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This work has been prepared in an attempt to satisfy the demand 
for a handy volume on coal. There already exists a very valuable 
literature on this important subject, but it is so voluminous and 
scattered that much of it is not accessible to the average reader. Many 
of our older works need revision because of new discoveries in the 
study of coal, such, for example, as the practical application of the 
microscope in the determination of its physical character and the 
discovery of more refined chemical processes for determining its 
chemical properties. The great advances in extracting coal from the 
earth by mechanical means and in the cleaning and coking of the 
products of the mine also make it necessary to bring new processes 
to the attention of the public. 

There are so many different phases in the discussion of a subject 
so broad as this that details regarding many matters must be omit- 
ted in a one-volume work, and readers desiring detailed descriptions 
of machines or complicated processes must consult works dealing 
with those matters alone. While many topics are fully dealt with 
in this text, such as the properties, the origin, the uses and the gen- 
eral distribution of coal, some others as mining machinery, and de- 
tails of distribution and character of local coal deposits can be treated 
only in works of several volumes. It is hoped, however, that the 
data presented will serve, for ready reference, those who make fre- 
quent use of a work of this type. 

I wish to take this opportunity of expressing my appreciation to 
those who have so generously contributed to this work. My thanks 
are specially due to Dr. H. Ries of Cornell University, at whose sug- 
gestion the preparation of this text was undertaken, for suggestions 
and the use of photographs and cuts. I am also particularly obli- 
gated to my friend, Professor A. Lacroix, Secretaire perpetuel de 
1' Academic des Sciences, Paris, for many favors, such as access to the 
library of the Academy and to valuable collections, including Ren- 




ault's slides on which he made his original study of bacteria in coal. 
The late Dr. Charles R. Zeiller kindly placed at my disposal his works 
on plant fossils and the coal basins of France, and Monsieur Peyerim- 
hoff de Fontenelle, President, le Comite Central des Houilleres de 
France generously presented me with a copy of the splendid work, 
Atlas General des Houilleres, by E. Gruner and G. Bousquet. Dr. 
Aubrey Strahan, Director of the Geological Survey of England and 
Wales kindly supplied an advance copy of one of his works in addition 
to other original data. My thanks are due also to Dr. D. F. Mc- 
Farland, and to Dr. J. B. Hill of the Pennsylvania State College, 
for criticism of the chapters dealing with the chemistry of coal and 
with paleobotany; to Professor A. L. Kocher for retouching photo- 
graphs, and to several of my students who aided greatly in copying 
diagrams, sections and other material. 

Although acknowledgment has been made in the text to those 
from whom photographs and plans have been received, I wish to 
mention particularly the officials of the Twelfth International Geol- 
ogical Congress, Dr. F. D. Adams, President, who kindly granted 
me permission to republish the various maps in the report on the 
Coal Resources of the World. I am also indebted to Coal Age, the 
Barrett Company, the Delaware and Hudson Company, the Koppers 
Company and the Semet-Solvay Company for the privilege of re- 
producing illustrations. Photographs or drawings were generously 
contributed by Dr. R. Thiessen of the United States Bureau of Mines, 
the Director of the United States Geological Survey, Dr. E. C. Jeffrey 
of Harvard University, Dr W. R. Crane, Mr. Francis Harper, the 
Hillman Coal Company, the Sullivan Machinery Company, the 
Bethlehem Fabricators, the Ebensburg Coal Company and Mr. John 
Bevan of Pottsville, Pa. In addition to those persons and organiza- 
tions specifically mentioned, there are many of my friends and col- 
leagues who have furnished information which has been very helpful, 
and their interest and aid have been much appreciated. 


October 27, 1921. 





















History. The first mention of coal in literature dates from the 
fourth century, B. C., but so rapidly has its use developed that it 
has become one of the most important among all commercial factors. 
The enormous production of approximately 1,478,000,000 short tons 1 
for the year 1913, the last year of normal production before the great 
war, indicates how useful a commodity it is to the world. This 
output reckoned at the average price of the coal, as sold at the mine 
throughout the United States for the same year, would reach the sum 
of $1,965,740,000, while if it were computed at the price prevailing 
in England or France it would be from nearly two to two and one- 
half times this amount. Scarcely any home or industrial concern 
among white races can exist without its use, directly or indirectly, 
although as recently as the reign of Henry II of France it was con- 
sidered so objectionable a fuel that the smiths in Paris obtained a 
special license or paid a fine for using it. There were regulations 
against its use in many of the cities of Europe during the seventeenth 
century although it began to enter actively into trade in England 
about the thirteenth century. Mining did not, however, become very 
extensive until after the invention of the steam engine. In America 
the first bituminous coal mining began in Virginia in 1787 and the 
first recorded shipments of anthracite were made about 1805, although 
anthracite was discovered about the year 1762, and bituminous coal 
in 1679. The earliest records of production of bituminous coal in 
this country date from 1820, when 3000 tons were produced. In 
1814 there were 22 tons of anthracite recorded. The million- ton 

1 Mineral Resources, U. S. Geol. Survey, 1914, Pt. 2, p. 639. 



mark was first passed for anthracite in 1837 and for bituminous coal 
in 1850. 

History shows that no country has reached an eminent industrial 
position which has not had large supplies of coal within its borders 
or had ready access to them. Reference to the prominent nations of 
the present day proves that coal and iron have been two essential 
factors in their development. 

It has been said that the Chinese knew the use of coal to a slight 
extent before the Greeks did, but the first definite record of its utiliza- 
tion is found in Aristotle's Meteorology. 1 Speaking of the combustible 
bodies he says, "Those bodies which have more of earth than of smoke 
are called coal-like substances." Theophrastus, a pupil of Aristotle, 
and Pliny both mention this substance and its use by the smiths. 
The coal mentioned in these writings was evidently all of the brown- 
coal variety, and it came from Thrace in northern Greece and from 
Liguria in northwestern Italy. It thus became known to the ancients 
as Thracius lapis and gemma Samothracia, while jet which came from 
Lycia in Asia Minor, was called Gagates after a river in that region. 

The word coal, as now used, is derived from the Saxon col. It 
was always cole in English until sometime in the seventeenth century, 
and coal then referred to charcoal as that term is now employed. At 
the present time the term coals is employed in two senses, one meaning 
glowing fragments of some combustible substance and the other the 
different varieties of the material known in a general way as coal. 
The Germans use for coal the term Steinkohle and the French speak of 
it as charbon or charbon de terre. 

Coal a rock, not a mineral. Coal is the term applied to vegetal 
matter with varying amounts of mineral matter and with or without 
small proportions of animal matter, which through geological processes 
has become so changed by loss of volatile constituents that it is more 
or less compact and dark in color. It burns with comparative slow- 
ness and decomposes slowly in the atmosphere. It has a variable 
chemical composition and it is not homogeneous. It grades into peat, 
and differs from that substance in composition chiefly in the smaller 
percentages of water, oxygen and volatile hydrocarbons which it 
contains. It is frequently spoken of as mineral coal 2 and in the 

1 Book IV, Chap. 9, Sections 36-37. (French translation by B. S. Hilaire.) 

2 Dana, E. S., System of mineralogy, 6th ed., 1892, p. 1021. 


United States coal lands are classed under the division of Mineral 
Lands. It is not, however, a mineral in the strict sense of the term 
because a mineral, as denned by Dana, 1 must be inorganic, homoge- 
neous, and have a definite chemical composition, all three of which 
requirements coal lacks. Yet it might be questioned whether the 
varying amount of impurity in the form of ash in the coal is not 
somewhat analogous to the impurities which are present in some 
minerals producing coloring effects and variation in other physical 
properties, and also whether the chemical formulae for some of the 
complex silicates, such as members of the amphibole group, do not 
vary almost as much as those for some varieties of coal when ash and 
moisture are eliminated. 

Although not a mineral, coal is a rock, since the geologist regards as 
rocks all natural, solid substances, organic or inorganic, which com- 
pose the earth's crust. It is as much a rock as are sandstone and 
limestone, and when one attempts to classify the different varieties 
of coal he meets with the same difficulties experienced in classifying 
other rocks, for the reason that Nature does not draw sharp lines 
between varieties. It is just as difficult to decide in some cases 
whether a certain coal is bituminous coal or anthracite as it is to 
determine when a shale, high in lime, passes into a limestone, or when 
an igneous rock by variation ceases to be a syenite and becomes a 
diorite. As a result of this lack of definiteness in the delineation of 
our varieties of coal, many attempts have been made in recent years 
to devise some concise method of classifying coals so that all the 
terms employed will have some definite meaning. These attempts 
have met with some of the same difficulties encountered by the petro- 
graphers who have attempted the quantitative classification of ig- 
neous rocks. Some of the objections are that in many cases elaborate 
chemical analyses are required, and in most cases the chemical and 
physical properties and the field characteristics are not closely enough 
related to make the classification readily applicable to all varieties 
under all conditions. 

1 A textbook of mineralogy, p. i. 


Physical Properties 

In the description of the varieties of coal certain common physical 
and chemical terms much used in mineralogy are employed. The 
physical properties include specific gravity, hardness, fracture, color, 
streak, luster, and physical constitution or texture. These are the 
properties by which the public recognizes the different varieties of 
coal in the trade, but the chemical composition is the determining 
factor in the value of coal. 

Specific gravity. The specific gravity of a body is the ratio of its 
weight to the weight of an equal volume of water at 4 C. When the 
average specific gravity of a quantity of coal is known the space which 
a ton will occupy can be roughly determined, it being always remem- 
bered that the volume of a ton will vary with the size to which the 
coal is broken. The gravity of the common varieties of coal varies 
as follows: Lignite 0.5-1.30; Bituminous coal 1.15-1.5; Cannel 
1.2-1.3; Anthracite 1.29-1.65. 

There are various methods for determining the specific gravity of 
coal. It may be determined approximately for compact fragments 
by drying the specimen carefully, weighing it in air (weight = W), 
and then in water (weight = Wi). Since the specimen loses in 
weight an amount equal to the weight of the water displaced, i.e., 
the weight of its own volume of water, the specific gravity is found 


from the following formula: G = . Fora more accurate 

W Wi 

determination of the solid substance with the pores omitted the 
specimen should be boiled in water in order that the air may be ex- 
pelled from the pores. On the other hand, if the specific gravity of 
a given mass of coal with all pores included is desired the body should 
be coated with a thin veneer of paraffin or varnish to exclude all 
water from the pores. 

Determination by use of pycnometer: Accurate laboratory deter- 
minations may be made on powdered coal by using the pycnometer. 
This is a glass vessel which when filled to a specified mark contains 
a given weight of water at a certain temperature. The dry powder 
is weighed in air (weight = W). The pycnometer is weighed full 
of water (weight = Wi), and then emptied. The powder is then 
placed in the vessel, all air is excluded, the water is brought to the 


same level as before the coal was added and the vessel is weighed 
(weight = W 2 ). The specific gravity is then obtained from the fol- 


lowing formula G = w + Wi _ w; 

The following methods for determining the specific gravity of coal 
and coke are used in the fuel-testing laboratories of the United States 
Bureau of Mines. 1 To determine the true specific gravity the pyc- 
nometer is ordinarily employed and about 3.5 grams of the 6o-mesh 
coal or coke is used as a sample. About 30 c.c. of distilled water is 
employed in a 5o-c.c. pycnometer, and the water is thoroughly boiled 
after the sample is placed in the bottle, for the purpose of excluding 
all air. The boiling is done on a water-bath and to avoid loss of par- 
ticles of the coal or coke a one-bulb, 6-inch drying tube is connected 
with the pycnometer by means of a small piece of pure gum tubing. 
This drying tube is then attached to an aspirator and suction is 
applied while the water in the flask is gently boiled for three hours. 
The tube is then detached, the flask removed from the bath, and 
almost filled with water previously boiled and cooled. When cooled 
to the temperature of the room at which original weighing was made, 
the pycnometer is stoppered and weighed. The formula employed 


is the same as that given above, G = _ . 

Determination by Hogarth-flask: A special method is recommended 
as being more convenient and accurate for routine determinations 
than the pycnometer method. This consists in the 
use of a Hogarth flask such as that used in deter- 
mining the specific gravity of iron ores. (Fig. i.) 
This flask has a capacity of 100 to 125 c.c. To 
make the test a lo-gram sample of 6o-mesh coal 
or coke is weighed and introduced into the weighed 
flask together with sufficient distilled water to fill it 
half full. The flask is placed on a small electric 
hot plate inside a lo-inch vacuum desiccator and 
the latter is evacuated by an aspirator or air pump. IG * It ? gar * f 

r specific gravity flask. 

The water in the flask is kept boiling and the air 

is expelled in thirty minutes with a good air pump. The flask is 

then removed from the desiccator and filled to the tubulure with 

1 Stanton, F. M., and Fieldner, A. C., Tech. Paper 8, 1913. 


distilled water which has recently been boiled and cooled. The 
stopper is inserted after having been coated with a thin film of vaseline 
to prevent leakage. 

After the flask has cooled to about 25 C. in a water thermostat, 
distilled water that has been cooled in the same thermostat is drawn 
through the tubulure until the water level is slightly above the mark 
on the capillary of the stopper. If the end of the tubulure be inserted 
in a small beaker of water and a slight suction applied to the stopper 
this operation may be performed without removing the flask from the 
thermostat. The flask should be left in the thermostat until the 
temperature is 25 C. The water level may be adjusted to the mark 
in the capillary by drawing in a little water. When this is done the 
flask is removed, wiped dry, and weighed. The true specific grav- 
ity is then- found by the formula used in the previously described 

Hydrometer method: To determine the apparent specific gravity 
an apparatus is used which consists of a brass hydrometer immersed 
in a galvanized-iron cylinder filled with water to a water-line. There 
are two pans on the top of the hydrometer, the upper one being used 
for weights and the lower for the sample of coal or coke. Below the 
copper air buoy there is a brass cage highly perforated so as to allow 
the air to escape during immersion. This cage carries the sample 
when it is weighed under water. 

To determine the specific gravity with this apparatus, brass weights 
are placed on the upper pan causing the hydrometer to sink to a mark 
on the stem between the pan and the buoy. This weight is desig- 
nated by (W). The weights are removed and about 500 grams of 
the sample in ij to 2 inch cubical lumps is placed in the copper dish. 
Weights are again added until the instrument sinks to the same 
mark on the stem as it did previously, (weight = Wi). The sample 
is then transferred to the perforated cage and weights are added until 
the same mark on the stem again touches the surface of the water; 
(weight = W 2 ). We now have the following, (W Wi) = weight 
of sample in air, and (W W 2 ) = weight of sample in water. Since 
the body loses in weight when weighed in water an amount equal to 
the weight of the water displaced the apparent specific gravity = 
W - Wt 

(w - wo - (w - w 2 y 


Further, in determining the specific gravity of coke 100 X 
apparent specific gravity = ntage by volume of coke subs tance, 

true specific gravity 

and 100 percentage by volume of coke substance = percentage 
by volume of cell space. 

Certain precautions are observed in making apparent specific 
gravity tests on coke. It should preferably be in lumps of nearly 
the same size and shape, and when the sample is immersed the hy- 
drometer should be moved rapidly up and down a few times to remove 
air bubbles. Coke samples, because of their marked porosity, should 
not remain in the water more than five minutes and all specimens of 
coal or coke should be thoroughly dried before tests are made. 

Use of heavy solutions in determination of specific gravity: In an 
investigation of the Canadian coals Porter and Durley 1 used a heavy 
solution consisting of calcium chloride and calcium nitrate mixed so 
as to obtain required densities. The crushed coal was placed in this 
solution and separated, the heavier sinking, the lighter rising to the 
top, and that of the same gravity as the solution floating suspended 
in the liquid. 

Gravity of "ash-free" and "moisture-free" specimens: In case it 
is desired to obtain the specific gravity of the pure fuel with moisture 
and ash excluded a correction must be made for these. The actual 
specific gravity of the ash may be obtained, or, as Pollard 2 suggests, 
the correction for ash may be made with a sufficient degree of accuracy 
for all practical purposes by deducting o.oi from the specific gravity 
of the coal for each per cent ash. 

As a rule, high-carbon coals have higher specific gravities than 
those low in carbon because of their more compact character. It 
might be expected that the percentage of ash would be the factor 
controlling the specific gravity of the coal in all cases since the mineral 
matter entering the ash has, as a rule, a higher specific gravity than 
the materials forming the combustible portion of the fuel, and this is 
generally true if the proportions of the other constituents remain 

1 Porter, J. B., and Durley, R. J., An investigation of the coals of Canada. Canada 
Dept. of Mines, Vol. i, pp. 194 and 199, 1912. 

2 Strahan, A., and Pollard, W., The Coals of South Wales with special reference to the 
origin and distribution of anthracite. Memoirs of the Geol. Survey of England and 
Wales, 2d ed., p. 12, 1915. 


constant. It is found, however, from a study of a large number of 
analyses that there is no regular ratio between the percentage of ash 
and the specific gravity, and this seems to be due to a variation in 
the volatile constituents, and the compactness of the fuel. It de- 
pends also upon the nature of the ash since the presence of iron com- 
pounds tends to raise the specific gravity above that for silica, alumina 
and many other constituents. 

That the specific gravity has a direct bearing on the burning qual- 
ities of the coal is seen in the statement of Porter and Durley, 1 who 
conclude as a result of their investigation of Canadian coals that few, 
if any, coals which have a specific gravity over 1.6 are worth burn- 
ing and that, excepting the anthracites and perhaps one or two special 
types of coals, the approximate limit for commercially profitable 
coals is 1.55. They add further that the pure bituminous coals of 
Canada have a specific gravity between 1.265 an d I -3 2 5- 

Hardness. The hardness of coal varies from that of the soft 
lignites to that of the hard anthracites. It is difficult to state any 
definite hardness for the coals other than anthracite because they 
vary so much in different portions of the same fragment. Anthracite 
varies from 2 to 2.5 in Moh's scale of hardness, which means that it 
can be scratched with difficulty by the finger nail. 

Fracture. The fracture in coal is a very important determining 
factor in recognizing the ordinary types in hand specimens. The 
anthracites break with a conchoidal fracture, i.e. the fracture leaves 
a concave surface like that of a shell. This is characteristic also of 
cannel coal, but the other varieties of bituminous coal generally break 
with a rectangular or cubical fracture. The lignites fracture so that, 
as a rule, they break into roughly tabular or flat, elongated fragments. 
(Plates III and IV.) 

In coal beds there are usually two sets of joints resulting from the 
drying out of the rocks and the movement of the strata and these 
run approximately normal to each other. Those which lie normal to 
the strike and cut across the bedding of the coal are frequently known 
as cleats. They are, as a rule, more clearly marked than the joints 
running in the other direction. 

Color and streak. The color of coal varies from light to dark 
brown in the lignites to grayish black and jet black in the higher 

1 Op. cit., p. 194. 


grades. The streak is the color of the powder and it is determined 
by making a mark on a piece of unglazed porcelain. For the coals 
below bituminous it is brown to yellow. In bituminous coal it is 
brownish to black and in cannel it is brown to black. The streak of 
the higher-rank coals is black. 

Luster. The luster, or the manner in which the coal reflects 
light from its surface, is, like the fracture, often an important diag- 
nostic property in a hand specimen. The anthracites have usually 
a bright to almost submetallic luster and the luster of natural coke is 
bright to submetallic, while that of cannel coal is usually, and that of 
mineral charcoal, always, dull to earthy. Slaty coal is dull. In bi- 
tuminous coal there are interlayered bright and dull bands, the former 
representing portions of the coal formed from trunks or branches of 
trees, and the latter portions being made up of mineral charcoal 
and the smaller particles of vegetal matter or sometimes of impure 
earthy layers. 

Physical constitution. That coal has been derived almost en- 
tirely from vegetal matter is proven by the presence in lignite of 
abundant remains of plants and by the presence in decreasing amounts 
of distinctly recognizable plant remains in all the varieties of coal 
from lignite to anthracite. While some anthracite may not show a 
trace of woody tissue to the naked eye, or even under the microscope, 
some other portions of this coal from the same seam may show dis- 
tinct evidence of the presence of vegetal constituents now altered to 
coal. The microscope has been of great service in recent years in 
aiding us in detecting the presence of altered vegetal remains in coals 
where they were not formerly recognized by the naked eye. The 
effects of the different kinds of vegetation or the different portions of 
the same types of vegetation which enter into the coal may now be 
recognized through the varying appearances of the coal produced 
from these different materials. It is found that the spores from the 
Cryptogamic plants which can be recognized under the microscope, 
if comparatively free from other materials will produce the dull- 
lustered cannel bands, the stems of trees usually produce bright 
bands in the coal, while resins generally produce light-colored spots 
or streaks. It has been found, therefore, that coal is usually made 
up of the following constituents: (a) distinctly woody or xyloid 
material, so abundant in lignite and to which Thiessen has given 


FIG. i. Photomicrograph of coal from No. 6 seam, Royalton, 111. (x 160). 
Distinct woody tissue and a few flattened spores are visible. (After R. 

