foreign countries producing important amounts of sulphur are Italy,
Japan, Spain, and Chile. Europe is the chief market for the Italian
sulphur. In spite of increased demands in Europe the Italian production
has decreased as the result of unfavorable labor, mining, and
transportation conditions, and the deficit has had to be met from the
United States. Japan's sulphur production has been increasing. Normally
about half of the material exported comes to the United States to supply
the needs of the paper industry in the Pacific states, and half goes to
Australia and other British colonies. Spain's production is relatively
small and has been increasing slowly; most of it is consumed locally.
Chile's small production is mainly consumed at home and large additional
amounts are imported.
The sulphur output of the United States, which in 1913-14 was second to
Italy, now amounts to three-fourths of the entire output of the world,
and the United States has become a large exporter of sulphur. Supplies
are ample and production increasing, with the result that the United
States can not only meet its own demands, but can use this commodity
extensively in world trade. Small amounts of sulphur are mined in some
of the western states, but over 98 per cent of the production comes from
Louisiana and Texas.
GEOLOGIC FEATURES
Native sulphur is found principally in sedimentary beds, where it is
associated with gypsum and usually with organic matter. Deposits of this
type are known in many places, the most important being those of Sicily
and of the Gulf Coast in the United States. In the latter region beds of
limestone carry lenses of sulphur and gypsum which are apparently
localized in dome-like upbowings of the strata. The deposits are
overlain by several hundred feet of loose, water-bearing sands, through
which it is difficult to sink a shaft. An ingenious and efficient
process of mining is used whereby superheated water is pumped down to
melt the sulphur, which is then forced to the surface by compressed air
and allowed to consolidate in large bins. The Sicilian deposits are
similar lenses in clayey limestones containing 20 to 25 per cent of
sulphur, associated with gypsum and bituminous marl; they are mined by
shafts.
Concerning the origin of these deposits several theories have been
advanced. It has been thought that the materials for the deposits were
precipitated at the same time as the enclosing sediments; and that the
sulphur may have been formed by the oxidation of hydrogen sulphide in
the precipitating waters through the agency of air or of
sulphur-secreting bacteria, or that it may have been produced by the
reduction of gypsum by organic matter or bacteria. Others have suggested
that hot waters rising from igneous rocks may have brought in both the
sulphur and the gypsum, which in crystallizing caused the upbowing of
the strata which is seen in the Gulf fields (see also p. 298).
Native sulphur is also found in mineral springs from which hydrogen
sulphide issues, where it is produced by the oxidation of the hydrogen
sulphide. It likewise occurs in fissures of lava and around volcanic
vents, where it has probably been formed by reactions between the
volcanic gases and the air. The Japanese and Chilean deposits are of the
volcanic type.
POTASH
ECONOMIC FEATURES
Potash is used principally as a component of fertilizers in agriculture.
It is also used in the manufacture of soap, certain kinds of glass,
matches, certain explosives, and chemical reagents.
For a long time potash production was essentially a German monopoly. The
principal deposits are in the vicinity of Stassfurt in north central
Germany (about the Harz Mountains). Stassfurt salts are undoubtedly
ample to supply the world's needs of potash for an indefinite future.
However, other deposits, discovered in the Rhine Valley in Alsace in
1904, have been proved to be of great extent; and though the production
has hitherto been limited by restrictions imposed by the German
Government, it has nevertheless become considerable.[15] The grade (18
per cent K_{2}O) is superior to the general run of material taken from
the main German deposits, and the deposits have a regularity of
structure and uniformity of material favorable to cheaper mining and
refining than obtains in the Stassfurt deposits.
Other countries have also developed supplies of potash, some of which
will probably continue to produce even in competition with the deposits
of recognized importance referred to above. Noteworthy among the newer
developments are those in Spain.[16] These have not yet produced on any
large scale, but their future production may be considerable. Less
important deposits are known in Galicia, Tunis, Russia, and eastern
Abyssinia, and the nitrate deposits of Chile contain a small percentage
of potash which is being recovered in some of the operations.
Prior to the war the United States obtained its potash from Germany. The
German potash industry was well organized and protected by the German
Government, which made every effort to maintain a world monopoly. During
the war the potash exports from Germany were cut off, excepting exports
to the neutrals immediately adjoining German territory. The result in
the United States was that the price of potash rose so far as to greatly
diminish its use as fertilizer.
The consequent efforts to increase potash production in the United
States met with considerable success, but the maximum production
attained was only about one-fourth of the ordinary pre-war requirements.
The principal American sources are alkaline beds and brines in Nebraska,
Utah, and California, and especially at Searles Lake, California. These
furnished 75 per cent of the total output. Minor amounts have been
extracted in Utah from the mineral alunite (a sulphate of potassium and
aluminum), in Wyoming from leucite (a potassium-aluminum silicate), in
California from kelp or seaweed, and in various localities from
cement-mill and blast-furnace dusts, from wood ashes, from wool
washings, from the waste residues of distilleries and beet-sugar
refineries, and from miscellaneous industrial wastes. At the close of
the war, sufficient progress had been made in the potash industry to
indicate that the United States might become self-supporting in the
future, though at high cost. The renewal of importation of cheap potash
from Germany, with probable further offerings from Alsace and Spain,
makes it impossible for the United States potash production to continue;
except, perhaps, for the recovery of by-products which will go on in
connection with other industries. Demand for a protective tariff has
been the inevitable result (see Chapters XVII and XVIII).
GEOLOGIC FEATURES
Potassium is one of the eight most abundant elements in the earth. It
occurs as a primary constituent of most igneous rocks, some of which
carry percentages as high as those in commercial potash salts used for
fertilizers. It is present in some sediments and likewise occurs in many
schists and gneisses. Various potassium silicates--leucite, feldspar,
sericite, and glauconite--and the potassium sulphate, alunite, have
received attention and certain of them have been utilized to a small
extent, but none of them are normally able to compete on the market.
Potential supplies are thus practically unlimited in amount and
distribution. Deposits from which the potash can be extracted at a
reasonable cost, however, are known in only a few places, where they
have been formed as saline sediments.
In the decomposition of rocks the potash, like the soda, is readily
soluble, but in large part it is absorbed and held by clayey materials
and is not carried off. Potash is therefore more sparingly present in
river and ocean waters than is soda, and deposits of potash salts are
much rarer than those of rock salt and other sodium compounds. The large
deposits in the Permian beds of Stassfurt, as well as those in the
Tertiary of Alsace and Spain, have been formed by the evaporation of
very large quantities of salt water, presumably sea water. They consist
of potassium salts, principally the chloride, mixed and
intercrystallized with chlorides and sulphates of magnesium, sodium, and
calcium. In the Stassfurt deposits the potassium-magnesium salts occupy
a relatively thin horizon at the top of about 500 feet of rock salt
beds, the whole underlying an area about 200 miles long and 140 miles
wide. The principal minerals in the potash horizon are carnallite
(hydrous potassium-magnesium chloride), kieserite (hydrous magnesium
sulphate), sylvite (potassium chloride), kainite (a hydrous double salt
of potassium chloride and magnesium sulphate), and common salt (sodium
chloride). The potash beds represent the last stage in the evaporation
of the waters of a great closed basin, and the peculiar climatic and
topographic conditions which caused their formation have been the
subject of much speculation. This subject is further treated in the
discussion of common salt beds (pp. 295-298).
In the United States the deposits at Searles Lake, California, have been
produced by the same processes on a smaller scale. In this case
evaporation has not been carried to completion, but the crystallization
and separation out of other salts has concentrated the potassium (with
the magnesium) in the residual brine or "mother liquor." The deposits of
this lake or marsh also contain borax (see p. 276), and differ in
proportions of salts from the Stassfurt deposits. This is due to the
fact that they were probably derived, not from ocean waters, but from
the leaching of materials from the rocks of surrounding uplands,
transportation of these materials in solution by rivers and ground
waters, and concentration in the desert basin by evaporation.
The alkali lakes of Nebraska are believed to be of very recent geologic
origin. They lie in depressions in a former sand dune area, and contain
large quantities of potash supposedly accumulated by leaching of the
ashes resulting from repeated burnings of the grass in the adjacent
country.
Of other natural mineral sources, alunite is the most important. The
principal deposits worked are at Marysville, Utah, but the mineral is a
rather common one in the western part of the United States, associated
with gold deposits, as at Goldfield, Nevada. Alunite occurs as veins and
replacement deposits, often in igneous associations, and is supposed to
be of igneous source. Its origin is referred to in connection with the
Goldfield ores (p. 230).
FOOTNOTES:
[15] Gale, Hoyt S., The potash deposits of Alsace: _Bull. 715-B, U. S.
Geol. Survey_, 1920, pp. 17-55.
[16] Gale, Hoyt S., Potash deposits in Spain: _Bull. 715-A, U. S. Geol.
Survey_, 1920, pp. 1-16.
CHAPTER VIII
THE ENERGY RESOURCES--COAL, OIL, GAS (AND ASPHALT)
COAL
ECONOMIC FEATURES
Coal overshadows all other mineral resources, except water, in
production, value, and demand. It is the greatest of the energy
sources--coal, petroleum, gas, and water power. Roughly two-thirds of
the world's coal is used for power, one-sixth for smelting and
metallurgical industries, and one-sixth for heating purposes. Coal
constitutes over one-third of the railroad tonnage of the United States
and is the largest single tonnage factor in international trade; 70 per
cent of the pre-war tonnage of outgoing cargoes from England was coal.
=World production and trade.= The great coal-producing countries of the
world border the North Atlantic basin. The United States produces about
40 per cent of the world's total, Great Britain about 20 per cent, and
Germany about 20 per cent. Other countries producing coal stand in about
the following order: Austria-Hungary, France, Russia, Belgium, Japan,
China, India, Canada, and New South Wales. There is similarity in the
major features of the distribution of coal production and of iron ore
production. The great centers of coal production--the Pennsylvania and
Illinois fields of the United States, the Midlands district of England,
and the lower Rhine or Westphalian fields of Germany--are also the great
centers of the iron and steel industries of these countries. As in the
case of iron ore, there is rather a striking absence of important coal
production in the southern hemisphere and in Asia. A significant item in
the world's distribution of coal supplies is England's world-wide system
of coaling stations for shipping.
The principal coal-producing countries all have large reserves of coal.
Outside of these countries the world's most important reserves are in
China, which may be looked to for great future development. For the most
part, except for the probable Chinese development, it is likely that
countries now producing most of the coal will continue to do so in the
future, and that outlying parts of the world will continue to be
supplied mainly from these countries.
The quantity and distribution of the coal reserves of the world have
been estimated with perhaps a greater degree of accuracy than those of
any other mineral resource. From these estimates it appears that the
North American continent contains about half of the world reserves
(principally in the United States, with lesser amounts in Canada) and
Asia about one-fourth (principally in China, with some in India). Europe
contains only one-sixth of the world total, chiefly in the area of the
former German Empire and in Great Britain, with smaller quantities in
Russia, Austria-Hungary, France, and Belgium. Australasia (New South
Wales), Africa (British South Africa), and South America (Chile, Brazil,
Peru, and Colombia), together contain less than a tenth of the total
reserves. Coal being one of the great bases for modern industrialism,
the large reserves of high grade-coals in China have led to the belief
that China may some day develop into a great manufacturing nation.
Similarly, the deficiency in coal of most of the South American and
African countries seems to preclude their developing any very large
manufacturing industries, except where water power is available. Coal
reserves and the conservation of coal are further discussed in Chapter
XVII.
The war resulted in considerable disturbances in coal production and
distribution. There has not yet been a return to normal conditions, and
some of the changes are probably permanent. The great overseas movement
of coal from Germany was stopped and that from England curtailed. To
some extent the deficiency was supplied by coal exports from the United
States, particularly to South America. The shutting off of the normal
German export to France and Mediterranean countries, the occupation of
the French and Belgian coal fields by the Germans, and the partial
restriction of German exports to Scandinavian countries, resulted in
Europe's absorbing most of the British coal available for export, and in
addition requiring coal from the United States. The stress in the
world's coal industry to meet the energy requirements of war is too
recent and vivid to require more than mention. The world was made to
realize almost for the first time the utterly vital and essential nature
of this industry.
