The gradual wasting of plant-tissue in the formation of peat, lignite,
coal, etc., may be estimated as averaging for peat, 20 to 30 per cent.;
lignite, 30 to 50 per cent.; coal, 50 to 70 per cent.; anthracite, 70
to 80; and graphite, 90 per cent. of the original mass. The evolved
products ultimately represent the entire organic portion of the
wood--the mineral matter, or ash, being the only residuum. These evolved
products include both liquids and gases, and by subsequent changes,
solids are produced from some of them. Carbonic acid, carbonic oxide,
nitrogenous and hydrocarbon gases, water, and petroleum, are mentioned
above as the substances which escape from wood-tissue during its
decomposition. That all these are eliminated in the decay of vegetable
and animal structures is now generally conceded by chemists and
geologists, although there is a wide difference of opinion as to the
nature of the process.
It has been claimed that the evolved products enumerated above are the
results of the primary decomposition of organic matter, and never of
further changes in the residual products; i.e., that in the breaking-up
of organic tissue, variable quantities of coal, anthracite, petroleum,
marsh gas, etc., are formed, but that these are never derived, the one
from the other. This opinion is, however, certainly erroneous, and the
formation of any or all the evolved products may take place throughout
the entire progress of the decomposition. Marsh gas and carbonic acid
are seen escaping from the surface of pools where recent vegetable
matter is submerged, and they are also eliminated in the further
decomposition of peat, lignite, coal, and carbonaceous shale. Fire damp
and choke-damp, common names for the gases mentioned above, are produced
in large quantities in the mines where Tertiary or Cretaceous lignites,
or Carboniferous coals or anthracites are mined. It has been said that
these gases are simply locked up in the interstices of the carbonaceous
matter and are liberated in its excavation; but all who have worked coal
mines know that such accumulations are not sufficient to supply the
enormous and continuous flow which comes from all parts of the mass
penetrated. We have ample proof, moreover, that coal, when exposed to
the air, undergoes a kind of distillation, in which the evolution
of carbonic acid and hydrocarbon gases is a necessary and prominent
feature.
The gas makers know that if their coal is permitted to lie for months or
years after being mined, it suffers serious deterioration, yielding a
less and less quantity of illuminating gas with the lapse of time.
So coking coals are rendered dry, non-caking, and valueless for this
purpose by long exposure.
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.
Dr. T. Sterry Hunt has regarded limestones, and especially the Niagara
and corniferous, as the principal sources of our petroleum; but, as I
have elsewhere suggested, no considerable flow of petroleum has ever
been obtained from the Niagara limestone, though at Chicago and Niagara
Falls it contains a large quantity of bituminous matter; also, that the
corniferous limestone which Dr. Hunt has regarded as the source of the
oil of Canada and Pennsylvania is too thin, and too barren of petroleum,
or the material out of which it is made, to justify the inference.
The corniferous limestone is never more than fifty or sixty feet thick,
and does not contain even one per cent. of hydrocarbons; and in southern
Kentucky, where oil is produced in large quantity, this limestone does
not exist.
That many limestones are more or less charged with petroleum is well
known; and in addition to those mentioned above, the Silurian limestone
at Collingwood, Canada, may be cited as an example. As I have elsewhere
shown, we have reason to believe that the petroleum here is indigenous,
and has been derived, in part, at least, from animal organisms; but the
limestones are generally compact, and if cellular, their cavities are
closed, and the amount of petroleum which, under any circumstances,
flows from or can be extracted from limestone rock is small. On the
other hand, the bituminous shales which underlie the different oil
regions afford an abundant source of supply, holding the proper
relations with the reservoirs that contain the oil, and are
spontaneously and constantly evolving gas and oil, as may be observed
in a great number of localities. For this reason, while confessing
the occurrence of petroleum and asphaltum in many limestones, I am
thoroughly convinced that little or none of the petroleum of commerce is
derived from them.
Prof. S.F. Peckham, who has studied the petroleum field of southern
California, attributes the abundant hydrocarbon emanations in that
locality to microscopic animals. It is quite possible that this is
true in this and other localities, but the bituminous shales which are
evidently the sources of the petroleum of Pennsylvania, Ohio, Kentucky,
etc., generally contain abundant impressions of sea weeds, and indeed
these are almost the only organisms which have left any traces in them.
I am inclined, therefore, now, as in my report on the rock oils of Ohio,
published in 1860, to ascribe the carbonaceous matter of the bituminous
shales of Pennsylvania and Ohio, and hence the petroleum derived from
them, to the easily decomposed cellular tissue of algæ which have
in their decomposition contributed a large percentage of diffused
carbonaceous matter to the sediments accumulating at the bottom of the
water where they grew. In a recent communication to the National Academy
of Sciences, Dr. T. Sterry Hunt has proposed the theory that anthracite
is the result of the decomposition of vegetable tissue when buried in
porous strata like sandstone; but an examination of even a few of the
important deposits of anthracite in the world will show that no such
relationship as he suggests obtains.
Anthracite may and does occur in sedimentary rocks of varied character,
but, so far as my observation has extended, never in quantity in
sandstone. In the Lower Silurian rocks anthracite occurs, both in the
Old World and in the New, where no metamorphism has affected it, and
where it is simply the normal result of the long continued distillation
of plant tissue; but the anthracite beds which are known and mined in so
many countries are the results of the metamorphism of coal-beds of one
or another age, by local outbursts of trap, or the steaming and baking
of the disturbed strata in mountain chains, numerous instances of which
are given on a preceding page.
M. Mendeleeff, in his article already referred to, misled by a want of
knowledge of the geology of our oil-fields, and ascribing the petroleum
to an inorganic cause, connects the production of oil in Pennsylvania
and Caucasia with the neighboring mountain chains of the Alleghanies and
the Caucasus; but in these localities a sufficient amount of organic
matter can be found to supply a source for the petroleum, while the
upheaval and loosening of the strata along lines parallel with the axes
of elevation has favored the decomposition (spontaneous distillation) of
the carbonaceous strata. It should be distinctly stated, also, that no
igneous rocks are found in the vicinity of productive oil-wells, here or
elsewhere, and there are no facts to sustain the view that petroleum is
a volcanic product.
In the valley of the Mississippi, in Ohio, Illinois, and Kentucky, are
great deposits of petroleum, far removed from any mountain chain or
volcanic vent, and the cases which have been cited of the limited
production of hydrocarbons in the vicinity of, and probably in
connection with, volcanic centers may be explained by supposing that
in these cases the petroleum is distilled from sedimentary strata
containing organic matter by the proximity of melted rock, or steam.
Everything indicates that the distillation which has produced
the greatest quantities of petroleum known was effected at a low
temperature, and the constant escape of petroleum and carbureted
hydrogen from the outcrops of bituminous shales, as well as the result
of weathering on the shales, depriving them of all their carbon, shows
that the distillation and complete elimination of the organic matter
they contain may take place at the ordinary temperature.
* * * * *