FIG. 2. Same as Fig. i. Shows little xyloid tissue but many flattened 
spores as white lines. / Io ) 


the name anthraxylon, from the Greek anthrax, coal and xylon, wood. 
(b) canneloid, consisting chiefly of spores and forming the bulk of 
cannel coal; (c) resins found in all coals but especially evident in 
lignite and scarce in cannel; (d) de"bris, or the macerated material 
mixed with the woody matter and derived from a great variety of 
substances by the breaking up of stems, cells, cuticles, spores, and 
particles of resin; (e) the " fundamental matter," 1 or the colloidal 
groundmass in which the other constituents of the coal are embedded 
and which is made up chiefly of the remains of the more readily de- 
composable parts of the vegetal matter. It seems to consist chiefly 
of fragments of cellulosic material, cuticles, cutinized cell walls, spore- 
exines, pollen-exines, fragments of wood fiber, bits of resin, and all 
the other finer particles of the material entering into the composition 
of the coal. Some authors consider that large quantities of algal 
remains are included in this substance and this subject will be dis- 
cussed more fully in the chapter on the origin of coal 

The Microscopic Study of Coal 

Development of the microscopic study. The subject of the 
physical constitution of coal has received a great deal of attention 
during the last century and a half, and the historic development of 
this study is well treated in the work by White and Thiessen. As 
early as 1778 Franz von Beroldingen 2 outlined a logical theory for 
the development of the coal swamps and for the origin of petroleum. 
In 1833 H. Witham 3 made what was probably the first microscopic 
examination of coal and his work was followed by that of Hutton. 4 
In 1838 Link 5 boiled coal fragments in kerosene to render them more 
nearly transparent for microscopic study. In 1855 Franz Schulze 6 

1 White, D., and Thiessen, R., The origin of coal. U. S. Bur. of Mines, Bull. 38, p. 
227, 1913. 

2 Von Beroldingen, Franz, Beobachtungen, Zweifel, und Fragen, die Mineralogie 
iiberhaupt, und insbesondere ein natiirliches Mineral System betreffend, vol. i, ist ed., 
1778, 2d ed., 1792. 

3 Witham, Henry, On the internal structure of fossil vegetables found in the carbon- 
iferous and oolitic deposits of Great Britain, 1833. 

4 Hutton, W., Observations on coal. London and Edinburgh Phil. Mag. and Jour, 
of Science, vol. 2, p. 302, 1833. 

5 Link, Frederick, Uber den Ursprung der Steinkohlen und Braunkohlen nach mikro- 
skopischen untersuchungen. Abhandl. k. Preuss. Akad. Wiss. Berlin, pp. 33-34, 1838. 

6 Schulze, Franz, Uber das Vorkommenwohlerhaltenes Cellulose in Braunkohle und 
Steinkohle; Ber. k. Akad. Wiss. Berlin, pp. 676-678, 1855. 


adopted the maceration process for lignite and bituminous coal. 
He digested the material in a mixture of dilute nitric acid and potas- 
sium chlorate and then washed it in ammonium hydroxide and hot 
alcohol, thus isolating woody fibers. 

FIG. 2. Photomicrograph of bituminous coal showing bright bands due to 
woody material and dark bands due to debris. (Photo by Thiessen.) 

The work of these investigators was followed by that of J. W. 
Dawson, C. W. von Giimbel, C. E. Bertrand, B. Renault, H. Potonie, 
O. Barsch, D. White, and E. C. Jeffrey, all of whom have paid par- 
ticular attention to the microscopic characters of coal. It was not, 
however, until about 1910 that a satisfactory method was found for 
preparing thin sections for study. This was discovered by Jeffrey 
and described in his article published in that year. 1 

Preparation of thin sections. In the preparation of thin sections 
with the microtome there are two chief operations necessary, one the 
removal of the mineral matter and the other the softening of the coal 

1 Jeffrey, E. C., The nature of some supposed algal coals. Proc. Am. Acad. of Arts 
and Sci., vol. 46, pp. 273-290, 1910. 


so that it may be cut on the microtome like an ordinary botanical 
or zoological section. The chief agent used for the removal of the 
mineral matter, which consists mainly of silica, pyrite and carbon- 
ates 3 is hydrofluoric acid and the softening agent is potassium or 
sodium hydroxide. Jeffrey has recently concluded, however, that 
phenol is a still better softening agent since it does not cause so much 
swelling of the coal. 1 As to whether the hydroxide should have water 
or alcohol added to it or be employed hot or cold depends upon the 
resistance of the coal Thiessen 2 points out that alcohol, by causing 
shrinkage, has the advantage of counteracting the expanding influence 
of the hydroxide but it causes a more violent reaction. For cannel 
Jeffrey 3 used a mixture of yo-per cent alcohol saturated with sodium 
or potassium hydroxide. He allowed the coal to stand in this for 
a week or more at a temperature of 60 to 70 C. until it was softened. 
The mixture was then carefully removed by hot alcohol and the frag- 
ments later treated with hydrofluoric acid for two or three weeks. 
After this treatment the acid was washed out very thoroughly so 
that no trace of it might attack the knife, the coal was embedded in 
celloidin to stiffen it, and was then cut on a microtome. The celloidin 
recommended is that known as Schering's. For those coals which 
are more resistant to the softening process he uses either aqua regia 
(HNO 3 + 3 HC1) or nitric and hydrofluoric acid of full strength. 
He found that the acid treatment in many cases must be followed 
by a treatment with sodium or potassium hydroxide after the acid 
is removed. After the sections are cut they are dehydrated in a 
mixture of absolute alcohol and chloroform. One difficulty was 
experienced in preparing the sections for cutting; this was the fact 
that hot alcohol and ether must be used in embedding the specimens 
in the celloidin and these solvents dissolve some portions of the lower 
grades of coal. 

After various experiments Thiessen recommends that mineral 
acids such as nitric acid, be avoided if possible, owing to their oxidiz- 
ing action on the coal. In place of nitric acid alternate applications 
of hydrofluoric acid and potassium or sodium hydroxide may be used 
to soften resistant samples. In treating the samples with hydro- 

1 Jeffrey, E. C., Methods of studying coal. Conspectus, Vol. 6, No. 3, 1916. 

2 .Thiessen, R., Op. cit., p. 207 

3 Jeffrey, E. C., Op. cit. 


fluoric acid they should be placed in paraffin, ceresin, or rubber bottles 
rather than in lead. For lignite a good solution is one part commer- 
cial hydrofluoric acid and one part of 30 to 50 per cent alcohol In 
which the blocks, which have been cut about 2 to 4 millimeters square 
and 10 millimeters long, are placed until the mineral matter is dis- 
solved. The acid may then be removed by potassium hydroxide 
or sodium hydroxide and the section cut on the microtome without 

further softening. 

If the specimens are 
resistant and need sof- 
tening a 5 per cent solu- 
tion of sodium hydroxide 
in 50 per cent alcohol is 
used. If they are friable 
they may be embedded 
in paraffin but this must 
not be allowed to actually 
penetrate the coal. The 
sections may be bleached 
in nitric acid or Javel 
water. After dehydra- 
tion they may be mounted 
on slides with Canada 

Thiessen has, in his 
more recent work, abandoned the use of the microtome and 
adopted the grinding method since this has one distinct advantage 
over the slicing method. 1 By preparing the specimens in this way 
no part of the coal or its included foreign matter is removed by 
the acids or other reagents and all the features of the coal may 
be studied. It has a disadvantage, however, in that several 
sections cannot be cut from the same specimen of coal almost as 
easily as one. When the coal is once softened it is an easy task to 
cut on the microtome many sections from the same block, for the 
study of the internal structure of bodies occurring in the coal. The 
sections of anthracite or bituminous coal must be ground extremely 

1 White D., and Thiessen R., The origin of coal. Bull. 38, U. S. Bur. Mines. Also 
Thiessen R., Structure in paleozoic bituminous coals. Bull. 117, 1920. 

FIG. 3. Baxton megaspores from coal, with 
air sacks and showing tri-radiate lines (x 25). 
(After R. Thiessen.) 


thin to permit any light to pass through them and it is only after 
considerable practice that this grinding process can be successfully 
carried out. 

In preparing the sections a block less than an inch in diameter is 
cut from the coal. The preliminary grinding is done with a paste 
of carborundum powder on a fine textured carborundum lap, then 
on the lap without any powder but with a stream of water playing on 
the lap. The specimen is then rubbed on a hone with a stream of 
water running over it until it is perfectly smooth and flat on the 
polished side. After this operation the specimen is waterproofed 
to prevent water entering the coal and causing it to swell. This 
process consists of soaking the polished surface, first heated to about 
105 C., in paraffin heated to the same temperature. This requires 
only a few minutes. 

After waterproofing, the specimen is cemented to a slide with a 
strong, transparent cement consisting of 3 parts of Canada balsam to 
2 parts of marine glue which have been heated together in a drying 
oven at a temperature of about 105 C. for a sufficiently long time to 
make a quickly setting, strong, but not brittle cement. This cement 
is warmed until it is completely liquid and the specimen, wiped free 
of any excess paraffin, is placed in it and pressed down in such a way 
as to exclude all air bubbles. 

The grinding of the section is continued by first grinding the speci- 
men down as far as possible in the same manner as the first grinding 
was done and then finishing it on the hone. Considerable care must 
be exercised in doing the fine grinding, especially when the section 
becomes very thin, to avoid breaking it up, and frequent exami- 
nations should be made with the microscope to test its condition. 
All powder must be removed from the specimen by washing before 
it is rubbed on the hone. If the section is to be studied in oblique 
illumination the dry specimen should be polished on a dry hone by 
drawing it over the hone in one direction only. 

By means of thin sections prepared as described above photo- 
micrographs may be made with a magnification of 2000 diameters. 
A detailed study can be made of the internal structure of the coal and 
such a study throws a great deal of light on the composition and 
origin of coals. Thiessen has made use of this in a very practical 
way in the study of the occurrence of sulphur in coal and in the cor- 


FIG. i. Photomicrograph of horizontal section of coal from the 
Pittsburgh seam showing numerous spores (x 800). (Photo by R. 

FIG. 2. Photomicrograph of a section from the coal in the Black 
Creek seam (x 800). It shows flattened spores peculiar to this seam. 
(Photo by R. Thiessen.) 



relation of coal seams. It has been found that most coal seams carry 
certain plant spores which are characteristic of those seams and 
which distinguish them from other seams, just as animal fossils dis- 
tinguish one formation from another in a sedimentary series (Plate II). 
While certain spores may be common to several seams there are 
usually one or more types found only in one seam. The microscope 
has also been of the greatest service in determining the origin and 
character of boghead coals and oil shales. 



The chemistry of coal and its derivatives is a subject of extreme 
complexity and of very comprehensive range. It cannot be treated 
fully in a text of this sort but the main principles of the subject are 
here set forth. 

Since coal has been derived chiefly from woody constituents it 
consists mainly of the elements which go to compose wood, but it 
differs from wood in composition inasmuch as certain proportions 
of those elements have been changed during the fermentation and 
metamorphic processes which have altered the wood to coal. There 
have been additions to the woody matter during the growth of the 
vegetation, through streams and winds carrying particles of mineral 
matter into the coal swamps. Again, after the woody matter has 
changed to peat and even to the higher grades of coal, percolating 
meteoric waters or hot magmatic waters, the latter rising in regions 
where igneous rocks occur, may add a quota of their dissolved salts 
to the coal and increase the ash and sulphur content. In some 
regions of igneous activity a great variety of mineral compounds, 
some comparatively rare, have been found in the coals. Besides the 
vegetal and mineral matter a certain amount of animal matter may 
have been imprisoned in the coal and this may have caused a variation 
in some constituents, especially in the nitrogen and phosphorous 
content. Fish remains have been found in the rocks associated with 
coal seams in many localities, a notable example being that of the coal 
basin at Commentry, central France. Fish remains have been 
found also in some seams of cannel coal in England. 

Constituents of Vegetation 

Cellulose and lignocellulose. The chief constituent of vegetation 
which goes to form coal is cellulose, the formula of which is (C 6 Hi O 6 ). 
Many writers have discussed the derivation of coal from woody ma- 
terials as if cellulose were practically the only important constituent 



of the vegetal matter but Clarke 1 considers that wood consists more 
nearly of equal proportions of cellulose and lignocellulose (Ci 2 Hi 8 O 9 ). 
The latter is known also as lignone and lignin and its composition is 
similar to that of jute fiber. From the formulae of these two com- 
pounds their percentage composition is as follows: 

Cellulose Lignocellulose 

C 44 . 44 per cent C 47 . 06 per cent 

H 6.18 " H 5.89 

O49-38 O 47-05 

If the composition of these substances be compared with that of 
wood it is seen that the wood runs higher in carbon, averages about 

FIG. 4. Photomicrograph of section of bituminous coal from No. 
5 seam, Vandalia, Indiana (x 160). Consists chiefly of particles of 
resin. (Photo by R. Thiessen.) 

the same in hydrogen, and is considerably lower in oxygen. A fair 
average composition for wood is C; 49.50, H; 6.25, and O; 44.00 per 
cent. It will vary somewhat with the inclusion or exclusion of the 
oils, waxes, and gums because they are much higher in carbon and 
hydrogen and lower in oxygen than cellulose and lignocellulose. 

1 Clarke, F. W., The data of geochemistry. U. S. Geol. Survey, Bull. 616, 3d ed., 
p. 739, 1916. 


Resins, fats and oils. According to Thiessen 1 the coniferous 
resins, resinoles, or resinolic acids contain C; 76.8 to 83.63, H; 9.7 to 
12.9, and 0; o.o to ii.n per cent. The waxes contain C; 80.32 to 
81.6, H; 13.07 to 14.1 and O; 4.5 to 6.61 per cent. The fats and oils 
are composed of C; 74 to 78, H; 10.26 to 13.36, and O; 9.43 to 15.71 
per cent. 

Salts of organic acids. There have also been found in lignites 
salts of organic acids such as whewellite, calcium oxalate, hum- 
bold tine, ferrous oxalate, and mellite, the latter a salt of aluminum 
and mellitic acid. Clarke 2 considers that since oxalic acid is readily 
formed from cellulose, and calcium oxalate *is insoluble it is remark- 
able that the oxalate is not more common in coal. 

Humus acids. Humic acid occurs abundantly in peat and to a 
considerable extent in lignite. The analyses of Borntrager 3 show 
that in the black humus varieties of some German peats there are 
12.50 to 30.00 per cent of humus acids to about 50 per cent of fiber. 
In the brown coal at Falkenau, Bohemia, Von John 4 has found native 
humic acid as a black crumbling coaly mass. It is soluble in ammonia 
and sodium carbonate, and hydrochloric acid precipitates all ot the 
organic material from solution. The percentage composition is 
C, 54.98; H, 4.64; O, 39.98; and ash, 0.40; dried at 100. The 
calculated formula is C 46 H46O25 and it resembles somewhat a sub- 
stance found in the brown coal of Bavaria. The " paper coals" 
of Russia also contain humic acid in considerable quantity. 

The paraffin series. The presence of at least one of the lower 
gaseous members of the paraffin series in coal has long been recog- 
nized because methane (CH 4 ) or marsh gas is a well-known gas in 
mines. Chamberlin 5 has also found ethane (C 2 H 6 ) to be present in 
much smaller quantities. It is found in pulverizing the coal. The 
presence of some of the higher members of the series as liquids and 
solids has been pointed out by Thiessen who mentions the compounds 
(CnHae), (C 2 4H 5 o), and (C 2 6H 54 ) discovered by Krafft in brown coal. 

1 White, D., and Thiessen, R., The origin of coal. U. S. Geol. Survey, Bull. 38, p.. 

293, 1913- 

2 Op. cit., p. 741. 

3 Quoted by Clarke, Op. cit., p. 744. 

4 Von John, C., Verhandl. K. k. Reichsanstalt, p. 64, Feb. 3, 1891. 

6 Chamberlin, R. T., Notes on explosive mine gases and dusts. U. S. Bur. of Mines, 
Bull. 26, 1911. 


Paraffins with formulae (Ci H 2 2) and (C 32 H G 6) have been described 
by Cohen and Finn 1 as occurring in the roof of a Yorkshire coal seam. 
Hall 2 separated the oils (CiiH 24 ) and (Ci 3 H 28 ) from material taken 
from the roof of a coal seam in North Staffordshire, and Bedson 3 
found paraffins in the Whitehaven Collieries, whose formulae were 
believed to vary from (Ci 3 H 28 ) to (CisH 38 ). It is probable that 
members of the paraffin series are. much more common in coal than 
they were formerly believed to be but they are likely to be over- 
looked and not separated in analyses. Jones and Wheeler 4 have 
found solid paraffins apparently existing free in several British coals 
by treating the extract obtained by the solvent action of pyridine 
and chloroform with pentane. This solution yields crystals of paraf- 
fin wax melting between 55 and 59 C. and similar in composition 
to those obtained by the destructive distillation of the coal. The 
wax forms about per cent of the total weight of the coals exam- 
ined but it may not be present in all coals. It is the opinion of these 
writers that the paraffins exist as alkyl or paraffinoid groups attached 
chemically to another non-alkyl group, R. H. The paraffin would 
thus be in a so-called " bound" condition and would occur as a com- 
ponent part of a molecule whose general formula would be repre- 
sented by RH C n H 2n +i where n may have any value up to at least 
32. When coal is decomposed thermally the "free" paraffins are 
rapidly distilled from the " bound" molecules according to the fol- 
lowing system: 

R H.C n H 2n+ i - R + C n H 2n + 2 or 
R H.C R H 2n +i > R ~h C n H 2n + 2 H- C ni H 2ni 

In somewhat the same way the formation of free naphthenes is ex- 

1 Cohen, J. B., and Finn, C. P., Paraffin from Yorkshire coal seams. Jour. Soc. Chem. 
Ind., Vol. 31, p. 12, 1915. 

2 Hall, A. A., Oil from the roof of the Cockshead coal seam, North Staffordshire. 
Jour. Soc. Chem. Ind., Vol. 26, p. 1223, 1907. 

3 Bedson, P. P., Paraffin wax from the Ladysmith Pit. Jour. Soc. Chem. Ind., Vol. 
26, p. 1224, 1907. 

4 Jones, D. T., and Wheeler, R. V., The composition of coal. Trans. Chem. Soc., 
Vol. 105, p. 140, 1914. 


Gases in Coal 

Gases given off at normal temperatures. In many coal mines 
methane, CH 4 , (marsh gas or, when mixed with air, fire damp) and 
carbon dioxide, CO 2 , (choke damp or black damp) are found in large 
quantities. Carbon monoxide, CO, (white damp) occurs in lesser 
amounts than the other two but it is present in small proportions 
in many mines. The quantity of gas, consisting chiefly of carbon 
dioxide and methane, which escapes from some mines is very great, 
running into many thousands of cubic feet. What is regarded as 
the most gaseous mine in the anthracite region of Pennsylvania has 
emitted as high as 2400 cubic feet of methane per minute. 

Experiments have shown that coals will absorb gases in much the 
same way as charcoal but regarding the actual condition of the gas 
in the coal before mining there is still much uncertainty. Some 
investigators have considered it as occluded but as Porter and Ovitz 1 
have pointed out it is doubtful whether the gas exists as occluded gas, 
or in a condensed condition, in the true sense of the term occluded. 
The experiments of Chamberlin 2 and others have shown that the coal 
gives up a considerable quantity of methane and some ethane when 
pulverized but only a small percentage of that given off if the coal be 
allowed to stand at atmospheric temperature for several months in 
vacuo in a closed vessel. Porter and Ovitz have shown that although 
the escape of methane from a mine seems to be dependent to some 
extent upon the atmospheric pressure, the gas from broken coal after 
a time escapes at approximately the same rate under atmospheric 
pressure as in vacuo. The proportion of oxygen in the gas surround- 
ing the coal does, however, have a great influence on the rate and 
amount of the methane given off without causing a marked effect 
upon the proportion of carbon dioxide set free. 

From a practical standpoint these conclusions are important 
because ventilating a mine carries off the gas set free but it also fur- 
nishes more oxygen to the coal and thus facilitates the escape of 

1 Porter, H. C., and Ovitz, F. K., The escape of gas from coal. U. S. Bur. of Mines, 
Tech. Paper 2, 191 1. Also Parr S. W., and Barker, P., The occluded gases in coal. Uni- 
versity of 111., Bull. No. 20, Vol. VI, 1909. 

2 Chamberlin, R. T., Notes on explosive mine gases and dusts with special reference 
to the explosions in the Monongala, Darr and Naomi coal mines. U. S. Geol. Survey, 
Bull. 383, 1909. 


deleterious gases. The amount of gas, both methane and carbon 
dioxide, given off from coal which has been mined varies greatly with 
different coals, but in practically all cases the proportion given off 
during the first few days is much greater than that which escapes with 
an increase in the length of time during which the experiment is con- 
tinued. The loss of gas is usually complete in from three to eighteen 
months and the deterioration in heating value is small. When coal 
absorbs methane it gives up nitrogen somewhat less in amount than 
the volume of methane absorbed 1 . 

