On the other hand it is to be specially noticed that, with a few unimportant exceptions, all bituminous deposits are found in the sedimentary rocks, and that just as these are constantly changing in composition, so the organic matter present changes, there being a definite relationship between the chemical constitution of the petroleum and the age of the strata in which it is found. It is almost certain that in the most recent alluvial formations no oil is ever found, its latest appearance being in the rocks of the tertiary period, the place where the solid paraffin is almost exclusively met with; thus helping to show that the latter has been formed from the decomposition of the oil, and is not a residue remaining after the oil has been distilled off. To this conclusion the fact also strongly points, that the paraffin is much simpler in constitution, purer, and often of far lighter color than the crude oil, which could not be the case if it were the original substance.
On examining by the aid of a map the position of the chief oil-bearing localities it will be noticed that the most prolific spots follow fairly accurately the contour lines of the country, so that at one time they formed in all probability a coast line whereon would be concentrated for climatic reasons most of the animal life both of the land and sea. During succeeding generations their dead bodies would accumulate in enormous quantities and be buried in the slowly depositing sand and mud, till, owing to the gradual alterations of level, the sea no longer reached the same point. This theory is borne out by the fact that oil deposits are usually found in marine sediments, sea fossils being frequently met with. The first process of the decomposition of the animal remains would consist in the formation of ammonia and nitrogenous bases, the action being aided by the presence of air, moisture, and micro-organisms, at the same time, owing to the well known antiseptic properties of salt, the decomposition would go on slowly, allowing time for more sand and inorganic matter to be deposited. In this way the decomposing matter would be gradually protected from the action of the air, and finally the various fatty substances would be found mixed with large amounts of salt, under considerable pressure, and at a somewhat high temperature. From this adipocere, fatty acids would be gradually formed, the glycerol being washed away, and finally the acids would be decomposed by the pressure into hydrocarbons and free carbonic acid gas. That many of these hydrocarbons would be solid at ordinary temperatures, forming the so-called mineral wax, which exists in many places in large quantities, is much easier to imagine, in the light of modern chemical knowledge, than that the fatty acids were at once split up into the simpler liquid hydrocarbons, to be afterward condensed into the more complex molecular forms of the solid substance.
In this way from animal matter are in all probability formed the vast petroleum deposits, the three substances, adipocere, ozokerite, and petroleum oil being produced in chronological order, just as lignite, brown coal and coal are formed by the gradual decomposition of vegetable remains.
THE ORIGIN OF PETROLEUM.[1]
By O.C.D. Ross, M.Inst.C.E.
Petroleum is one of the most widely distributed substances in nature, but the question how it was originally produced has never yet been satisfactorily determined, and continues a problem for philosophers. In 1889 the total production exceeded 2,600,000,000 gallons, or about 10,000,000 tons, and, at fourpence per gallon, was worth about £44,000,000, while the recognition of its superior utility as an economical source of light, heat, and power steadily increases; but, notwithstanding its importance in industry, the increasing abundance of the foreign supply, and the ever-widening area of production, practical men in England continue to distrust its permanence, and owing to the mystery surrounding its origin, and the paucity of indications where and how to undertake the boring of wells, they hesitate to seek for it in this country, or even to extend the use of it whenever that would involve alterations of existing machinery. The object of this paper is to suggest an explanation of the mystery which seems calculated to dissipate that distrust, since it points to very abundant stores, both native and foreign, yet undiscovered, and even in some localities to daily renovated provisions of this remarkable oil.
The theories of its origin suggested by Reichenbach, Berthelot, Mendeleeff, Peckham, and others, made no attempt to account for the exceeding variety in its chemical composition, in its specific gravity, its boiling points, etc., and are all founded on some hypothetical process which differs from any with which we are acquainted; but modern geologists are agreed that, as a rule, the records of the earth's history should be read in accordance with those laws of nature which continue in force at the present day, e.g., the decomposition of fish and cetaceous animals could not now produce oil containing paraffin. Hence we can hardly believe it was possible thousands or millions of years ago, if it can be proved that any of the processes of nature with which we are familiar is calculated to produce it.
The chief characteristics of petroleum strata are enumerated as:
I. The existence of adjoining beds of limestone, gypsum, etc.
II. The evidence of volcanic action in close proximity to them.
III. The presence of salt water in the wells.