At first sand is thrown out with the oil, and frequently it is ejected with such force that a plate of iron three inches thick struck by the stream is worn through in less than a day by this liquid sand blast. When the wells cease spouting and it is not deemed advisable to bore deeper, pumping is employed. Generally the oil coming from the wells is conducted into large, carefully tamped excavations in the ground forming ponds or lakes. In these huge reservoirs the sand and heavier parts soon sink, making the bottom impervious. After the settling the petroleum is either pumped into large iron tanks or sent directly to the refinery by pipe-lines. Since petroleum is vastly cheaper than coal, the steamers plying on the Caspian Sea and the locomotives of many of the Russian railroads use oil for fuel. At one time so great was the accumulation of petroleum that it sold at the wells for a few cents a ton. A fleet of tank-steamers conveys the oil products to the interior of Russia by the Caspian Sea and Volga River route. The crude petroleum of Baku yields a lower percentage of kerosene than the American wells, but it contains more lubricating oil. Millions of gallons of lubricating oil are shipped from Baku each year to all parts of Europe. On the opposite side of the Caspian there are great cliffs of mineral wax such as is obtained from petroleum and used extensively in the manufacture of paraffin candles. More than two hundred different products are made from petroleum, among the chief of which are kerosene, lubricating oil, benzine, gasoline, vaseline, and paraffin. CHAPTER XXI THE SOUTH AFRICAN DIAMOND FIELDS Many of the great treasure fields of the world have been discovered by chance rather than careful search. The diamonds of the Deccan, India, were trodden under foot for ages before they were recognized as diamonds. In Brazil the gold placer miners threw away the glassy pebbles as worthless and the black slaves used them as counters in their card games. A visitor who was acquainted with the diamond fields of India happened one day to notice the shining stones which two men were using in a card game at a public-house. The brilliancy of the pebbles piqued his curiosity. Having secured some, he tested them and found them to be diamonds of the first water. Yet so great was the prejudice against the Brazilian diamonds at first that for years many were secretly shipped to India and thence sent to the diamond market as Indian diamonds. A trivial circumstance often leads to a marvellous change in the conditions of men, communities, and nations. The playful act of a Boer lad picking up a shining pebble on the banks of the Orange River served as a beacon to lure persons to search for the most precious and hardest of gems, the diamond, and thereby transformed South Africa.