Gases evolved from coal heated below temperature of decom- 
position. In addition to the gases given off in the coal seams at 
atmospheric temperature and pressure considerable quantities are 
driven out of the coal by heating it to a point a little below the tem- 
perature at which decomposition begins. In view of the effect of 
the absorption of oxygen on the gases given off it seems probable that 
the increase of temperature not only expels the gas because of increas- 
ing the volume but that it aids chemical action to a slight degree. 
In peat the gases given off seem to consist chiefly of nitrogen and 
marsh gas with smaller amounts of carbon dioxide. The presence of 
the nitrogen is probably largely the result of air being imprisoned in 
the fuel. The oxygen of the air is taken up by carbon or hydrogen 
during the chemical processes accompanying the decay of the vegeta- 
tion, leaving the nitrogen free in the peat. 

The gases from lignite, heated to 100 C. in vacuo, consist, so far 
as they have been tested, chiefly of carbon dioxide with small amounts 
of carbon monoxide, nitrogen, oxygen, olefmes, and marsh gas. From 
cannel coals the gases are largely methane and carbon dioxide. In 
a series of analyses of English and Scotch cannels Thomas 2 shows that 
when they are heated to 100 C. in vacuo they give from 16.8 to 
421.3 c.c. of gas per 100 grams of coal and the composition of the gas 
varies as follows: 

CO2 6 . 44-84 . 55 per cent. 

CH4 77 . 19-80. 69 per cent. Absent in three samples 

C2He 2 . 67-7 . 80 per cent. Absent in two samples 

C 3 H 8 0.91 percent. Present in one sample only 

C4Hio Not present 

N 2 5 . 96-46 . 06 per cent. 

1 Katz, S. H., Absorption of methane and other gases by coal. U. S. Bur. of Mines, 
Tech. Paper 147, 1917. Also McConnell, W., Gases enclosed in coal and coal dust. 
Jour. Soc. Chem. Ind., Vol. 13, p. 25, 1894. 

2 Thomas, J. W., Jour. Chem. Soc., Vol. 30, p. 144, 1876. 


A sample of Whitby jet yielded 30.2 c.c. of gas consisting of CO 2 , 
10.93; C 4 Hio, 86.90; and N 2 , 21.7 per cent. From these analyses 
it is seen that carbon dioxide is present in all, and abundant in some 
coals. Nitrogen is present in fairly large proportion in all these 
coals and is present also in jet. While these results obtained by 
Thomas are interesting it may be questioned whether they can be 
fully relied upon in view of the difficulty experienced at the present 
day with more modern analytical methods, in our attempts to rec- 
ognize certain of these rarer gases. 

The gases obtained from bituminous coal and anthracite under 
the conditions stated above are very variable in amount and com- 
position. Von Meyer 1 found ethane up to 23 per cent and other 
undetermined hydrocarbon gases in small amounts in some Saxon 
and Westphalian coals. From the works of W. McConnell 2 on the 
coals from Newcastle and of Thomas 3 on the Welsh coals the following 
figures were compiled: 

Volumes of gases derived from 100 grams of bituminous coal heated 
in vacuo at 100 C., 1.61 to 818 c.c.; from semibituminous and steam 
coal, 73.6 to 375.4 c.c.; and from anthracite, 555.3 to 600.6 c.c. The 
composition of the gases varied as follows: 

Semibituminous and 
steam coal 



C0 2 
CH 4 and other 
O 2 

5 .04-1 8. 90 per cent 

0.33 i .02 

o . 7 2-36 . 42 per cent 

o . 40-88 . 50 
0.80 9 .41 

2. 62-14. 72 per cent 

N 2 



1. 10- 4.25 '* 

The paraffins in the bituminous coals consisted in some cases almost 
entirely of methane although ethane was present in greater or lesser 
amount. The steam coal of Seaton Delaval gave off no hydrocar- 
bons, the gas consisting entirely of carbon dioxide, oxygen, and nitro- 

The above figures go to show that in anthracite the predominant 
gas is methane, while in the lower types of coal carbon dioxide, nitro- 

1 Quoted by F. W. Clarke, Op. cit, p. 759. 

2 Op. cit. 

3 Thomas, J. W., Jour. Chem. Soc., Vol. 28, p. 793, 1876. 


gen and methane form the main constituents of the gas. This is 
further illustrated by the fact that if heated to higher temperatures 
but still below the point of decomposition the relative proportion of 
methane increases while that of nitrogen decreases. The longer the 
coal is heated the more gas is given off, this being especially true of 
hard compact coals such as anthracites. The bulk of the gas, however, 
is evolved early in the experiment. 

Relation of mine gases to volatile constituents in coal. The 
proportion of volatile matter in coal seems to have little or no relation 
to the percentage of gas evolved on heating below the temperature 
of decomposition and the explosibility of mine gases and dusts seems 
to depend much more upon the nature of the gases evolved than upon 
the relative percentage of volatile matter in the coal. 

Analyses made by Thomas of the gases from blowers in coal seams 
and of those gases obtained from the seam by boring show that there 
is little difference between them. In some blowers the oxygen reaches 
over 10 per cent and nitrogen over 41 per cent of the gas, but oxygen 
is lacking in many. Carbon dioxide is less than i per cent in nearly 
all, while marsh gas constitutes over 90 per cent of the gases derived 
from practically all blowers and borings in the seams. 

Products o Distillation 

The chief products resulting from the distillation of coal are coke, 
tar, light oils, water of decomposition, and a mixture of gases con- 
sisting chiefly of NH 3 , H 2 S, H, C0 2 , CO, unsaturated hydrocarbons, 
and C n H 2 n+2. The processes of distillation and the chemistry of 
the resulting products are subjects which are so complex that a de- 
tailed discussion of them involves a treatment of the subjects of gas 
manufacture, the dye industry, and many other related problems. 

(Fig. 5) 1 - 

The relative proportions of the volatile constituents obtained 
depend upon many factors, such as the kind of coal and the con- 
ditions under which the coal is heated, including the temperature, the 
pressure and the length of time involved. It has also been found that 

1 For detailed descriptions of experiments and conclusions regarding the volatile 
matter in coal, see Porter, H. C., and Ovitz, F. K.. The volatile matter of coal. U. S. 
Bur. of Mines, Bull, i, 1910; and The primary volatile products of the carbonization of 
coal. Tech. Paper 140, 1916. Also Rittman, W. F., and Whitaker, M. C., A bibliog- 
raphy of the chemistry of gas manufacture. U. S. Bur. of Mines, Tech. Paper 120, 1915. 



a wet coal will produce a greater ammonia yield and less gas, but a 
gas richer in hydrocarbons, than a dry coal. 

Effect of temperature on quantity and kind of constituents 
evolved. The experiments of Porter and Ovitz have shown that, 
as a rule, more than two-thirds of the organic substances are de- 
composed at temperatures below 500 C. It is probable that some 
change takes place in exposed coal at atmospheric temperatures but 
appreciable quantities of volatile matter are given off from most 
coals at 250 C. In a series of experiments on bituminous coals 
Burgess and Wheeler 1 found that occluded or " condensed" gases 
which are unextractable at atmospheric temperatures are extracted 
in vacuo by heating from 150 to 200 C. These gases consist mainly 
of the higher members of the paraffin hydrocarbons. The following 
table shows the quantity of gas and its composition evolved from 100 
grams of coal heated to 100 C. and the same amount heated to 200 C. 


Volume of gas 

Composition per cent 

C0 2 



CH 2n(n72) 



C.H 2n+2 


34 c.c. 
65.5 c.c. 




2 .90 





Of the gas obtained at 200 about 7.5 per cent consisted of butane. 
The identification of this gas has, however, been called in question 
by some chemists. 

The younger coals of the western and middle-western states break 
down more quickly, as a rule, than the Appalachian coals. This 
greater ease of disintegration is probably related to the proportions 
of resinous and cellulosic constituents, the older coals yielding a 
larger proportion of hydrocarbon constituents from the resinous 
materials and the less mature coals a greater proportion of carbon 
dioxide and water. The early products of distillation are mostly 
CO 2 , CO, and H 2 O and these come off slowly up to 450 C. At this 
temperature the products of the lower grades of coal are mostly water 
and carbon dioxide, and those from bituminous coal largely members 

1 Burgess, M. J., and Wheeler, R. V., The distillation of coal in a vacuum; Trans. 
Chem. Soc., Vol. 105. 


of the paraffin series, with gases of the series C n H 2n +2, higher than 
CH 4 , predominating below 400 C. Water of decomposition is ex- 
pelled much more rapidly between 250 C. and 500 C. than at a 
higher temperature. 

Sulphurous gases, such as H 2 S, begin to be formed at 250 C. and 
the production rises to a climax more rapidly than that of hydrogen 
or the hydrocarbons. The thermal decomposition of the volatile 
matter takes place very readily at temperatures above 750 C. and 
the percentage of hydrogen and the hydrocarbons increases, with 
hydrogen predominating, at the higher temperatures. The increase 
of these gases takes place, however, at the expense of the tar, which 
has been increased 13 per cent in yield from Pittsburgh coal by heat- 
ing it below 500 C. rather than at the usual temperature employed 
in carbonizing coal. It is evident that the composition of the tar 
obtained at the different temperatures will vary considerably. At 
900 C. the volatile matter is practically all expelled from a coal of 
the Pittsburgh type although heated only a few seconds, which is 
the time necessary to raise the temperature to that point. 

The experiments of Burgess and Wheeler 1 in England produced 
results for low temperature distillation gases, very similar to those 
described above, but these authors concluded that there is a decompo- 
sition point between 700 and 800 C. at which hydrogen is distilled 
at a marked increase in rate. This change is considered as indicating 
the presence in the coal of two types of compounds, one type decom- 
posing at a lower temperature than the other and yielding mostly 
hydrocarbons in contrast to the other which yields hydrogen as the 
chief decomposition product. Although Porter and Ovitz found that 
hydrogen was given off in greater proportions above 750 C. they do 
not consider that any line of demarcation may be drawn near this 
point which would indicate the decomposition of distinct compounds. 

1 Burgess, M. J., and Wheeler, R. V., The volatile constituents of coal. Jour. Chem. 
Soc., Vol. 97, p. 1917, 1910; Vol. 99, p. 649, 1911. Clark, A. H., and Wheeler, R. V., 
The volatile constituents of coal. Jour. Chem. Soc., Vol. 103, p. 1704, 1913. 



By-product tests on coals: 


Number of Samples 








Number of tests 

averaged. . . . 







Coke, per cent. . . 








Tar, per cent .... 








Water, per cent . 






ii. 8 


Ammonia, pounds 

of sulphate per 


12 Q 

23 8 

2C 2 

27 ^ 

26 7 

26 i 

26 7 

CO 2 , per cent. . . . 


*o * w 


o o 

^ / 


^.\J . j 


*\> . ^ 

' v } 


H 2 S, per cent. . . . 








Gas, cu. ft. per 

ton (a) 







7 Q4.O 

Composition of 

y / *** 

^> AiJ.W 


/ J^O 

Uf ft y W 

^ )\J 4\S 

/ >:7T- W 

gas (6) . . . 





2 .2 












CH 4 , C 2 H 6 , etc. . . 



26. 3 (C) 









^4 o 

4Q. 2(^) 


C2 I 


I .2 



OT- * ^ 

T^^'O \ / 




Value of "n" in 

C n H 2n+2 








Total volatile 

products with- 

out moisture. . . 








Water of consti- 









Inert volatile 

matter (d) 








(a) Calculated to dry basis at o C. and 760 mm. pressure, free of air and 
carbon dioxide. (6) Calculated to carbon dioxide and oxygen-free basis, (c) 
Hydrogen not determined separately by palladium but calculated from com- 
bustion: Methane probably high and hydrogen low. (d) Sum of carbon dioxide, 
ammonia and water of constitution. 

The coals used in these tests were as follows: No. 16, Pocahontas; 
No. 3, Connellsville; No. 23, Harrisburg, 111.; No. n, Sheridan, 
Wyoming subbituminous coal; No. 25, Utah bituminous coal; No. 
46, Wyoming bituminous coal. 

Burgess and Wheeler 2 distilled anthracite at 900 C. for varying 

1 Porter and Ovitz, U. S. Bur. of Mines, Bull. I, p. 26, 1910. See also Church, S. R., 
Methods for testing coal tar and refined tars, oils, and pitches derived therefrom. Jour. 
Ind. and Eng. Chem., Vol. 3 p., 227, 1911. 

2 Burgess, M. J., and Wheeler, R. V., The volatile constituents of coal, Pt. II. Trans. 
Chem. Soc., Vol. 99, pp. 665-6, 1910. 

=1 . 




" " 'I 







I C ""jr" ||. U T,,LO,U,| | 




| PHENOL | CRE80L | I BA . . [. ,,. | 


P"H T E 

^NO'L' 1 

h'REslNS-||^S-S- || j*W | 


L^^'N||8AL,C^?C\CI D llk^ 



fffr. |P 





1 I 














LOY^^Fr, j| SOLVENT | | "JTROin^ 


II "gffl I L_ 



FIG. 5 Distillation products of coal and their commerci 




1 1 

1 1 

! 1 - 




j PRES^TION 1 * C1N | | LAMP . 


F~l 1 iM^SoN I 

I 1 




.Kg | 1 ^ NTAN j | 




1 QU.NONE 1 



J , 




1 1 ALGOL I 


, 1 

, 1 1 


| III 



ITCH; 1 







i ! " " ' T ' 


r L_ 

1 ""FUMES | .88m. 



es. (Reproduced by permission 

of the Barrett Company.) 




L i ..;.-. i^ _ 


periods of time and recorded the results for periods of five seconds 
each. During the first five seconds 6.65 c.c. of gas at o C. and 760 
mm. were evolved, and during the tenth five-second period 20.95 c - c - 
The composition of the gas taken at the periods mentioned was as 
follows when calculated on a " nitrogen-free " basis: 

A B 

NH 3 6.10 0.20 

C 6 H 6 3-80 o-35 

H 2 S 2.75 0.35 

CO 2 9.85 1.40 

C 2 H 2 0.30 nil 

C 2 H4 2.35 nil 

CO 16.65 5-6o 

H 2 31-20 82.30 

CH4 25.95 8 -4o 

C 2 H 6 1. 10 1.35 

The tarry products derived from the distillation of coal are of great 
industrial importance and their derivatives are obtained by numerous 
chemical processes, some of which are of remarkable complexity. 1 
The following plan shows the main products derived from coal and 
it sets forth the relations among these various compounds. (Fig. 5.) 

The Solubility of Coal and its Destruction by Acids 

The degree of solubility of different coals varies greatly owing 
to the fact that they are not homogeneous and their resinous con- 
stituents will dissolve much more readily in some reagents than their 
cellulosic constituents. Coals which contain much humic acid will 
dissolve to a considerable extent in alkaline solutions, while the 
cellulosic constituents may be attacked by nitric acid. Most of the 
resinous constituents are soluble to some extent in organic solvents 
such as benzine. 

Peat and the xyloid lignites are partially soluble in caustic alkalies 
and almost completely soluble in alkaline hypochlorites. The com- 
pact lignites or subbituminous coals are readily attacked by the al- 
kaline hypochlorites but are only slightly soluble in caustic alkalies, 
while bituminous coals and anthracite are not dissolved by alkaline 
solutions. Dilute nitric acid will attack lignite and strong acid will 
slowly attack the higher coals but a mixture of nitric and sulphuric 

1 Hoffman, A. W., Etudes sur les matieres colorantes derivees du goudron de houille 
Compt. Rend., Vol. 55, pp. 781, 805, 817, 849 and 901, 1862, and Vol. 56, pp. 1033 and 1062. 


acids will completely break down the more reshtant coals leaving a 
deep brown solution from which the coloring matter is precipitated 
on the addition of water. 1 

By the action of nitric acid on finely pulverized coal Guignet 2 ob- 
tained oxypicric acid and a mixture of oxide of iron and sulphuric 
acid resulting from the pyrite in the coal. By boiling the mixture 
in water with barium carbonate the oxide of iron and the oxalic and 
sulphuric acids were thrown out while the oxypicrato of barium re- 
mained. On precipitating the barium as sulphate, crystals of oxy- 
picric acid remained. There were left on filtering the original nitric 
acid solution compounds which were insoluble and which exploded 
when heated. 

Most of the resinous compounds in coal are partially soluble in 
the strong acids, they are partially or entirely soluble m alcohol, 
and most of them partially so in ether and in turpentine. The sol- 
vent action of benzine is variable. It is thus evident that the pro- 
portion of resinous constituents in coal will affect to a considerable 
extent its solubility in various solvents. 

Relation of solubility to coking qualities. The results of Vig- 
non's 3 work show that there is some definite relation between the 
composition of the coal, its solubility in various organic solvents and 
incidentally its coking quality. The coals from the Loire region 
showed the following results when treated with aniline. Taking 
fat gas coals, semi-fat coals, and lean or dry coals he obtained the 
following results: 

Initial weight 

Weight after 
treatment with 


soluble, ash 



(i) Fat gas coal. . . 
(2) Semi-fat coal. . 


I .12-1 .29 
I .09-1 .23 



(3) Lean or dry 


2 . 172 .OI 

2 . 142 .OI 



1 Fremy, E., Recherches chimiques sur les combustibles mineraux. Compt. Rend., 
Vol. 52, pp. 114-117, 1861. 

2 Guignet, E., Sur la constitution de la houille. Compt. Rend., Vol. 88, pp. 590-592, 

3 Vignon, Leo, Sur les dissolvants de la houille. Compt. Rend. VoL 158, pp. 1421- 
1424, 1914. 


The portion of the coal which is soluble is richer in hydrogen than 
the insoluble portion and from this it may be inferred that the coking 
coals will differ from non-coking coals in their solvent action with 

On treating coal with alcohol, ether, benzine, toluene, aniline and 
nitro-benzine, Vignon obtained the following results with 50 c.c. 
of the solvent and 10 grams of coal. 

Soluble at ordinary temperature for 
24 hours 

Soluble at boiling point for 3 hours 


0.076 per cent 

0.0167 per cent 



Benzine .... 

0.080 ' 




0.190 " 


i .410 


From this table it is evident that aniline js the most active solvent 
for these bituminous coals of the Loire basin. Of the other common 
solvents pyridine and phenol may be regarded as the most active. 
Clark and Wheeler 1 claim that a coal may be divided into two types 
of compounds recognized by their differential solvent action with 
pyridine and chloroform, one of these compounds being higher in 
hydrogen and the other in hydrocarbons. 

Phenol has been employed as a solvent for coal by a number of 
chemists, but the first extensive experiments to determine the deriva- 
tives of the solution with phenol were carried out by Parr and Hadley 2 
and by Frazer and Hoffman. 3 The latter authors found that 10.87 
per cent of an Illinois non-coking, bituminous coal was dissolved in 
phenol. From this solution a large number of derivatives were 
extracted, some of which are believed to be pure compounds. Parr 
and Hadley found that there is a distinct relation between the per- 
centage of the coal dissolved in phenol and its coking qualities. The 
coking constituents are almost all dissolved in this solvent and oxi- 

4 Clark, A. H., and Wheeler, R. V., Op. cit. 

2 Parr, S. W., and Hadley, H. F., The analysis of coal with phenol as a solvent, Uni- 
versity of 111., Bull No. 10, Vol. XII. 

3 Frazer, J. C. W., and Hoffman, E. J., The constituents of coal soluble in phenol. 
U. S. Bur. of Mines, Tech. Paper 5, 1912. 


dation of the coal greatly affects its relative solubility. This solvent 
was also used to extract organic sulphur. 

Chemical Causes of Spontaneous Combustion 1 

There has been a great deal of speculation regarding the cause of 
spontaneous combustion of coal and many have assigned it to the 
oxidation of pyrite. It is now recognized, however, that while the 
oxidation of pyrite and the action of the sulphuric acid on moisture 
in the coal may produce some heat, the fundamental cause of the 
heating is the oxidation of the coal itself. The sulphuric acid re- 
sulting from the oxidation of pyrite is a powerful oxidizing agent and 
its presence facilitates oxidation of the coal, but coal itself will oxidize 
rather rapidly for a time after mining. If there is a good circulation 
of air it will not take fire but if there is only a partial supply of air 
oxidation goes on and the heat is retained. As the temperature of 
the fuel rises the rate of oxidation is greatly accelerated and in con- 
sequence there is cumulative action progressing towards the tempera- 
ture of combustion which varies from about 300 C. upward depending 
upon the character of the coal. According to Fayol finely powdered 
lignite may ignite at a temperature as low as 150 C. and gas coal 
at 200 C. 

There is a fairly definite relation, as shown by Wheeler, 2 between 
the temperature of ignition of coal dust and the proportion of its 
resinous constituents, which are soluble in pyridine. 