Since the war, there has been a gradual resumption of England's export
of coal along old lines of international trade. The German overseas
export trade has not been reestablished, and cannot be for a long time
to come if Germany fulfills the terms of the Peace Treaty. Indeed,
because of slow recovery in output of German coal, there is yet
considerable lag in the supply available for European countries. The
terms of the Peace Treaty lessened the territory of German coal reserves
and required considerable additional contributions of coal to be
delivered to France, Belgium, Luxemburg, and Italy.
The increased export of coal from the United States during the war is
likely to be in part continued in the future, although the great bulk of
the United States production will in the future, as in the past, be
absorbed locally. Most of the coal in the United States available for
export is higher in volatile matter than the British and German export
coal. This quality will in some degree be a limiting factor in
exportation. On the other hand, it may result in wider introduction of
briquetting, coking, and other processes, which will tend to improve the
local industry and be conservational in their effect.
Japan will doubtless hold some of the Asiatic coal market gained during
the war.
International coal relations are further discussed in Chapter XVIII.[17]
=Production in the United States.= The main features of the distribution
of coal supplies in the United States are:
(1) Localization of the anthracite production and reserves in a limited
area in the Lawton region of Pennsylvania. Low-grade anthracite coal
also occurs in Rhode Island, North Carolina, Colorado, and Idaho.
(2) Localization of the bituminous production in the eastern and
interior states of Pennsylvania, West Virginia, Ohio, Indiana, Illinois,
and Kentucky. The principal reserves of bituminous coal occur in the
same provinces, but important additional reserves are known in Texas, in
North and South Carolina, and in the Rocky Mountain and Pacific Coast
provinces.
(3) The existence of large tonnages of subbituminous coal in the west,
which have not been mined to any extent.
(4) The existence of large fields of lignite in the Gulf Coast region,
and in the Northern Plains region, which have not been mined.
=Coke.= About one-sixth of the bituminous coal mined in the United
States is made into _coke_, that is, it is subjected to heat in ovens
from which oxygen is excluded in order to drive off the volatile gases
(chiefly hydrocarbons and water) which constitute about 40 per cent of
the weight of the coal. The residual product, the coke, is a light,
porous mass with a considerably higher percentage of fixed carbon than
bituminous coal. In regard to composition, coking accomplishes
artificially somewhat the same result reached by nature in its slow
development of high-grade coals, but the texture of coke is far
different from that of coal. Not all bituminous coals are suitable for
coke manufacture; and such coals are frequently divided into two
classes, known as _coking_ and _non-coking_ coals. Coke is used
principally for smelting purposes. Because of its spongy, porous
texture, it burns more rapidly and intensely than coal.
The gases eliminated in coking are wasted in the old-fashioned "beehive"
ovens, but in modern "by-product" coke ovens these gases by proper
treatment yield valuable coal tar products and ammonia. It is estimated
that the sum of the value of the products thus recovered from a ton of
coal multiplies the value of the ton of coal at the mine by at least
thirteen times. The importance of this fact from the conservational
standpoint cannot be too much emphasized. At present over half of the
total coke produced in the United States comes from by-product ovens,
and this proportion will doubtless increase in the future.
BALANCE SHEET SHOWING CONTRAST BETWEEN VALUE OF 1 TON OF BITUMINOUS COAL
AT MINE AND VALUE OF PRODUCTS WHICH IT CONTAINS, BASED ON CONDITIONS
PREVAILING IN 1915.[1]
_Value at _Value at point of
mine 1915_ _Quantity_ production, 1915_
-------------------------------------------------------------------------
1 ton (2,000 pounds) |(1,500 pounds smokeless fuel $5.00[2]
bituminous coal |(10,000 cubic feet gas, at
contains $1.13 | 90c. per 1,000 9.00[3]
|(22 pounds ammonium sulphate at 2.8c. .61
|(2-1/2 gallons benzol, at 30c. .75[4]
|(9 gallons tar, at 2.6c. .23[4]
Total $1.13[5]| $15.59
-------------------------------------------------------------------------
1: Gilbert, Chester G., and Pogue, Joseph E., The energy resources of
the United States--A field for reconstruction: _Bull. 102, U. S.
National Museum_, vol. 1, 1919, p. 11.
2: Figure based upon approximate selling price of anthracite.
3: Figure based upon average price of city gas.
4: These figures would be much higher if an adequate coal products
industry were in existence.
5: This figure shows clearly that lowering the cost of production cannot
be expected to lower the price of coal. Even if the cost of production
were eliminated, the price of coal would merely be a dollar less.
=Classification of coals.= The accurate naming and classification of
different varieties of coal is not an easy matter. The three main
classes,--anthracite, bituminous, and lignite,--have group
characteristics determined by their composition, color, texture, origin,
and uses, and for general purposes these names have reasonably definite
significance. However, there is complete gradation in coal materials
from peat through lignite to bituminous and anthracite coals; many
varieties fall near the border lines of the main groups, and their
specific naming then becomes difficult. In addition, coal is made up of
several substances which vary unequally in their proportions. It is
difficult to arrange all of these variables in a graded series in such a
fashion as to permit of precise naming of the coal. Furthermore, the
scientific naming of a coal may not serve the purpose of discriminating
coals used for different commercial purposes. Even the commercial names
vary among themselves, depending on the use for which the coal is being
considered.
Thus it is that the naming and classification of coals is a perennial
source of difficulty and controversy. The earliest and most widely used
classification is based on the ratio between fixed (or non-volatile)
carbon and volatile constituents, called the "fuel ratio." For this
purpose "proximate" analyses of coal are made, in terms of fixed carbon,
volatile matter, moisture, ash, and sulphur. Anthracite has a higher
fuel ratio than bituminous coal; that is, it has more fixed carbon in
relation to volatile matter. Similarly bituminous coal has a higher fuel
ratio than lignite. The fuel ratio measures roughly the heat or
calorific power of the coal, in other words, its fuel value. However,
some bituminous coals have a higher calorific power than some
anthracites, because a large part of their volatile matter is
combustible and yields more heat than the corresponding weight of fixed
carbon in the anthracite. The fuel ratio pretty well discriminates coals
of the higher ranks, and gives a classification corresponding roughly
with their commercial uses. For the lower ranks of coal it is not so
satisfactory, because the volatile constituents of such coals contain
large and varying percentages of non-combustible hydrogen, oxygen, and
nitrogen. Also such coals contain larger and more variable amounts of
moisture, which is inert to combustion and requires heat for its
evaporation. Two coals of the lower ranks with the same fuel ratio may
have very different fuel qualities and different commercial uses,
because of their different amounts of inert volatile matter and of
water. For these coals it is sometimes desirable to supplement the
chemical classification by physical criteria. For instance,
subbituminous coal may be distinguished from lignite, not by its fuel
ratio alone, but by its shiny, black appearance as contrasted with the
dull, woody appearance of lignite. Bituminous may be distinguished from
subbituminous by the manner of weathering. Other classifications have
attempted to recognize these difficulties and still maintain a purely
chemical basis by considering separately the combustible and
non-combustible volatile constituents. For this purpose, it is necessary
to have not merely approximate analyses, but the ultimate analyses in
terms of elements.
Definitions of the principal kinds of coal by Campbell,[18] of the
United States Geological Survey, are as follows:
_Anthracite._ Anthracite is generally well known and may be
defined as a hard coal having a fuel ratio (fixed carbon
divided by the volatile matter) of not more than 50 or 60 and
not less than 10.
_Semianthracite._ Semianthracite is also a hard coal, but it
is not so hard as true anthracite. It is high in fixed carbon,
but not so high as anthracite. It may be defined as a hard
coal having a fuel ratio ranging from 6 to 10. The lower limit
is uncertain, as it is difficult to say where the line should
be drawn to separate "hard" from "soft" coal and at the same
time to divide the two ranks according to their fuel ratio.
_Semibituminous._ The name "semibituminous" is exceedingly
unfortunate, as literally it implies that this coal is half
the rank of bituminous, whereas it is applied to a kind of
coal that is of higher rank than bituminous--really
superbituminous. Semibituminous coal may be defined as coal
having a fuel ratio ranging from 3 to 7. Its relatively high
percentage of fixed carbon makes it nearly smokeless when it
is burned properly, and consequently most of these coals go
into the market as "smokeless coals."
_Bituminous._ The term "bituminous," as generally understood,
is applied to a group of coals having a maximum fuel ratio of
about 3, and hence it is a kind of coal in which the volatile
matter and the fixed carbon are nearly equal; but this
criterion cannot be used without qualification, for the same
statement might be made of subbituminous coal and lignite. As
noted before, the distinguishing feature which serves to
separate bituminous coal from coals of lower rank is the
manner in which it is affected by weathering.
_Subbituminous._ The term "subbituminous" is adopted by the
Geological Survey for what has generally been called "black
lignite," a term that is objectionable because the coal is not
lignitic in the sense of being distinctly woody, and because
the use of the term seems to imply that this coal is little
better than the brown, woody lignite of North Dakota, whereas
many coals of this rank approach in excellence the lowest
grade of bituminous coal. Subbituminous coal is generally
distinguishable from lignite by its black color and its
apparent freedom from distinctly woody texture and structure,
and from bituminous coal by its loss of moisture and the
consequent breaking down of "slacking" that it undergoes when
subjected to alternate wetting and drying.
_Lignite._ The term "lignite," as used by the Geological
Survey, is restricted to those coals which are distinctly
brown and either markedly woody or claylike in their
appearance. They are intermediate in quality and in
development between peat and subbituminous coal.
[Illustration: FIG. 5. Diagrams showing the chemical
composition and heat efficiency of the several ranks of coal. Upper
diagram: Comparative heat value of the samples of coal represented in
the lower diagram, computed on the ash-free basis. Lower diagram:
Variation in the fixed carbon, volatile matter, and moisture of coals of
different ranks, from lignite to anthracite, computed on samples as
received, on the ash-free basis. After Campbell.]
GEOLOGIC FEATURES
Geologic features of coal may be conveniently described in terms of
origin or genesis. Coal has essential features in common with asphalt,
oil, and gas. They are all composed of carbon, hydrogen, and oxygen,
with minor quantities of other materials, combined in various
proportions. They are all "organic" products which owe their origin to
the decay of the tissues of plants and perhaps animals. They have all
been buried with other rocks beneath the surface. The common geologic
processes affecting all rocks have in the main determined the evolution
of these organic products and the forms in which we now find them.
Originating at the surface, they have participated in the constructive
or anamorphic changes of the metamorphic cycle, which occur beneath the
surface, and under these influences have undergone various stages of
condensation, refinement, distillation, and hardening.
All stages in the development of coal have been traced. In brief, the
story is this:
[Illustration: FIG. 6. Origin and development of coal. After
Gilbert.]
This exhibit shows the successive chemical stages in the
evolution of coal. The striking qualities of the original are
lost in the reproduction through the use of designs in the
place of realistic coloring, but the effect is retained
sufficiently to indicate the nature of the sequence and the
directness with which it leads back to an origin in vegetal
accumulations. The evolutionary process is seen to take the
form of increasing density through the progressive expulsion
of volatilizable matters in the course of geologic time. This
inference is substantiated beyond reasonable question by the
actual presence of organic remains in coal beds.
Grasses, trees, and other plants growing in swamps and bogs decay and
form a vegetable mold in the nature of _peat_. A peat bog from the top
downward consists of (1) living plants, (2) dead plants, and (3) a dense
brownish-black mass, of decayed and condensed vegetable material, in
which the vegetable structure is more or less indistinct. Peat consists
chiefly of fixed carbon and volatile matter, also of sulphur, moisture,
and ash. The volatile matter consists mainly of various combinations of
hydrogen and carbon, called hydrocarbons; it goes off in gas or smoke
when the peat is heated to a red heat. The fixed carbon is the carbon
left after the volatile matter has been driven off. The ash represents
the more incombustible mineral matter, usually of the nature of clay or
slate. The moisture in peat may be as high as 90 per cent.
