Lucas, and a series from a recent And in the Tiffany exhibit, northwest gallery, Mines and Mining building, World's Oolumbian Exposition.
In Montana, sapphires are found at what are known as Eldorado Bar, Emerald Bar, French Bar, Buby Bar, and for some 6 miles along the Missouri Biver; also in Missoula county, 70 miles distant. Stubb's Ferry, 12 miles east of Helena, is about the central point of the Missouri river district. Although these bars had been sluiced for gold, no systematic attempt had been made before 1891 to work them for gems. Occasionally sapphires were sent to the large cities, but owing to the cost of cutting them, and the small demand for any other than the true ruby-red or sapphire-blue stones, they received but little recognition.
The greater part of the region above described passed in 1891 into the hands of an English company bearing the name of the Buby and Sapphire Mining Company, which has since obtained a large number of stones, some of which have been cut and exhibited in London. They embrace a great variety of the lighter shades red, yellow, blue, and green. The latter color is quite pronounced and rather a blue green than an emerald green. Nearly all the stones, when finely cut, have a certain metallic luster strikingly beautiful and peculiar to the sapphires from this locality. No true red rubies or true blue sapphires have been found. A fine series of these gems was shown by Mr. Spratt in the Montana exhibit of the Mines and Mining building, World's Oolumbian Exposition, and mounted in jewelry by an American jeweler in the Manufacturers' building.
At all these bars along the upper Missouri the sapphires occur chiefly in a layer of auriferous glacial gravel, a few inches thick, which lies immediately in a slaty bed rock. Associated in the same layer were topaz in small crystals, garnets of a rich, ruby-red color, often mistaken for and called rubies, cyanite in broken crystals, cassiterite (stream tin), and other commoner minerals. The original source of the sapphires found at these bars is indicated in an eruptive dike, found cutting the slaty rock at Buby Bar, on which rests the glacial gravel. In this eruptive rock there were found crystals of sapphire, pyrope, garnet, and sauidine feldspar. There seems no doubt that all the sapphire along these bars of the Missouri is derived from the breaking down, by glacial action, of a rock similar to this. The outcrop at Buby Bar can not, however, account for the deposit of sapphires at Eldorado Bar, 6 miles to the north; and it will be necessary to await further discoveries before attempting to determine the exact source of these gems.
Mr. H. Miers finds the rock at Buby Bar to be a vesicular mica-augiteandesite, containing an abundance of brown mica and porphyritic crystals of augite. The ground mass consists chiefly of feldspar microlites with a considerable amount of glassy, interstitial matter and much magnetite. Many of the cavities are occupied by a brown glass which appears yellow in thin sections and displays a speculitic structure originating in the sides of the cavities.
