OIL WELLS.--Where there are marks of disturbance and misplacement of the rocks, there the experienced sink wells. Rugged hills and sharply-defined valleys are, generally, signs of such dislocation. The line or “break” from which the rocks dip like the roof of a house is considered most favorable. There is no such thing as an “oil rock,” for the oil is found at different depths, and the fissure containing it is more or less vertical. In Pennsylvania, the greatest flowing wells have been found in the third sand rock. No limestone has afforded any large supply of oil. Coal in no large quantities is ever found upon or in the immediate vicinity of the oil territory. The “show of oil” increases in value as a sign, with the depth at which it is found. Especially is the finding of a large amount of imprisoned gas, though no oil may be present, regarded as a good indication that oil is near. In the bituminous coal region, a gas spring indicates the probable existence of oil in the rocks below. But generally, “surface shows” are seductive. The great oil belt runs south-westerly from Oil Creek, Pa., to Burning Springs, West Va. But Ohio, Kentucky, Tennessee, Georgia, Alabama, Missouri, Texas, Illinois, Indiana, Michigan and Southern California are also rich in petroleum. CHAPTER VII. ARTIFICIAL JEWELRY--HOW MADE AND HOW DETECTED. MOCK DIAMONDS--“PARIS BRILLIANTS”--THE MANUFACTURE OF PASTES--FALSE RUBY, TOPAZ, SAPPHIRE, EMERALD AND CARNELIAN--HOW TO DISTINGUISH TRUE AND FALSE GEMS--IMITATION PEARL AND CORAL--ARTIFICIAL GOLD--LIST OF PRECIOUS STONES. “Bristol Stones,” “Irish Diamonds,” “Cape May Diamonds,” and “California Diamonds,” are skillfully-cut quartz crystals. They are easily detected by the file and by their lightness. “Paris Brilliants” are more dangerous counterfeits, and are very often sold for genuine. The great establishment of Boarguiguon, in Paris, is the most famous manufactory of artificial gems in the world, employing about one hundred hands. The gems are such perfect imitations that they can be distinguished from real stones only by the closest scrutiny of those experienced in such matters. They fail chiefly in hardness; in brilliancy and gravity they nearly or quite equal the genuine. Nature has made the most precious stones with the most common materials. The diamond is purified charcoal; while the matter of clay and white pebbles is the base of all other gems.