Chapter 8

Carbureted hydrogen, olefiant gas, etc., are constant associates of the petroleum of springs or wells, and this escape of gas and oil has been going on in some localities, without apparent diminution, for two or three thousand years. We can only account for the persistence of this flow by supposing that it is maintained by the gradual distillation of the carbonaceous masses with which such evolutions of gas or of liquid hydro-carbons are always connected. If it were true that carbureted hydrogen and petroleum are produced only from the primary decomposition of organic tissue, it would be inevitable that at least the elastic gases would have escaped long since.

Oil wells which have been nominally exhausted--that is, from which the accumulations of centuries in rock reservoirs have been pumped--and therefore have been abandoned, have in all cases been found to be slowly replenished by a current and constant secretion, apparently the product of an unceasing distillation.

In the valley of the Cumberland, about Burkesville, one of the oil regions of the country, the gases escaping from the equivalent of the Utica shale accumulate under the plates of impervious limestone above until masses of rock and earth, hundreds of tons in weight, are sometimes thrown out with great violence. Unless these gases had been produced by comparatively recent distillation, such explosions could not occur.

In opening a coal mine on a hillside, the first traces of the coal seam are found in a dark stain in the superficial clay; then a substance like rotten wood is reached, from which all the volatile constituents have escaped. These appear, however, later, and continue to increase as the mine is deepened, until under water or a heavy covering of rock the coal attains its normal physical and chemical characters. Here it is evident that the coal has undergone a long-continued distillation, which must have resulted in the constant production of carbonic acid and carbureted hydrogen.

A line of perennial oil and gas springs marks the outcrop of every great stratum of carbonaceous matter in the country. Of these, the most considerable and remarkable are the bituminous shales of the Silurian (Utica shale), of the Devonian (Hamilton and Huron shales), the Carboniferous, etc. Here the carbonaceous constituent (10 to 20 per cent.) is disseminated through a great proportion of inorganic material, clay and sand, and seems, both from the nature of the materials which furnished it--cellular plants and minute animal organisms--and its dissemination, to be specially prone to spontaneous distillation. The Utica shale is the lowest of these great sheets of carbonaceous matter, and that supplies the hydro-carbon gases and liquids which issue from the earth at Collingwood, Canada, and in the valley of the Cumberland. The next carbonaceous sheet is formed by the great bituminous shale beds of the upper Devonian, which underlie and supply the oil wells in western Pennsylvania. In some places the shale is several hundred feet in thickness, and contains more carbonaceous matter than all the overlying coal strata. The outcrop of this formation, from central New York to Tennessee, is conspicuously marked by gas springs, the flow from which is apparently unfailing.

Petroleum is scarcely less constant in its connection with these carbonaceous rocks than carbureted hydrogen, and it only escapes notice from the little space it occupies. The two substances are so closely allied that they must have a common origin, and they are, in fact, generated simultaneously in thousands of localities.

During the oil excitement of some years since, when the whole country was hunted over for "oil sign," in many lagoons, from which bubbles of marsh-gas were constantly escaping, films of genuine petroleum were found on the surface; and as the underlying strata were barren of oil, this could only have been derived from the decaying vegetable tissue below. In the Bay of Marquette, two or three miles north of the town, where the shore is a peat bog underlain by Archæan rocks, I have seen bubbles of carbureted hydrogen rising in great numbers attended by drops of petroleum which spread as iridescent films on the surface.

The remarks which have been made in regard to the heterogeneous nature of the solid hydrocarbons apply with scarcely less force to the gaseous and liquid products of vegetable decomposition. The gases which escape from marshes contain carbonic acid, a number of hydrocarbon gases (or the materials out of which they may be composed in the process of analysis), and finally a larger or smaller volume of nitrogenous gas. It is possible that the elimination of these gases takes the form of fractional distillation, and definite compounds may be formed directly from the wood-tissue or its derivatives, and mingle as they escape. This is, however, not certain, for the gases, as we find them, are always mixtures and never pure. In the liquid evolved products, the petroleums, this is emphatically true, for we combine under this name fluids which vary greatly in both their physical and chemical characters; some are light and ethereal, others are thick and tarry; some are transparent, some opaque; some red, some brown, others green; some have an offensive and others an agreeable odor; some contain asphalt in large quantity, others paraffine, etc. Thus they form a heterogeneous assemblage of liquid hydrocarbons, of which naphtha and maltha may be said to form the extremes, and which have little in common, except their undefinable name. The causes of these differences are but imperfectly understood, but we know that they are in part dependent on the nature of the organic material that has furnished the petroleums, and in part upon influences affecting them after their formation. For example, the oil which saturates the Niagara limestone at Chicago, and--which is undoubtedly indigenous in this rock, and probably of animal origin, is black and thick; that from Enniskillen, Canada, is also black, has a vile odor, probably in virtue of sulphur compounds, and, we have reason to believe, is derived from animal matter. The oils of northwestern Pennsylvania are mostly brown, sometimes green by reflected light, and have a pungent and characteristic odor. These are undoubtedly derived from the Hamilton shales, which contain ten or twenty per cent, of carbonaceous matter, apparently produced from the decomposition of sea-weeds, since these are in places exceedingly abundant, and nearly all other fossils are absent.