The oxidation process goes on in both moist and dry coals, although 
moisture aids the process very greatly. If the coal be completely 
covered with stagnant water oxidation almost ceases after a bref 
time but circulating water may bring in new supplies of oxygen to le 
coal. The finer the coal, the more rapid is the oxidation of a given 
surface, other things being equal. The percentage of volatile matter 

1 Parr, S. W., and Kressmann, F. W., The spontaneous combustion of coal. Univer- 
sity of 111., Bull. 16, 1910. 

Moissan, H., Traite de chimie minerale, Vol. 2, pp. 363-364, 1905, (on spontaneous 

Stansfield, E., An investigation of the coals o* Canada. Vol. 6, Dept. of Mines, Canada, 

Hapke, L., The causes and prevention of spontaneous combustion. Chem. Zeit. 
17, p. 916, 1893. 

2 Wheeler, R. V., The volatile constituent? of coal, Pt. IV: The relative inflamma- 
bilities of coal dusts. Trans. Chem. Soc., Vol. 103, p. 1715, 1913. 


seems to make little difference in the spontaneous heating as all 
types of coal have been known to heat. 1 There are, however, no 
authentic cases reported where anthracite has actually taken fire in 
storage. The natural process of heating is often accelerated by the 
proximity of the coal bins to furnaces and other sources of heat and 
this, no doubt, explains why coal on shipboard and in other places 
adjacent to boilers often takes fire while in the bins. 

A certain amount of loss in the heating value of coal takes place 
during weathering and the accompanying oxidation. This may be 
readily understood when the results of White's investigations are 
considered, since he found oxygen and ash to be of almost equal anti- 
calorific value. 2 Further, the loss of methane accompanies the oxi- 
dation process and the heating value of this gas amounts to a small 

Source of Mineral Constituents 

The source of many of the constituents of coal is self-evident when 
the composition of wood is considered. The carbon, hydrogen, 
oxygen, and nitrogen may all be derived directly from the wood but 
there are many other constituents whose source and whose condition 
in the coal are not so readily recognized. In addition to the nitrogen 
in wood, which varies from less than i per cent to over 3 per cent, 
some is supplied by animal matter and it is probable that a little is 
added to the coal from the air through its imprisonment in the vege- 
tation before it becomes coal. 

Sulphur. Sulphur is a constituent of considerable economic im- 
portance in coal because it reduces the quality of coke for metallurgical 
purposes, it increases corrosion of boilers and in quantities of more 
than about 2 per cent it increases clinkering in furnaces by aiding 
the fusion of ash. This 2-per cent limit will vary, however, with the 
varying proportions of ash and sulphur present and it is probable 
that the iron combined with the sulphur in pyrite may aid the fusi- 
bility of the ash almost as much as the sulphur. In coking approxi- 
mately one-half of the sulphur in the coal is supposed to enter the 
coke. This proportion will apparently vary with the proportion of 

1 Porter, H. C., and Ovitz, F. K., Deterioration and spontaneous heating of coal 
in storage. U. S. Bur. of Mines, Tech. Paper 16, 1912. 

2 White, D., The effect of oxygen in coal. U. S. Geol. Survey, Bull. 382, 1909. 


organic and inorganic sulphur. While one molecule of the sulphur 
in pyrite (FeS 2 ) may be removed in the burning process leaving the 
other to enter the coke with the iron, this relation will not hold for 
the proportions of organic sulphur, the compounds of which are not 
so well known. 

Sulphur occurs in varying amounts in coal, from less than i per 
cent to 10 per cent or more. It commonly amounts to between one- 
half of i per cent and 3 per cent although many of the coals of our 
middle-west states carry between 3 and 5 per cent. The sulphur is 
in two forms: organic and inorganic. The inorganic type is most 
familiar and it occurs in the following forms: (i) Mineral sulphides, 
(2) Sulphates and (3) Free sulphur. 

Inorganic sulphur. Of the sulphides iron pyrite (FeS2, Isometric) 
and marcasite (FeS 2 , Orthorhombic) are the most common. Chal- 
copyrite (Cu'FeS 2 ), arsenopyrite (FeAsS), stibnite (Sb 2 S 3 ) and a few 
other sulphides have been found but they are rare except in some 
regions where volcanic activity has occurred. Pyrite or iron pyrites, 
also known as " fools' gold" is responsible for most of the "sulphur 
balls," "coal brasses," and "sulphur diamonds" found in coal seams 
although marcasite frequently occurs in sulphur balls and is mis- 
taken for pyrite since many people do not distinguish these two 
minerals from each other. The sulphide occurs in largest quantities 
in concretions, commonly known as "sulphur balls," in lenses or 
bands running parallel with the coal seam or in veinlets cutting across 
the seam. When in sufficiently large quantities it is separated from 
the coal in mining and at some mines it is sold for the manufacture 
of sulphuric acid. In addition to the masses of pyrite which are so 
evident to the naked eye, Thiessen 1 has shown that in practically all 
coals and also in peat there are numerous grains of pyrite averaging 
25 to 40 microns in diameter, distributed through the fuel (Fig. 6). 
These appear to be more abundant in the xyloid bands in the coal 
and it seems quite probable that at least part of the pyrite has been 
formed by combination of iron with hydrogen sulphide derived from 
organic sulphur. These grains of sulphide are so small that they 
cannot be removed from the coal by washing unless the coal has been 
ground to fine powder. 

1 Thiessen, R., Finely disseminated sulphur compounds in coal. Trans. Amer. Inst. 
Min. Met. Eng. Vol. LXIII, p. 913, 1920. 



The most common sulphate known is calcium sulphate or gypsum 
(CaSO4.2H 2 O). Sulphates of iron, copper and magnesium may also 
occur but they are not abundant. These salts occur as a result of 
the action of sulphuric acid on carbonates or by the oxidation of 
sulphides. The sulphuric acid may result from the oxidation of 
iron pyrite as in the following equation : FeS 2 + 76 + H 2 = FeSCX 
+ H 2 S0 4 . 

Native sulphur occurs only as the result of extreme oxidation of 
some of the minerals mentioned above and it is rare. 


FIG. 6. Photomicrograph showing finely disseminated pyrite in coal (x 155). 
(Photo by R. Thiessen.) 

Organic sulphur. It has for many years been recognized that a 
portion of the sulphur in coal must exist in some form other than 
the mineral sulphides and sulphates. This is shown by the fact that 
in some coals the sulphur does not exist in such proportions that it 
can be combined with the elements necessary to form these mineral 
compounds. Sulphur which gives every indication of being com- 


bined in organic compounds in coal has been found running from 0.5 
to 2 per cent, and 3 per cent is reported in one coal. Thiessen points 
out that there is sulphur in the proteins of practically all plants and 
in addition to the protein sulphur there is some non-protein sulphur 
in most of them. This organic sulphur by putrefaction is changed 
to hydrogen sulphide (H 2 S) which can precipitate sulphides of the 
metals from their soluble salts. The plants obtain the sulphur, 
which they assimilate in the form of sulphates, from the weathering 
of sulphides in the rocks or from the products of sulphur bacteria, 
which oxidize hydrogen sulphide to sulphuric acid. The sulphuric 
acid can then form calcium, magnesium or potassium sulphates, 
which are assimilated by the plants. R. Dawson Hall has also called 
attention to the fact that many coal seams contain a larger proportion 
of sulphur than the rocks lying above and below them, indicating 
the presence of organic sulphur compounds in coal. He early sus- 
pected that some of the sulphur in pyrite had an organic origin. 

Phosphorous. Like sulphur, phosphorous is an important con- 
stituent in coal which is to be used in making coke since they both 
enter the coke to at least some degree. Its presence in the coal may 
be due to solutions formed by streams running over rocks which 
contain calcium phosphate in some form and these solutions then 
precipitating the phosphate in the swamps where the coal vegetation 
was laid down. It is evident, however, that a certain percentage of 
the phosphorous is derived directly from the vegetation which produces 
the coal. In a study of the origin and distribution of phosphorous 
in bituminous and cannel coals Carnot 1 has found that certain parts 
of plants, especially the spores, contain considerable phosphorous. 
In a series of analyses he found in the Grande Couche, a thick seam 
at Commentry, 0.00163 per cent of phosphorous; in the coal of Fer- 
rieres 0.01385 per cent and in anthracite 0.01467 per cent of phos- 
phorous. In several stems of typical Coal Measure plants changed 
to coal he found from a trace to 0.007 per cent phosphorous. Various 
cannels from England and central France were found to contain 
considerably more of this element than the other coals, the percentage 
varying from a trace to 0.028. Several bogheads gave 0.019 to 0.0627 
per cent. 

1 Carnot, Ad., Sur Porigine et la distribution du phosphore dans la houille et le cannel 
coal. Compt. Rend., Vol. 99, pp. 154-156, 1884. 


For comparison the spores of several modern types of ferns related 
to the Carboniferous plants were analysed and they contained from 
0.078 to 0.228 per cent of phosphorous compared with 0.009 to o.oio 
per cent for the body of the fern. The Ceratizamia mexicana yielded 
0.28857 P er cent phosphorous from the pollen grains and 0.11899 P er 
cent from the envelopes which had become fairly well separated from 
the pollen grains. Mineral charcoal appears to be higher in phos- 
phorous than the coal associated with it because during the change 
from coal to mineral charcoal the phosphorous remained while vola- 
tile constituents were lost, thus increasing the proportion of the former. 

The alkalies and chlorine. Sodium chloride and other alkaline 
salts may be carried into the coal in saline solutions which have 
been derived from the surrounding rocks. The alkalies are derived 
chiefly from the feldspars and related minerals and they are set free 
by weathering of these minerals. The chlorine comes from plants 
and from igneous rocks. 

Silica. This compound enters the ash of the coal and is derived 
chiefly from mineral matter deposited in the swamp by wind and 
water both as mechanical sediment and in solution. It is, however, 
derived partly from such plants as the horsetails which may contain 
upwards of 12 per cent of it in their stems. 

Calcium, magnesium and iron. All three of these elements may 
be carried in solution as carbonates in the presence of carbon dioxide. 
They may also be carried as sulphates and in small amounts as chlor- 
ides. The iron in the form of sulphate or chloride on coming in con- 
tact with a soluble salt, such as a salt of calcium, would normally 
be thrown down as the hydrous oxide unless there were an excess 
of carbon dioxide present to prevent oxidation in which case iron 
carbonate might be precipitated instead of the oxide. The presence 
of so much iron carbonate or " black band" associated with the 
coal deposits in parts of America and England is explained 
by assuming that the carbon dioxide, furnished by decomposing 
vegetation, caused the iron to be precipitated as the carbonate (sider- 
ite) rather than as the more commonly occurring hydrous oxide. 

In addition to the elements mentioned there may be found in coal 
ash, traces of gold, silver, zinc, lead, copper, titanium, vanadium, 
manganese and a vast number of other elements of no particular 
economic importance but of some scientific interest. Of these ele- 


ments zinc has been found in wood, and manganese occurs up to 
25.53 P er cen t as Mn 3 O4 in the ash from leaves of Norway spruce, and 
41.23 per cent in the ash of the bark. Some Hawaiian pineapples 
show 1.15 to 2.12 per cent Mn 3 O 4 . 1 It is thus evident that most of 
the elements have been derived in part directly from the vegetation 
and in part from solutions carried into the swamps. 

The following table 2 illustrates the composition of the ash from 
several types of trees and it shows that at least small percentages 
of most of the elements may be supplied to the coal from the vegetal 
matter which goes to form it. Some elements seem to be entirely 
lacking in the ash of the common plants, while others are extremely 
rare. For example, molybdenum and caesium are lacking while 

(Dried at 105 in oven) 

Birch Leaves 
Per cent 

Birch Stems 
Per cent 

Oak Leaves 
Per cent 

Oak Stems 
Per cent 

Pine Needles 
Per cent 

Pine Stems 
Per cent 

SiO 2 






o .014 

TiO 2 







A1 2 3 .... 







Fe 2 3 . . . 














Cr,O 6 .... 

N F. 






V 2 6 







MoO 2 . . . 












o 320 























K 2 O 






Na 2 0.... 







Li 2 O ... 




o . 000003 



Rb 2 O.... 







CS20. ... 







P 2 5 .... 

i .10 






SO 3 














H 2 O..... 









ents by 








1 Kelley, W. P., Manganese in some of its relations to the growth of pineapples. Jour. 
Ind. & Eng. Chem., Vol. I, p. 533, 1909. 

2 Robinson, W. O., Stemkoenig, L. A., and Miller, C. F., The relation of some of the 
rarer elements in soils and plants. U. S. Dept. Agr., Bull. No. 600, Dec. 10, 1917. 


chromium and vanadium are very rare. It is evident that the high 
percentage of vanadium in the ash analysis quoted below is due 
entirely to some external source. 

An analysis of ash from coal near the town of San Raphael in the 
province of Mendozza, Argentina, gave the following results: 1 

Soluble in Acids Percent Insoluble in Acids Percent 

Vanadic acid 38 . 5 SiO 2 13.6 

H 2 SO 4 12. i A1 2 O 3 5.5 

P 2 O 5 0.8 Fe 2 O 3 9.4 

Fe 2 O 3 4.1 MgO 0.9 

A1 2 O 3 4.0 

CaO 8.44 

K 2 O i. 80 

This coal contained 0.24 per cent of vanadic acid and this constitu- 
ent was no doubt injected into the coal by solutions which percolated 
through the. seam and which may have been derived from igneous 
sources. Igneous rocks are the source of most of such rare constit- 
uents in coal. 

1 Mourlot, A., Analyse de la houille vanadifere. Compt. Rend., Vol. 117, pp. 546- 
548, 1893. 



The analyzing of coal has long been recognized as the best laboratory 
means of determining its commercial qualities. Much attention, 
therefore, has been paid by chemists, geologists, and mining men, 
to the various methods for obtaining samples and making analyses. 
To be of any real value for purposes of comparison with other coals 
or as a means of determining the commercial qualities of a seam the 
coal analysed must be selected from the mine according to some 
definite scheme. The uninitiated person invariably pays too little 
attention to sampling and he very often picks out the best appearing 
coal, thus deceiving not only his customers but himself regarding the 
quality of the coal which is to be analysed. Too much attention 
cannot be paid to the selection of samples which properly represent 
the average composition of a coal seam or a shipment of coal. 

Sampling for Analysis 

The importance of a standard method. Different companies or 
institutions may have their own methods of sampling, but it is de- 
sirable that some uniform system be adopted for sampling coal in 
all countries in order that the analyses made from the samples may 
be available for comparative purposes. Much care has been taken 
to standardize methods of analysis but much less attention has been 
paid to standardizing methods of sampling. When a sample is 
selected from a seam it should be taken in such a way that it will 
represent the coal which will be mined. If a certain portion of the 
parting is included in mining, this should also be included in the 
sample. A standard of size for the material selected is also of im- 
portance because the manner in which the portions of the seam 
high in ash or low in ash break down on crushing will vary greatly. 
This is owing to the varying character of the material constituting 
bony streaks in the coal. In some places these may be sandy and in 
others argillaceous. An analysis of the finely powdered material 



may differ distinctly from the lumpy portion, and standard crushing 
and screening are therefore essential. The portion of the seam selec- 
ted is a factor of importance because weathered coals differ in com- 
position, heating value, and coking qualities from the unweathered 
coal of the same seam owing to the effects of oxidation. The nature 
of the roof and floor of the seam has an important bearing on the 
probable weathered condition and in many places on the sulphur 
content. Care should be taken, therefore, to observe faulted zones 
and other disturbed areas. Examples are known where the coal 
near the outcrop is higher in sulphur than that some distance under- 
ground owing to the fact that, where the roof is fractured as a result 
of weathering, sulphur compounds have been carried into the coal 
from overlying pyrite-bearing rocks. The writer knows of one case 
where the decision to purchase an important property on which the 
coal was regarded as a high-sulphur type was based entirely on the 
consideration of this phenomenon and the deal turned out very suc- 
cessfully. In some mines there is much more sulphur in the "rolls" 
under the seam than in the adjacent rocks and if water works through 
fractures in these rolls the sulphur content may be increased in the 
coal adjacent to them. 

After the coal is obtained from the mine, car, or stock pile, care 
should be taken to see that if it is not analysed at once it is kept in 
air-tight receptacles in order that it may not lose or gain moisture, 
lose gas or become oxidized. It is well known that coals lose a large 
amount of methane on exposure to the atmosphere and take up oxy- 
gen rapidly, especially just after removal from the seam, unless they 
are carefully sealed. The altitude at which a sample is exposed to 
the air also has a bearing on its composition since a marked change 
in barometric conditions will affect the rate of evaporation of moisture 
and the escape of gases. 

United States Bureau of Mines and Geological Survey mine samp- 
ling methods. In proceeding to sample a mine it is well to procure 
a map if possible, so that the location where each sample is taken 
may be properly fixed. The number of samples to be taken will 
vary a great deal with the uniformity of the coal in a seam but about 
four samples for a daily production of 200 tons or less, with an extra 
sample for each additional 200 tons mined per diem, is considered 


In taking the sample the United States Geological Survey and the 
Bureau of Mines 1 recommend that a space 5 feet in width be cleared 
of dirt and powder from top to bottom of the seam. Down the 
center of this cleared space a zone i foot wide is cut to a depth of at 
least i inch, in order to get perfectly clean coal behind that removed. 
A cut is then made up the center of this zone to a depth of 2 inches 
and a width of 6 inches or, if the coal be soft, to a depth of 3 inches 
and a width of 4 inches. There should thus be obtained not less 
than 5 to 6 pounds of coal for each foot thickness of the seam and 
this should include, as nearly as possible, all bony coal retained in 
mining operations, and it should exclude all partings discarded in 
mining. It is suggested that in most places partings over f inch 
thick, and sulphur balls, or other impurities, more than 2 inches in 
maximum diameter and -| inch thick be omitted from the sample. 

The sample taken as described above is collected on a collecting 
cloth and then screened. The lumps are broken in a mortar and all 
passed through a ^-inch or f-inch screen. The sample is thoroughly 
mixed with the coarser materials evenly distributed. It is then 
quartered and after remixing, it is requartered, if it be still too large 
for convenient handling. The mixing complete, the sample is placed 
in a can, the top screwed on and sealed with adhesive tape. The 
can is carefully labeled with the name of the collector, the location, 
the date, and all other information which might be of service when 
the analysis is prepared. The government bureaus have prepared 
very elaborate blank forms, which are filled out and shipped with 
the cans. 

Equipment for mine sampling. As equipment for the special 
work of sampling, the following materials and tools have been sug- 
gested: A portable mortar with sides 5 inches high and having a 
capacity of 500 cubic inches; a pestle consisting of a steel head, 
i inch thick and 3 to 4 inches long; a good spring balance of 50 pounds 
capacity graduated to ^ pound; a galvanized iron wire screen of 
f-inch mesh and provided with a wooden frame; a galvanized sheet- 

1 Holmes, J. A., The sampling of coal in the mine. U. S. Bur. of Mines Tech. Paper 
I, 191 1 ; Campbell, M. R., The commercial value of coal-mine sampling. Trans. Amer. 
Inst. of Mng. Eng., Vol. 36, p. 341, 1906; The value of coal-mine sampling. Econ. 
Geol. Vol. 2, p. 48, 1907; also Parr, S. W., Chemical study of Illinois coals. Illinois 
Coal Mining Investigations. State Geol. Survey, Bull. 3, 1916. 


iron scoop 8 inches long, 2 inches deep and ii inches wide, but a 
trowel or shingle will serve in place of this; a stiff brush; a 2O-foot 
waterproof measuring tape; a sampling can about 9 inches deep 
by 3 inches in diameter made of No. 27 galvanized iron which is 
crimped and soldered to make it strong and air-tight; adhesive tape; 
a pick; and a shovel. 

Sampling wagon, car, or cargo lots. In sampling wagon-loads, 
carloads, or cargo lots of coal care should be taken to collect a repre- 
sentative sample by choosing shovelfuls from different parts of the 
load or pile and including an average amount of impurities. If the 
coal be in coarse fragments, a larger sample should be collected than 
if it be finely broken. About 1000 pounds should be taken as a gross 
sample for carload or cargo lots and this should be increased to at 
least 1500 pounds if the coal contains much impurity in coarse frag- 
ments. It has been found that the analysis of a large gross sample 
comes closer to the average for the lot than a small one, up to a certain 
limit, above which there is no advantage in increasing the size of 
the gross sample. 1 

The looo-pound sample may be crushed so as to pass a i-inch 
screen. It is then mixed, halved, by quartering method, and passed 
through a f-inch screen. This process is continued until a 3o-pound 
sample is obtained which will pass a T \-inch screen. After thorough 
mixing and quartering a sample weighing 5 pounds is taken for an- 

From the tests of various coals by the United States Geological 
Survey and Bureau of Mines it has been found that certain differences 
exist between the analyses of mine samples and carload lots of the 
same coal. These differences are due chiefly to oxidation and to 
the changes in the moisture and gas content while exposed to the 
atmosphere during transportation. The following statements apply 
in most cases. In lignite and lignitic coals the moisture content is 
greater in the car sample than in that taken in the mine and the de- 
crease in calorific value may amount to 1.3 per cent in the moisture- 
free and ash-free coal. If bituminous coals have a moisture content 

1 Pope, G. S., Methods of sampling delivered coal. U. S. Bur. of Mines, Bulls. 63, 
1913 and 116, 1916; Bailey, E. G., Accuracy in sampling coal. Jour. Ind. Eng. Chem., 
Vol. i, p. 1612, 1909; also Parr, S. W., Purchase and sale of Illinois coal on specification. 
111. State Geol. Survey, Bull. 29, 1914. (Methods of Sampling.) 


of over 5 per cent in mine samples they usually lose moisture in tran- 
sit but they also lose calorific value from 0.3 to 0.8 per cent. Those 
with less than 5 per cent usually show a gain in moisture up to about 
1.5 per cent and the change in calorific value amounts to a very small 
decrease. 1 

Standard method of sampling. The Joint Committee of the 
American Society for Testing Materials and the American Chemical 
Society 2 suggests the following methods for sampling and the method 
described in the final report of the Committee will hereafter be known 
in this work as the standard method of sampling and analyzing coal. 
It is insisted that the method outlined should be used in obtaining 
a sample whether it is taken from a i-ton lot or from a lot containing 
hundreds of tons. Also if this method is adopted in a contract the 
following provisions shall be agreed upon (i) Place sampling is done, 
(2) Approximate size of sample required when standard conditions 
do not apply, (3) The number of samples to be taken or the amount 
of coal to be represented by each sample when the standard con- 
ditions (i.e. those outlined below) do not apply. 

