United
States of Colombia, seventy-five miles north-northwest of Bogota. It is
a somewhat inaccessible region, and the mining of the gems is a
precarious occupation. The emeralds occur in a dark, bituminous
limestone, which is shown by fossils to be of Cretaceous age. As
emeralds in other localities occur only in eruptive or metamorphic
rocks, it seems possible that the Muso emeralds have washed in from an
older formation. The emerald-bearing beds are horizontal, overlying
red sandstone and clay slate. Calcite, quartz, pyrite, and the rare
mineral parisite are other minerals found associated with the emerald.
The manner of working these emerald mines is thus described by
Streeter:
"The
mine is worked by a company, who pay an annual rent for it to the
government, and employ one hundred and twenty workmen. It has the form
of a tunnel, of about one hundred yards deep, with very inclined walls.
On the summit of the mountains, and quite near to the mouth of the
mine, are large lakes, whose waters are shut off by means of
water-gates, which can be easily shifted when the laborers require
water. When the waters are freed they rush with great rapidity down the
walls of the mine, and on reaching the bottom of it they are conducted
by means of an underground canal through the mountain into a basin. To
obtain the emeralds the workmen begin by cutting steps on the inclined
walls of the mine, in order to make firm resting-places for their feet.
The overseer places the men at certain distances from each other to
cut out wide steps with the help of pickaxes. The loosened stones fall
by their own weight to the bottom of the mine. When this begins to
fill, a sign is given to let the waters loose, which rush down with
great vehemence, carrying the fragments of rock with them through the
mountain into the basin. This operation is repeated until the
horizontal beds are exposed in which the emeralds are found."
The
mines are owned by the government, by whom they are leased for terms of
seven to fifteen years to the highest bidder. The working of the mines
has been almost continuous since 1558, and they have been the principal
source of emeralds obtained in modern times. Emeralds also occur in
small numbers throughout the black aluminous schists of the Eastern
Cordilleras of Colombia. A few are thus obtained from Cozenez,
Somondose, Nemocon, etc. They are not mined systematically except at
Cozenez.
The
next most prominent locality whence gem emeralds are obtained is in
Siberia, on the river Takovaya, forty-five miles east of Ekaterinburg.
The emeralds here found are often larger than any yet obtained in South
America, but they are not of so good quality. They occur in
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