The oils of Italy, though varying much in appearance, have usually an ethereal odor that is rather agreeable; they are of Tertiary age. The oils of Japan, differing much among themselves, have as, a common character an odor quite different from the Pennsylvania oils. So the petroleums of the Caspian, of India, California, etc., occurring at different geological horizons, exhibit a diversity of physical and chemical characters which may be fairly supposed to depend upon the material from which they have been distilled. The oils in the same region, however, are found to exhibit a series of differences which are plainly the result of causes operating upon them after their production. Near the surface, they are thicker and darker; below, and near the carbonaceous mass from which they have been generated, they are of lighter gravity and color. We find, in limited quantity, oils which are nearly white and may be used in lamps without refining--which have been refined, in fact, in Nature's laboratory. Others, that are reddish yellow by transmitted light, sometimes green by reflected light, are called amber oils; these also occur in small quantity, and, as I am led to believe, have acquired their characteristics by filtration through masses of sandstone. Whatever the variety of petroleum may be, if exposed for a long time to the air it undergoes a spontaneous distillation, in which gases and vapors, existing or formed, escape, and solid residues are left. The nature of these solids varies with the petroleums from which they come, some producing asphaltum, others paraffine, others ozokerite, and so on through a long list of substances, which have received distinct names as mineral species, though rarely, if ever, possessing a definite and invariable composition. The change of petroleum to asphalt may be witnessed at a great number of localities. In Canada, the black asphaltic oil forms by its evaporation great sheets of hard or tarry asphalt, called gum beds, around the oil-springs. In the far West are numerous springs of petroleum, which are known to the hunters as "_tar springs_," because of the accumulations about them of the products of the evaporation and oxidation of petroleum to tar or asphalt. Certain less common oils yield ozokerite as a solid, and considerable accumulations of this are known in Galicia and Utah.

Natural paraffine is less abundant, and yet in places it occurs in considerable quantity. Asphalt is the common name for the solid residue from the evaporation and oxidation of petroleum; and large accumulations of this substance are known in many parts of the world, perhaps the most noted of all being that of the "Pitch Lake". of the Island of Trinidad; there, as everywhere else, the derivation of asphalt from petroleum is obvious, and traceable in all stages. The asphalts, then, have a common history in this, that they are produced by the evaporation and oxidation of petroleum. But it should also be said that they share the diversity of character of petroleums, and the term asphalt represents a group of substances of which the physical characters and chemical composition differ greatly in virtue of their derivation, and also differ from changes which they are constantly undergoing. Thus at the Pitch Lake in Trinidad, the central portion is a tarry petroleum, near the sides a plastic asphalt, and finally that which is of almost rock-like solidity. Hence we see that the solid residues from petroleum are unstable compounds like the coals and lignites, and in virtue of their organic nature are constantly undergoing a series of changes of which the final term is combustion or oxidation. From these facts we might fairly infer that asphalts formed in geological ages anterior to the present would exhibit characters resulting from still further distillation; that they would be harder and drier, i.e., containing less volatile ingredients and more fixed carbon. Such is, in fact, the case; and these older asphalts are represented by _Grahamite, Albertite_, etc., which I have designated as asphaltic coals. These are found in fissures and cavities in rocks of various ages, which have been more or less disturbed, and usually in regions where springs of petroleum now exist. The Albertite fills fissures in Carboniferous rocks in New Brunswick, on a line of disturbance and near oil-springs. Precisely the same may be said of the Grahamite of West Virginia. It fills a vertical fissure, which was cut through the sandstones and shales of the coal-measures; in the sandstones it remained open, in the shales it has been closed by the yielding of the rock. The Grahamite fills the open fissure in the sandstone, and was plainly introduced when in a liquid state. In the vicinity are oil springs, and it is on an axis of disturbance. From near Tampico, Mexico, I have received a hydrocarbon solid--essentially Grahamite, asphalt, and petroleum. These are described as occurring near together, and evidently represent phases of different dates in the same substance. I have collected asphaltic coals, very similar to Grahamite and Albertite in appearance and chemical composition, in Colorado and Utah, where they occur with the game associates as at Tampico. I have found at Canajoharie, New York, in cavities in the lead-veins which rut the Utica shale, a hydrocarbon solid which must have infiltrated into these cavities as petroleum, but which, since the remote period when the fissures were formed, has been distilled until it is now _anthracite_. Similar anthracitic asphalt or asphaltic anthracite is common in the Calciferous sand-rock in Herkimer County, New York, where it is associated with, and often contained in, the beautiful crystals of quartz for which the locality is famous. Here the same phase of distillation is reached as in the coke residuum of the petroleum stills.