For the determination of all constituents except that of total 
moisture the following regulations are observed (i) The coal is sampled 
as it is loaded into or unloaded from conveyances or bins. If the 
coal is crushed as received samples may be taken after the crushing. 
Samples from the surfaces of piles are not reliable. (2) For taking 
samples a shovel or specially designed tool capable of taking equal 
portions of the coal shall be used. For slack or small sizes of an- 
thracite increments as small as 5 to 10 pounds may be taken but for 
run-of-mine or lump coal 10 to 30 pounds may be taken. (3) The 
gross sample shall be not less than 1000 pounds and the increments 
shall be so regularly and systematically collected that the entire 
quantity of coal shall be properly represented in the sample. If 
the fragments are small, not exceeding f inch in size a sample of 500 
pounds is sufficient. If there is an unusual amount of slate or other 
impurities or if the fragments are unusually large 1 500 pounds should 

1 Campbell, M. R., Op. cit. Also Fieldner, A. C., Notes on the sampling and analysis 
of coal. U. S. Bur. of Mines, Tech. Paper 76, 1914. For detailed descriptions of analyses 
see: Methods of analyzing coal and coke, by F. M. Stanton and A. C. Fieldner, U. S. 
Bur. of Mines, Tech. Paper 8, 1913. 

2 American Society for Testing Materials, A. S. T. M. Standards, (D 21-16), 1918, 
P- 673. 


be taken. The following table shows the relation of the sizes of the 
fragments of the coal to the weight of the sample taken. (4) A 


Weight of sample to be divided. 
In pounds 

Largest size of coal and impurities in sample 
before division. In inches 

1000 or more 





T \ or 4-mesh screen 

gross sample shall be taken for each 500 tons or less, or in larger 
tonnages according to agreement. (5) The gross sample shall be 
systematically crushed, mixed and reduced in quantity to convenient 
size for transmittal to the laboratory. The crushing may be done 
by hand or by mechanical means, but loss and addition of foreign 
matter must be prevented. (6) The progressive reduction of the 
sample to the various quantities and sizes mentioned in the table 
above shall be carried out in the following way : (a) The gross sample 
is reduced to 250 pounds by the alternate shovel method observing 
the requirements for relative sizes and weights in Table A, and div- 
iding the coal as follows: The crushed coal is shoveled into a conical 
pile by placing each shovelful on top of the one previously deposited 
and then piling the coal in this pile in a long pile as wide as the shovel 
and 5 to 10 feet long. This long pile is made by spreading each shovel- 
ful out for the full width and length of the pile with alternate shovel- 
fuls spread from opposite ends of the pile. The pile is flattened from 
time to time. Half of this pile is discarded by beginning at the end 
of the pile and taking shovelfuls side by side and one after the other 
along the side of the pile. These alternate shovelfuls are placed in 
two different piles and the operation continued until the long pile 
is completely encompassed and practically all the coal divided be- 
tween the two piles, (b) The sample now reduced to about 250 
pounds is quartered, observing the relations outlined in Table A. 
Quantities of 125 to 250 pounds are coned and re-coned while smaller 
samples are placed on a cloth about 6 by 8 feet and mixed by raising 
first one end and then the other so as to roll the coal back and forth. 


By gathering the four corners of the cloth a conical pile is formed and 
then quartered by first flattening down the apex uniformly and care- 
fully and then dividing the pile into quarters so that the dividing 
lines intersect at a point beneath the apex of the original cone. The 
alternate quarters are discarded and the process described above is 
repeated until a sample of about 30 pounds is secured, (c) The 
3o-pound sample is crushed to T \ inch or 4-mesh size, mixed, flattened 
and quartered. The laboratory samples shall include all of one of 
the quarters or all of two opposite quarters if required and it is im- 
mediately placed in a container designed for this purpose and sealed. 
For the total moisture determination a special sample of about 
100 pounds weight is made up by placing in a waterproof receptacle 
equal parts of freshly taken increments of the standard gross sample. 
This sample shall be rapidly crushed and reduced mechanically or by 
hand to about 5 pounds. This smaller sample is at once sealed air- 
tight in a container and sent immediately to the laboratory. The 
standard gross sample shall not be used in place of this special moisture 
sample unless equally representative results can be obtained from it. 

Preparation of Laboratory Samples by Standard Method 1 
Apparatus. (a) Jaw crusher for crushing coarse samples to pass 
a 4-mesh sieve, (b) Roll crusher or coffee-mill type of grinder for 
reducing samples to 2o-mesh. This mill should be entirely enclosed 
and have an enclosed hopper capable of holding 10 pounds of coal. 
(c) Abbe Ball Mill, Planetary Disk Crusher, Chrome-steel bucking 
board or any satisfactory form of pulverizer for reducing the 2o-mesh 
material to 6o-mesh. For the ball mill the porcelain jars should be 
approximately 9 inches in diameter and 10 inches high. The flint 
pebbles should be smooth and well-rounded, (d) Large Riffle sam- 
pler with -j- or | -inch divisions for reducing the 4-mesh sample to 
10 pounds, (e) Small Riffle sampler with J- or f-inch division for 
dividing down the 20-mesh and 6o-mesh material to a laboratory 
sample. (/) Eight-inch, 6o-mesh sieve with cover and receiver. 
(g) Galvanized iron pans, 18 by 18 by ij inches deep for air-drying 
wet samples, (h) Balance or solution scale for weighing the pans 

1 Final report on coal analysis of the Joint Committee of the American Society for 
Testing Materials and the American Chemical Society. Jour. Ind. and Eng. Chem., 
Vol. 9, No. i, p. 100, 1917. Also American Society for Testing Materials, A. S. T. M. 
Standards (D 22-16), p. 679, 1918. 


and samples. (Required capacity 5 kilograms and sensitive to 0.5 
gram.) (i) Air-drying oven to be used for drying wet samples. 
Not absolutely necessary. (Description in Bull. No. 9, Geol. Survey 
of Ohio, p. 312.) 

Method of sampling. There are two methods, the choice de- 
pending upon whether coal appears wet or dry. 

I. When coal appears dry the first procedure is to reduce the coal 
in the jaw crusher to pass a 4-mesh sieve and reduce the sample to 
10 pounds weight, on the larger riffle sampler. (If crushed to pass 
6-mesh the sample may be reduced to 5 pounds.) The lo-pound 
4-mesh sample is ground in a roll crusher or coffee-mill to 2O-mesh. 
From various parts of this sample, take with a spoon, without sieving, 
a composite 6o-gram total-moisture sample which should be placed 
directly in a rubber-stoppered bottle. 

Thoroughly mix the main portion of the sample, reduce on the 
smaller riffle sampler to about 120 grams and pulverize to 6o-mesh 
by suitable grinder, disregarding loss of moisture. After passing 
6o-mesh the sample is mixed and reduced to 60 grams on the small 
riffle sampler. This final sample is transferred to a 4-oz. rubber- 
stoppered bottle. Moisture is determined on both the 6o-mesh and 
20-mesh samples. The following computation is made: The analysis 
of the 6o-mesh coal which has become partly air-dried during samp- 
ling is computed to the dry-coal basis by dividing each result by i 
minus its content of moisture. The analysis of the coal " as received " 
is computed from the dry-coal analysis by multiplying by i minus the 
total moisture found in the 2o-mesh sample. 

II. When coal appears wet the following method is followed: 
The sample is spread on tared pans, weighed and air-dried at room 
temperature, or in the special drying oven previously mentioned, at 
10 to 15 C. above room temperature. It is weighed again. This 
drying is continued until the loss of weight is not more than o.i per 
cent per hour. The sampling is then completed as under I for dry 

The following computation should be made: Correct the moisture 
found in the 2O-mesh air-dried sample to total moisture "as received" 
according to the following formula. 

loo percentage of air-drying loss vx f r 

X (percentage of moisture in 



2o-mesh coal) + (percentage of air-drying loss) = (total moisture 
"as received")- Compute the analysis to " dry-coal" and "as re- 
ceived" bases as under dry coal, using for the "as received" compu- 
tations the total moisture as found by the formula in place of the 
moisture found in the 20-mesh coal. 

Precautions: Owing to the fact that freshly mined or wet coal 
loses moisture rapidly in the laboratory the sampling operations should 
be carried out as quickly as possible between the time of opening the 
container and the securing of the 2o-mesh sample and the sample 
should be exposed to the air as little as possible. The accuracy of 
the method of preparing the laboratory samples should be frequently 
checked by using duplicate samples and by resampling rejected por- 
tions of samples. The ash in two samples should not differ more than 
the following amounts under the conditions stated: if no carbonates 
are present 0.4 per cent; considerable carbonates and pyrite present 
0.7 per cent; coals with more than 12 per cent ash, containing con- 
siderable carbonate and pyrite i .o per cent. 

English method. In the English government laboratories 1 the 
coal is usually received in the laboratory in tins such as biscuit tins, 
enclosed in wooden boxes, each sample weighing 20 to 30 pounds. 
The sample is passed through a i-inch sieve, mixed thoroughly, 
quartered and one-half returned to the tin. The other half is crushed 
in a small Marsden-Blake crusher and by quartering reduced to about 
i pound. It is then ground in a closely set coffee-mill and divided 
into two parts, one of which is placed in a stoppered bottle and sealed 
for future reference purposes, the other being placed in a similar bottle 
for analysis. The sample taken from the coffee-mill is used for tests 
on moisture and volatile matter but for other estimations a portion 
is ground to pass a 5o-mesh sieve. The moisture is also determined 
in the latter portion but the practice of determining the volatile mat- 
ter in this portion also, has been discontinued as it has been found 
that the results differ very little for the two samples. 

The Proximate Analysis 

The proximate analysis or the determination of moisture, volatile 
matter, fixed carbon, ash and sulphur is the analysis usually made for 
practical purposes since it is much more readily made than the ulti- 
1 Pollard, W., Memoirs of the Geol. Survey, England and Wales, p. 6, 1915. 



mate analysis and it furnishes most of the data necessary for the 
purpose of arriving at the quality of the coal. From it the grouping 
of the elements in the form most closely affecting combustion can be 

Moisture determination by the standard method. Apparatus: 
The apparatus recommended consists of the following articles: (i) 
Moisture oven so constructed as to provide a minimum air space and a 
uniform temperature in all parts of the chamber. The air in the 
oven must be renewed 2 to 4 times every minute and the air must be 
dried by passing it through sulphuric acid. (2) Capsules with covers 
which permit the determination of ash in the same sample. Those 
recommended are the Royal Meissen porcelain capsule No. 2, J inch 
deep and if inches in diameter, or a fused silica capsule of similar 
shape with a well-fitting flat aluminum cover. Glass capsules with 
ground glass caps may also be used and they should be as shallow as 
possible consistent with conven- 
ient handling. 

Method: (i) For determination 
of moisture in the 6o-mesh sample 
the empty capsules are heated 
under the conditions at which the 
coal is to be dried, then covered 
and cooled over concentrated 
sulphuric acid (sp. gr. 1.84) for 
thirty minutes and weighed. Ap- 
proximately i gram of the sample 
is dipped from the bottle with a 
spatula and placed in the capsules 
which are immediately closed and 

The covers are removed and the 
capsules quickly placed in a pre- 
heated oven (at 104 to 110 C.) through which passes a current of 
air dried by concentrated sulphuric acid. The oven is closed at 
once and the specimens are heated for one hour. The oven is then 
opened, the capsules quickly covered, and cooled in a desiccator over 
concentrated sulphuric acid. When cool they are weighed and the 
moisture computed. 

FIG. 7. Moisture oven. (After Stan- 
ton and Fieldner, U. S. Bureau of 
Mines. Tech. Paper 8.) 


(2) For the determination of moisture in the 2o-mesh sample 
5-gram samples are used and they are weighed with an accuracy of 2 
milligrams. They are heated for one and a half hours, otherwise 
the procedure is the same as that described above for the 6o-mesh 

Notes: The permissible differences in duplicate determinations are 
as follows: 

Same analyst 

Different analysts 

Moisture under 5 per cent 
Moisture over 5 per cent 

o . 2 per cent 
o 3 per cent 

0.3 per cent 
o <? per cent 

Determination of ash by the standard method. The ash in coal 
or coke is a non-combustible mixture consisting of silicates of the 
alkalies, calcium, magnesium, iron, and titanium; oxides of iron and 
silicon; carbonates of iron, calcium and magnesium which may 
change to oxides on heating; sulphates, the most common one being 
that of calcium; phosphates; and arsenides. The color of the ash 
is often an indication of its composition, as a pure white ash generally 
indicates the absence of iron and a red ash its presence, although lime 
may counteract the color of the iron and a cream-colored ash may 
indicate the presence of both lime and iron. Effervescence with 
acid shows that carbonates are present. 

Apparatus: (i) A gas or electric muffle furnace. It should have a 
good air circulation and be capable of maintaining a regular tempera- 
ture between 700 and 750 C. (2) Porcelain capsules. Those rec- 
ommended are the Royal Meissen No. 2, J inch deep and if inches 
in diameter. 

Method: The procelain capsules, containing the dried coal from 
the moisture determination, are placed in a cold muffle furnace or on 
the hearth at a low temperature and gradually heated to redness at 
such a rate as to avoid loss of particles of the sample from the rapid 
expulsion of the volatile matter. The ignition is finished when con- 
stant weight is obtained (o.ooi gram) at a temperature between 700 
and 750 C. The capsules are cooled in a desiccator and weighed. 

Notes and precautions: The permissible differences in duplicate 
determinations are as follows: 


Same analyst 

Different analysts 

No carbonates present 

o . 2 per cent 

o . 3 per cent 

Carbonates present 

0.3 " 

o.<> " 

Coal with more than 12 per 
cent ash containing carbon- 
ates and pyrite 

0.5 " 


Before the capsules are placed in the muffle for ignition to constant 
weight the ash should be stirred with a platinum or nichrome wire. 
Stirring once or twice before the first weighing hastens complete 

The result obtained as above is " uncorrected " ash. The mineral 
matter in the ash differs materially from the actual minerals in the 

Other notes and methods: Some analysts have used a platinum 
crucible but this is not suitable for this purpose because, as stated 
by Carnot, if a platinum crucible which contains carbon is heated 
for some time a deposit of carbon and platinum dust may be made 
which affects the weight of the ash. A platinum crucible should 
never be used with coal containing pyrites. A coal high in pyrites 
is liable to cause more trouble if heated too rapidly than one without 
this mineral. 

For the rapid determination of ash in coal, in the field, Lesher has 
designed an apparatus for the use of the geologists of the United 
States Geological Survey. By means of it the ash can usually be 
determined within 2 per cent of the figures obtained by laboratory 
methods. 1 

There are often considerable errors in the result obtained in the 
analyses of ash owing to the fact that the carbonates may change 
to oxides or to sulphates, depending upon certain conditions. If a 
carbonate changes to an oxide during combustion the carbon dioxide 
driven off escapes and is lost to the ash while its carbon is computed 
with the carbon, making it too high. This carbon is not in a com- 
bustible form and therefore does not add to the value of the coal. 
It will be seen that the oxygen is also affected by the error. Although 
these errors in the determination of ash, carbon and oxygen, are not 

1 Lesher, C. E., Field apparatus for determining ash in coal. U. S. Geol. Survey, 
Bull. 62I-A, 1915. 


considered in technical operation, where they are large they have an 
important bearing on correct methods of analysis and on the heating 
value of the coal. They have been fully discussed by a number of 
writers and formulae have been suggested for their correction. 1 

After the ash has been obtained from the coal, it may be analyzed 
in much the same way as any other inorganic mixture. 

The following figures show the composition of some typical coal 


Per cent 

Per cent 

SiO 2 

I .O-lS.I 
0.3- 2.9 
o-i- 5-3 

- 2.6 

Included with A1 2 O 3 

45 . 24-50 . 23 
2.76- 8.52 
0.78- 2.88 

A1 2 O 3 

Fe 2 O 3 . . . 



K 2 O 

Na 2 O 

TiO 2 

P 2 O 5 

0.26- 1.85 
0-96- 3.92 

SO 3 

Temperature of fusio 


ii5o-i5oo C. 

I. = Variations in composition shown in 9 analyses of ash from various types 

of coals. Quoted by Fieldner, Op. cit., p. 29. 

II. = Variations in composition shown in 4 analyses quoted by Carnot, Op. cit., 
p. 212. 

The fusibility of the ash of coal is very variable. Like that of clay 
it is lowered by the presence of such constituents as lime, iron, al- 
kalies and magnesia. The temperature of fusibility is determined 
by use of seger cones or the pyrometer. The ash itself may be molded 
into a pyramid and the temperature at which the pyramid bends over 
to its base is considered the point of fusibility. The more readily the 
ash fuses the greater the difficulty arising from clinkers in the fur- 
nace. The formation of clinkers can, however, be controlled to a 
considerable extent by careful firing. 

A list of analyses and the softening temperatures of a large number 
of western coals is as follows. 2 

1 Parr, S. W., Determination of ash. Jour. Ind. and Eng. Chem., Vol. 5, p. 523, 1913. 
Fieldner, A. C., Op. cit., p. 27. Pollard, Op. cit., p. 40. 

2 Selvig, W. A., Lenhart, L. R., and Fieldner, A. C., Temperatures at which ash from 
western coals fuses to a sphere. Coal Age, Vol. 18, No. 14, p. 677, 1920. 


Average for samples tested: 

Alaska 2040-3010 F. Nevada 2190-2480 F. 

California 2220-2340 New Mexico 2000-3000 + 

Idaho 1950-2640 Oregon 2060-2890 

Montana 1930-2790 Utah 2040-2880 

Washington 1870-3000 -f 

Determination of phosphorous in ash by the standard method. I. 

First method: The following method is to cover all cases: To the 
ash from 5 grams of coal in a platinum capsule there is added 10 c.c. 
of HNO 3 and 3 to 5 c.c. of HF. The liquid is evaporated and the 
residue fused with 3 grams of Na 2 CO 3 . If unburned carbon is present 
in the ash 0.2 grams of NaNO 3 is mixed with the carbonate. The 
melt is leached with water and the solution filtered. The residue is 
then ignited, fused with Na 2 CO 3 alone, the melt leached and the 
solution filtered. The filtrates are combined, held in a flask, acidified 
with HNOa and concentrated to a volume of 100 c.c. To this solution 
raised to 85 C. there is added 50 c.c. of molybdate solution and the 
flask is shaken for ten minutes. If the precipitate does not form 
promptly and settle quickly, enough NH 4 NO 3 is added to cause it 
to do so. The precipitate is washed six times or until free from acid, 
with a 2 per cent solution of KNO 3 , then returned to the flask and 
titrated with standard NaOH solution. The alkali solution may be 
made equal to 0.00025 gram phosphorous per cubic centimeter, or 
0.005 P er cent f r a 5- ram sample of coal and is 0.995 f one-fifth 
normal. Or the phosphorous in the precipitate is determined by 
reduction and titration of the molybdenum with permanganate. 

The advantage in the use of HF in the initial attack on the ash 
lies in the removal of silica. Fusion with alkali carbonate is necessary 
for the elimination of titanium, which if present and not removed will 
contaminate the phospho-molybdate and is said to sometimes retard 
its precipitation. 

II. Second method: Where titanium is so low as to offer no ob- 
jection, the ash is decomposed in the same manner as in the first 
method described above, but evaporation is carried only to a volume 
of about 5 c.c. The solution is diluted with water to 30 c.c., boiled 
and filtered. If the washings are turbid they are again passed through 
the filter. 

The residue is ignited in a platinum crucible, fused with a little 



Na 2 CO 3 , and the melt is dissolved in HNO 3 . If the solution is clear it 
is added to the main one but if not clear it is filtered. For the re- 
mainder of the operation this method is the same as the first method. 
The fusing of the residue may be omitted in routine work in a given 
coal if it is certain that it does not contain phosphorous. 

