In dealing with the question of petroleum and its origin, the subject can well be defined under two headings: one, the origin of the word “petroleum”; the other, the origin of the mineral itself. As to the former, this is a matter of historical interest; of the latter, the question is still in doubt—and the doubt becomes even the more doubtful, the more the question is debated.

Let us, therefore, take first the word “petroleum” as we know it to-day. It covers a multitude of products derived from the refining of crude oil, though the word does not suggest any of them. It is quite a generic term, and in a general way represents the whole of that ever-increasing family of hydrocarbons—the refined products of crude oil. There is no doubt that it derives its name from the Latin petra oleum, which, literally, is rock oil, and equivalents of the name are found in all languages. Even in modern practice we use the word, though not in a specific sense, while our own Government usually refers to “petroleum oil,” which, of course, involves tautology. Crude petroleum is known throughout the oil-fields of the world as denoting the crude oil coming from the wells: then we have petroleum spirit, otherwise the lightest form of refined oil; we have petroleum distillate, designating an illuminating oil; but, “petroleum oil” is, it is to be regretted, generally used as suggesting some form of petroleum product.

Though the petroleum industry—in its commercial sense—only goes back some sixty years, the use of petroleum can be traced to Biblical times, for was it not the great Prophet Elisha who told the widow to “Go, sell the oil and pay thy debts and live”?

Job also speaks of the rock which poured him out rivers of oil; in Maccabees we find that the priests hid the fire which they took from the altar in a deep pit without water; while Nehemiah called the liquid which burst into flame and kindled a great fire by the name “Nephthar, which is as much as to say, a cleansing; but many call it Nephai.” And so, in many parts of the Old as well as in the New Testament, oil is clearly referred to, and, in Biblical times, as much later, was looked upon as a sacred fire.

Many ancient authors make extensive reference to oil, prominent among them being Herodotus, who described the methods adopted at the pits of Kirab for the raising of the oil, which liquid “gives off a very strong odour.”

Petroleum, as known in Biblical times, and as so widely known to-day, occurs in greater or less quantity throughout the world, and it is found in the whole range of strata of the earth’s crust, from the Laurentian rocks to the most recent members of the Quaternary period, though it is found in commercial quantities almost wholly in the comparatively old Devonian and Carboniferous formations on the one hand or in the various divisions of the comparatively young Tertiary rocks on the other.

The problem of the origin of petroleum has been the subject of considerable scientific controversy for many years. Not a few of the leading scientists hold to the theory that petroleum is derived from metallic carbides lying far beneath the porous strata in which the oil is stored by Nature, and that even at the present time the process is in operation. This idea, which may be termed the inorganic theory of petroleum origin, was considered to have received substantial support when it was found that the action of water on the carbides of certain metals resulted in the liberation of hydrocarbons.

The view that petroleum is of organic origin is to-day almost universally accepted, although there is no general agreement either as to whether petroleum is derived from vegetable or animal matter, or as to the forms of life that provided for its genesis. In certain places in the world—notably on the eastern side of the Caspian Sea and also near the Mediterranean—there is some conversion of organic matter into petroleum actually to be seen to-day. It is not difficult, as the late Sir Boverton Redwood, Bart., pointed out in an address before the Royal Institution of Great Britain in 1918, to account for the formation of adequate deposits of the necessary material. In the comparatively deep and quiescent water along the margin of the land in past ages, there would be abundant opportunity for the deposition not only of the remains of marine animals and plants, but also of vegetable matter brought down to the coast by the water courses, and the changes which the earth has undergone would result in the burial of these substances under sedimentary mineral matter, the deposits thus formed being ultimately, as the result of further alterations in the earth’s surface, frequently found occupying positions far removed from the sea, and sometimes beneath immense thicknesses of subsequent deposits.

That vegetable matter may be the source of certain petroleums is an opinion that has found increasing evidence to support it. There are two kinds of vegetable matter which are possible, terrestrial and aquatic, and in the deltaic conditions that characterize so many oil-fields, either could be equally well appealed to as a source of accumulation. The extensive coal and lignite deposits in many geological periods bear eloquent testimony to the presence of carbonaceous matter far in excess of that required to provide proved supplies of petroleum. Every important coal-field demonstrates the fact that vegetable matter can be partially converted into bituminous compounds or hydrocarbons by natural processes. Marsh gases often occur in great quantities in faulted zones in the coal measures, though the bituminous substances found in coal are not true bitumens that dissolve in the usual solvents, while the tars derived from the destructive distillation of coal in no way resemble natural petroleums or the products of oil-shale distillation.

In spite, however, of the outstanding differences between petroleum, oil-shales and coal, I might here point out in favour of the vegetable theory of origin, that actual petroleum and true bitumens have been found in some coals, though in small quantities, while solid paraffins have been extracted by means of pyridine and chloroform. Again, low temperature distillations have yielded petroleum hydrocarbons, all of which appear to indicate that even when coal was the overwhelming product, at certain times and places the conditions were merging into those which could yield petroleum. There is no doubt that each of the various views expressed as to the organic origin of petroleum contains elements of truth, and it is reasonable to assume that a substance so varied in its physical and chemical properties as petroleum has not in all cases been created under precisely the same conditions, or from an exactly similar source.

Summing up the whole question of origin, however, the balance of opinion points to its being the result of organic action, and that the petroleum which we now find in the Palaeozoic and Tertiary rocks is substantially of the same geological age as the rocks themselves.

Volumes of technological literature have been written upon this complex question of petroleum origin, and though these may be of intense interest to the student of geology, the brief references which I have already given to the question are sufficient for the purpose of this little publication.

The geographical distribution of petroleum throughout the two hemispheres is no less wide than the geological. The deposits mainly occur along well-defined lines, often associated with the mountain ranges. This is chiefly due to the formation, in the elevatory process, of minor folds which have arrested and collected the oil in richly productive belts.