R. Zaloziecki, in Dingl. Polyt. Jour., gives a lengthy physical and chemical argument in favor of the modern view that petroleum and paraffin owe their origin to animal sources; that they are formed from animal remains in a manner strictly analogous to that of the formation of ordinary coal from wood and other vegetable debris. For geological as well as chemical reasons, the author holds that Mendeleeff's theory of their igneous origin is untenable, pointing out that the hydrocarbons could not have been formed by the action of water percolating through clefts in the gradually solidifying crust until it reached the molten metallic carbides, as these clefts could only occur where complete solidification had taken place, and between this point and the metallic stratum a considerable space would be taken up by semi-solid, slag-like material which would be quite impervious to water. Under the conditions, too, existing beneath the surface of the earth, such polymerization as is necessary to account for the presence of the different classes of hydrocarbons found in petroleum is scarcely credible.
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.