The essential condition for thick accumulation of peat seems to be
abundance of moisture, which favors luxuriant growth and protects the
plant remains from complete oxidation or decay. Without moisture the
vegetable material would completely oxidize, leaving practically no
residue, as it does in dry climates. For the formation of thick peat
beds, there seems to be implied some sort of a balance between the slow
building up of organic accumulations and the settling of the area to
keep it near the elevation of the water table. Present day bog deposits
are known in some cases to have a thickness of forty feet. This
thickness is not enough to account for some of the great coal seams
within the earth; but there seems to be no escape from the conclusion
that the same sort of deposits, formed on a larger scale in the past,
were the first step in the formation of the coal seams. Flat, swampy
coastal plains are believed to furnish the best conditions for thick
accumulation of peat. There is good evidence that most of the deposits
accumulate essentially in place, without appreciable transportation.
In time these surface accumulations of vegetable material may subside
and be buried under clay, sand, or other rock materials. The processes
of condensation begun in the peat bog are then carried further. They
result in the second stage of coal formation, that of _lignite_ or
_brown coal_. This is brown, woody in texture, and has a brown streak.
It has a higher percentage of fixed carbon, and less volatile matter and
water, than peat.
Continuation of the processes of induration produces _subbituminous
coal_, or _black lignite_, which is usually black and sometimes has a
fairly bright luster. It is sometimes distinguished from bituminous
coal, where weathered or dried, by the manner in which it checks
irregularly or splits parallel to the bedding,--the characteristic
feature of bituminous coal being columnar fracture.
The next stage in coal formation is _bituminous coal_. It has greater
density than the lignites or subbituminous coals, is black, more
brittle, and breaks with a cubical or conchoidal fracture. It is higher
in fixed carbon, lower in volatile matter and water. A variety of
bituminous coal, called _cannel coal_, is characterized by an unusually
high percentage of volatile matter, which causes it to ignite easily.
This material has a dull luster and a conchoidal fracture. It is
composed almost entirely of the spores and spore cases, which are
resinous or waxy products, of such plants as lived in the parent coal
swamp.
There are gradations from bituminous coal into _anthracite coal_.
_Semibituminous_ and _semianthracite_ are names used to some extent for
these intermediate varieties. The final stage of coal formation is
anthracite,--hard, brittle, black, with high luster and conchoidal
fracture. It has a higher percentage of fixed carbon and correspondingly
less of the volatile constituents, than any of the other coals.
The coals form a completely graded series from peat to the hard
anthracite. Comparison of the compositions of the coal materials at
different stages shows clearly what has happened. Moisture has
diminished, certain volatile hydrocarbons have been eliminated as gases,
and oxygen has decreased. On the other hand, the residual fixed carbon,
sulphur, and usually ash, have remained in higher percentage. This
change in composition is graphically represented in Figure 6.
During this process volume has been progressively reduced and density
increased. Five feet of wood or plant may produce about one foot of
bituminous coal, or six-tenths of a foot of anthracite.
The exact physical conditions in the earth which determine the
progressive changes in coals, above outlined, cannot be fully specified.
Time is one of the factors--the longer the time, the greater the
opportunity for accomplishing these results. Another factor is
undoubtedly pressure, due to the weight of overlying sediments, or to
earth movements. In peat condensational changes of this nature are
accomplished artificially by the pressure of briquetting machines.
Another factor is believed to be the heat developed by earth movements
and vulcanism, which presumably facilitates the elimination of volatile
materials, and thus accelerates the gradational changes above
described. This is suggested by the fact that in places where hot
volcanic lavas have gone through coal beds they have locally produced
coals of anthracitic and coke-like varieties. In general, however, it
has not been possible to determine the degree to which heat has been
responsible for the changes. Coals which have been developed in
different localities, under what seem to be much the same heat
conditions, may show quite different degrees of progress toward the
anthracite stage. Another factor that has been suggested as possibly
contributing to the change, is the degree of permeability of the rocks
overlying the coal to the volatile materials which escape from the coal
during its refinement. It is argued that in areas of folding or of
brittle rock where the cover is cracked, volatile gases have a better
chance to escape, and that the change toward anthracite is likely to
advance further here than elsewhere.
Bacterial action is an important factor in the earlier stages, in the
partial decay of vegetable matter to form peat; accumulation of waste
products from this action, however, appears to inhibit further bacterial
activity.
Coal deposits have the primary shapes of sedimentary beds. They are
ordinarily thin and tabular, and broadly lenticular,--on true scale
being like sheets of thin paper. At a maximum they seldom run over 100
feet in thickness, and they average less than 10 feet. Seldom is a
workable coal bed entirely alone; there are likely to be several
superposed and overlapping seams of coal, separated by sandstones,
shales, or other rocks. In Illinois and Indiana there are nine workable
coal seams, in Pennsylvania in some places about twenty, and in Wales
there are over one hundred, many of which are worked. Some of the seams
are of very limited extent; others are remarkably persistent, one seam
in Pennsylvania having an average thickness of 6 to 10 feet over about
6,000 square miles of its area. Only 2 per cent of the coal-bearing
measures of the eastern United States is actually coal.
Even where not subsequently disturbed by deformation, coal beds are not
free from structural irregularity. They are originally deposited in
variable thicknesses on irregular surfaces. During their consolidation
there is a great reduction of volume, resulting in minor faults and
folds. Subsequent deformation by earth forces may develop further faults
and folds, with the result that the convolutions of a coal bed may be
very complex. The beds of a coal-bearing series are usually of differing
thickness and competency, and as a consequence they do not take the same
forms under folding. Shearing between the beds may result in an
intricate outline for one bed, while the beds above and below may have
much more simple outlines. In short, the following of a coal seam
requires at almost every stage the application of principles of
structural geology. It is obvious, also, that the identification and
location of sedimentary geologic horizons are essential, and hence the
application of principles of stratigraphy.
The folios of the United States Geological Survey on coal-bearing areas
present highly developed methods of mapping and representing the
geologic features of coal beds. On the surface map are indicated the
topography, the geologic horizons, and the lines of outcrop of the coal
seams. In addition, there are indicated the sub-surface contours of one
or more of the coal seams which are selected as datum horizons. The
sub-surface structure, even though complex, can be readily read from one
of these surface maps. With the addition of suitable cross sections and
comparative columnar sections, the story is made complete. In the study
of the occurrence of coal seams, the reader cannot do better than
familiarize himself with one or more of the Geological Survey folios.
The high-grade coals of the eastern and central United States are found
in rocks of Carboniferous age. The very name Carboniferous originated in
the fact that the rocks of this geologic period contain productive coal
beds in so many parts of the world. The coal measures of Great Britain,
of Germany, Belgium, and northern France, of Russia, and the largest
coal beds of China are all of Carboniferous age. Deposits of this period
include the bulk of the world's anthracite and high-grade bituminous
coal. Coal deposits of more recent age are numerous, but in general they
have had less time in which to undergo the processes of condensation and
refinement, and hence their general grade is lower. In the western
United States there are great quantities of subbituminous coal of
Cretaceous age, and of Tertiary lignites which have locally been
converted by mountain upbuilding into bituminous and semibituminous
coals. Jurassic coals are known in many parts of the world outside of
North America, and lignites of Tertiary age are widely distributed
through Asia and Europe.
PETROLEUM
ECONOMIC FEATURES
Petroleum is second only to coal as an energy resource. The rapid
acceleration in demand from the automobile industry and in the use of
fuel oil for power seems to be limited only by the amounts of raw
material available.
=Production and reserves.= The distribution by countries of the present
annual production of petroleum, the past total production, and the
estimated reserves, is indicated in terms of percentages of the world's
total in the table[19] on the opposite page.
This table indicates the great dominance of the United States both in
present and past production of petroleum, as well as the concentration
of the industry in a few countries. In addition the United States
controls much of the Mexican production as well as production in other
parts of the world, making its total control of production at least 70
per cent. of the world's total. Notwithstanding its large domestic
production, the United States has recently consumed more oil than it
produces. Imports of crude oil are about balanced by exports of
kerosene, fuel oils, lubricants, etc. The per capita consumption of
petroleum in the United States is said to be twenty times greater than
in England. On the other hand, the remaining principal producers consume
far less than they produce, the excess being exported.
The oil from the United States, Russia, the Dutch East Indies, India,
Roumania, and Galicia is for the most part treated at refineries near
the source of supply or at tidewater, and exports consist of refined
products. The Mexican oil is largely exported in crude form to the
United States though increasing quantities are being refined within
Mexico.
The figures shown in the table for oil reserves are of course the
roughest approximations, particularly for some of the less explored
countries. However, they are compiled from the best available sources
and may serve at least to show the apparent relative positions of the
different countries at this time. Further exploration is likely to
change the percentages and add very greatly to the totals. The
significant feature of these figures is the contrast which they indicate
between distribution of reserves and distribution of past production.
Particularly do they show that the reserves of the United States, which
are more closely estimated than those of any other country, are in a far
lower ratio to past production than are the reserves in other countries.
It was estimated in 1920 that about 40 per cent of the United States
reserves are exhausted.[20]
PRESENT AND PAST PRODUCTION AND RESERVES OF OIL, BY COUNTRIES, IN TERMS
OF PERCENTAGE OF WORLD'S TOTAL
-------------------------+--------------+--------------+-------------
| | _Per cent | _Per cent
Country |_Per cent of | of total | of total
| production, | production, | oil
| 1918_ | 1857-1918_ | resources_
-------------------------+--------------+--------------+-------------
United States and Alaska | 69.15 | 61.42 | 16.26
Mexico | 12.40 | 3.80 | 10.51
Russia (southeastern | | |
Russia, southwestern | | |
Siberia, region of the | | |
Caucasus, northern | | |
Russia, and Saghalien) | 7.86 | 24.96 | 15.69
East Indies | 2.58 | 2.51 | 7.00
Roumania, Galicia, and | | |
western Europe | 2.79 | 4.07 | 2.64
India | 1.55 | 1.41 | 2.31
Persia and Mesopotamia | 1.40 | .19 | 13.52
Japan and Formosa | .48 | .51 | 2.87
Egypt and Algeria | .40 | .07 | 2.15
Germany | .14 | .22 | --
Canada | .06 | .33 | 2.31
Northern South America, | | |
including Peru, | | |
Trinidad and Venezuela | .93 | .43 | 13.31
Southern South America, | | |
including Bolivia and | | |
Argentina | .26 | .06 | 8.24
China | -- | -- | 3.19
Italy | } | |
Cuba | } | .02 |
Other countries | } | |
| ------ | ------ | ------
World total | 100.00 | 100.00 | 100.00
-------------------------+--------------+--------------+-------------
Looking forward to the future, it is clear that there will be
considerable shifts in the centers of principal production of petroleum
in the directions indicated by the reserve figures. In particular,
conspicuous development of production may be expected in the immediate
future in the countries bordering the Caribbean Sea and the Gulf of
Mexico. In the eastern hemisphere production is rapidly increasing in
Persia and Mesopotamia; and Russia, with the stabilization of political
conditions, may become ultimately the world's leading oil producer. At
the now indicated rate of production, world reserves now estimated would
be exhausted in eighty-six years and the peak of production would be
passed earlier. With continuing acceleration of production, total
reserves would be exhausted in considerably less time,--providing
physical conditions would allow the oil to be pumped from the ground at
the necessary speed, which they probably will not. These figures taken
at face value are alarming; but the earth offers such huge possibilities
for further discoveries that the life of oil reserves above indicated is
likely to be considerably extended. At many times in the history of the
mineral industry the end has apparently been in sight for certain
products; but with the increased demand for these products has come
increased activity in exploration, with the result that as yet no
definite end has been approached for any one of them. The more immediate
problems of the petroleum industry seem to the writer to be of rather
different nature: first, whether the discovery and winning of the oil
can be made to keep pace with the enormous acceleration of demand; and
second, the adjustment of political and financial control of oil
resources, the possession of which is becoming so increasingly vital to
national prosperity.
In regard to the first question, it is a much more difficult problem
today to locate and develop a supply of oil to replace the annual world
production (recently half a billion barrels), than it was twenty years
ago, when it was necessary for this purpose to find only one-fifth this
amount; and if the demand is unchecked, it will be still more difficult
to replace the three-quarters of a billion barrels of oil which will
doubtless be required in a very few years. Regardless of the amount of
oil actually in the ground, it is entirely possible that physical
limitations on its rate of discovery and recovery will prevent its being
made available as fast as necessary to meet the increasing demand. This
fact is likely to make itself felt through increase of price. Other
natural results should be the development of substitutes, such as
alcohol or benzol for gasoline; the larger recovery of oil from oil
shales; and the general speeding up of conservational measures of
various kinds. These are all palliatives and not essential remedies. To
make enough alcohol to substitute for the gasoline now coming from oil
would use a very considerable fraction of the world's food supply. To
make enough benzol (a by-product of coke) to replace gasoline would
necessitate the manufacture of many times the amount of coke now
required by the world's industries. To develop the oil shale industry to
a point where it could supply anything like the amount of oil now
derived from oil pools would mean the building of great plants,
including towns, railroads, and other equipment, equivalent to the
plants of the coal mining industry. To apply any one of the various
conservational measures discussed on later pages would only temporarily
alleviate the situation.
