Quartz may be classified under two varieties—the common and the rare. Sand, pebbles, many conglomerates, all sandstone rocks come under the former head. The old red sandstone described by Hugh Miller,[2] in which fossil fish are so abundant, and the new red sandstone of the Connecticut valley, famous for its bird or reptile tracks, brought to light through the labors of Dr. Hitchcock,[3] were formed of sand cemented together under pressure by the peroxide of iron. There are many beautiful varieties of the rarer forms of quartz. Not a few of these were known to the ancients, as may be seen by reading the twenty-first chapter of Revelations, where a number are mentioned in the description of the heavenly city. “The wall of it was of jasper, and the foundations of the wall of the city were garnished with all manner of precious stones. The first foundation was jasper; the second, sapphire; the third, a chalcedony; the fourth, an emerald; the fifth, a sardonyx; the sixth, sardius; the seventh, chrysolite; the eighth, beryl; the ninth, a topaz; the tenth, a chrysoprasus; the eleventh, a jacinth; the twelfth, an amethyst.” All of these excepting the sapphire, which is crystallized alumina, are either pure or mixed varieties of quartz, colored with some metallic oxide. One of the most beautiful forms of these precious stones is the agate, especially that kind called the onyx, which consists of a succession of opaque and transparent layers. When carved into gems, this is called the cameo. A wonderful carved cameo was in the Tiffany exhibit at the Centennial Exposition, valued at four thousand dollars. The several layers were so cut as to represent a man looking through the bars of his prison. LIME. Another very plentiful substance in the earth is lime. It is chiefly found in the form of three salts, the carbonate, sulphate and phosphate (CaCO₃) (CaSO₄) (Ca₃(PO₄)₂), respectively. The first is familiarly known as limestone. When crystallized, it appears as marble. The shades of marble are due to the tinting of metallic oxides, and sometimes to the presence of fossils. The most beautiful marble is obtained from Carrara, Italy, which has long been famous for furnishing the material used for statues. It is pure white. Pure black marble is found in some ancient Roman sculptures. Sienna marble is yellow. Italy furnishes one kind that is red. Verd-antique is a mixture of green serpentine and white limestone, while our beautiful Tennessee marble, used so profusely in the new Capitol at Washington, is a blended red and white.