Formation of Petroleum—Enormous Production of the Pennsylvanian Wells—Asphalte used by the Ancients—Asphalte Pavements—The Pitch Lake of Trinidad—Jet—Its Manufacture in Whitby.

The class of bituminous minerals exhibits a long series of inflammable substances, which are supposed to be derived from the decomposition of organic matter in the rocks containing them. Some (Petroleum—Rock-naphtha) issue in a fluid state from the earth, while others pass by insensible gradations from petroleum into pittasphalte or maltha (viscid bitumen), and the latter as insensibly into the solid form of asphalte. Certain bitumens, again, differ but slightly in composition from bituminous coals, so that it is, in reality, very difficult to draw a decided line between them. Hence it is highly probable that in petroleum we see the product of a primeval vegetation which, under the influence of chemical change and heat, has partly assumed a liquid form, and oozing from the deep-seated strata in which it was confined by terrestrial revolution, now permeates the superficial rocks, or exists collected in subterranean cavities, whence it issues in jets and fountains whenever an outlet is made by boring.

Petroleum springs have been known for many ages in Burmah, where there are about one hundred wells from one hundred and eighty to three hundred and six feet deep, each lined with horizontal tubes, but not all now worked; at Baku, in the neighbourhood of the holy fires, already mentioned; near the village of Amiano, in Parma, whence enough was formerly obtained to light the streets of Genoa; at Zante, one of the Ionian islands, which has furnished oil for more than two thousand years, its petroleum spring having been mentioned by Herodotus; at Agrigentum, in Sicily, which, according to Pliny, furnished a mineral oil that was collected and used for burning in lamps; on the banks of the Kuban, and many other localities; but it is only since the discovery of the immense sources of supply in the north-eastern States of America and in Canada that petroleum has become not only an article of the greatest commercial importance, but a blessing to millions in all parts of the world. It gladdens the long winter evenings of the Icelandic peasant, and enlivens the hut of the Australian settler; it has found its way into the remotest glens of the Alps, and to the distant sea-ports of China. No wonder that its economical and cheerful light has caused its consumption to increase with a rapidity almost without a precedent in the annals of commerce. Though scarcely ten years have passed since the American wells first began to pour forth their streams of oil, no less than 670,000,000 gallons were exported in 1866 from the ports of Philadelphia and New York. One-third of this enormous quantity found its way to England; one-fifth to the port of Antwerp, its chief staple place for Western Germany and the North of France; the remainder was distributed among all the sea-ports of the world from Hamburg to Hong Kong, and from the Cape to Valparaiso. When we reflect that this amazing mass of liquid bitumen, which formed the cargo of no less than seven hundred and thirty-one large vessels, must necessarily be increased from year to year to meet a constantly increasing demand, it might almost be feared that, in spite of the prodigality of nature, its subterranean reservoirs must one day be exhausted.

Asphalte, a mineral pitch of a deep black colour and a conchoidal brilliant fracture, is frequently found swimming on the surface of the Lake Asphaltites, or Dead Sea, in JudÆa, which receives its name from the circumstance. It also occurs in many parts of Egypt, where it was used for embalming. The ancients also frequently employed it, combined with lime, in their buildings. Not only do we find the ruined walls of temples and palaces in the East with the stones cemented with this material, but some of the old Roman castles in this country are found to hold bitumen in the cement by which their stones are secured.