The question of political and financial control of oil supplies may be
illustrated by particular reference to the United States. On present
figures it appears that within three to five years the peak of
production in this country will be passed; and at the present rate of
production the life of the reserves may not be over seventeen to twenty
years. Of course production could not continue to the end at this rate,
and the actual life will necessarily be longer. Again the doubtful
factor is the possibility for further discoveries. Many favorable
structures have been mapped which have not yet been drilled, and there
are considerable unexplored areas where the outcrops are so few that
there is no clue at the surface to the location of favorable structures.
The future is likely to see a considerable amount of shallow drilling
for the sole purpose of geological reconnaissance. For upwards of ten
years important parts of the public domain have not been available for
exploration, but Congress has now enacted legislation which opens up
vast territories for this purpose.
Even with large allowance for these possibilities, it seems unlikely
that production in the United States can increase very long at the
accelerating rate of the domestic demand, which is already in excess of
domestic production. The supplies of Mexico are in a large part
controlled by American capital and are thus made available to the
United States (subject, of course, to political conditions); but even
with these added, the United States is in a somewhat unfavorable
situation as compared with certain other countries. This situation is
directing attention to the possibility of curtailment of oil exports,
and to the possibility of acquiring additional oil supplies in foreign
countries. In this quest the United States is peculiarly handicapped in
that most foreign countries, in recognition of the vital national
importance of the oil resource, have imposed severe restrictions on
exploration by outsiders. Nationals of the United States are excluded
from acquiring oil concessions, or permitted to do so only under
conditions which invalidate control, in the British Empire, France,
Japan, Netherlands, and elsewhere, and the current is still moving
strong in the direction of further exclusion. As the United States
fields are yet open to all comers, it has been suggested that some
restriction by the United States might be necessary for purposes of
self-protection, or as an aid in securing access to foreign fields. The
activity of England during and since the war has increased the amount of
oil controlled by that country from an insignificant quantity to
potentially over half of the world's oil reserves. The problem of future
oil supplies for the United States presents an acute phase of the
general question of government cooperation or participation in mineral
industries, which is further discussed in Chapter XVIII.
The following table summarizes the distribution of the oil production in
the United States, together with the salient features of its geologic
distribution and character.
This table, in conjunction with Fig. 8 below, shows clearly that the
bulk of the United States production of oil comes from two great
sources--the Pennsylvanian sandstones of the Mid-Continent field in
Kansas and Oklahoma, and the Cretaceous and Tertiary sediments of the
southern half of California. Phenomenal development of the Central and
North Texas field in 1919 increased its yield to about one-sixth of the
country's total. The older Appalachian oil field, extending from New
York to West Virginia and Tennessee, was the earliest area discovered;
it is still one of the more productive fields, though it has long since
passed its maximum production. The other principal sources of oil are
the Gulf Coast field in Louisiana and Texas, the North Louisiana field,
the southern Illinois field, and the Rocky Mountain region. This last
region, containing large amounts of government land recently opened to
exploration, bids fair to produce increasing quantities of oil for some
time.
PAST PRODUCTION OF PETROLEUM IN THE UNITED STATES. (FIGURES FROM U. S.
GEOLOGICAL SURVEY)
-------------+-----------------+----------+-----------+---------------
| | | | _Total
| _Age of | |_Production| production
| containing | | for 1918 |including 1918
_State_ | rocks_ | _Base_ |(barrels)_ |(barrels)_
-------------+-----------------+----------+-----------+---------------
Alaska |East-Low. |Paraffin | (a) | (a)
| Tertiary | | |
| West-Jurassic | | |
California |Cretaceous: | | |
| Tertiary |Asphalt | 97,531,997| 1,110,226,576
Colorado |Pierre-Cretaceous|Paraffin | 143,286| 11,319,370
Illinois |Mississippian- |Paraffin | 13,365,974| 298,225,380
| Pennsylvanian | | |
Indiana |East-Ordovician |Paraffin | 877,558| 106,105,584
| (Trenton) West-| | |
| Pennsylvanian | | |
Kansas |Pennsylvanian |Par.-Asph.| 45,451,017| 148,450,298
Kentucky, |Mississippian |Paraffin | 4,376,342| 18,213,188
Tennessee | | | |
Louisiana |Cretaceous-Quat. |Paraffin | 16,042,600| 150,769,911
| Cretaceous- | | |
| Eocene | | |
Michigan, |Carboniferous |Paraffin | (a) | (a)
Missouri | | | |
Montana | -- | -- | 69,323| 213,639
New Mexico |Carboniferous- | -- | (a) | (a)
| Cretaceous | | |
New York, |Devonian- |Paraffin | 8,216,655| 788,202,717
Pennsylvania| Carboniferous | | |
Ohio, East |Ordovician- |Paraffin | 7,285,005| 463,367,386
and West | Carboniferous | | |
Oklahoma |Pennsylvanian |Paraffin |103,347,070| 851,320,457
Texas |Pennsylvanian, |Asph.-Par.| 38,750,031| 327,550,005
| Cretaceous-Quat.| | |
Utah | -- | -- | (b) | (b)
West |Devonian- | -- | 7,866,628| 294,474,710
Virginia | Carboniferous | | |
Wyoming |Carboniferous- |Asph.-Par.| 12,596,287| 40,019,573
| Cretaceous | | |
Other | -- | -- | 7,943| 112,925
| | |-----------| -------------
| | |355,927,716| 4,608,571,719
-------------+-----------------+----------+-----------+---------------
(a) Included in "Other."
(b) Included in Wyoming.
[Illustration: FIG. 7. Chart showing the present tendency of
the United States in respect to its unmined reserve of petroleum. Data
from U.S. Geological Survey. After Gilbert and Pogue.]
=Methods of estimating reserves.= It may be of interest to inquire into
the basis on which predictions are made of the life of an oil pool. The
process is essentially a matter of platting curves of production, and of
projecting them into the future with the approximate slopes exhibited in
districts which are already approaching exhaustion.[21] While no two
wells or two districts act exactly alike, these curves have group
characteristics which are used as a rough basis for interpreting the
future.
[Illustration: FIG. 8. The annual output of the principal oil
fields of the United States for the last twenty years. Data from U.S.
Geological Survey.]
A less reliable method is to calculate from geologic data the volume and
porosity of the oil-bearing reservoirs, and to estimate the percentage
of recovery on the basis of current practices and conditions. Complete
data for this method are often not available; but in the early years of
a field, before production curves are established, this method may serve
for a rough approximation.
[Illustration: FIG. 9. Curve showing the usual decline in oil
field production after the period of maximum output is reached. After
Ralph Arnold. The Petroleum Resources of the United States, Smithsonian
report for 1916, p. 283. Compare this theoretical curve of final
decrease with the production curve shown in Fig. 8.]
=Classes of oils.= When crude petroleum is distilled, it gives off in
succession various substances and gradually thickens until it leaves a
solid residue, which may be largely either paraffin wax or asphalt. The
two main classes of oils are determined by the nature of this solid
residual. The products given off are natural gas and then liquid
hydrocarbons of various kinds, which evaporate in the order of their
lightness. Petroleum is thus a mixture or mutual solution of different
liquids, gases, and solids. Nearly one-fifth of the domestic consumption
of crude petroleum is burned directly as fuel, and four-fifths are
refined. The several principal primary products of refinement are
gasoline, kerosene, fuel oil, and lubricating oil; but these may be
broken up into other substances, each the starting point of further
refinements, with the result that present commercial practice yields
several hundred substances of commercial value. With increasing chemical
and technical knowledge these products are being multiplied. The rapidly
increasing demand for gasoline has led to the use of processes which
extract a large proportion of this substance from the raw material, by
"cracking" or breaking up other substances; but while, under the stress
of necessity, there is possibility of slight modification of the
proportions of principal substances extracted from the crude oil, it is
not possible to change these proportions essentially. It is, therefore,
a problem to adjust relative demands to supplies of the different
products. The domestic demand for gasoline is greater than the supply.
On the other hand, the demand for kerosene, which must be produced at
the same time, is much less than the domestic supply. Hence the
importance of maintaining export markets for kerosene.
The nature or grade of the oil of various fields is an important matter
in considering reserves for the future. Perhaps half of the United
States reserves consist of the asphalt-base oils of the California and
certain of the Gulf fields, which yield comparatively small amounts of
gasoline and other valuable light products, though they are very
satisfactory for fuel purposes. Similarly the large reserve tonnages of
oil in Mexico and the Caribbean countries, in Peru, and probably in
Russia, are essentially of the heavier, lower grade oils. The oils of
the Mid-Continental and eastern fields of the United States, of Ontario,
of the Dutch East Indies, of Burma, and of Persia and Mesopotamia are
reported to be largely of the paraffin base type, which, because of its
larger yield of gasoline and light oils, is at present considerably more
valuable. These generalizations are of course subject to qualifications,
in that the oils of a given region may vary considerably, and that some
oils are intermediate in character, containing both asphalt and paraffin
wax.
=Conservation of oil.= The rapid increase in demand for oil as compared
with discovery of new sources is leading naturally to a more intensive
study of the conservational aspects of the industry. This is a complex
and difficult subject which we shall not take up in detail, but we may
point out some of the phases of the problem which are receiving especial
attention.
[Illustration: FIG. 10. Chart showing the relative values of
the principal petroleum products manufactured in the United States from
1899 to 1914. After Gilbert and Pogue. Note the decreasing importance of
kerosene in sustaining the cost of refining, and the necessity of
exports for maintaining a balanced outlet of products. Data from Story
B. Ladd, Petroleum Refining. Census of Manufactures: 1914, Bureau of
Census, Washington, 1917, p. 10.]
About 50 per cent of the oil in the porous strata, of oil pools is
ordinarily not recovered, because it clings to the rock. Efforts are
being made along various lines to increase the percentage of
recovery,--as, for instance, in preventing infiltration of water to the
oil beds and in the use of artificial pressures and better pumping.
"Casing-head gasoline" is being recovered to an increasing extent from
the natural gas which was formerly allowed to dissipate in the air.
Minute division of the ownership of a pool, with consequent
multiplication of wells and unrestricted competition, tends to gross
over-production and highly wasteful methods. The more rapid exhaustion
of one well than the others may result in the flooding of the oil sands
by salt waters coming in from below. Various efforts have been made
toward a more systematic and coordinated development of oil fields.
In general, the organization and technique involved in the development
of an oil field are improving in the direction of extracting a greater
percentage of the total available oil.
Better methods of refining the oil, and the refining of a larger
percentage of the crude oil, make the oil more available for a greater
variety of purposes and therefore more valuable. Great advances have
been made along these lines, particularly in the application of the
"cracking" method for a greater recovery of the more valuable light oils
at the expense of the less valuable heavy oils. Similarly, modifications
of internal combustion engines will probably permit the use, in an
increasing number of cases, of products of lower volatility than
gasoline.
One of the conservational advances in coming years will probably be a
restriction in the amount of crude oil used directly for fuel and road
purposes without refining. These crude uses cut down the output of much
desired products from the distillation of the oil. Various other
restrictions in the use of oil have been proposed, such as the
curtailment of the use of gasoline in pleasure cars. The gasless Sundays
during the war represented an attempt of this kind. In general, it seems
likely that such restrictions will come mainly through increase in the
price of oil products.
The substitution of oil from oil shales, and of alcohol for gasolene,
already mentioned, will be conservational so far as the oil is
concerned, though perhaps not so in regard to other elements of the
problem.
GEOLOGIC FEATURES
=Organic theory of origin.= According to this theory, accumulations of
organic materials in sedimentary beds, usually muds or marls, have been
slowly altered and distilled during geologic ages; the products of
distillation have migrated chiefly upward to porous strata like
sandstones or cavernous limestones, where, under suitable conditions,
they have become trapped.
