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Australian Diamonds. 97
north-west
of Mudgee. The Cudgegong empties itself into the Macquarie, which is an
affluent of the Darling. As soon as the gold diggers had set to work
they detected Diamonds ; and in July, 1869, operations were conducted
by the Australian Diamond Mines' Company of Melbourne,
At
the Mudgee workings, gems were found in an old river-drift, believed to
be of Pliocene age, distributed in local patches, which are remnants of
deposits once widely spread over the district, but now partially
removed by denudation. These ancient river-gravels occur at various
distances from the actual channel, and at elevations of forty feet or
more above the level of the river. They are generally covered by a
protective layer of basalt, sometimes columnar ; and shafts have been
sunk through the basaltic cap, so as to reach the under-lying
Diamond-drift, which rests either on vertical palaeozoic strata- or on
massive greenstone. The older drifts have been in some cases
re-distributed, thus forming gravels of the Pleistocene and later
periods. The drifts contain pebbles and boulders of Quartz, Tin-Stone,
Rock-Crystal, Jasper, Agate, and other siliceous minerals, mixed with
coarse sand and clay, and in some places united by a siliceous cement,
into a compact mass. Among the pebbles of the gravel, the diligent
seeker may find many of the rarer minerals, including crystals of
Topaz, Sapphire, Ruby, Zircon, Spinel, and Garnet ; with Gold and
Diamonds. The Diamonds are irregularly distributed through the gravels
; but hardly in sufficient numbers to pay for the working, though some
of the Diamonds from the Cudgegong Field are remarkable for their
beauty and purity of colour.
Within
the last few years a Diamond-field has been opened up near Bingara, New
South Wales. This town is about 400 miles north of Sydney, on the river
Horton,
H
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