Again, in some crystalline limestones, detached scales or crystals of _graphite_ occur, which are undoubtedly the product of the complete distillation of liquid hydrocarbons with which the rock was once impregnated. The remarkable purity of such graphite is the natural result of its mode of formation, and such cases resemble the occurrence of graphite in cast iron and basalt. The black clouds and bands which stain many otherwise white marbles are generally due to specks of graphite, the residue of hydrocarbons which once saturated the rock. Some limestones are quite black from the carbonaceous matter they contain (Lycoming Valley, Pa., Glenn's Falls, N. Y., and Collingwood, Canada), and these are sold as black marbles, but if exposed to heat, such limestones are blanched by the expulsion of the contained carbon; usually a residue of anthracite or graphite is left, forming dark spots or streaks, as we find in the clouded and banded marbles.

Finally, the great work going on in Nature's laboratory may be closely imitated by art; the differences in the results being simply the consequence of differing conditions in the experiments. Vegetable tissue has been converted artificially into the equivalents of lignite, coal, anthracite, and graphite, with the emission of vapors, gases, and oils closely resembling those evolved in natural processes. So petroleum may be distilled to form asphalt, and this in turn converted into Albertite and coke (i.e., anthracite). Grahamite has been artificially produced from petroleum by Mr. W. P. Jenney.

In the preceding remarks, no effort has been made even to enumerate all the so-called carbon minerals which have been described. This was unnecessary in a discussion of the relations of the more important groups, and would have extended this article much beyond its prescribed length. Those who care to gain a fuller knowledge of the different members of the various groups are referred to the admirable chapter on the "Hydrocarbon Compounds" in Dana's Mineralogy.

It will, however, add to the value of this paper, if brief mention be made of a few carbon minerals of which the genesis and relations are not generally known, and in regard to which special interest is felt, such as the diamond, jet, the hydrocarbon jellies, "Dopplerite," etc.

The diamond is found in the _débris_ of metamorphic rocks in many countries, and is probably one of the evolved products of the distillation of organic matter they once contained. Under peculiar circumstances it has apparently been formed by precipitation from sulphide of carbon or some other volatile carbon compound by elective affinity. Laboratory experiments have proved the possibility of producing it by such a process, but the artificial crystals are microscopic, perhaps only because a long time is required to build up those of larger size.

Jet is a carbonaceous solid which in most cases is a true lignite, and generally retains more or less of the structure of wood. Masses are sometimes found that show no structure, and these are probably formed from bitumen which has separated from the wood of which it once formed part, and which it generally saturates or invests. In some cases, however, these masses of jet-like substance are plainly the residuum of excrementitious matter voided by fishes or reptiles. These latter are often found in the Triassic fish-beds of Connecticut and New Jersey, and in the Cretaceous marls of the latter State.

The discovery of a quantity of hydrocarbon jelly, recently, in a peat-bed at Scranton, Pa., has caused some wonder, but similar substances (Dopplerite, etc.) have been met with in the peat-beds of other countries; and while the history of the formation of this singular group of hydrocarbons is not yet well understood, and offers an interesting subject for future research, we have reason to believe that these jellies have been of common occurrence among the evolved products of the decomposition of vegetable tissue in all ages.

The fossil resins--often erroneously called gums--amber, kauri, copal, etc., though interestingly related to the hydro-carbons enumerated on the preceding pages, form no essential part of the series, and demand only the briefest notice here.

_Amber_ is the resin which exuded from certain coniferous trees that, in Tertiary times, grew abundantly in northern Europe. The leaves and trunks of these trees have generally perished; but masses of their resin, more enduring, buried in the earth on the shores of the Baltic, have in the lapse of time changed physically and chemically, and have become fitted for the ornamental purposes for which they have been used by all civilized nations.

_Kauri_ is the resin of _Dammara australis_, a living coniferous tree of New Zealand, and the "gum" is dug from the earth on the sites of forests which have now disappeared.

_Copal_ is a commercial name given to the resins of several different trees, but the most esteemed, and indeed the only true copal, is the product of _Trachylobium Mozambicense_, a tree which grows along the Zanzibar coast, and has left its resin buried in the sands of old raised beaches which it has abandoned.