The original organic material is believed to have been plants of low
order and animal organisms (such as foraminifera) which were deposited
as organic detritus with mud and marl in the bottoms of ponds, lakes,
estuaries, and on the sea bottom,--in both salt and fresh waters.
Bacteria are supposed to have played a part in the early stage of
alteration, sometimes called the biochemical stage. When the organic
matter was buried under later sediments and subjected to pressure,
physical conditions were responsible for further volatilization or
distillation. This stage is called the geochemical stage. There is much
in common as to origin between coal, oil shales, and petroleum.
According to White,[22]
whether the ingredient organic matter, be it plant or animal,
will be in part transformed to coal of the ordinary type, to
cannel, to oil shale, to the organic residues in so-called
bituminous shales and carbonaceous shales, or to petroleum and
natural gas, is dependent upon the composition of the
ingredient organic debris, the conditions of its accumulation
or deposition, and the extent of the microbian action.
White has further developed the important principle that, in the
geochemical stage of development, both coal and oil react to physical
influences in much the same way; and that therefore when both are found
in the same geologic series, the degree of concentration of the coal,
measured by its percentage of carbon, may be an indication of the stage
of development of the oil. More specifically where the coal contains
more than 65 to 70 per cent of fixed carbon, chances for finding oil in
the vicinity are not good (though commercial gaspools may be found),
probably for the reason that the geochemical processes of distillation
have gone so far as to volatilize the oils, leaving the solid residues
in the rock. White also finds that the lowest rank oils, with
considerable asphalt, are found in regions and formations where the
coal deposits are the least altered, and the lighter, higher rank oils,
on the whole, where the coal has been brought to the correspondingly
higher ranks; in other words, up to the point of complete elimination of
the oil, improvement in quality of the oil accompanies increased
carbonization of the coal. The principle, therefore, becomes useful in
exploration in geologic series where oil is associated with coal. Where
the coal is in one series and the oil in another, separated by
unconformity (indicating different conditions of development), the
principle may not hold, even though there is close geographical
association.
The oil and gas distillates migrate upward under gas pressure and under
pressure of the ground-water. If there are no overlying impervious beds
to furnish suitable trapping conditions, or conditions to retard the
flow, the oil may be lost. The conditions favorable for trapping are
overlying impervious beds bowed into anticlines, or other structural
irregularities, due either to secondary deformation or to original
deposition, which may arrest the oil in its upward course. A dome-like
structure or anticline may be due to stresses which have buckled up the
beds, or to unequal settling of sediments varying in character or
thickness; thus some of the anticlinal structures of the Mid-Continent
field may be due to settling of shaley sediments around less
compressible lenses of sandstone which may act as oil reservoirs, or
around islands which stood above the seas in which the oil-bearing
sediments were deposited and on the shores of which sands capable of
acting as oil reservoirs were laid down. Favorable conditions for
trapping the oil may be furnished by impervious clay "gouges" along
fault planes, or by dikes of igneous rock. Favorable conditions may also
be merely differences in porosity of beds in irregular zones, determined
by differences either in original deposition or in later cementation.
The thickness of oil-producing strata may vary between 2 or 3 feet and
200 feet. The porosity varies between 5 and 50 per cent. In sandstones
the average is from 5 to 15 per cent. In shales and clays, which are
commonly the impervious "cap-rocks," porosity may be equally high, but
the pores are too small and discontinuous to permit movement.
When the impervious capping is punctured by a drill hole, gas is likely
to be first encountered, then oil, and then water, which is usually
salty. The gas pressure is often released with almost explosive
violence, which has suggested that this is an important cause of the
underground pressures. It has been supposed also that the pressures are
partly those of artesian flows. The vertical arrangement of oil, gas,
and water under the impervious capping is the result of the lighter
materials rising to the top. In certain fields, oil and gas have been
found in the tops of anticlines in water-saturated rocks, and farther
down the flanks of folds or in synclines in unsaturated rocks.
The localization of oil pools is evidently determined partly by original
organic deposition, often in alignment with old shore lines, and partly
by the structural, textural, and other conditions which trap the oil in
its migration from the source.
=Effect of differential pressures and folding on oil genesis and
migration.= Another organic hypothesis proposed somewhat recently[23] is
that oil is formed by differential movement or shearing in bituminous
shales, which are often in close relationship with the producing sand of
an oil field, and that the movement of oil to the adjacent sands is
accomplished by capillary pressure of water and not by ordinary free
circulation of water under gravity. The capillary forces have been shown
to be strong enough to hold the oil in the larger pores against the
influence of gravity and circulation. The accumulation of the oil into
commercial pools is supposed to take place in local areas where the
oil-soaked shale, due to jointing or faulting, is in direct contact with
the water of the reservoir rock. This suggests lack of wide migration.
This hypothesis is based on experimental work with bituminous shales.
The general association of oil pools with anticlinal areas is explained
on the assumption that anticlines on the whole are areas of maximum
differential movement, resulting in oil distillation, and that they are
ordinarily accompanied by tension joints or faults, affording the
conditions for oil migration. Data are insufficient, however, to
indicate the extent to which the anticlinal areas are really areas of
maximum shearing. As regards the exact nature of the process, it is not
clear to what extent differential movement may involve increase in
temperature which may be the controlling factor in distillation,--although
in McCoy's experiment oil was formed when no appreciable amount of heat
was generated.
The development of petroleum by pressure alone acting on unaltered
shale, as shown by these experiments, has been taken by White[24] to
have a significant bearing on the geochemical processes of oil
formation. Under differential stresses acting on fine-grained
carbonaceous strata under sufficient load, there is considerable
molecular rearrangement, as well as actual movement of the rock
grains,--thus promoting the distillation of oil and gas from the organic
matter in the rocks, and the squeezing out of the oil, gas, and water
into adjacent rocks, such as coarse round-grained sandstones and porous
limestones, which are more resistant to change of volume under pressure.
Migration, concentration and segregation of the oil, gas, and water is
supposed to be brought about, partly through the effect of capillary
forces--the water, by reason of its greater capillary tension, tending
to seize and hold the smaller voids, and thus driving the oil and gas
into the larger ones--and partly through the action of gravity.
White also suggests that the process may go further where the parent
carbonaceous strata are of such thickness and under such load of
overlying rocks that they undergo considerable interior adjustment and
volume change before yielding to stress by anticlinal buckling,--than
where the strata yield quickly. It is not clear to the writer that the
interior adjustment assumed under this hypothesis is necessarily slowed
up or stopped by anticlinal buckling. Interior stresses are inherent in
any sedimentary formation, when settling and consolidating and
recrystallizing under gravity, and these may be independent of regional
thrusts from without.
The first oils evolved by pressure from the organic mother substance are
probably heavy, the later oils lighter, and the oils from formations and
regions where the alteration is approaching the carbonization limit are
characteristically of the highest grade. This is the reverse of the
order of products obtained by heat distillation. Whether there is also a
natural fractionation and improvement of the first heavy oils as they
undergo repeated migrations is not known.
=Inorganic theory of origin.= Another theory of the source of oil has
had some supporters, although they are much in the minority. This is the
so-called "inorganic" theory, that oil comes from magmas and volcanic
exhalations. In support of this theory attention is called to the fact
that igneous rocks and the gases associated with them frequently carry
carbides or hydrocarbons; that many oil fields have a suggestive
geographic relationship with volcanic rocks; and that certain of the oil
domes, as for instance in Mexico, are caused by plugs of igneous rocks
from below. It has been suggested that deep within the earth carbon is
combined with iron in the form of an iron carbide, and that from the
iron carbide are generated the hydrocarbons of the oil, either by or
without the agency of water. Iron carbide is magnetic, and significance
has been attached to the general correspondence between the locations of
oil in the western United States and regions of magnetic disturbance.
It seems not unlikely that some inorganic theory of this sort is
necessary to explain the ultimate source of oil or of the substances
which become oil, but the evidence is overwhelming that organic agencies
have been mainly responsible for the principal oil pools now known.
=Oil exploration.= A simple geographic basis for oil exploration is the
fact that the major oil fields of the world are situated between 20 deg. and
50 deg. north latitude, and that thus far there are no major oil areas
within the tropics or within the southern hemisphere. This broad
generalization may have little value when exploration is carried
further. It has also been suggested that the geographic distribution of
oil corresponds roughly with the average annual temperatures, or
isotherms, between 40 deg. and 70. deg.[25] It is thought that this present
distribution of temperatures may indicate roughly the temperatures of
the past when the oil was accumulated; and the inference is drawn that
there was some sort of limitation of areal deposition within these
temperature limits. If this be true, the only reasons why the southern
hemisphere is not productive are the relatively small size of the land
areas and the lack of exploration to date.
In approaching broadly the problem of oil exploration, the geologist
considers in a general way the kinds and conditions of rocks which are
likely to be petroliferous or non-petroliferous. Schuchert[26]
summarizes these conditions for North America as follows:
1. The impossible areas for petroliferous rocks.
(_a_) The more extensive areas of igneous rocks and especially
those of the ancient shields; exception, the smaller dikes.
(_b_) All pre-Cambrian strata.
(_c_) All decidedly folded mountainous tracts older than the
Cretaceous; exceptions, domed and block-faulted
mountains.
(_d_) All regionally metamorphosed strata.
(_e_) Practically all continental or fresh-water deposits; relic
seas, so long as they are partly salty, and saline lakes are
excluded from this classification.
(_f_) Practically all marine formations that are thick and uniform
in rock character and that are devoid of interbedded dark
shales, thin-bedded dark impure limestones, dark marls, or
thin-bedded limy and fossiliferous sandstones.
(_g_) Practically all oceanic abyssal deposits; these, however, are
but rarely present on the continents.
2. Possible petroliferous areas.
(_a_) Highly folded marine and brackish water strata younger than
the Jurassic, but more especially those of Cenozoic time.
(_b_) Cambrian and Ordovician unfolded strata.
(_c_) Lake deposits formed under arid climates that cause the
waters to become saline; it appears that only in salty
waters (not over 4 per cent?) are the bituminous materials
made and preserved in the form of kerogen, the source of
petroleum; some of the Green River (Eocene) continental
deposits (the oil shales of Utah and Colorado) may be of
saline lakes.
3. Petroliferous areas.
(_a_) All marine and brackish water strata younger than the
Ordovician and but slightly warped, faulted, or folded; here
are included also the marine and brackish deposits of relic
seas like the Caspian, formed during the later Cenozoic. The
more certain oil-bearing strata are the porous thin-bedded
sandstones, limestones, and dolomites that are interbedded
with black, brown, blue, or green shales. Coal-bearing strata
of fresh-water origin are excluded. Series of strata with
disconformities may also be petroliferous, because beneath
former erosional surfaces the top strata have induced
porosity and therefore are possible reservoir rocks.
(_b_) All marine strata that are, roughly, within 100 miles of
former lands; here are more apt to occur the alternating
series of thin and thick-bedded sandstones and limestones
interbedded with shale zones.
The extent to which marine or brackish water conditions of sedimentation
are requisite to the later formation of oil, as is suggested in the
above quotation, has long been a debatable question. It may be noted
that certain oil shales formed in fresh water basins contain abundant
organic matter which is undoubtedly suitable for the generation of oil
and gas, and that these shales on distillation yield oil essentially
like that obtained from oil shales of marine origin; that certain
important oil-bearing sands of the younger Appalachian formations were
laid down in waters which are believed to have been only slightly
saline; that natural gas is present in fresh water basins; and that it
has not been demonstrated that salt in appreciable amounts is necessary
for the geologic, any more than for the artificial, distillation of oil.
Most of the great oil fields have been in regions of marine or other
saline water deposits, but it has not been proved that this is a
necessary condition. White[27] says: "At the present stage of our
knowledge, fresh-water basins appearing otherwise to meet the
requirements should be wildcatted without prejudice."
The principal oil-bearing horizons in any locality are comparatively
few, and it is ordinarily easy to determine by stratigraphic methods the
presence or absence of a favorable geologic horizon. By knowing the
succession and thicknesses of the beds in a given region it is possible
to infer from surface outcrops the approximate depth below the surface
at which the desired horizon can be found. To do this, however, the
conditions of sedimentation, the initial irregularities of the beds, the
structural conditions, including unconformities, and other factors must
be studied.
