546 PETROLEUM 



Persia and the Caspian Sea. It is only within the last few years, however, that the 

 largest source of supply in the north-eastern states of America and Canada have 

 been developed, although the existence of petroleum in Pennsylvania (where it 

 was collected and sold by the Seneca Indians, under the name of Seneca oil) has 

 been known for a very long period. Many different bituminous formations are 

 known at different horizons in the palaeozoic rocks of America ; in the Silurian series 

 traces of the former existence of Bitumen are afforded by the occurrence of shining 

 anthracitic substances in cracks and fissures in the Quebec group, and its equivalent, 

 the Calciferous sand-rock, at several localities in Eastern Canada and the State of New 

 York. In the Trenton limestone, liquid petroleum is found in the chambers of the 

 larger orthoceratites, some of these fossils containing at times several ounces of oil ; 

 and a spring yielding small quantities rises from the Utica slate on Great Mani- 

 toulin Island, on Lake Huron. A more important but as yet scarcely developed 

 locality, probably at the top of the Silurian series, is in the peninsula of Gaspe\ in 

 the easternmost part of Canada. It is, however, from the Devonian rocks that the 

 greatest quantities of petroleum are derived in America. At Oil Springs and Ennis- 

 killen, near Sarnia, Canada West, natural oil-springs occur upon the outcrop of the 

 Corniferous limestone, or the overlying Hamilton shale, along the line of a broad 

 and low anticlinal traversing the district in a nearly east-and-west line, both forma- 

 tions being generally covered by from forty to sixty feet of drift and alluvial clays 

 and sands. At the Wyoming Company's wells, the overflow of the natural springs, 

 rising through the superficial beds, have produced deposits of hardened and slightly 

 elastic bitumen or asphalt, which are locally known as ' gum-beds.' They are some- 

 what irregular in thickness, varying from a few inches to two feet, and cover an area 

 of about two acres. According to Delesse, this substance fuses at 180 Fahr. and con- 

 tains 62 per cent, of bitumen, soluble in benzole ; 24'8 per cent, of organic matter, 

 the remains of plants which have grown upon the present surface, and have become 

 imbedded in the 'gum'; and 12'7 per cent, of clay and sand. The occurrence of 

 these beds is instructive, as showing how bituminous rocks may be formed by the 

 gradual drying-up and oxidation of liquid petroleum. When wells are sunk in the 

 overlying clays and sands, there is usually found, at the junction with the shales, a 

 bed of coarse gravel holding large quantities of oil of a treacly consistency and dark 

 colour. This is the oil of the surface-wells, so called from their being situated 

 entirely in superficial deposits, as distinguished from the rock-wells, which are bored 

 into the Hamilton shales and Corniferous limestone strata below. It has a very 

 offensive smell, but is actually of greater value than the more limpid product of the 

 rock-wells, being sold without any further preparation as a lubricating medium for 

 the axles of railway-carriages. The rock-wells are of two characters, namely, 

 ' pumping ' and ' flowing : ' the former being mostly intermittent in their discharge, 

 and requiring the aid of machinery to bring their contents to the surface, while in 

 the latter the oil rises, like water in a true artesian well, above the level of the 

 surface ; the free discharge being, however, due not to hydrostatic pressure so much 

 as to the elastic force of light carburetted hydrogen gas, which is almost always 

 present in oil-wells. Unlike wells sunk for water, the gathering-ground of an oil- 

 well is extremely local, being probably confined to a lenticular belt of porous rock in 

 its immediate neighbourhood ; and when this is exhausted, the supply fails : and unless 

 the hole be bored deeper, on the chance of striking another vein in depth, it is 

 abandoned for a fresh locality. The first great flowing-well at Enniskillen yielded 

 1,500 barrels when first struck, the greater part of which, for want of sufficient col- 

 lecting vats, overflowed into the valley of the neighbouring brook, and was lost ; but 

 in a short time it was exhausted. The best wells in this locality, in July 1865, yielded 

 about 100 barrels, or 4,000 gallons each, daily ; but only five were in this category, the 

 greater number not exceeding 10 or 20 barrels. The Wyoming Company's wells, 

 9 in number, sunk on the gum-beds, yielded from 5 to 6 barrels each, per day, at 

 the same period. It was computed that the working expenses of a well, pumped by 

 sieam-power, could be covered by a yield of a single barrel daily. The conditions 

 under which petroleum occurs in Pennsylvania, are somewhat similar to those 

 observed in Canada, but on a somewhat higher geological horizon ; the chief oil- 

 bearing rocks being the sandstones, limestones, and slates, overlying the Hamilton 

 and Geneseo groups. The deepest wells in Oil Creek, the principal Pennsylvanian 

 locality, are supposed to be in the Portage, while the shallower ones are in the 

 Chemung group, both members of the Upper Devonian series. At the commence- 

 ment of the year 1865, in the district of Oil Cretk, Pennsylvania, 480 wells wero 

 already sunk, and 542 more were in progress of sinking, within an area of 5 square 

 miles. Of these, 189 produced oil, the total estimated yield being 4,000 barrels, or 

 160,000 gallons daily. Some of the earlier wells, sunk in the year 1861, at first 

 yielded from 600 to 3,000 and 4,000 barrels each, daily, but in no instance have these 