Determination of volatile matter by standard method. Apparatus: 
(i) Platinum crucible with tightly fitting cover and a capacity of 

not less than 10 c.c. nor more 
than 20 c.c. Dimensions to be 
not less than 25 nor more than 
35 mm. in diameter and not 
less than 30 nor more than 35 
mm. in height. (2) A vertical 
electric tube furnace, or a gas 
or electrically heated muffle fur- 
nace regulated to maintain a 
temperature of 950 C. ( 20 
C.) in the crucible as indicated 
by a thermometer in the fur- 
nace (Fig. 8). If the deter- 
mination of volatile matter is 

not an essential feature of the 
specifications under which the 
coal is bought a Meker burner 
may be used. 

Method: In a weighed plat- 
inum crucible of 10 to 20 c.c. 
capacity, closed with a capsule 
cover, i gram of coal is placed. 
The crucible is placed on platin- 
um or nichrome-wire supports in the furnace chamber which must be 
kept at 950 C. ( 20 C.). After the more rapid discharge of 
volatile matter has subsided, as indicated by the dying down of the 
flame, the cover is gently tapped to close the crucible more tightly, and 
thus prevent the admission of air. The crucible is heated just 
seven minutes and then removed from the furnace without dis- 
turbing the lid. As soon as cool it is weighed. The loss of weight 
minus moisture equals the volatile matter. 


\^ Platinnm- 

" Rhodium 

FIG. 8 Electric furnace for deter- 
mination of volatile matter. 


For subbituminous coal, lignite or peat, a modified method is 
employed to avoid mechanical loss resulting from sudden heating of 
these coals high in volatile matter. This consists in playing a burner 
flame on the bottom of the crucible for five minutes thus gradually 
heating it to a high temperature before it is placed in the volatile- 
matter furnace. It is then heated in the furnace for six minutes at 
950 C. as in the regular method. 

Notes and precautions: The permissible differences in duplicate 
determinations are as follows: 

Same analyst 

Different analysts 

Bituminous coals 

0.5 per cent 

i o per cent 


TO " 

20 " 

The cover should fit close enough so that the carbon deposit from 
bituminous coal or lignite does not burn away from the under. side of 
the lid. Temperatures should be carefully regulated to the stand- 
ards outlined. 

Other methods: According to the preliminary report of the Joint 
Committee 1 the method recommended was that in which the crucible 
of 10 c.c. capacity was heated for seven minutes over a Bunsen burner 
with the crucible 8 cm. above the mouth of the burner. The gas 
pressure required was 50 mm. and the flame about 18 cm. in height. 
The burner was to be surrounded with a refractory cylinder to pre- 
vent air currents from disturbing the flame. The specifications for 
the size of the crucible were: 2.4 cm., diameter at the base, 3.4 cm. 
diameter at the top and 4 cm. high. This method is still used where 
a suitable volatile-matter furnace is not available although a Meker 
burner is more reliable. When this type of burner is used the crucible 
is placed 2 cm. above the orifice with a flame 16 to 18 cm. high. A 
No. 3 Meker is the type specified. These methods are not so reliable 
as that with a proper furnace because of the varying conditions which 
it is possible to have. 

Carnofs method: Carnot, a French chemist, 2 suggests using 5 
grams of coal in a platinum or porcelain crucible, the size of which 

1 Jour. Ind. and Eng. Chem. Vol. 5, p. 517, 1913. 

2 Carnot, Adolphe, Traite d'analyse des substances minerales, Vol. I and II, p. 205, 


will depend upon the extent to which the coal is likely to swell. The 
use of platinum should, however, be avoided if the coal contains 
pyrite, and most coals carry some of this mineral although not always 
in a megascopic condition. The crucible is covered with a closely 
fitting lid and placed in a crucible of pottery with blocks of wood 
charcoal surrounding it. The charcoal prevents the entrance of 
oxygen on cooling. The clay crucible is covered with a lid, placed in 
a calcination furnace, and heated for half an hour at a bright heat. 
It is cooled, the small crucible wiped clean and weighed. Carnot 
has also used a muffle furnace and, while he considers the Bunsen 
burner method the simpler, he thinks that the results are more liable 
to variation than those obtained by using a furnace. 

Determination of fixed carbon by standard method. Fixed car- 
bon is always determined by difference as follows: 100 (per- 
centage moisture + percentage ash + percentage volatile matter) 
= fixed carbon. 

Determination of sulphur by the Eschka method. 1 While such 
a method as the calorimeter method may be used for purposes of 
control in such a laboratory as the fuel-inspection laboratory of the 
United States Bureau of Mines no other method is considered quite 
so reliable as the Eschka method although it is not so rapid as some 
of the others. 

Apparatus: (i) Gas or electric muffle furnace, or burners for 
igniting the coal with the Eschka mixture arid for igniting the barium 
sulphate. (2) Porcelain, silica or platinum crucibles or capsules for 
igniting coal with the Eschka mixture. (3) No. i Royal Meissen 
porcelain capsule i inch deep and 2 inches in diameter. This capsule 
presents more surface for oxidation and it is more convenient to 
handle than the ordinary crucible. (4) No. i Royal Berlin porcelain 
crucibles of shallow form and a platinum crucible of similar size 
may be used. (5) No. o or oo porcelain crucibles or platinum, alun- 
dum or silica crucibles of similar size must be used for igniting the 
barium sulphate. 

Solutions and reagents: (i) Barium chloride. Dissolve 100 grams 

of barium chloride in 1000 c.c. of distilled water (2) Saturated 

bromine water. Add an excess of bromine to 1000 c.c. of distilled 

water. (3) Eschka mixture. Thoroughly mix 2 parts ; by weight, 

1 Oesterreichische Zeitschr. XXII, p. in, 1874. 


of light calcined magnesium oxide and i part of anhydrous sodium 
carbonate. Both materials should be as nearly as possible free from 
sulphur. (4) Methyl orange; Dissolve 0.02 gram in 100 c.c. of 
hot distilled water and then filter. (5) Hydrochloric acid. Mix 
500 c.c. of hydrochloric acid (Sp. gr. 1.20) and 500 c.c. of distilled 
water. (6) Normal hydrochloric acid Dilute 80 c.c. of hydro- 
chloric acid (Sp. gr. 1.20) to i liter with distilled water. (7) Sodium 
carbonate. A saturated solution taking approximately 60 grams of 
crystallized or 22 grams of anhydrous sodium carbonate in 100 c.c. 
of distilled water. (8) Sodium hydroxide solution. Dissolve 100 
grams of sodium hydroxide in i liter of distilled water. This solution 
may be used in place of the sodium-carbonate solution. 

Standard Method: Thoroughly mix on glazed paper i gram of coal 
and 3 grams of Eschka mixture. Transfer the mixture to a No. i 
Royal Meissen capsule, a No. i Royal Berlin crucible, or a platinum 
crucible of similar size. Cover with about i gram of Eschka mixture. 
Ignition shall be performed by heating the crucible over an alcohol, 
gasoline, or a natural gas flame or in a gas or electrically heated muffle. 
Artificial gas must not be used owing to its sulphur content, unless 
the crucible is heated in a muffle. When heated over a flame the 
crucible is placed in a slanting position on a triangle over a very 
low flame. This is necessary to avoid rapid expulsion of volatile 
matter which tends to prevent complete absorption of the products 
of combustion of the sulphur. The crucible is heated slowly for 
thirty minutes, the temperature being increased gradually and the 
mixture being stirred after all black particles have disappeared. The 
latter condition indicates the completeness of the operation. 

If the crucible is heated in a muffle, it should be placed in a cold 
muffle and the temperature gradually raised to 87o-975 C. (cherry- 
red heat) in about one hour. This maximum temperature is main- 
tained for about ij hours and the crucible is then allowed to cool in 
the muffle. 

After cooling, the contents are emptied into a 200 c.c. beaker and 
digested with 100 c.c. of hot water for one-half to three-quarters of an 
hour with occasional stirring. The solution is filtered and the residue 
washed by decantation. After several washings insoluble matter is 
transferred to the filter and washed five times, the mixture being 
kept well agitated. The filtrate amounting to about 250 c.c. is 


treated with 10 to 20 c.c. of saturated bromine water which is then 
made slightly acid with hydrochloric acid and boiled to expel the 
liberated bromine. The so ution is then made just neutral to methyl 
orange either with sodium hydroxide or sodium carbonate solution 
and i c.c. of normal hydrochloric acid is then added. It is boiled 
again and 10 c.c. of a 10 per cent-solution of barium chloride (BaCl 2 - 
2H 2 O) is added slowly from a pipette with constant stirring. The 
boiling is continued for fifteen minutes and the solution allowed to 
stand for at least two hours, or better over night, at a temperature 
just below boiling. It is filtered through an ashless filter paper and 
washed with hot distilled water until a silver nitrate solution shows 
no precipitate with a drop of the filtrate. The wet filter containing 
the precipitate of barium sulphate is placed in a weighed platinum, 
porcelain, silica or alundum crucible, free access of air being allowed 
by folding the paper over the precipitate loosely so as to prevent 
spattering. The paper is smoked off gradually and at no time al- 
lowed to burn with flame. After the paper is practically consumed the 
temperature is raised to approximately 925 C. and heated to constant 

The residue of magnesia, etc., after leaching should be dissolved 
in hydrochloric acid and very carefully tested for sulphur. If an 
appreciable amount is found it should be determined quantitatively 
as the amount of sulphur obtained is important. 

Blanks and Corrections: A correction must always be applied 
either (i) by running a blank exactly as described above using the 
same amount of all reagents that were employed in the regular de- 
termination, or more surely (2) by determining a known amount of 
sulphate added to a solution of the reagents after these have been put 
through the prescribed series of operations. If the latter procedure 
is adopted and carried out once a week or whenever a new supply of 
a reagent must be used and for a series of solutions covering the 
range of sulphur content likely to be met with in coals, it is only 
necessary to add to or subtract from the weight of barium sulphate 
obtained from a coal, whatever deficiency or excess may have been 
found in the appropriate " check" in order to obtain a result that is 
more certain to be correct than if a " blank" correction as determined 
by the former procedure is applied. This is due to the fact that the 
solubility error for BaSO 4 for the amounts of sulphur in question and 


the conditions of precipitation prescribed, is probably the largest 
one to be considered. BaSO 4 is soluble in acids and even in pure 
water and the solubility limit is reached almost immediately on 
contact with the solvent. Hence, in the event of using reagents 
of very superior quality or of exercising more than ordinary precautions 
there may be no apparent " blank" because the solubility limit of 
the solution for BaSO4 has not been reached or, at any rate, not 

The Atkinson and sodium-peroxide methods give results similar 
to those obtained by the Eschka method. According to Register if 
5 per cent of nitrogen is present in the gases contained in the bomb 
calorimeter, the sulphur of a coal is almost completely oxidized to 
H 2 SO4 and the washings of the calorimeter may be used for the de- 
termination of sulphur. 

The permissible differences in duplicate determinations are as 
follows : 

Same analyst 

Different analysts 

Sulphur under 

2 per cent 

o 5 per cent 

o 10 per cent 

Sulphur over 2 

per cent 

O.IO " 

o . 20 " 

Sulphur determined by the bomb calorimeter. To determine the 
sulphur content of a coal by means of the bomb calorimeter the 
washings from the calorimeter are collected in a 250 c.c. beaker. 
The solution is titrated with standard ammonia (0.00587 gram per 
c.c.) to make the "acid correction" for the heating value, methyl 
orange being used as an indicator. To this solution is added 5 c.c. 
of dilute hydrochloric acid (1:2) and it is then raised to the boiling 
point before filtering off any insoluble matter. After thorough wash- 
ing, the filtrate is boiled and the sulphur precipitated with barium 
chloride as in the Eschka method. The percentage of sulphur is 
then derived as follows: 

Weight of BaS0 4 X 13. 74 

' TTT 14. i * = percentage of sulphur. 
Weight of sample 

The results obtained by the calorimeter are usually 3 to 8 per 
cent lower than those by the Eschka method. (For a further note 
on this method see discussion under "The bomb calorimeter. " 



The calorimetric method is recommended by Parr 1 who also uses 
it for sulphur in coke. The coke is pulverized and burned in the 
Parr peroxide calorimeter with sodium peroxide and the sulphur 
determined in the washings. 

The Photometric Method with Turbidimeter. There are many 
variations of the photometric method but they can only be used for 
rough determinations. One apparatus which seems to give satis- 
factory results is a modified form of the Jackson candle turbidimeter 
(Fig. 9). This is one type of the turbidimeter which is being adop- 
ted by many analysts for rapid determinations of sulphur in control 
work. The principle of this apparatus is a 
brass stand, in the center of the base of which 
there is a holder for an English standard 
candle. This candle is regulated so that a 
flame 30 to 40 mm. long is maintained. 
Above this candle is a horizontal support with 
a hole in the center. Over this hole a grad- 
uated glass cylinder with flat polished bottom 
is placed in a vertical, opaque cylinder more 
than half the height of the glass vessel. 
Since this apparatus is used mainly for rapid 
water analysis 2 the vessel is graduated so 
that the lines correspond to turbidities pro- 
duced in distilled water by silica when present 
in certain parts per million. A 25-centimeter tube may show tur- 
bidities of 100 to 5000 parts per million of silica and a 75-centimeter 
tube 25 to 5000 parts per million. 

The early designs of this instrument were not very satisfactory for 
the determination of sulphur, but after an extended series of experi- 
ments Muer 3 found that with certain revised tables quite satisfactory 
results could be obtained. A series of experiments by this modified 
method gave results which compare favorably with those obtained 
by the gravimetric method. The method as outlined as is follows: 
The washings from the bomb calorimeter amounting to about 150 c.c. 

1 Parr, S. W., Composition and character of Illinois Coals. 111. State Geol. Survey, 
Bull. 3, p. 55, 1906. 

2 U. S. Geol. Survey, Water supply and irrigation paper No. 651, 1905. 

3 Muer, H. F., The determination of sulphur in coal by means of Jackson's candle 
turbidimeter. Jour. Ind. and Eng. Chem., Vol. 3, p. 553, 1911. 

FIG. 9. Jackson's candle 


are filtered and then titrated with N/io sodium carbonate, using 
methyl orange as indicator. The titrated solution is then made up 
to 200 c.c. The acidity of the solution may be taken as an index 
of the amount of solution to be taken for the sulphur test. For 
anthracite the proportion taken is i to and for soft coals J to T V 
of the whole. This portion of the solution is measured in the turbidi- 
meter tube diluted to near the 100 c.c. mark on the tube. It is shaken, 
acidified with i c.c. of i : i hydrochloric acid and made up to the 
100 c.c. mark. It is mixed thoroughly by shaking. A tablet of 
barium chloride, weighing i gram and having been compressed without 
the use of a binder is placed in the solution. The barium chloride 
in this particular form seems to give the most finely divided precip- 
itate and therefore the best results. After the tablet is placed in 
the tube the latter is closed by a clean rubber stopper and then rolled 
gently until the precipitation of the sulphur is complete. The turbid 
liquid is transferred to a beaker. The candle is lighted, the gradu- 
ated tube is put in place, and enough of the liquid is at once poured 
in to prevent the tube from cracking. The liquid is then gradually 
poured in, being allowed to run down the side of the tube, until the 
flame becomes dim as one looks down the tube. The liquid is then 
added very slowly until the flame just disappears. The depth of the 
liquid in centimeters is noted, the liquid returned to the beaker and 
a new reading made. This process is repeated until a good average 
reading is obtained. Knowing the depth of the liquid in centi- 
meters the weight of sulphur and sulphur trioxide in milligrams may 
be obtained from a table which Muer has prepared. In his experi- 
ments he found that for a depth of less than 2.5 cm. of liquid there 
was a sharp deviation from a straight line curve in which the increase 
in depth in centimeters was inversely proportional to the weight of 
sulphur in milligrams. This variation seems to be due to the lens 
effect of the bottom of the tube and to avoid it the solution should 
be diluted so that the depth will be greater than 2.5 cm. For depths 
above 17.0 cm. there was also a marked variation from the straight 
line and to avoid this it is better to concentrate the solution. For 
all readings between these two limits it was found that the following 
formula is applicable: 


where S is the weight of sulphur in milligrams and C is the depth of 
the liquid in centimeters at the time the flame becomes obscured. 

Methods for determining the proportions of the various forms of 
sulphur in coal. In a recent article Powell and Parr 1 have enumer- 
ated methods for determining the proportions of the various forms 
of sulphur in coal, as follows : For sulphate sulphur the coal is treated 
with hydrochloric acid after fine grinding. A sample of 5 grams is 
treated with 300 c.c. of a 3-per cent solution of the acid, for forty 
hours at 60 C. The solution is filtered and the filtrate analyzed for 
sulphur as in the regular method by precipitation with barium chlo- 
ride (BaCl 2 ). For the pyrite sulphur determination the sulphate 
sulphur is first removed as described above with hydrochloric acid 
and the coal is then treated with nitric acid. A i-gram sample of the 
finely powdered coal is employed and about 80 c.c. of nitric acid 
(i part HNOs sp. gr. 1.42 to 3 parts water, resulting sp. gr. about 
1.12) is used. The solution stands at room temperature for twenty- 
four hours before being filtered. The nitric acid is disposed of by 
evaporating the filtrate to dryness and after taking up with a little 
hydrochloric acid the sulphur is precipitated by barium chloride 
(BaCl 2 ). 

The resinic sulphur is determined by treating the coal with phenol: 
this treatment involves prolonged extraction with this reagent. The 
other form of organic sulphur, known as the humus sulphur, is de- 
termined directly by taking the residue from the nitric acid extraction 
and adding 25 c.c. ammonium hydroxide (sp. gr. 0.90). This mix- 
ture is allowed to stand for several hours; it is then diluted, passed 
through a large filter and the filtrate evaporated to dryness. The 
sulphur may then be determined in the usual manner by fusing the 
residue with sodium peroxide. It is evident that the total organic 
sulphur may be determined by subtracting the sum of the sulphate 
and pyrite sulphur determinations from the total sulphur, or the 
humus sulphur might be determined by difference between total sul- 
phur and the sum of the other three types. 

Sulphur in ash. A determination of sulphur in the ash may be 
made by placing the ash in an evaporating dish, adding hydrochloric 
acid, evaporating to dryness, then taking up with hydrochloric acid 

1 Powell, A. R., and Parr, S. W., Forms in which sulphur occurs in coal. Trans. 
Amer. Inst. Min. Met. Eng., Vol. LXIII. p. 674, 1920. 


and hot water. This solution is 
filtered and, after washing, the sul- 
phur is precipitated as barium sul- 
phate (BaSO 4 ) by adding barium 
chloride (BaCl 2 ). From the result 
obtained the combustible sulphur in 
the coal may be determined by sub- 
tracting the above result from the 
total sulphur. 1 

Ultimate Analysis 

Determination of carbon and hy- 
drogen. The determination of car- 
bon and hydrogen is made with a 
combustion furnace, either gas or 
electric. The gas furnace used is 
usually the Glaser type with twenty- 
five burners. The Fletcher furnace 
is often used in England. The prin- 
ciple involved is the complete oxida- 
tion of the carbon and hydrogen by 
passing the products of combustion 
over red-hot copper oxide. The sul- 
phur is taken up by lead chromate. 

Description of the furnace: The 
apparatus consists of a purifying 
train in duplicate, a combustion tube 
and an absorption train (Fig. 10). 
The purifying train is in duplicate 
so that oxygen may be fed from a 
gas vessel, such as a Linde oxygen 
cylinder, through one set of tubes 
and air through the other. It is 
connected to the combustion tube by 
a three-way tap so that the currents 
may be regulated. The air and oxy- 
gen are first passed through sul- 

1 Pollard. Op. cit., p. 9. 


phuric acid, then through a 30 per cent potassium hydroxide solution, 
then over soda lime and granular calcium chloride in a U-tube. 
Some English analysts use two U-tubes filled with pumice saturated 
with sulphuric acid, the pumice having previously been ignited with 
sulphuric acid to remove chlorides and other impurities, in place of the 
soda lime and calcium chloride tube A small bottle of sulphuric 
acid may be connected in series next to the combustion tube for the 
purpose of indicating the rate at which the gases are being fed to 
the combustion tube. 

The combustion tube should be from 100 to no cm. in length by 
about 21 mm. in external or 12 to 15 mm. internal diameter. It 
should be of hard Jena or similar glass. 

The absorption train consists of a Marchand tube filled with gran- 
ular calcium chloride (CaCl 2 ) for absorption of the water. Instead 
of this material a U-tube filled with pumice saturated with sulphuric 
acid may be used. If the acid be used it is well to fill the tube, allow 
it to stand over night and then drain off the acid just before using. 
Following the Marchand tube there is a Liebig or Geissler bulb filled 
with 30 per cent potash solution to absorb the carbon dioxide given 
off. This solution should be treated with a little potassium perman- 
ganate for the purpose of oxidizing any ferrous iron or nitrates. In 
place of this solution powdered potash is often used. A guard tube 
comes next and is filled with soda lime and granular calcium chloride 
so as to absorb any traces of carbon dioxide and moisture which have 
passed the other tubes. Some analysts use sulphuric acid and pumice 
for this purpose. 