In exploration for oil the determination of the existence and location
of the proper horizon is but an initial step. For instance, the oil of
the Midcontinent field of the United States is in the beds of the
Pennsylvanian, which are known to occupy an enormous area extending from
Illinois and Wyoming south to the Gulf of Mexico. This information is
clearly not sufficiently specific to limit the location of drill holes.
Sometimes seepages of oil or showings of gas near the surface are
sufficient basis for localizing the drill holes.[28] Commonly, however,
it is necessary to find some structural feature in the nature of a dome
or anticline which suggests proper trapping conditions for an oil pool.
This is accomplished by geologic and topographic mapping of the surface.
Levels and contours are run and outcrops are platted. As the outcrops
are usually of different geologic horizons, it is necessary to select
some one or more identifiable beds as horizon markers, and to map their
elevations at different points as a means of determining the structural
contours of the beds. When several key horizons are thus used, their
elevations must be reduced to the elevations of one common horizon by
the addition or subtraction of the intervals between them. For instance,
knowing the succession, an outcrop of a certain sandstone may indicate
that the marking horizon is 200 feet below, and the structural contour
is then drawn accordingly. Observations of strike and dip at the surface
are helpful; but where the beds are but slightly flexed, small
irregularities in deposition may make strike and dip observations
useless in determining major structures. It is then necessary to have
recourse to the elevations of the marking horizons.
In the selection of key horizons, knowledge of the conditions of
sedimentation is very important. For example, some of the oil fields
occur in great delta deposits, where successive advances and retreats of
the sea have resulted in the interleaving of marine and land deposits.
The land-deposited sediments usually show great variations in character
and thickness laterally and vertically; and a given bed is likely to
thin out and disappear when traced for a short distance, rendering
futile its use as a marker. The marine sediments, on the either hand,
show a much greater degree of uniformity and continuity, and a bed of
marine limestone may extend over a large area and be very useful as a
key horizon.
Over large areas outcrops and records of previously drilled water and
oil wells may not be sufficient to give an indication of structure; it
then becomes necessary to secure cross sections by drilling shallow
holes to some identifiable bed, and to determine the structure from
these cross sections, in advance of deeper drilling through a favorable
structure thus located. The cooperative effort of the Illinois State
Survey and private interests, cited on page 306, is a good illustration
of this procedure. This method is only in its infancy, because
well-drilling has not yet exhausted the possibilities of structures
located from surface outcrops.
The so-called anticlinal structures, which have been found by experience
to be so favorable to the accumulation of oil, are by no means
symmetrical in shape or uniform in size. They may be elongated arches
with equal dip on the two sides, or one side may dip and the other be
nearly flat. In a territory with a general dip in one direction, a
slight change in the angle, though not in the direction of dip,
sometimes called an arrested dip, may cause sufficient irregularity to
produce the necessary trapping conditions. In other cases the anticline
may be of nearly equidimensional dome form. The largest anticlines which
have been found to act as specific reservoirs are rarely more than a few
miles in extent, and in many cases only a mile or two. The "closure" of
an anticline is the difference between the height of a given stratum at
the highest point and at the edges of the structure. A considerable
number of productive anticlines are known in which the beds dip so
gently as to give a closure of 20 feet or less.
After the structural outlines of beds near the surface have been
determined, all possible information should be used in projecting these
structures downward to the oil-producing horizons. Where a number of
wells have been previously drilled in the vicinity, examination of their
records may indicate certain lateral variations in the thickness of the
beds between the horizon which has been mapped and the producing
horizon. The effect of such lateral variations may be either to
accentuate the surface structure, or to cause it to disappear entirely
and thus to indicate lack of favorable trapping conditions. The
possibility of several oil-producing beds, at different depths--a not
uncommon condition in many fields--should also be kept in mind.
As already indicated, anticlines are not always essential to make the
necessary trapping conditions. In the Beaumont field of Texas, for
instance, it has been shown that irregular primary deposition of
sediments differing in porosity both vertically and horizontally allowed
the oil to migrate upward irregularly along the porous beds and parts
of beds, and to be trapped between the more impervious portions of the
beds.
Further questions to be considered in the exploration of an area are the
content of organic matter in the sediments which may have served as a
source of oil, the presence of impervious cap-rocks or of variations in
porosity sufficient to retain the oil, the thickness of sediments and
the extent to which they have undergone differential stresses, the
amount of erosion and the possibilities that oil, if formed, has escaped
from the eroded edges of porous strata, and, where carbonaceous beds are
present, their degree of carbonization, and many other similar matters.
Each field in fact has its own "habit," determined by the interaction of
several geologic factors. This habit may be learned empirically.
Geologists have often gone wrong in applying to a new district certain
principles determined elsewhere, without sufficient consideration of the
complexity and relative importance of the sundry geologic factors which
in the aggregate determine the local habit of oil occurrence.
Geographically associated fields characterized by similarity of oil
occurrence, age, and origin, are known as _petroliferous provinces_. The
factors entering into the classification of fields are so numerous that
more precise definition of a petroliferous province is hardly yet agreed
upon.
The part played by the economic geologist in oil exploration and
development is a large one for the obvious reasons given above. Probably
no other single division of economic geology now employs so large a
number of geologists. Practically no large oil company, or large piece
of oil exploration and development, is now handled without geologic
advice. Quoting from Arnold:[29]
It ought to be as obvious that exploration with the drill
should be preceded by careful geologic studies as it is that
railroad construction should be based on surveys. These
studies should include such subjects as topography,
stratigraphy, structure, and surface evidence of petroleum in
the regions to be tested. The work divides itself into two
stages--preliminary reconnaissances and detailed surveys.
The preliminary reconnaissance should consist in procuring all
the available published and hearsay evidence regarding the
occurrence of oil or gas seepages or hydrocarbon deposits in
the region; in making preliminary geologic surveys to
determine from which formations the oil is to come and the
areal distribution of these formations; in determining those
general regions in which the surface evidence is supposed to
be most favorable for the accumulation of hydrocarbons; and in
determining the best routes and methods of transportation.
The second stage includes detailed geologic surveys of those
regions where the surface evidence indicates that petroleum is
most likely to be found and the location of test holes at
favorable points. By working out the surface distribution and
structure of the formations it is usually possible to select
the areas offering the best chances of success. Geology should
always be the dominant factor in determining the location of
test holes, although modifications to meet natural conditions
must sometimes be made.
OIL SHALES
One of the sources of oil which is likely to become important in the
future is oil shales,--that is, shales from which oil product can be
extracted by distillation. These have already been referred to on
previous pages. Such shales are now mined only in Scotland and in France
to a relatively small extent, but there are immense reserves of these
shales in various parts of the world which are likely to be drawn upon
when commercial conditions require it. In the United States alone it is
estimated that the oil shales are a potential source of oil in amounts
far greater than all the natural petroleum of this hemisphere.[30] The
solution of the problem of extraction of oil from shales is fairly well
advanced technically, and the problem has now become principally one of
cost. In order to recover any large amount of oil from this source,
operations of stupendous magnitude, approximately on the scale of the
coal industry, must be established. As long as there are sufficient
supplies of oil concentrated by nature to be drawn upon, it is unlikely
that oil shale will furnish any considerable percentage of the world's
oil requirements. With the great increase in world demand for oil,
however, which may very possibly outstrip the available annual supply in
the future, and particularly with the increase in the United States
demand relative to domestic supplies, exhaustive surveys of the
situation are being made with a view to development of oil shales when
warranted by market conditions.
Oil shales are sedimentary strata containing decomposed products of
plants and animals. Locally they grade into cannel coal, with which they
are genetically related. They may be regarded as representing the kinds
of sediments from which the oil of oil pools has in the main originated.
The most extensive of the oil shales of the United States are found in
the Eocene beds of northwestern Colorado, northeastern Utah, and
southwestern Wyoming, and in the Miocene beds of northern Nevada. The
largest known foreign deposits occur in Brazil and Russia.
NATURAL GAS
ECONOMIC FEATURES
Natural gas is used both for lighting and for fuel purposes. In the
United States it has become the basis of a great industry, the value of
the product ranging above that of lead and zinc. The United States is
the largest producer of natural gas. Other producers are Canada, Dutch
East Indies, Mexico, Hungary, Japan, and Italy. Nearly all producing oil
fields furnish also some natural gas.
In the United States nearly 40 per cent of the total production of
natural gas comes from West Virginia, about 17 per cent from
Pennsylvania, about 17 per cent from Oklahoma, and less than 10 per cent
from each of Ohio, California, Louisiana, Kansas, Texas, and several
other states.
One of the recent interesting developments in this industry is the
recovery of gasoline from the natural gas. This is obtained by
compression and condensation of the casing-head gas from oil wells, and
also, more recently, by an absorption process which is applied not only
to "wet" gas from oil wells but also to so-called "dry" gas occurring
independently of oil. It is a high-grade product which in recent years
has amounted to about 10 per cent of the total output of gasoline for
the United States.
GEOLOGIC FEATURES
Natural gas, like oil, originates in the distillation of organic
substances in sediments, and migrates to reservoirs capped by impervious
strata. It is commonly, though not always, associated with oil and coal.
The geologic features of its occurrence have so much in common with oil
that a description would essentially duplicate the above account of the
geologic features of oil.
ASPHALT AND BITUMEN
ECONOMIC FEATURES
Asphalt and bitumen are not used as energy resources, but they have so
much in common with oil in occurrence and origin that they are included
in this chapter.
Asphalt and bitumen find their main use in paving. Other important uses
are in paints and varnishes, in the manufacture of prepared roofing, for
various insulating purposes, and in substitutes for rubber.
Nearly the entire world's supply of natural asphalt comes from the
British Island of Trinidad and from Venezuela. Both of these deposits
are under United States commercial control probably affiliated with
Dutch-English interests. Prior to the war about half the product went to
Europe and half to the United States. Large amounts of asphaltic and
bituminous rock, used mainly in paving, are normally produced in Alsace,
France, and in Italy. Prior to the war both the Alsatian and Italian
deposits were under German commercial control. Their output is
practically all consumed in Europe.
The United States takes a large part in the world's trade in natural
asphalt, by importation from Trinidad and Venezuela, and by some
reexportation chiefly to Canada and Mexico. The United States also
produces some natural asphalt and bituminous rock for domestic
consumption. Deposits of natural asphaltic material are widely
distributed through the United States, but commercial production is
limited to a few localities in Kentucky, Texas, Utah, Colorado,
Oklahoma, and California.
The asphalt manufactured from petroleum constitutes a much larger
tonnage than natural asphalt though it does not enter so largely into
world trade. The manufactured product is largely but not exclusively in
American control. Large amounts are made in this country and will no
doubt be made for the next decade, from oil produced in the southwestern
states and in Mexico. At the present time as much or more asphalt is
made in the United States from Mexican as from domestic crude oil. The
refineries are located near the Gulf coast so that exports can avoid
overland shipments. The relative merits of natural asphalt and asphalt
manufactured from oil may be subject to some discussion; but it is
perfectly clear that the manufactured material is sufficient, both in
quantity and variety, to make the United States entirely independent and
have an exportable surplus.
GEOLOGIC FEATURES
Natural asphalt and similar products are in the main merely the
residuals of oil and gas distillation accumulated by nature under
certain conditions already described in connection with oil (pp.
140-144). In some cases the asphaltic material is found as impregnations
of sediments, and appears to have remained in place while the lighter
organic materials were volatilized and migrated upward. In other cases
it occurs in distinct fissure veins; the fissures and cavities
apparently were once filled with liquid petroleum, which has
subsequently undergone further distillation. The original liquid
character of some of these bitumens is shown by occasional fragments of
unworn "country rock" imbedded in the veins. The effect of surface
waters, carrying oxidizing materials and sulphuric acid, is believed to
have contributed to the drying out and hardening of these veins or
dikes.
Asphalts and bitumens include a wide variety of hydrocarbon materials,
such as gilsonite, grahamite, elaterite, ozokerite, etc., which are used
for somewhat different purposes. The deposits of the United States show
much variety in form, composition, age, and geologic associations. The
important Kentucky deposits occur as impregnations of Carboniferous
sandstones at the base of the Coal Measures of that state.
