PETROLEUM—ITS ORIGIN.

South Canterbury Times, Issue 2791, 4 March 1882, Page 2

PETROLEUM—ITS ORIGIN.

A good many opinions have been expressed by scientific and quasi scientific persons as to the origin of the vast quantities of petroleum, or mineral oil, which have been found in several parts of the world, and turned to so useful an account, especially in the United States, and the question, we believe, is not yet generally considered to be finally settled. Seeing that so much doubt, not to say ignorance, prevails concerning petroleum, which when refined becomes kerosene, one of our commonest articles of domestic consumption, our readers will probably be pleased to learn the view entertained by so able and experienced a geologist as Mr Denton, as set forth in the second lecture of the conrse he is now delivering, supplemented by notes on the subject courteously supplied to us by Mr Denton. In his lecture, before before stating the theory he had him self adopted as the result of personal observations (observations made, be it remarked, before the first “ ile ” well was sunk). Mr Denton mentioned and criticised a few of the other hypotheses that had been advanced to account for the origin of petroleum. The only one of these worthy of attention was one asserting that it was derived from coal, an opinion that finds expression in the term “ coal oil," still applied in some quarters to this extraordinary natural product. The advocates of this opinion assert that the oil had been either expressed from the coal beds by the weight of over-lying strata, as linseed oil is expressed by an hydraulic press, or its components had been driven off by subterranean heat in the shape of gases, which, either simply or in combination, had condensed into the liquid oil. This explanation Mr Denton disposed of by showing that the oil is met with in areas remote from coal, geographically and geologically, while it is not found associated with coal. He had been down coal mines in various countries, including coal mines in fourteen different States in the Union, and not only never saw petroleum in the mines, but never smelt it—and the smell of crude petroleum was its most striking characteristic. If it came from coal, coal mines would be the places to discover it; coal districts should aboundwith it,coal miners should be familiar with it; and it should never be found in rocks older than the coal measures: —the contrary of all which is the truth. As to its geological distribution, be koewjof petroleum wells forty miles from the nearest coal field. But the great and fatal objection to the theory, that petroleum came from coal was the fact that it is most abundantly found in formations geologically older than the coal —chiefly in a formation equivalent to the Devonian or Old Red Sandstone series of Great Britain, while some of the oil was obtained from members of the Silurian, a still lower series. In the United ' States the former series contained immense beds of coralline limestone, and it was from these beds, and from porous sandstone beds a little above them, that the oil was obtained, the whole of the oil-bearing beds being much older than the coal measures. Frequently the oil was obtained from the limestone and from two separate beds of sandstone lying above ; sometimes from the limestone and sandstone bed nearer to it; sometimes from the limestone only ; —but never from the sandstones if not from the limestone below. The three cases taken together, conclusively showed the limestone bed to bo‘the original source of the oil. This oil-bearing limestone rock cropped out at the surface at certain spots, one being near the city of Buffalo. Cutting into the rock through its weathered coating, and obtaining a clean piece of stone, the minute cells could be distinctly discerned, and each contained a drop of oil, often perfectly pure and transparent when found, but gradually becoming thick and black on exposure to the air. Of course the rock maintained its character as it passed under other rocks, away from the outcrops to the “oil regions.’’ Of the magnitude of one group of the oil-bearing rocks in the United States, Mr Denton, says “ The period of its deposition was an age of crowding crinoids and spreading coral reefs.” He quotes Professor Hall: “We may follow the outcrop of this formation leaving in many places the aspect of a coral reef along a line of more than fifteen hundred miles.” Also Professor Owen : “ The old-rock corals are remarkable for the manner in which they are partitioned off by horizontal tabulae. Of the one hundred and twentynine Silurian corals, one hundred and twenty-one belong to the tabulated divisions.” And these tabulated corals, pursues Mr Denton appear to have been the oil secreters. Petroleum is a coral oil, npt a coal oil. The oily character of the rocks at their outcrops being proved,and necessarily admitted to be persistent when they disappear beneath subsequent formations, the phenomenon of a supply of free oil, through natural springs, or pumping, flowing, or spouting wells,and also the immense evolutions of inflammable gas in certain localities, are readily explained. The weight of the rocks above would crush the cells of the coral—and the liquid oil would find its way into crevices, and into porous strata such as the sandstones from which it is often obtained. It would be subject to the pressure of the water with which the rocks below the surface are saturated, and being lighter than water would be driven upwards rather than down, as is found to be the case. The same pressure of the rooks which forced the oil out of the cells in the coral, and the bvdraulic pressure just mentioned, would force the oil up a pipe put down to reach it, exactly asj the artesian wells of Christchurch are supplied. The question of whence the coral animal procured the oil which in those longago ages it stored up in the cellular walls of its enduring tenement, for man’s future use, is one difficult •to answer, but Mr Denton has something to say upon the point—“ It was not formed from the bodies of the coral polype —‘for when dry they are a mere film that could be blown away by a child’s breath—but was secreted hy them as bees secrete honey, the material being probably obtained from their food—the infusoria which swarmed in the ocean of that period.” The question, however, of whence the coral animal obtained the oil is one of secondary importance ; the important matter, both from a scientific and from a practical point of view, is to locate the primary geological somcj of this in rortant mineral, and this tr Mr Denton appears to have successfully aceomplishcd. The result of hL enquiries adds another to the more stupendous wonders of nature, for who, uninstructed, could have imagined that petroleum, the parent of our common lamp oil, was secreted by a coral animal? The whole question should bo of great interest to New Zealanders, owing to to the recent discovery of a profitable oil deposit at Poverty Bay—a name which Mr Denton predicts will soon be, if it is not at present, a complete misnomer.