Testing the apparatus: To prepare the apparatus for a determin- 
ation care should be taken to see that all the reagents used are fresh 
and pure. A blank test may be run by passing about a liter of air 
through the train, heated as in a regular test; if there is a change in 
weight in the absorption tubes of less than 0.5 mg. each the apparatus 
is considered ready for use. 

Method of making the determination with furnace: The sample of 
dry coal ground to 50 or 6o-mesh is weighed into a platinum or por- 
celain boat. The weight of the sample used varies with different 
analysts, some considering that a o. 5-gram sample is best while others 
use a o.2-gram sample. The latter is recommended by the analysts 
of the United States Bureau of Mines. The boat containing the 


sample is kept in a weighing tube to exclude moisture while prepar- 
ations are being made for placing it in the combustion tube. 

The combustion tube is filled in different ways by different analysts. 
For example, Pollard leaves a space of 10 cm. at each end of the tube. 
The space is followed by 6-8 cm. of copper-oxide roll; 16-20 cm. 
for the boat; 45 cm. of copper oxide; 8 cm. lead chromate; and 
10 cm. of silver spiral. Stan ton and Fieldner leave the first 30 cm. 
of the tube empty. This space is followed by an asbestos, acid- 
washed and ignited plug, or a roll of copper gauze. Following 
this is 40 cm. filled loosely with copper-oxide wire. The wire is 
separated from 10 cm. of lead chromate by another asbestos plug. 
A third asbestos plug 20 cm. from the end of the tube keeps the 
chromate in place. 

The combustion tube containing the boat in which the coal is spread 
out flat is connected in the train and the train is connected with an 
aspirator which produces a steady suction. The suction may be 
kept constant by using a Mariotte flask. It is easier to keep the 
joints tight if the gases be drawn through the apparatus than if they 
be forced through by pressure. A satisfactory test for the tightness 
of the apparatus is to draw air through the potash bulb at the rate of 
three bubbles per second. The three-way tap is then closed and if 
not more than three bubbles of gas pass the potash bulb per minute 
it is considered satisfactory. 

When the boat is placed in the combustion tube care must be taken 
to have the copper oxide at a bright red heat and the lead chromate 
at a dull red before the coal is heated. Otherwise methane may 
escape combustion. Before the coal is heated a current of oxygen 
is passed. The coal must be heated gradually; otherwise too much 
tarry matter may be driven off in a short space of time to permit 
complete combustion. The heat is increased gradually and the cur- 
rent of oxygen is maintained for about two minutes after the sample 
ceases to glow when it is turned off and about 1200 c.c. of air is drawn 
through the train. 

The absorption bulbs or tubes are disconnected and weighed. 
The hydrogen percentage in a o. 2-gram sample is determined by 
multiplying the increase in weight in the calcium chloride tube by 
55.55 and the carbon percentage by multiplying the increase in 
weight in the potassium hydroxide bulb by 136.36. It is evident that 


the percentage of carbon will vary slightly if there are carbonates in 
the coal and the hydrogen will vary if there are hydrous minerals or 
moisture present. 

The ash in this sample may be weighed and its percentage also 
determined. Duplicates should agree within o.i per cent for hy- 
drogen and 0.2 per cent for carbon. 

A convenient electric furnace of the Heraeus type may be used 
in place of the gas combustion furnace. This furnace as used by 
Stanton and Fieldner 1 consists of three independent heaters. Two 
of these are on wheels and mounted on a track so that they are mov- 
able. The third one is stationary around the tube where the lead 
chromate is located. The stationary heater is not a part of the 
regular Heraeus furnace but it was added by winding an alundum 
tube 12 cm. long with No. 16 nichrome II wire and enclosing it in a 
cylinder packed with magnesia-asbestos. 

The movable heaters have very thin platinum foil, weighing about 
9 grams in all, wound on a porcelain tube of 30 mm. internal diameter. 
The combustion tube is about 21 mm. external diameter and 900 
mm. in length. It consists of Jena glass or fused silica. It is sup- 
ported in an asbestos-lined nickel trough. Each heater has a separate 
rheostat and the current required is about 4.5 amperes with 220 

The purifying train consists of a Tauber s drying apparatus which 
contains sulphuric acid, a 30 per cent potassium hydroxide solution 
of granular soda lime and calcium chloride. The absorption train 
consists of a 5 -inch U-tube containing granular calcium chloride; 
a Vanier potash bulb containing a 30 per cent potassium hydroxide 
solution and granular calcium chloride; a guard tube, containing 
granular calcium chloride and soda lime; and a Mario tte flask for 
preserving a constant pressure. The calcium chloride used in the 
tube should be saturated with carbon dioxide before using by being 
placed in a large drying jar and having the jar filled with carbon 
dioxide. The jar is left over night and dry air is then drawn through 
it to remove the carbon dioxide. The saturated material may then 
be kept in tightly stoppered bottles. 

It is possible with this furnace to so adjust the heaters that the 
tube may be dried carefully, the lead chromate may be kept hot and 

1 Op. cit., p. 22. 


6 7 

the copper oxide may be raised to a red heat before the boat con- 
taining the sample is heated to a high temperature. The boat is 
then heated until all the carbon is burned off as indicated by the fact 
that the residue ceases to glow. The tubes are then weighed and the 
calculation made as in the determination described above with the 
gas combustion furnace. 

In addition to the methods described above Parr 1 has described a 
process for determining total carbon with the improved Parr Calor- 

A description of this calorimeter is as follows: A A (Fig. na), is 
a liter can for water; BB and CC are insulating vessels of indurated 
fiber; D is a cartridge to receive the charge of coal and chemicals. 

Fig. ii. (a) Parr peroxide bomb calorimeter. (V) Bomb enlarged. 

It rests on the pivot F and is made to revolve by means of the pulley P. 
The small turbine wings produce complete circulation of the water. 
The temperature is recorded on the thermometer T. Figure nb is 
an enlargement of the bomb or cartridge which has been improved 
by placing the air chambers around the inner shell. These chambers 
contain air which the sudden rise in temperature expels. The air 

1 Op. cit. 


at first prevents the cooling of the sides of the chamber to such a 
point that the chemical action around the walls is checked and then 
on being expelled it permits the cooler water to come into contact 
with the hot walls of the shell and produce a more rapid transfer 
of heat and consequently greater efficiency. 

Parr used sodium peroxide and the reaction is approximately as 

56 Na 2 O 2 + C 25 Hi 8 O3 = 25 Na 2 CO 3 + iSNaOH + 22Na 2 O. 

Sodium Coal Sodium Sodium Sodium 

peroxide carbonate hydrate oxide 

For such substances as coke, petroleum, and anthracite a more 
vigorous oxidizing medium is used. The most effective is a mixture 
of potassium chlorate and nitrate in proportion of i to 4 and used 
with sodium peroxide in proportion of i to 10. This was used to 
good advantage on the slaty coals. 

Parr devised this method in order that there might be some ready 
means of obtaining the total carbon as this was necessary in his 
classification of coals. He also devised a curve from which can be 
read the percentage of combustible or available hydrogen when the 
carbon content is known. The curve is based on the principle that 
there is a more or less definite relation in the various coals between 
the total carbon, the fixed carbon, and the " available" hydrogen. 
(For a discussion of the subject of available hydrogen in coal, see 
Parr's Classification in Chapter 5.) 

The determination of nitrogen. The method usually employed 
for the determination of nitrogen is the modified Kjeldahl- Gunning 
method. 1 A gram of coal is placed in a 500 c.c. Kjeldahl flask to- 
gether with 30 c.c. of concentrated sulphuric acid, 5 to 8 grams of 
potassium sulphate (K 2 SO4) and 0.6 grams of mercury. Mercury 
oxide may be used instead of mercury, but a gram of the oxide is 
necessary. The solution should be boiled until the coal is all oxi- 

1 Dyer, B., Kjeldahl's method for the determination of nitrogen. Jour. Chem. Soc., 
Vol. 67, pp. 811-817, l8 95- Also, Trescot, T. C., Comparison of the Kjeldahl-Gunning- 
Arnold method with the official Kjeldahl and official Gunning method of determining 
nitrogen. Jour. Ind. Eng. Chem., Vol. 5, pp. 914-915, 1913 and Wedemeyer, K., Ein 
Wort zur Stickstoffbestimmung nach Kjeldahl-Gunning. Chem. Ztg. Jahrg. 22. p. 21, 


dized and the solution has become practically colorless. The boiling 
may require two hours or more, depending upon the nature of the 
coal. The solution is allowed to cool and a little potassium perman- 
ganate (K Mn O 4 ) is added or it may be added without cooling. 
Some analysts add this while the solution is hot, while others cool 
it first. After boiling for an hour, the permanganate is added to- 
gether with more mercury and then boiled again until complete 
oxidation results. 

The solution is cooled and diluted to about 200 c.c. with cold water. 
To this is added 20 to 25 c.c. of potassium sulphide (K 2 S) solution 
(40 grams per liter) to precipitate the mercury. Sodium sulphide 
(Na 2 S) of same strength is sometimes used in place of the potassium 
sulphide. A little zinc is added to prevent bumping and then about 
80 to 100 c.c., or enough to make the solution alkaline, of a 50 per 
cent solution of sodium hydroxide (NaOH). The Kjeldahl flask is 
at once connected with the condenser and the ammonia is distilled 
over into a measured amount (usually 10 c.c.) of standard sulphuric 
acid, to which cochineal indicator is added for titration. The dis- 
tillation is continued until about 200 c.c. has passed over. The 
distillate is then titrated with standard ammonia solution. (In this 
case 20 c.c. NH 4 OH = 10 c.c. H 2 SO4 = 0.05 grams nitrogen.) 

Pollard 1 states that the following modification was used in the 
English Government laboratory with good results, a sharper end- 
point being obtained by this method than in the former practice. 
The duplicates agreed to within 0.05 per cent. To i gram of coal 
30 c.c. of pure, concentrated sulphuric acid containing i gram of 
salicylic acid was added. The vessel was kept cool by being im- 
mersed in water while the acid was added. To this solution 5 grams 
of sodium thiosulphate were carefully added and then 7 grams of 
potassium sulphate, followed by a crystal of copper sulphate. This 
mixture was heated gradually at first and then strongly until complete 
oxidation occurred. It was cooled, and distilled with excess of soda 
and a little sodium sulphide in the usual way, into 25 c.c. of N/io 
sulphuric acid. The excess of soda was determined by adding to the 
solution 10 c.c. of a 10 per cent solution of potassium iodide, the 
liberated iodine being determined in the usual way. Pollard's use 
of copper sulphate is interesting in view of the fact that Fieldner and 

1 Op. cit., p. 9. 


Taylor 1 found that copper sulphate was not as good a catalytic agent 
as mercury. 

The determination of oxygen. A great many different analytical 
methods have been suggested for the determination of oxygen but 
none of them are sufficiently simple or accurate to be generally ac- 
cepted. 2 The scheme almost universally adopted is to obtain oxy- 
gen by difference, the sum of carbon, hydrogen, nitrogen, sulphur, and 
ash being subtracted from 100 per cent. This has one great disad- 
vantage because it throws upon the oxygen the accumulated errors 
in the determination of carbon, hydrogen, nitrogen, sulphur and ash. 
These errors may tend to balance one another to some extent but 
there are many indefinite factors which may affect the result. If the 
coal contains iron pyrite this tends to make the oxygen too low; if 
it contains argillaceous materials, which would naturally carry water 
of composition, the oxygen in the coal will be too high. 3 Carbonates 
from the coal, as already pointed out, will have a bearing on the 
proportions of oxygen and carbon in the coal. This is because there 
is no means, with our present methods, of distinguishing between 
the carbon and oxygen from the coal and that from the carbonates 
unless an analysis of the ash be made and the various constituents 
computed in terms of carbonates, sulphides, etc., an operation which 
cannot be carried out in practice. 

Some of the methods used for the direct determination of oxygen 
in coal are based on the following principles: Baumhauer 4 en- 
deavored to reoxidize the copper reduced in the combustion tube. 
He also employed iodate of silver. Mitscherlich 5 has used at different 
times a current of chlorine which united with hydrogen to form 
hydrochloric acid, leaving the oxygen free or to unite with carbon, 
and mercury dioxide. Since a certain amount of oxygen must be 
supplied in addition to that in the coal in order to produce complete 

1 Fieldner, A. C., and Taylor, C. A., Determination of nitrogen in coal. U. S. Bur. 
of Mines, Tech. Paper 64, p. 22, 1915. 

2 For a good summary of various methods see Carnot, Op. cit., p. 229. 

3 Parr, S. W., An initial coal substance having a constant heating value. 111. State 
Geol. Survey ; Bull. 8, 1907. 

4 Baumhauer, E.H.V., Ueber die Elementaranalyse organische Korper. Zeitschr. 
f. Analyt. Chem., Vol. V, p. 143, 1866. 

8 Mitscherlich, A., Neue Methoden zur Bestimmung der Zusammensetzung organischer 
Verbindungen, Zeitschr. f. Analyt. Chem., Vol. VI, p. 136, 1867. 


combustion it is supplied by the mercury dioxide and its weight can 
be determined. 

Maumene 1 has employed litharge and calcium phosphate and has 
calculated the oxygen supplied by the litharge for combustion of 
the organic material. 

Determination of the Calorific Value 

The calorific value of a coal is the heat developed by the com- 
bustion of a unit weight of the substance. It is usually expressed in 
terms of the calorie or the British thermal unit (B.t.u.). The cal- 
orie is the unit in the metric system and the standard calorie is the 
heat required to raise i gram of water i C. at the point of its greatest 
density (4 C.). It is, however, often stated more conveniently as 
the heat required to raise one gram of water from 15 to 16 C. The 
large calorie is. the same except that a kilogram of water is used in- 
stead of a gram. 

The standard British thermal unit (B.t.u.) which is generally 
employed by English-speaking engineers is the heat required to raise 
i pound of water from 39.1 F. to 40.1 F., this corresponding in the 
English system to the point of greatest density of the water. In 
recent years the unit is often described as the heat required to raise 
i pound of water from 60 to 61 F., or from 62 to 63 F., as this is a 
little more convenient and the latter figures are usually adopted in 
practice. The difference in all these cases is very small. 

To express calories as British thermal units, multiply the number 
of calories by f or 1.8. 

The calorific value is sometimes expressed as the real calorific value 
and sometimes as the industrial calorific value. The real calorific 
value is the result obtained when complete combustion occurs in the 
laboratory in an apparatus such as the calorimeter and the industrial 
calorific value is the value obtained when the coal is burned under a 
boiler. The latter result approaches much more closely that which 
is obtained in industrial operations and it is always lower, owing to 
various losses, than the real value. It is measured as the heat neces- 
sary to vaporize large quantities of water and the weight of the coal 
used in some cases may be 1500 to 2000 kilograms. 

1 Maumene, J., Compt. Rend., Vol. 55, p. 432, 1862. 


The Bomb Calorimeter 

The calorimeter in some form has been in use at least since the 
time of Laplace and Lavoisier and it was practically perfected by 
Berthelot and Vielle, but it was not until Mahler took up the work 
for the Societe d'Encouragement a ITndustrie Nationale in France 
that a satisfactory calorimeter for practical uses was designed. The 
early calorimeters contained a great deal of platinum and this made 

Fig. 12. Emerson fuel calorimeter with diagram of bomb and pressure 
gauge and details of the ignition wiring. 

them very expensive. The Mahler bomb calorimeter was so much 
cheaper and so efficient that this general type, now known under 
many modifications, is almost universally adopted. The calori- 
meters which may be used for standard determinations are the Em- 
erson, Atwater, Davis, Peters, Parr, Mahler and Williams or similar 
types. One of the requirements is an inner surface of platinum, gold, 
porcelain, enamel or other material which is not attacked by products 
of combustion such as sulphuric and nitric acids. 


Determination by calorimeter. To determine the calorific value 
by means of one of these calorimeters of the Mahler type, 1 place i 
gram of 6o-mesh coal on an asbestos mat in the platinum tray. The 
asbestos should be washed and ignited before using. The terminals 
of the firing circuit are connected by about 13 mg. of fine iron wire 
about 105 mm. long by 0.16 mm. in diameter. Platinum wire should 
be used if the bomb is platinum-lined and care must be taken to see 
that the terminals are clean. The wire is pressed down on the coal 
and the tray placed in the bomb. The lid is screwed down tightly 
on the lead gasket. Oxygen is forced into the bomb very slowly 
until the pressure within the bomb reaches 1 8 to 20 atmospheres with 
the needle-point valve closed just tight enough to avoid leakage. 

The brass bucket is placed in the insulating jacket and the bomb, 
full of oxygen, is placed in the brass bucket which contains about 
2000 to 2500 c.c. of distilled water. The quantity of water used 
varies with the type of calorimeter. 

The stirring apparatus is adjusted so that it does not strike the 
bomb or bucket. The thermometer, which is graduated to 0.01 C. or, 
better, to 0.001 C., must not touch any metal parts and its bulb 
should be about 5 cm. from the bottom of the bucket. The terminals 
of the bomb are connected with wires leading to the switch. After 
the stirrer has been in motion until the water is thoroughly mixed the 
first reading of the thermometer is taken by means of a reading 
telescope attached to a ca the tome ter. The stirring is continued 
uniformly during the test and in a covered calorimeter trie temperature 
should never be allowed to rise more than i C. above that of the 
water jacket. 

Taking readings: The time required for the determination may 
be divided into the preliminary period, the combustion period and the 
final period. In the preliminary period five readings are usually 
taken one minute apart until the rate of change per minute is prac- 
tically constant. After the fifth reading is taken a current of 75 
volts is turned on for about one-half second thus starting the com- 
bustion period. The first two readings in this period are taken one- 
half minute apart because of the great change in ratio. The tem- 
perature rises to a maximum and then begins to fall. The readings 

1 Lord, N. W., and others. Analysis of coals. U. S. Bur. of Mines, Bull. 22, Part I, 
p. 17, 1913. Also Stanton and Fieldner, Op. cit., p. 26. 



are made regularly every minute after the first minute and the first 
reading taken after the rate of fall becomes uniform is the last read- 
ing of the combustion period. The readings are continued every 
minute for five or six minutes composing the final period. 

Calculation of the readings: The following plan shows the method 
of calculating the calorimeter readings (weight of sample i.oooo 

Time Readings 
p. m. C. 

23 . 874 o . 0058 rate of 





change per minute 
in preliminary 

. S 8(T) 23.897 + 0.00580 

+ O.OO27 6 

.585 24.160 + 0.00490 

+ o.ooi4 6 



25.430 + o.ooo8 a 

- o.ooo6 6 

26. 280 O.OO2O a 

26.439 0.00250 

26.463 0.0026 
26.466 0.0026 

- 0.00236 
O.OO26 6 

O.OO26 6 


Observed temperature 

change 2 . 566 

Thermometer correction 002 

(Supplied with thermometer) 

Heat loss o . 0066 

Water equivalent 

Total heat developed in cal- 

ories. . . 

Heat developed by combus- 
tion of sample in calories 


.04 (t) 26.463 


0.0066 algebraic sum. 

.05 26.460 

.06 26.458 

.07 26.455 ~ 0.0026, rate of change in final period 

.08 26.454 

.09 26.450 

= 17-9 
= 12.5 

Wire burned = 11.2 mg 

Titer (i c.c. = 5 cal.) 2.5 c.c 

Sulphur (o.oi g. or i per cent = 13 cal.) 0.76 per cent 

Room temperature = 24 C. 

a Computed rate per minute of temperature change at each reading: b Temperature 
correction for heat loss during each interval. 


Let A equal the rate of change during the preliminary period and 
B equal the rate of change during the final period, then A-B will equal 
the change in rate during the combustion period. 

Let T equal the initial temperature of the combustion period and 
/ the final temperature of the combustion period, then T-t equals 
the apparent change in temperature during the combustion period. 

Then - - = the change in rate per degree of temperature change 
J. / 

during the combustion period. 

If the temperature readings during the combustion period be 
represented by t\, /2, ^3, etc., or in a general way by /, then the com- 
puted rate per minute of temperature change at each reading is 
found by the following formula: 

To obtain the temperature correction for heat loss during each 
interval multiply the mean of the computed rate per minute of tem- 
perature change, for any two readings, by the interval in minutes. 
The algebraic sum of these corrections gives the total correction for 
heat loss (e. g. 0.0066 C.). This quantity is added to the ob- 
served temperature change, and this sum multiplied by the weight 
of the water plus the water equivalent of the apparatus gives the 
total heat developed. 

Corrections for various factors: The observed temperature should 
be corrected for errors in the thermometer. The correction for the 
combustion of the iron wire is 1.6 calories per milligram. The cor- 
rection for sulphur burned to sulphuric acid is 1.3 calories per milli- 
gram. The correction for nitrogen to aqueous nitric acid is made 
by titrating the bomb liquor with standard ammonia solution (0.00587 
grams NH 3 per cubic centimeter). This solution is equivalent to 5 
calories per cubic centimeter. 

