Origin and Occurrence.—The origin of petroleum has been a subject of much 'speculation among geologists. The most widely accepted notion is that it is due to the very slow decomposition of organic remains, animal, vegetable, or both combined. But the occurrence of any organic detritus in such formations as the Silurian, in sufficient quantity to account for the enormous yield of oil, is doubted by many. Another attempted explanation of its origin is the percolation of sea-water to depths where the temperature is sufficiently high, in contact with such minerals as iron and its sulphides, to form carburats, in support of which is adduced the frequent occurrence of petroleum and similar products as accompaniments of volcanic action. A third plausible argument refers the formation of all the members of this hydrocarbon series to the condensation of carbon vapours escaping from a depth in the earth on meeting with hydrogen combined as water, the new compound becoming condensed to various degrees according to local circumstances. Reflecting on the vast geological distribution of petroleum, it is only reasonable to suppose that more than one cause has been instrumental in its production. All experience hitherto gained tends to prove that, though in a few unimportant cases, the creative agency, whatever it may be, seems to be still at work, yet in the great majority of instances, the active formation of the article is a work of the far past, and that we are recklessly exhausting the supplies which have been countless ages in course of collection.
Petroleum is found in strata of almost all ages, from Silurian upwards. In Canada, it occurs mainly in the corniferous limestone of the Lower Devonian, also more or less in the bird's-eye lime stone of the Lower Silurian, and the Lower Helderherg limestone of the Upper Silurian. In the United States, it is obtained chiefly from Devonian and Carboniferous formations ; in S. California, from Tertiary shales; in Trinidad, from Tertiary lignites ; in Persia and the Caspian region, from Tertiary shales and limestones ; in Burma, from shallow Tertiary and Post-tertiary clays and lignites.
Commercial Sources.—Petroleum has been discovered in W. Staffordshire and in Scotland. It is obtained at Beehelbronn and Schwabwiller, Department of Bas-Rhin, France. Germany possesses petroleum-springs affording a limited quantity near Luneburg, in Alsace ; borings ate being made in the district S. of Celle, in Hanover, where those reaching 60 ft. in depth are yielding 4 cwt. of oil daily, of improving quality ; and an experimental sinking near Heide, in Holstein, has struck a flowing well giving a superior product. The oil-wells of Italy number about 5, situated in the Valley of Cocco, in the Abruzzi, and at Riva-Nazzano, near Voghera, in Piedmont. The exploita tion has been on a primitive scale hitherto, and the production trifling.
The resources of the previously-cited localities appear insignificant in comparison with those of a portion of E. Europe embracing parts of Hungary, Galicia, Bukowina, Roumania, mad Moldavia. Dr. H. Gintl, a great authority in these matters, considers this petroleum (and oznkerit) region uniform in origin and history with the similar formation in the Caspian and Trans-Caucasian countries. He declares that the whole N. flank of the Carpathians, from Librautowa, in Neu
Sandezer, to Sloboda, in Kolomea'er, or a length of over 270 miles, will be found to yield petroleum and ozokerit ; some 13,500 wells in about 126 localities, give a yearly yield of about 520,000 centners (of 110/ lb.) of petroleum, and 360,000 centners of ozokerit, representing a capital of about 600,000/. There are 9 districts of Galicia where petroleum is obtained, the principal being Boryslav, where are situated 3200 of the 4000-5000 wells now being worked. The ground is divided into very small lots, of different ownership; the wells are sunk very near together, and, in this district, to very shallow depths, 18-25 fathoms being the average, and 65 fathoms the maximum. In 1873, Boryslav produced 200,000 cwt. of crude petroleum, and Wolanka, 20,000 cwt. ; the total value (including a larger quantity of ozokerit) was 462,0001., and the total labour employed was 9000. The common method of working is to sink a shaft down to the stratum of plastic clay; with favour able soil and little water, the sides are lined with 2-in. boards; so far as the clay extends, the only lining used is wicker-work. The ordinary dimensions of the shafts are 26 in. x 32-37 in., and 20 in. x 36 in. when lined with wicker. The sinking is always carried on with the aid of venti lators and air-tubes ; no light is admitted, except while cutting through ozokerit, when a safety lamp is used. Large quantities of gas are always present in the workings. The petroleum is usually met with at a shallower level than the ozokerit. When oil is struck, operations are temporarily suspended. The pit is covered with boards, so that the well may not cool, and the oil is then extracted by a crude arrangement of buckets and winding apparatus. The average daily yield of a well is 30 gal., but some give 140 gal. When the flow stops, the well is usually deepened, so as to obtain a second supply. Between the marl strata and sandstone strata, are often de posits of ozokerit, whose working will be described in another article (see Wax—Ozokerit). In the district of Barka, which, according to Dr. Gintl, is by far the most advanced, the petroleum is found in a conglomerate containing rounded quartz particles as large as lentils, the whole being a porous mass perfectly free from lime, and emitting much smoke and a strong odour of petroleum when burned. Wells sunk 66 ft. have produced 3000 cwt. of petroleum monthly for a considerable time. The depth first driven does not exceed 50-200 ft., but as the yield decreases, they are deepened to 800-1000 ft. This ie the only district where anything like the American system has been introduced. Boring-rods making a 6-in. or 7-in. hole are used, and generally worked by steam. The petroleum is drawn off by 2-in. tubes. A rule obtains that where ozokerit occurs, there petroleum also will be found ; but the converse does not hold. The wells are far less produc tive than those of America, though the latter do not yield ozokerit. The petroleum obtained is distilled in the ordinary way, so as to afford a good burning-oil.