The finest emeralds in the world come from Muso, a locality in the United States of Colombia, seventy-five miles N. N. W. of Bogota. It is a wild and inaccessible region and the mining of the gems is a precarious occupation. The emeralds occur according to Bauer 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 probable 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 now 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 next most prominent locality whence gem emeralds are obtained is that in Siberia on the river Tokovoya, 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 mica schist (see colored plate), and often associated with the mineral phenacite, chrysoberyl, rutile, etc. Other localities whence emeralds are obtained are Upper Egypt (the source of those known to the ancients), the Heubachthal in Austria, and Alexander county, North Carolina, in our own country. The latter locality is no longer worked, but it has afforded a number of fine crystals.