The diversity of character which the fossil resins exhibit shows the complexity of the vital processes in operation in the vegetable kingdom, and gives probability to the theory that some of the differences we find in the carbon minerals are due to differences in the plants from which they have been derived.

The variations in the physical and chemical characters of different coals from the same basin, and from different parts of the same stratum, have been sometimes credited to the same cause; but they are probably in greater degree due to the differences in the conditions under which these varieties have been formed.

Cannel coal, as I have shown elsewhere (_Amer. Jour. Science_, March, 1857), is completely macerated vegetable tissue which was deposited as carbonaceous mud at the bottom of lagoons in the coal-marshes.

Caking coals were probably peat, which accumulated under somewhat uniform conditions, was constantly saturated with moisture, and became a comparatively homogeneous and partially gelatinous carbonaceous mass; while the open-burning coals which show a distinctly laminated structure and consist of layers of pitch-coal, alternating with bands of mineral charcoal or cannel, seem to have been formed in alternating conditions, of more or less moisture, and the bituminous portions are inclosed in cells or are separated by partitions, so that the mass does not melt down, but more or less perfectly holds its form when exposed to heat.

The generalities of the origin and relations of the carbon minerals have now been briefly considered; but a review of the subject would be incomplete without some reference to the theories which have been advanced by others, that are in conflict with the views now presented. There have always been some who denied the organic nature of the mineral hydrocarbons, but it has been regarded as a sufficient answer to their theories, that chemists and geologists are generally agreed in saying that no instances are known of the occurrence in nature of hydrocarbons, solid, liquid, or gaseous, in which the evidence was not satisfactory that they had been derived from animal or vegetable tissue. A few exceptional cases, however, in which chemists and geologists of deserved distinction have claimed the possibility and even probability of the production of marsh gas, petroleum, etc., through inorganic agencies, require notice.

In a paper published in the _Annales de Chimie et de Physique_, Vol. IX., p.481, M. Berthelot attempts to show that the formation of petroleum and carbureted hydrogen from inorganic substances is possible, if it be true, as suggested by Daubre, that there are vast masses of the alkaline metals--potassium, sodium, etc.--deeply buried in the earth, and at a high temperature, to which carbonic acid should gain access; and he demonstrates that, these premises being granted, the formation of hydrocarbons would necessarily follow.

But it should be said that no satisfactory evidence has ever been offered of the existence of zones or masses of the unoxidized alkaline metals in the earth, and it is not claimed by Berthelot that there are any facts in the occurrence of petroleum and carbureted hydrogen in nature which seem to exemplify the chemical action which he simply claims is theoretically possible. Berthelot also says that, in most cases, there can be no doubt of the organic origin of the hydrocarbons.

Mendeleeff, in the _Revue Scientifique_, 1877, p. 409, discusses at considerable length the genesis of petroleum, and attempts to sustain the view that it is of inorganic origin. His arguments and illustrations are chiefly drawn from the oil wells of Pennsylvania and Canada, and for the petroleum of these two districts he claims an inorganic origin, because, as he says, there are no accumulations of organic matter below the horizons at which the oils and gases occur. He then goes into a lengthy discussion of the possible and probable source of petroleum, where, as in the instances cited, an organic origin "is not possible." It is a sufficient answer to M. Mendeleeff to say, that beneath the oil bearing strata of western Pennsylvania are sheets of bituminous shale, from one hundred to five hundred feet in thickness, which afford an adequate, and it may be proved the true source, of the petroleum, and that no petroleum has been found below these shales; also that the oil-fields of Canada are all underlain by the Collingwood shales, the equivalent of the Utica carbonaceous shales of New York, and that from the out-crops of these shales petroleum and hydrocarbon gases are constantly escaping. With a better knowledge of the geology of the districts he refers to, he would have seen that the facts in the cases he cites afford the strongest evidence of the organic origin of petroleum.

Among those who are agreed as to the organic origin of the hydrocarbons, there is yet some diversity of opinion in regard to the nature of the process by which they have been produced.

Prof. J. P. Lesley has at various times advocated the theory that petroleum is indigenous in the sand-rocks which hold it, and has been derived from plants buried in them. ("Proc. Amer. Philos. Soc.," Vol. X., pp. 33, 187, etc.)

My own observations do not sanction this view, as the limited number of plants buried in the sandstones which are now reservoirs of petroleum must always have borne a small proportion in volume to the mass of inorganic matter; and some of those which are saturated with petroleum are almost completely destitute of the impressions of plants.

In all cases where sandstones contain petroleum in quantity, I think it will be found that there are sheets of carbonaceous matter below, from which carbureted hydrogen and petroleum are constantly issuing. A more probable explanation of the occurrence of petrolem in the sandstones is that they have, from their porosity, become convenient receptacles for that which flowed from some organic stratum below.