DIAMOND MINING 213
posed
to bromide of radium it glowed and became luminous in the dark. It
showed a faint greenish-yellow tint at its terminations.
Some
idea of the size and quality of Australian diamonds may be had from
the estimate of the production of New South Wales, from whence most of
them come, up to the end of 1901, which was 109,425 carats valued at
$326,455, or a carat value of about half that of the Kimberley diamonds
at the time of the De Beers Consolidation, before the London Syndicate
began to advance the price. The yield of 1902 is estimated at
$48,-780. The production of 1906 is estimated at 2,251 carats, worth
£1,992, and of 1907 at 2,539 carats valued at £2,056.
The
diamonds are found in an alluvial deposit of gravel overlain usually by
a basaltic flow. The deposits are near the present beds of streams, but
are frequently at an elevation of some feet above the banks. According
to Llewellyn Parker, the country rock under the gravel consists of
carboniferous clay stones and tuffs, resting on granite. Doleritic
dykes break through the granite and the leads lie above them and
beneath the basaltic flow. A small diamond enclosed in a piece of rock
was found in one of these dykes, about ten feet below the gravel layer.
Five feet of the upper part of the dyke was decomposed into a soft
yellow earth. Below, it was a hard, bluish-green, coarsely crystalline
dolerite. Another diamond was found under similar conditions, and much
interest in the matter was aroused among scientists, who thought it
might afford a clew to the matrix of the diamonds. Four in all were
found in a rock matrix, but a further examination of nearly 90 tons of
the rock