‘It is a remarkable fact,’ says the late Dr. Ure, ‘that the substance thus employed in the earliest constructions upon record, should for so many thousand years have fallen well-nigh into disuse among civilised nations; for there is certainly no class of minerals so well fitted as the bituminous, by their plasticity, fusibility, tenacity, adhesiveness to surfaces, impenetrability by water, and unchangeableness in the atmosphere, to enter into the composition of terraces, foot pavements, roofs, and every kind of hydraulic work. Bitumen, combined with calcareous earth, forms a compact semi-elastic solid, which is not liable to suffer injury by the greatest alternations of frost and thaw, which often disintegrate in a few years the hardest stone, nor can it be ground to dust and worn away by the attrition of the feet of men and animals, as sandstone, flags, and even blocks of granite are. An asphalte pavement rightly tempered in tenacity, solidity, and elasticity, seems to be incapable of suffering abrasion in the most crowded thoroughfares; a fact exemplified of late in a few places in London, but much more extensively and for a much longer time in Paris.’ Many of the asphalte pavements made in England have, indeed, proved failures; but as the proper proportions of the respective ingredients may not have been maintained, further trials are advisable. At present, although bitumen is employed, and with seeming advantage, as a cement between paving-stones, its use in the formation of foot pavement has been confined within narrow limits.

In Europe, the most extensive mine of asphaltic rock is undoubtedly that of the Val de Travers in the canton of NeufchÂtel; but the most remarkable deposit of bitumen in the world is the celebrated Great Pitch Lake in the island of Trinidad. With regard to its formation, Sir Charles Lyell remarks that the Orinoco, which discharges its vast volume of water right opposite to the island, has for ages been rolling down great quantities of woody and vegetable bodies into the surrounding sea, where, by the influence of currents and eddies, they may be arrested and accumulated in particular places. The frequent occurrence of earthquakes and other indications of volcanic action in these parts lends countenance to the opinion that these vegetable substances may have undergone, by the agency of subterranean fire, those transformations or chemical changes which produce petroleum; and this may, by the same causes, be forced up to the surface, where, by exposure to the air, it becomes inspissated, and forms the different varieties of pure and earthy pitch or asphaltum so abundant in the island. The Pitch Lake is a mile and a half in circumference; the bitumen is solid and cold near the shores, but gradually increases in temperature and softness towards the centre, where it is boiling. The solidified bitumen appears as if it had cooled as the surface boiled in large bubbles. The ascent from the lake to the sea, a distance of three-quarters of a mile, is covered with a hardened pitch, on which trees and vegetables flourish, and the best pine-apples in the West Indies, called black pines, grow wild. As the Trinidad pitch has been found by chemical analysis to be an excellent material for the making of gas, it will probably become an important article of commerce. The wonder is that it has been so long neglected.

Though Jet is frequently considered to be wood in a high state of bituminisation, yet the fact that we find this beautiful substance surrounding fossils, and casing adventitious masses of stone, seems to show that a liquid, or, at all events, a plastic condition must at one time have prevailed in its formation. This opinion is further strengthened by the circumstance that petroleum strongly impregnates the rock in which it is found, giving out a strong odour when it is exposed to the air.

Jet occurs chiefly in the neighbourhood of Whitby in Yorkshire, the estates of Lord Mulgrave being especially productive. The jet miner searches with great care the slaty rocks, and finding the jet spread out, often in extreme thinness, between the laminations of the rock, he follows it with great care, and is frequently rewarded by its thickening out to two or three inches.

The art of working jet is of very ancient date in this country, for the Romans certainly employed it for ornamental purposes, and probably found it in use among the Britons whom they conquered. Lionel Charlton, in the ‘History of Whitby,’ says that in one of the Roman tumuli, lying close to the jaw-bone, he found the earring of a lady having the form of a heart, with a hole in the upper end for suspension from the ear. There exists no doubt that, when the Abbey of Whitby was the seat of learning and the resort of pilgrims, jet-rosaries and crosses were common. The manufacture was carried on till the time of Elizabeth, when it seems to have ceased suddenly, and was not resumed till the year 1800, when Robert Jefferson, a painter, and John Carter made beads and crosses with files and knives. A stranger coming to Whitby, and seeing them working in this rude way, advised them to try to turn it; they followed his advice, and found it answer. Several more then joined them, and the trade has been gradually increasing since; so that at present the total annual value of the mourning ornaments made at Whitby and Scarborough amounts to no less than 125,000l. About 250 men and boys are employed in searching for jet, and between 600 and 700 are engaged in its manufacture.