring
material. Whatever the cause of their superiority "River" stones have
always been more highly regarded than stones from the volcanic pipes.

Brazil furnished the world's principal supply of diamonds until the
discovery of the African stones in 1867. At present relatively small
numbers of Brazilian stones reach the world's markets. Most of these
come from the great Bahia district (discovered in 1844) rather than from
the older mines of Brazil. The present Brazilian stones average of small
size. They are, however, of very good quality as a rule. A few green
stones are found in Brazil and these may be of an absinthe-green or of a
pistachio-green tint.

AUSTRALIAN AND AMERICAN SOURCES. While a few diamonds now come on the
market from New South Wales, and while an occasional stone is found in
the United States (usually in glacial drift in the north central States,
or in volcanic material somewhat resembling that of South Africa in
Arkansas) yet the world's output now comes almost entirely from South
Africa and mainly from the enormous volcanic pipes of the Kimberly
district and those of the Premier Co. in the Transvaal.

SOUTH AFRICAN DIAMONDS. The nature of the occurrence of diamond in the
"pipes" of South Africa is so well known to all who deal in diamonds
to-day that but little space need be devoted to it. The "blue ground,"
as the rock in which the diamonds are found is called, seems to have
been forced up from below, perhaps as the material of a mud volcano,
bringing with it the diamonds, garnets, zircons, and the fifty or more
other minerals that have been found in the blue ground. The fragmentary
character of some of these minerals would indicate that the blue ground
was not their original matrix. How the diamonds originally crystallized
and where, is still probably a matter for further speculation.

While at first the mines were worked, like quarries, from the surface,
and while the great Premier mine is still so worked, most of the present
mines are worked by sinking shafts in the native rock outside of the
blue ground and then tunneling into the diamond-bearing rock laterally,
removing it to the surface, allowing it to weathe