The Trinidad asphalt comes from the famous "pitch lake," which is a
nearly circular deposit covering about a hundred acres 150 feet above
sea level, and which is believed to fill the crater of an old mud
volcano. The so-called pitch consists of a mixture of bitumen, water,
mineral and vegetable matter, the whole inflated with gas, which escapes
to some extent and keeps the mass in a state of constant ebullition. The
surface of the lake is hard, and yet the mass as a whole is plastic and
tends to refill the excavations. The lake is believed to be on the
outcrop of a petroleum-bearing stratum, and the pitch to represent the
unevaporated residue of millions of tons of petroleum which have exuded
from the oil-sands. The pitch is refined by melting,--the heat expelling
the water, the wood and other light impurities rising, and the heavy
mineral matter sinking to the bottom.
The asphalt of Venezuela is similar in nature, but the pitch "lake" is
here covered with vegetation and the soft pitch wells up at certain
points as if from subterranean springs.
FOOTNOTES:
[17] For more detailed treatment of international coal movements before
the war and of coal movements within the United States, see the U. S.
Geological Survey's _World Atlas of Commercial Geology_, Pt. 1, 1921,
pp. 11-16.
[18] Campbell, Marius R., The coal fields of the United States: _Prof.
Paper 100-A, U. S. Geol. Survey_, 1917, pp. 5, 6, 7.
[19] Compiled from tables quoted by White, David, The petroleum
resources of the world: _Annals Am. Acad. Social and Political Sci._,
vol. 89, 1920, pp. 123 and 126.
[20] White, David, _loc. cit._, p. 113.
[21] See Arnold, Ralph, Petroleum resources of the United States: _Econ.
Geol._, vol. 10, 1915, p. 707.
[22] White, David, Late theories regarding the origin of oil: _Bull.
Geol. Soc. Am._, vol. 28, 1917, p. 732.
[23] McCoy, A. W., Notes on principles of oil accumulation: _Jour.
Geol._, vol. 27, 1919, pp. 252-262.
[24] White, David, Genetic problems affecting search for new oil
regions: _Mining and Metallurgy_, _Am. Inst. of Min. Engrs._, No. 158,
Sec. 21, Feb., 1920.
[25] Mehl, M. G., Some factors in the geographic distribution of
petroleum: _Bull. Sci. Lab._, _Denison Univ._, vol. 19, 1919, pp. 55-63.
[26] Schuchert, Charles, Petroliferous provinces: _Bull. 155_, _Am.
Inst. Mining and Metallurgical Engrs._, 1919, pp. 3059-3060.
[27] Loc. cit., p. 20.
[28] Seepages or residual bituminous matter near the surface may be due
to upward escape of oil material through joints in the rocks capping a
reservoir, and productive pools may be found directly below such
showings. In other regions similar surface indications may mean that the
stratum in the outcrop of which they are found is oil-bearing; but
accumulations of oil, if present, may be several miles down the dip, at
places where the structural conditions have been favorable. In still
other cases the seepage may have been in existence for such a long time
as to exhaust the reservoir. It must also be remembered that gas seeps
are common in sloughs and marshes where vegetation is decaying, and may
be of no significance in the search for petroleum.
[29] Arnold, Ralph, Conservation of the oil and gas resources of the
Americas: _Econ. Geol._, vol. 11, 1916, pp. 321-322.
[30] Oil shales may also be made to yield large quantities of fuel and
illuminating gas, and of ammonia (see pp. 101-102).
CHAPTER IX
MINERALS USED IN THE PRODUCTION OF IRON AND STEEL (THE FERRO-ALLOY
GROUP)
GENERAL FEATURES
Iron and steel and their alloys are the most generally used of the
metals. The raw materials necessary for their manufacture include a wide
variety of minerals.
Iron is the principal element in this group; but in the manufacture of
iron and steel, manganese, chromium, nickel, tungsten, molybdenum,
vanadium, zirconium, titanium, aluminum, uranium, magnesium, fluorine,
silicon, and other substances play important parts, either as
accessories in the furnace reactions or as ingredients introduced to
give certain qualities to the products.
Nearly all parts of the world are plentifully supplied with iron ores
for an indefinite period in the future, but their abundant use has thus
far been confined mainly to the countries bordering the North
Atlantic,--the United States, Germany, and England,--which, possessing
ample coal supplies, have had the initiative to develop great iron and
steel industries. China has abundant coal, moderate quantities of iron
ore, and a large population, but a low per capita consumption of iron
and steel products. Development of its iron and steel industry is just
beginning. Japan has neither coal nor iron in sufficient quantities, and
hence the Japanese effort in recent years to control the mineral
resources of China and other countries. As a result of the war Germany
has been largely deprived of its iron ores, and France may assume
somewhat the rank in iron ore production once held by Germany. Sweden
and Spain have been considerable producers of iron ore, but both lack
coal, with the result that their ores have been largely exported to
England and Germany. With increase of per capita consumption in outlying
parts of the world, iron and steel industries are beginning to develop
locally on a small scale, as in India, South Africa, and Australia.
Russia has had sufficient supplies of coal and iron, but the stage of
industrial development in that country has not called for great
expansion of its iron and steel industry.
There has been a tendency for iron and steel manufacture to become
concentrated at a comparatively few places on the globe favored by the
proper combinations of coal, iron, transportation, proximity to
consuming populations, initiative and capacity to take advantage of a
situation, and other factors. Even though on paper conditions may seem
to be favorable in outlying territories for the development of
additional plants, this development is often held back by competition
from the established centers. On the west coast of the United States,
there are raw materials for an iron and steel industry and there has
been discussion for years as to the possibilities of starting a
successful large scale steel industry. The consuming power of the local
population for all kinds of iron and steel would seem to be great enough
to warrant such action. However, the demand is for an extremely varied
assortment of iron and steel products; and to start an industry, making
only a few of the cruder products such as pig iron and semi-finished
forms, would not meet this demand. All varieties of finishing plants and
associated factories would also need to be started in order to meet the
situation. This would require large capital. Furthermore the local
demand for some of the accessory finished products might not warrant the
establishment of the accessory plants.
Throughout the history of the iron and steel business there has been a
marked tendency for the iron ore to move to regions of coal production
rather than for the coal to move to the iron ore regions. The coal or
energy factor seems ultimately to control. This is due in considerable
part to the fact that coal furnishes the basis of a great variety of
industries for which iron ore is only one of the feeders, and which are
so interrelated that it is not always easy to move the iron and steel
industry to a spot near the sources of iron ore where iron and steel
alone could be produced.
In regard to iron ore supplies of proper grade and quantity, the United
States is more nearly self-sufficing than any of its competitors. It
imports minor amounts of ore from Cuba and Canada, and even from Chile
and Sweden, to border points, in the main merely because these imported
ores can compete on a price basis with the domestic ores. The entire
exclusion of these ores, however, would make comparatively little
difference in the total volume of our iron and steel industry; though it
would probably make some difference in distribution, to the disadvantage
of plants along the coast. There is only one kind of iron ore in which
the United States has anything approaching deficiency, and that is ore
extremely low in phosphorus, adapted to making the so-called
low-phosphorus pig which is needed for certain special steels. Ordnance
requirements during the war put a premium on these steels. While some of
these extremely low-phosphorus ores are mined in the United States,
additional quantities have been required from Spain and Canada and to a
lesser extent from North Africa and Sweden. Also the Spanish pyrite,
imported ordinarily for its sulphur content, on roasting leaves a
residue of iron oxide extremely low in phosphorus which is similarly
used. The elimination of pyrite imports from Spain during the war,
therefore, was a considerable contributing factor to the stringency in
low-phosphorus iron ores. War experience showed that the United States
was dependent on foreign sources for 40 per cent or upwards of its needs
in this regard. Certain developments in progress, notably the project
for concentration of siliceous eastern Mesabi Range ores, make it likely
that future domestic production will more nearly be able to meet the
requirements.
The equivalent of 15 per cent of the iron ore mined in the United States
is exported as ore to Canadian ports on the Great Lakes and in the form
of crude iron and steel products to many parts of the world. England and
Germany are almost the sole competitors in the export trade.
When we turn to the minerals used for making the alloys of iron and as
accessories in the manufacture of iron, it appears that no one of the
principal iron and steel producing countries of the world is
self-supporting, but that these "sweeteners" must be drawn in from the
far corners of the earth. The importance of these minor constituents is
altogether out of proportion to their volume. For instance, only
fourteen pounds of manganese are necessary in the making of a ton of
steel, yet a ton of steel cannot be made without manganese. The
increasing specialization in iron and steel products, and the rapidly
widening knowledge of the qualities of the different alloys, are
constantly shifting the demand from one to the other of the ferro-alloy
minerals. Each one of the ferro-alloy minerals may be regarded as being
in the nature of a key mineral for the iron and steel industry, and the
control of deposits of these minerals is a matter of international
concern. Control is not a difficult matter, in view of the fact that the
principal supplies of practically every one of the alloy minerals are
concentrated in comparatively few spots on the globe,--as indicated on
succeeding pages.
Nature has not endowed the United States, nor in fact the North American
continent, with adequate high-grade supplies of the principal
ferro-alloy minerals,--with the exception of molybdenum, and with the
exception of silica, magnesite, and fluorspar, which are used as
accessories in the process of steel making. With plenty of iron ore and
coal, and with an iron and steel capacity amounting to over 50 per cent
of the world's total, the United States is very largely dependent on
other countries for its supplies of the ferro-alloy minerals. The war
brought this fact home. With the closing of foreign sources of supplies,
it looked at one time as if our steel industry was to be very greatly
hampered; and extraordinary efforts were made to keep channels of
importation open until something could be done in the way of
development, even at excessive cost, of domestic supplies. The result of
war efforts was a very large development of domestic supplies of
practically all the ferro-alloy minerals; but in no case, with the
exceptions noted above, did these prove sufficient to meet the total
requirements. This development was at great cost and at some sacrifice
to metallurgical efficiency, due to the low and variable grades of the
raw materials. With the post-war reopening of importation much of the
domestic production has necessarily ceased, and large amounts of money
patriotically spent in the effort to meet the domestic requirements have
been lost. These circumstances have resulted in the demand in Congress
from producers for direct financial relief and in demand for protective
tariffs, in order to enable the new struggling industries to exist, and
to permit of development of adequate home supplies. Such tariffs might
be beneficial to these particular domestic industries if wisely planned;
but also, in view of the limited amounts of these particular ores in
this country, their general low grade, and the high cost of mining,
tariffs might very probably hasten exhaustion of our limited supplies
and might handicap our metallurgical industries both in efficiency and
cost (see pp. 365-366, 393-394).
IRON ORES
ECONOMIC FEATURES
=Technical and commercial factors determining use of iron ore minerals.=
Popularly, an iron ore is an iron ore, and there is little realization
of its really great complexity of composition and the difficulty of
determining what is or is not a commercial ore. Percentage of iron is of
course an important factor; but an ore in which the iron is in the
mineral hematite is more valuable than one with an equivalent percentage
of iron which is in the form of magnetite. Substances present in the ore
in minor quantities, such as phosphorus, sulphur, and titanium, have a
tendency to make the iron product brittle, either when it is cold or
when it is being made, so that excessive amounts of these substances may
disqualify an ore. Excessive quantities of silica, lime, or magnesia may
make the ore undesirable. Where an acid substance, like silica, is
balanced by basic constituents like lime and magnesia, considerable
amounts of both may be used. Excessive moisture content may spoil an ore
because of the amount of heat necessary to eliminate it in smelting.
The metallurgical processes of the iron and steel industry are
essentially adapted to the principal grades of ore available. The
cheapest of the steel-making processes, called the acid Bessemer
process, requires a very low-phosphorus ore (usually below .050 per cent
in the United States and below .030 per cent in England.) The basic
open-hearth processes, making two-thirds of the steel in the United
States, allow higher percentages of phosphorus, but not unlimited
amounts. The basic Bessemer (Thomas) process, used for the "minette"
ores of western Europe and the Swedish magnetites, may use an ore with
any amount of phosphorus over 1.5 per cent. The phosphatic slag from
this process is used as fertilizer. The supply of low-phosphorus
Bessemer ore in the United States is at present limited as compared with
that of the non-Bessemer ores, with the result that steel-plant
construction for many years past has been largely open-hearth. The
open-hearth process is favored also because it allows closer control of
phosphorus content in the steel.
