Engineering Wonders of the World
Volume I

ENGINEERING IN THE however, the Russian Government has pro- hibited the pilgrimages as being the cause of spreading cholera. In many petroleum districts heavy petro- leum exudes at points where the oil-bearing strata “ outcrop,” becomes oxidized by ex- posure to the air, mingles with Asphalt , , , ,, . p. dust and organic matter, and Deposits. e ° forms an impure kind of as- phalt. Where conditions are peculiarly fa- vourable, enormous masses of asphalt have accumulated. The most wonderful example is the Trinidad Pitch Lake, estimated to contain 10,000,000 tons of the material, and covering an area of about 100 acres. The lake is in reality the crater of a huge mud volcano, while the pitch is nothing more than the residue of the oil that once found access to the crater from its containing strata. This oil gradually became more and more viscous as its lighter constituents were evaporated under the influence of a hot tropical sun, until finally it reached its present consistency. During this process it became admixed with sand and other mineral and vegetable matter, which have rendered it a first-class material for making “ asphalt ” pavements. Now, the lake, although suffi- ciently solid to allow heavy transport over it, is plastic, and has a constant but slow motion which imparts to its surface a series of wave- like and ever-changing creases and wrinkles. Objects which sink into the pitch reappear long afterwards at distant points, and the tramway running across the lake to remove the material has to be shifted every few days to prevent its being engulfed. The enormous extent of the lake’s overflow is proved by the reefs of asphalt which extend far out to sea. Another interesting and most valuable natural product of oil is found in the form of earth-wax or “ ozokerite.” This is ex- tensively mined at Boryslaw in Galicia. The wax occurs in thin seams or pockets, filling WORLD'S OIL FIELDS. 325 cracks and crevices in the strata, which are mostly of a stiff clayey nature. In Scotland there are large deposits of shales, dark in colour and inodorous, showing to the naked eye no traces of petroleum, but which on being subjected to destructive dis- tillation have in some cases yielded as much as 100 gallons per ton. Nowadays the average ROUMANIAN OIL-WELL SINKERS AT WORK. These men dig wells 300 to 500 feet deep, and only 1 metre square in section. run is about 25 gallons a ton, as the highest grade shales have been exhausted ; but the shales are treated more scientifically, and the diminished yield of oil is more than compen- sated by the recovery of such valuable bye- products as sulphate of ammonia and paraffin wax in increased quantities. THE SINKING OF OIL WELLS. Originally many oil wells were dug by hand, and in Roumania this system is still largely