Page:Encyclopædia Britannica, Ninth Edition, v. 18.djvu/748

716 PETROLEUM tions of nature. No evidence appears to be lacking to show that those operations of nature in which heat, pressure, and steam have joined, usually denominated by physicists " metamorphism," when acting upon strata con taining organic remains, are an adequate origin for petro leum as it occurs in the oil-regions of Pennsylvania and in Galicia. Petroleum occurs on the western slope of the Appalachian system from Point Gaspe on the Gulf of St Lawrence to northern Alabama, and there it is most abun dant in the neighbourhood of strata in which there is the greatest accumulation of organic remains. The accumu lations of sediment from which this mountain-system was constructed were deposited in a current whose course was parallel with the axis of the system, and, as has been so fully shown by Professor James Hall (Paleontology of Xew York, vol. iii., Introduction), these sediments were deposited in great thickness and of very coarse materials in the north-east, gradually thinning and increasing in fine ness as they reached the Mississippi valley in the south west. From the latest conclusions of American geologists it may be inferred that originally the eastern border of these deposits lay over a region now covered by the Atlantic Ocean. When the elevation took place that brought the metamorphic rocks of New, England, New York, Pennsylvania, and Virginia to the surface, the eastern border remained submerged, while the western border was brought above the sea-level. The facts that concern petroleum are found in the comparatively un disturbed and nearly level position of this western border, in which the rocks holding the petroleum lie at present, like sand-bars in a current, and the further evidence that they afford that the metamorphic action which has altered nearly all the formations of the eastern border became extinct along a plane that descended deeper and deeper from the surface as the western slope of the system is traversed. This evidence further shows that along the western borders of the system, although the rocks and the coal that they enclose are unaltered near the surface, at the same time vast areas of the fucoidal shale and even limestones containing indigenous petroleum may have been invaded by the heat -action and their volatile con tents distilled at great depths. This distillate, being forced up by heat and hydrostatic pressure, would natur ally accumulate in any overlying bed of rock porous enough to receive it. In Galicia, Roumania, and Tran sylvania the metamorphic core of the Carpathians is flanked by beds of fucoidal shale rich in the remains of marine animals, which are intercalated with the beds of sandstone that contain the oil. This hypothesis, which regards petroleum as a distillate, includes the facts as thus far observed, is in harmony with scientific possi bilities, and is reasonable, as it does not require any ex traordinary assumption of either chemical or geological con ditions. While the maintenance of any particular theory concerning the origin of petroleum is primarily of very little practical value, it is indirectly of value to conclude whether by some deep-seated chemical action the oil is at present being prepared in the laboratories of nature, or whether its generation has been long since completed. If a correct interpretation of the phenomena observed in rela tion to petroleum leads to the hypothesis that the fluid is in most instances a distillate, and especially in those localities where it is most abundant, then the conclusion is inevitable that the generation of petroleum is practically completed, and the deposits are vast natural storehouses which when once emptied are as completely removed from future production as a worked-out bed of coal. Methods of Production. While petroleum has been pro duced for an immemorial period in Persia, China, Japan, Burrnah, Baku, and Galicia, and while the primitive methods employed in each country in its production fur nish interesting subjects for study, it is scarcely possible in this article to do more than indicate in a general man ner how the vast quantities produced at the present time in the United States and Canada are brought to the surface, stored, and transported. In both Galicia and the Caucasus, which, with Canada and the United States, now furnish the petroleum of commerce, the ancient methods of production are being rapidly superseded by those employed in America. In the United States the development of oil-territory has acquired a habit that has become well defined, and has been repeatedly exemplified during the last twenty years. The first step is the sinking of a test or "wild-cat " well outside the limits of any proved productive territory, the progress of such well being eagerly watched not only by those who pay for it but also by many others who hope to profit by the experi ment. The striking of oil in such a well is the signal for a grand rush, and a speculative floating population invades the place. After a time the speculative phase is succeeded by that of settled development. The oil-territory has be come outlined. The sagacious ones have secured control of the most profitable tracts, while the floating element has moved on to a new field. Between the period of active development and absolute exhaustion comes that of decay, when the derricks are rotting and falling to wreck, and when property that has ceased to be productive has been sold at an extravagant price, and after accumulating debts has been abandoned. Finally the wave passes over and nature restores as she restores after the ruin of battle fields. A visit to Pithole city, which in 1865 was, next to Philadelphia, the largest post-office in Pennsylvania, showed in 1881 fields of maize and timothy where some of the most famous wells had been, and of the city a score of houses tumbling to decay and not an inhabitant. It is not to be inferred, however, that any of the sections into which the oil-regions have been divided entirely cease to produce oil. There are wells now producing within sight of the spot where Drake drilled the first well ; but large tracts cease to be centres of speculative investment, the old wells cease to be remunerative, and the new wells no longer hold out the possibilities of a grand lottery. Wells are sometimes drilled by the owners of the land, but the larger part are drilled under leases. These leases are drawn with a great variety of conditions, but they usually stipulate that the lessor shall pay to the lessee a certain portion of the oil produced, the amount varying from one-tenth to one-fourth in proportion to the supposed richness of the territory. One well to five acres is considered as many as a judicious arrangement will allow, but many- wells have been drilled much closer, and in some instances several wells have been drilled on one acre. The oil-sand of different localities varies as it occupies different geological horizons. The Venango oil -sand extends from Tidioute in Warren county to Herman Station in Butler county, Pennsylvania, a distance of 62 miles. It is uniformly a conglomerate of smooth white quartz pebbles, from a quarter to three-quarters of an inch in thickness. In other districts of the United States, Canada, and Galicia the oil-sand is a true sandstone of varying colour and texture. In the Caucasus the sand is fine, and resembles a quicksand, as it rises with the oil and accumulates around the wells. When the location of a well has been determined, a derrick or "rig" is built, which consists of the derrick itself and a small house for an engine, with the necessary foundation for both. This foundation is made of heavy timbers dovetailed and keyed together. The derrick consists of a framework firmly braced in the form of a truncated pyramid, and about 70 feet high. At its base are two large reels, upon one of which the drilling cable is coiled and upon the other the sand-pump rope. At one side of the derrick a heavy post, called the Samson post, is framed into the main sill, upon the top of which rests the walking-beam, one end of it being connected with the engine of from 12 to 15 horse -power, whilst the other supports the drill. When the engine is in motion the walking- beam alternately raises and drops the drill. The boiler is made like the tubular boilers usually employed on locomotives, and is placed at a distance from the well to prevent the ignition of the gas that often accompanies the oil. The engine should be reversible, and so