Small but increasing amounts of steel are also made in the electric
furnace; for the most part, however, this process is more expensive than
the others, and it is used principally for special alloy steels.
Iron ores are seldom so uniform in quality that they can be shipped
without careful attention to sampling and grade. In the Lake Superior
region the ores are sampled daily as mined, and the utmost care is taken
to mix and load the ore in such a way that the desired grades can be
obtained. Ordinarily a single deposit produces several grades of ore.
When ores are put into the furnace for smelting the mixtures are
selected with great care for the particular purpose for which the
product is to be used. The mixture is compounded as carefully as a
druggist's prescription. An ore salesman, after ascertaining the nature
of the iron and steel products of a plant, has to use great skill in
offering particular ores for sale which not only will meet the desired
grade in regard to all elements, but also will meet competition in
price. In some respects, the marketing of different grades of iron ore
is as complex as the marketing of a miscellaneous stock of merchandise.
With ores, as with merchandise, custom and sentiment play their
part,--with the result that two ores of identical grade mineralogically
and chemically may have quite a different vogue and price, simply
because of the fact that furnace men are used to one and not to the
other and are not willing to experiment.
The geologist is ordinarily concerned merely with finding an ore of as
good a general grade as possible; but he often finds to his surprise
that his efforts have been directed toward the discovery of something
which, due to some minor defect in texture, in mineralogical
composition, or in chemical composition, is difficult to introduce on
the market. There is here a promising field, intermediate between
geology (or mineralogy) and metallurgy, for the application of
principles of chemistry, metallurgy, and mineralogy, which is occupied
at the present time mainly by the ore salesman. Both the mineralogist
and metallurgist touch the problem but they do not cover it. With
increasingly precise and rapidly changing metallurgical requirements,
this field calls for scientific development.
=Geographic distribution of iron ore production.= Iron ores are widely
distributed over the world, but are produced and smelted on a large
scale only in a few places where there is a fortunate conjunction of
high grades, large quantity, proximity of coal, cheap transportation to
markets, and manufacturing enterprise. Over 90 per cent of the iron ore
production of the world is in countries bordering the North Atlantic
basin. The United States produces about 40 per cent, France about 12 per
cent, England about 10 per cent, Germany before the war 15 to 20 per
cent, and Spain, Russia, and Sweden each about 5 per cent. Lesser
producing countries are Luxemburg, Austria-Hungary, Cuba, Newfoundland,
and Algeria; and insignificant amounts are produced in many other parts
of the world. Of the world's iron and steel manufacturing capacity, the
United States has about 53 per cent, Germany 16 per cent, England 14 per
cent, France 10 per cent, the remainder of Europe (chiefly Russia,
Austria-Hungary, and Belgium) 7 per cent. The absence of important iron
ore production and of iron and steel manufacture either in the southern
hemisphere or in any of the countries bordering the Pacific is a
significant feature, when we remember what part iron plays in modern
civilization. Japan, however, is beginning to develop a considerable
iron and steel industry, which promises to use a large amount of ore
from China, Manchuria, and Korea, and possibly to compete in American
Pacific Coast markets.
In the United States about 85 per cent of the production, or one-third
of the world's production, comes from the Lake Superior region, a large
part of the remainder from the Birmingham district, Alabama, and smaller
quantities from the Adirondacks. For the rest of the North American
continent, the only largely producing deposit is that at Belle Isle,
Newfoundland, which is the basis of the iron industry of eastern Canada.
Cuba supplies some ore to the east coast of the United States.
In Europe there are only three large sources of high-grade iron ore
which have heretofore been drawn on largely,--the magnetite deposits of
northern Sweden, the hematites and siderites of the Bilbao and adjacent
districts of northern Spain, and the magnetite-hematite deposits of
southern Russia. The first two of these ores have been used to raise the
percentage of iron in the low-grade ores which are the principal
reliance of western Europe. The Swedish ores have also been necessary
in order to raise the percentage of phosphorus and thus make the ores
suitable for the Thomas process; on the other hand the Spanish ores and
a small part of the Swedish material have been desired because of their
low phosphorus content, adapted to the acid Bessemer process and to the
manufacture of low-phosphorus pig. The Russian ores have largely been
smelted in that country.
The largest of the western European low-grade deposits is a geographic
and geologic unit spreading over parts of Lorraine, Luxemburg, and the
immediately adjacent Briey, Longwy, and Nancy districts of France. The
ores of this region are called "minette" ores. This unit produces about
a fourth of the world's iron ore. Low-grade deposits of a somewhat
similar nature in the Cleveland, Lincolnshire, and adjacent districts of
England form the main basis for the British industry. There is minor
production of iron ores in other parts of France and Germany, in
Austria-Hungary, and in North Africa (these last being important because
of their low phosphorus content).
Comparison of figures of consumption and production of iron ores
indicates that the United States, France, Russia, and Austria-Hungary
are self-supporting so far as quantity of materials is concerned.
Certain ores of special grades, and ores of other minerals of the
ferro-alloy group required in steel making, however, must be imported
from foreign sources; this matter has been discussed above. Great
Britain and Germany appear to be dependent on foreign sources, even
under pre-war conditions, for part of the material for their furnaces.
During the war there was considerable development of the low-grade
English ores, but this does not eliminate the necessity for importing
high-grade ores for mixture. Belgium produces a very small percentage of
her ore requirements and is practically dependent on the
Lorraine-Luxemburg field.
The principal effect of the war on iron ore production was the
occupation of the great French mining and smelting field by the Germans,
thereby depriving the French of their largest source of iron ore. Since
the war the situation has been reversed, France now possessing the
Lorraine field, which formerly supplied Germany with 70 per cent of its
iron ore. As the German industrial life is largely based on iron and
steel manufacture, the problem of ore supplies for Germany is now a
critical one. It has led to German activity in Chile and may lead to
German developments in eastern Europe and western Asia, particularly in
the large and favorably located reserves of southern Russia. It seems
likely, however, that arrangements will also be made to continue the
export of ore from the Lorraine field down the Rhine to the principal
German smelting centers. France needs the German coal for coking as
badly as Germany needs the French iron ore. The Rhine valley is the
connecting channel for a balanced movement of commodities determined by
the natural conditions. These basic conditions are likely in the long
run to override political considerations.
The Lake Superior deposits, the Swedish magnetites, the Spanish
hematites, and the Russian ores carry 50 to 65 per cent of metallic
iron. The Birmingham deposits of southeastern United States, the main
British supplies, and the main French and German supplies contain about
35 per cent or less. It is only where ores are fortunately located with
reference to consuming centers that the low-grade deposits can be used.
For outlying territories only the higher-grade deposits are likely to be
developed, and even there many high-grade deposits are known which are
not mined. The largest single group not yet drawn on is in Brazil.
Others in a very early stage of development are in North Africa and
Chile.
=World reserves and future production of iron ore.= The average rate of
consumption of iron ore for the world in recent years has been about 170
million tons per year. At this rate the proved ore reserves would last
about 180 years. If it be assumed that consumption in the future will
increase at about the same rate as it has in the past, the total
measured reserve would still last about a century. These calculations of
life, however, are based only on the known reserves; and when potential
reserves are included the life is greatly increased. And this is not
all; for beyond the total reported reserves (both actual and potential),
there are known additional large quantities of lower-grade ores, at
present not commercially available, but which will be available in the
future,--to say nothing of expected future discoveries of ores of all
grades in unexplored territories. Both geological inference and the
history of iron ore exploration seem to make such future discoveries
practically certain. Iron ore constitutes about 4 per cent of the
earth's shell and it shows all stages of concentration up to 70 per
cent. Only those rocks are called "iron ores" which have a sufficiently
high percentage of iron to be adapted to present processes for the
extraction of iron. When economic conditions demand it, it may be
assumed that iron-bearing rocks not now ordinarily regarded as ores may
be used to commercial advantage, and therefore will become ores.
Not only is an indefinitely long life assured for iron ore reserves as a
whole, but the same is true of many of the principal groups of deposits.
The question of practical concern to us, therefore, is not one of total
iron ore reserves, but one of degrees of _availability_ of different
ores to the markets which focus our requirements for iron.
The annual production of ore from a given district is roughly a measure
of that ore's ability to meet the competitive market, and therefore, of
its actual immediate or past availability. Annual production is the net
result of the interaction of all of the factors bearing on availability.
It may be argued that there are ores known and not yet mined which are
also immediately available. On the whole, they seem to be less available
than ores actually being produced; otherwise general economic pressure
would require their use and actual production.
In considering the future availability of iron ores, it is obvious that
tables of past production afford only a partial basis for prediction.
Presumably districts which have produced largely in the past may be
expected to continue as important factors. In these cases production has
demonstrated availability. Continued heavy production may thus be
expected from the ores of the Lake Superior region, from the Clinton
hematites of Alabama, from the ores of the Lorraine-Luxemburg-Briey
district, from the Cleveland ores of England, from the Bilbao ores of
Spain, from the high-grade magnetites of northern Sweden, and (assuming
political stability) from the ores of southern Russia.
Similarly, also, recent increases in production from certain districts
are probably significant of increased use of such ores in the future.
Among these developments are the increasing production of Swedish ores
and their importation into England and Germany, and the increasing use
of Clinton hematites and Adirondack magnetites in the United States.
Low-grade ores from the great reserves of Cuba are being mined and
brought to the east coast of the United States in increasing amounts,
and it is highly probable that they will take a larger share of the
market. A similar project in Chile, which lay dormant during the war
because of restricted shipping facilities, is expected in the near
future to yield important shipments to the United States. In none of
these cases will production be limited in the near future by ore
reserves. Increased production and use of iron ores are also to be
looked for in Newfoundland, North Africa, China, India, Australia, and
South Africa.
On the commercial horizon are ores of still newer districts, the
availability of which may not be read from tables of production. Their
availability must be determined by analysis and measurement of the
factors entering into availability. Availability of iron ore is
determined by percentage of iron, percentages of impurities, percentages
of advantageous or deleterious minor constituents, physical texture,
conditions for profitable mining, adaptability to present furnace
practice, distance from consuming centers, conditions and costs of
transportation, geographical and transportational relation to the coal
and fluxes necessary for smelting, trade relations, tariffs and taxes,
inertia of invested capital, and other considerations. All of these
factors are variable. A comparison of ores on the basis of any one of
these factors or of any two or three of them is likely to be misleading.
A comparison based on the quantitative consideration of all of the
several factors seems to be made practically impossible by the
difficulty of ascertaining accurately the quantitative range and
importance of each factor, and by the difficulty of integrating all of
the factors even if they should be determined. However, their combined
effect is expressed in the cost of bringing the product to market; and
comparison of costs furnishes a means of comparing availability of ores.
A high-grade ore, cheaply mined and favorably located with reference to
the points of demand, will command a relatively high price at the point
of production. The same ore so located that its transportation costs are
higher will command a lower price; or it may be so located that the
costs of mining and bringing it to places where it can be used are so
high that there is no profit in the operation. There are known
high-grade iron ores which, because of cost, are not available under
present conditions.
The availability of an ore, then, depends on its relation to a
market,--whether, after meeting the cost of transportation, it can be
sold at prevailing market prices at the consuming centers, and can still
leave a fair margin of profit for the mining operation. The price
equilibrium between consuming centers affords a reasonably uniform basis
against which to measure availability of ores.
Figures of cost are obtainable as a basis for comparison of availability
of iron ores of certain of the districts, but not enough are at hand for
comparison of the ores of all districts. Careful study of costs has
demonstrated the availability in the near future of the Brazilian
high-grade Bessemer hematites; and projects which are now under way for
exportation to England and the United States will doubtless make this
enormous reserve play an important part in the iron industry. Iron ore
is known but not yet mined in many parts of the western United States
and western Canada. With the increasing population along the west coast
of North America, projects for smelting the ore there are becoming more
definite. Establishment of smelters on the west coast would make
available a large reserve of ore (see also, however, p. 155).
The list of changes now under way or highly probable for the future
might be largely extended. The use of iron and steel is rapidly
spreading through populous parts of the world which have heretofore
demanded little of these products. This increased use is favoring the
development of local centers of smelting, which will make available
other large reserves of iron ore. The growth of smelting in India, China
and Australia illustrates this tendency.