Analysis of the calorimeter washings: The calorimeter is thor- 
oughly rinsed out after the combustion test is finished and the wash- 
ings are titrated with standard ammonia solution (0.00587 gram per 
cubic centimeter) to make the acid correction. Methyl orange is 
used as an indicator. The nitric acid which is present is developed 
from the nitrogen in the coal and from the air imprisoned in the 
bomb. The solution also derives some acidity from the sulphur in 


the coal. The sulphur is readily precipitated by barium chloride 
(BaCl 2 ) as in the Eschka method already described. Instead of the 
ammonia solution some analysts much prefer Stohman's solution, 
in which sodium carbonate (Na 2 CO 3 ) is used, because of the greater 
regularity of the results obtained with it. One cubic centimeter of 
this solution contains 0.003706 gram sodium carbonate and it is 
equivalent to 0.004406 gram nitric acid. One calorie of heat is 
produced when this acid is formed. Methyl orange is used as indic- 

It is convenient to make the ammonia solution used of such strength 
that i c.c. is equivalent to 0.00483 gram of nitrogen because this 
weight of nitrogen burned to nitrogen pentoxide (N 2 O 5 ), plus water 
generates 5 calories of heat. 

When nitrogen burns to N 2 O 5 -f water 1035 calories of heat per 
gram are produced. 

The ammonia solution is made up according to the following equa- 

HNO 3 + NH 3 = NH 4 NO 3 . 
Since N = 14 and NH 3 = 17, 

14 : 17 = 0.00483 gram : 00587 gram. 

Therefore 0.00587 gram NH 3 is equivalent to 0.00483 gram of nitro- 
gen which when burned to nitric acid generates 5 calories of heat. 
The standard solution contains 5.87 grams of NH 3 per liter. 

The ammonia used must also neutralize the sulphuric acid gener- 
ated in the bomb from the sulphur and the strength of the ammonia 
solution in terms of the sulphur in the form of sulphuric acid is de- 
termined by the following equation: 

2NH 3 + H 2 S0 4 = (NH 4 ) 2 S0 4 

2NH 3 : S = 34 : 32 = 0.00587 gram NH 3 : 0.0055 gram S. 
The heat of combustion of the sulphur when converted into aqueous 
sulphuric acid is 4450 calories per gram of sulphur provided it is 
burned in oxygen at high pressure, as it is in the bomb. Since the 
heat of combustion of the sulphur burned under a boiler in industrial 
operations where it only changes to sulphur dioxide (SO 2 ), is reck- 
oned as 2250 calories per gram of sulphur, a correction must be made, 
and the figure employed is 2200, or the difference between the above 
figures. Now, since i c.c. of the ammonia solution is equivalent to 
0.0055 gram of sulphur, 0.0055 X 2200 = 12.1 calories. This is the 


heat correction to be made on the basis that all the acidity in the 
washings from the bomb is due to the presence of sulphuric acid. 
A correction, however, must be made for the nitric acid as outlined 
above. The difference 12.1 5 = 7.1 calories, and 7.1 -5- 0.0055 
= 1291 calories per gram of sulphur, or practically 13 calories for 
each per cent of sulphur present. 

Standardization of the calorimeter: A number of methods have 
been suggested for the determination of the water-equivalent of the 
calorimeter. One method makes use of the specific heats of the 
various portions of the apparatus. Another is the electric method, 
another the mixing of portions of water having different temperatures, 1 
and still another the employment of different quantities of water 
while generating the same amount of heat in the bomb. None of 
these when considered from all points of view are as satisfactory for 
commercial operations as the method where substances of known 
calorific values are used. The calorific value of these substances is 
determined with elaborate electric apparatus by the Bureau of Stand- 
ards and samples may readily be obtained. The substances mostly 
used are benzoic acid, naphthalene, and sucrose. A weighed portion 
of one of these substances is placed in the bomb and the experiment 
carried out just as for a sample of coal. The weight of the sample 
should be such that its calorific value will be as nearly as possible 
that of a gram of coal. 

Method of calculating the relations between "air-dried" "as received" 
"moisture-free" and "ash-free" samples: The following system is 
adopted in calculating percentages in the "air-dried" sample to those 
in the "as received" sample: 

1 Bownocker, J. A., Lord, N. W., and Somermeier, E. E., Coals of Ohio. Ohio State 
Geol. Survey, Bull. 9, p. 331, 1908. 


"Air-dried" condition 

"As received" condition 
ioo air-drying loss 

Moisture at 105 ^. multiplied oy 

Volatile matter 
Fixed carbon 
Sulphur " " 

Carbon " " 
Nitrogen " " 
Oxygen " 

Calorific value " " 

Calculating percentages in the 
1 ' moisture-free ' ' sample . 

"Air-dried" condition 
Volatile matter multiplied by 

Fixed carbon 


air-drying loss = moisture 
ioo air-drying loss i_*:i.._ 

ioo - air-drying loss 


ioo air-drying loss 


ioo - air-drying loss 


ioo air-drying loss , 


air-drying loss _ , 

ioo - air-drying loss _ 


ioo - air-drying loss _ h 


ioo air-drying loss , 

8 (air-drying loss) 

ioo air-drying loss , .- , 

" air-dried" sample to those in the 

"Moisture-free" condition 
^~ volatile matter 

ioo moisture 


ioo moisture 

ioo moisture 

ioo moisture 

Hydrogen ( 9 moisture) 

ioo moisture 


, . _ , rrr carbon 

ioo moisture 


ioo moisture 


' oxygen 

Uxygen ^ -- moisture,; 
Calorific value " * 

ioo moisture 

ioo moisture 

(i calorie =1.8 B.t.u.) 


To calculate the analyses to an "ash-free" and " moisture-free" 
basis use as denominator 100 (moisture + ash) instead of " 100 
moisture." ~~ 

Calculation of the Calorific Value of Coal from the Analysis 

The formula of Dulong is recognized as the most satisfactory for- 
mula so far devised for determining the calorific value from the an- 
alysis. It has, however, been modified in a number of ways. It 
is usually expressed as: Calorific value in calories per gram = 8080 

C -f- 34,460 ( H J + S 2250, where C, H, O, and S, respectively, 

indicate the weights of the carbon, hydrogen, oxygen, and sulphur. 
This formula is not quite correct in view of the figures 1 lately ob- 
tained for the heating value of carbon, which should be approximately 
8100 C instead of 8080 C, and 34,500 is a better figure to employ than 

To avoid the necessity of analyzing the coal for hydrogen Parr 2 
uses the formula 8080 C + 34,500 "H" + 2250 S in which "H" rep- 
resents the available hydrogen in the coal, or hydrogen not combined 
with oxygen to form water, and it is derived from a curve which is 
based on the principle that the hydrogen is united with some of the 
volatile carbon. He considers that the value for hydrogen so de- 
rived and used in Dulong's formula will produce results practically as 
satisfactory as those obtained from the original formula, and they 
are obtained much more readily. 

The calorific value from the proximate analysis: If the calorific 
value could be calculated from the proximate analysis a great advance 
would be made over Dulong's formula. What appears to be a sat- 
isfactory method for computing the calorific value of certain coals 
from the proximate analysis, has been suggested by Goutal 3 as a 
result of experiments on over 600 specimens of various kinds of coal. 
He used the following formula: 

P = 82 C + a V in which 

P = the number of calories in a gram of fuel, 

C = the percentage weight of fixed carbon, and 

1 Richards, Metallurgical calculations, Part I. 

2 Parr, S. W., Op. cit, p. 64. 

3 Goutal, M., Sur le pouvoir calorifique de la houille. Compt. Rend., Vol. 135, p. 
477, 1902 



V = the percentage weight of the volatile matter; while 

a = a coefficient which varies with the percentage of volatile 

matter, V, in the pure coal. 
a is found from a curve (Fig. 13). This curve is constructed by 























5 10 15 20 25 30 35 

Fig. 13. Goutal's curve for the determination of the calorific value of coal 
from the proximate analysis. 

taking the values for V as the abscissae and the values for a as the 
ordinates. V is found from the formula 

and a was found as a result of a vast number of analyses which were 
made during this investigation. In the anthracites a = 100, a con- 

The values 5, 10, 15, 20, 25, 30, 35, 38, and 40 per cent for volatile 
matter in the pure fuel (V) give the corresponding figures for a as 
follows: 145, 130, 117, 109, 103, 98, 94, 85, and 80 per cent respec- 

For coals with a value for V between 5 and 35 per cent the variation 
between the results given by this method and those given by the 
calorimeter rarely vary more than i per cent. The value may reach 
2 per cent in some anthracites and in weathered coals or lignites, and 
for these the calorimeter method is the only accurate means of de- 
termining their calorific value. 

The following table from Carnot shows how closely the results 
obtained by Goutal's formula correspond to those obtained from 
Dulong's formula and the calorimeter. They are in every case closer 
to the calorimetric figures than are those from Dulong's formula. 





ous MEANS 




From Du- 
long's for- 


Anthracite of Pennsyl- 

Q7 .O 

3 .0 




Anthracite coal of 

Q4. 8 





Anthracite coal of Creu- 

8q 6 

IO 4. 




Semi-fat coal of Angers 
Fat coal of Porter 






Fat coal of Ronchamp. . 
Gas coal of Bethune 
Gas coal of Montram- 


6s 7 


2 A *} 









The various classifications of coal which have been suggested are 
discussed in another chapter. There are, however, certain varieties 
recognized almost universally in science and commerce which should 
be described in detail before a comprehensive description of the less 
familiar classifications can be given. These varieties are not sharply 
separated and they grade into one another, so that in describing 
them the proportions of their constituents must be stated as varying 
within wide limits. Two coals with a certain percentage of fixed 
carbon may have very different calorific properties owing to the fact 
that the moisture or the ash may vary considerably, and consequently 
if one constituent be chosen as a standard the others do not necessarily 
agree. An attempt has been made, therefore, to give the limits of 
variation as well as the average properties of these different varieties 
as they have been recognized by many writers from numerous coun- 
tries. The ideal manner of presenting all the constituents other than 
moisture and ash, would be on a "moisture-free" and " ash-free" 
basis, but since the analyses selected have not been so recorded they 
have not been computed on this basis in the following figures unless 
it be so stated in the text. 

Since it is so generally admitted that all coal has been derived from 
peat in some form and that it has arrived at its present state as the 
result of various geological processes, peat is briefly described with 
the varieties of coal. It is not regarded as a variety of coal, but 
rather as an incipient stage in the formation of that substance. 

Peat (Fr. Tourbe, Ger. Torf). Peat is an accumulation of 
vegetal matter which has suffered varying degrees of disintegration 
and decomposition, and it contains a high percentage of water and 
oxygen. It varies in physical character from a distinctly fibrous and 
woody, light-brown material to a dark-brown and black jelly-like 
substance. There are all gradations from peat to muck in which 


PEAT 83 

mineral matter becomes so abundant as to prevent its free burning. 
Although it may be cut from the bog in blocks peat is seldom suffi- 
ciently compact to make a good fuel without compressing. 

The composition of peat is illustrated by the following figures. 
Water in original samples from different parts of the bog is 62.98 to 
90.12 per cent, usually 80 to 90 per cent. In a large number of 
analyses of dried specimens from various countries the following 
variations and averages in composition are shown: 


Carbon 37 . 15-66 . 55 per cent 

Hydrogen 4 . 08-10 . 39 " 

Oxygen 18. 59-42 .63 " 

Nitrogen o . 77- 3 . 10 " 

Fixed carbon 10.39-33 .91 " 

Volatile matter 43 .38-73 .60 " 

Ash 1.05-32.95 " 

52.83 per cent 

5-97 " 

1-34 " 
23-59 " 
60. 18 " 

9.58 " 

Sulphur is often as low as one-tenth of i per cent and it is usually 
below i per cent, but it may rise higher in pyritiferous types. The 
calorific value varies from 5500 to 10,000 B.t.u. in air-dried samples. 

Fig. 14. Branch of tree altered to lignite but preserving the original 
markings. From the coast of Alaska. (Collected by W. R. Crane.) 

Dopplerite: This is a variety of peat, found chiefly in Styria but 
also occurring elsewhere in Europe, whose composition shows it to 
be highly acid. An analysis by Schrotter shows that it contains 

Carbon 48 . 06 per cent 

Hydrogen 4-98 " 

Oxygen 40 . 07 " 

Nitrogen i . 03 " 

Ash 5.86 " 

It is amorphous and in the fresh state is elastic like rubber. Its 


luster is greasy and its specific gravity is 1.089. It burns with little 
or no flame and emits an odor like peat. 

Lignite and brown coal (Fr. Lignite, Ger. Braunkohle). There 
seems to be no definite record of the first use of the term lignite. 
It is a French word and may possibly have arisen from the term 
Lithanthrax ligneus which, according to Hausmann 1 was used by 
Wallerius 2 for the distinctly woody type of brown coal. It was 
used by Brongniart 3 as early as 1807 and it is generally found in all 
French works since that time. The German word, Braunkohle was 
used in different ways by Karst, 4 Neuss, 5 and Blumenbach 6 about 
the beginning of the nineteenth century. 

In America the terms lignite and brown coal have come to be used 
interchangeably because both the amorphous and the xyloid, or 
woody types may be brown in color and may have similar chemical 
properties and uses. The two types grade into each other so that no 
sharp distinction can be made between them. In recent years, how- 
ever, the United States Geological Survey has decided to adopt the 
term subbituminous coal for the compact, so-called "black lignite" 
and to restrict the term lignite to the lower grade brown coal which is 
usually, but not always more or less woody and on drying splits up 
into slabs. 7 (Plate III, Fig. i.) The distinction is thus made on 
the basis of color. The composition of lignite or brown coal, as these 
terms are used in various countries, is indicated by the following 
figures compiled from numerous analyses of this coal from almost 
all parts of the world : 

Variation Average 

Moisture o . 75-43 . oo per cent 14.42 per cent 

Volatile matter 27 . 00-53 " 4 7^ " 

Fixed carbon 16 . 00-51 .00 " 36 . 37 

Ash 2.60-42.00 ' 9.32 

Sulphur 0.16-9.00 " i .14 " 

Hydrogen . 5 . 14 " 

Carbon 58.14 " 

Nitrogen i . 05 " 

Oxygen 25 . 17 " 

Hausmann, J. F. Ludw., Handbuch der Mineralogie, Vol. i, p. 79, 1813. 
Wallerius, J. G., Systema Mineralogicum, Vol. 2, p. 98, 1775. 
Brongniart, Alexandre, Traite 61ementaire de Mineralogie, Tome 2, 1807. 
Karst, Mineralogische Tabellen 58, 1800. 
Neuss, Min. II, 3, 154. 

Blumenbach, Handbuch Der Naturgeschichte I, 660. 

Campbell, M. R., A practical classification of low-grade coals. Econ. Geology, Vol. 
3, p. 134, 1908. 


Fig. i. North Dakota lignite showing characteristic fracture and xyloid 


Fig. 2. Bituminous coal showing characteristic cubical fracture. 85 


The calorific value of lignite, undried as received from the mine, 
is 5500-7000 B.t.u. moisture-and-ash-free, 10,000-12,000 B.t.u. 
The specific gravity is 0.5 to 1.30. It colors brown a solution of 
potash. Some lignites in France are so high in pyrite that they can 
be used in the manufacture of iron sulphate and alum, and certain 
earthy varieties, known as terre d'ombre or ombre de Cologne, 1 are used 
for coloring matter. 

Dysodile (Houille, or lignite papyracee): This is a laminated lig- 
nite high in siliceous ash. The color is a yellow to greenish-gray, the 
specific gravity 1.14 to 1.25. It burns readily with a bright flame 
and gives off an odor like asafetida. The ash has been found to con- 
tain abundant shells of diatoms. An analysis by Church 2 shows 
the following composition, ash free: 

Sulphur 2.35 per cent 

Hydrogen 10 . 04 " 

Carbon 69 . 01 " 

Nitrogen i . 70 " 

Oxygen 16 . 90 " 

It occurs in Tertiary formations, and is found in limestone in Sicily 
and in lignite in Germany and the Central Plateau of France. 

Subbituminous coal. This term has been officially adopted by 
the United States Geological Survey to include the glossy black coal 
which grades downward in properties from bituminous to lignite but 
which, as a rule, is of a considerably higher grade than the woody or 
ligneous type. It includes the black lignite and since it may be lig- 
neous in texture it can in some cases be distinguished from brown coal 
in the field only by its black color, while it is separated from bituminous 
coal above by its mode of weathering. According to Campbell. 3 
it parts along a surface nearly parallel to the bedding and thus breaks 
up into thin slabs, or it checks irregularly and does not disintegrate 
into cubes after the manner of bituminous coal. (Plate IV, Fig. i.) 
The fracture is sometimes conchoidal. It often has a distinctly 
pitchy luster and is therefore sometimes called Pechkohle (pitch coal) 
by the Germans. Analyses of samples of this variety of coal as it is 

1 Moissan, Traite" de chimie min^rale, Vol. 2, p. 356, 1905. 

2 Church, A. H., Dysodile. Chem. News, Vol. 34, p. 155, 1876. 

3 Op. cit. 


known in the United States show the following variations in per- 
centage composition, 1 

Moisture i 94~4Q . 58 per cent 

Volatile matter 7 50-70.86 " 

Fixed carbon 18 . 00-83 o " 

Ash 2.06-55.40 " 

Sulphur 0.15-8.65 " 

Hydrogen i . 76- 6 . 98 

Carbon 30.68^86.85 

Nitrogen o . 49- 2.13 

Oxygen 2 . 80-52 . 18 

Air-drying loss o . 80-28 . oo 

Calorific value 6205-14,843 B.t.u. 

Good grades of this coal have a calorific value of 8000 to 10,000 B.t.u. 

Bituminous coal (Fr. Houille, 2 Ger. Schwarzkohle 3 ). The term 
bituminous has evidently been handed down from the earliest writers 
on mineralogy because they frequently spoke of the volatile ma- 
terials given off this type of coal on distillation, as bitumen. Wal- 
lerius called this coal Bitumen lapideum. Among some modern 
writers there is a tendency to discard bituminous for the term humic 
since the coal lacks true bitumen in important amounts and contains 
a large percentage of humic acid. 

Bituminous coal burns with a long yellowish flame and gives off 
a suffocating bituminous odor. It is more or less laminated as a rule, 
and the luster of the different layers varies greatly. It may be resin- 
ous, silky, pitchy, or dull and earthy. It soils the fingers when 
handled. The color varies from pitch-black to dark gray. The 
fracture may be irregular and somewhat splintery but it is almost 
always roughly cubical. (Plate III, Fig. 2.) It is, as a rule, 
conchoidal in cannel coal. 

There are several types of bituminous coal. These include Caking 
and Non-caking coal the latter including the Cherry and Splint 
coals of England, Cannel coal and its related types, Torbanite and 

Caking or coking coal: This coal has the property of softening and 
running together into a pasty mass at the point of incipient decom- 

1 Lord, N. W., and others, Analyses of coals in the United States. U. S. Bur. Mines, 
Bull. 22, 1912. 

2 De Lisle, Vol. 2, p. 590, 1783. Hauy, Trait< de mineralogie, Vol. 3, p. 316, 1801. 
8 Hausmann, Op. cit., p. 73. 


position and then at higher temperatures giving off its volatile con- 
stituents as bubbles of gas. There remains a hard, gray, cellular 
mass called coke (Fr. Coke, Ger. Coaks). While there is no chemical 
or simple physical test which will distinguish coking coals in all cases, 
there are some tests which will usually indicate their coking proper- 
ties. White 1 states that practically all coals with H : O ratios of 59 
per cent or over seem to possess the quality of fusion and swelling 
necessary to good coking. Most with ratios down to 55 will make 
coke of some kind, while a few with ratios as low as 50 coke in the 
beehive oven, though very rarely producing a good article. Coals 
changing to anthracite, the weathered coals, and the coals of the 
boghead cannel group show considerable variation from this rule. 
It has been shown, also, that the solubility of coal in aniline may be 
used as an indication of coking properites. Vignon 2 says that the 
coke given by the coal insoluble in aniline is powdery and that of 
the coal soluble in aniline is agglomerated and swollen. 

A simple and, in many cases, a satisfactory test is that known as 
the agate mortar test. Coals which coke, when rubbed with a pestle 
in an agate mortar, cling to the sides of the mortar while the non- 
coking coals do not. 3 

Non-caking or non-coking coal: This coal may resemble the coking 
coal in all outward appearances but in composition it differs in the 
ratio of the hydrogen to the oxygen and it does not cling to the sides 
of an agate mortar when rubbed with the pestle. It burns freely 
without softening and it leaves a powdery mass instead of a strong 
cellular mass. The Cherry coal, so well known in England, is a 
variety of the non-coking coal. It received its name because of its 
fine luster. It is usually velvet-black in color, is brittle and crumbles 
rather readily. Splint coal or, as it is sometimes called, "Slate 
coal," is also an English name for a variety of non-coking coal. It is 
black and as a rule it has a resinous and glistening luster, but often 
it is dull and contrasts with the brilliant luster of the Cherry coal. 
It fractures in two directions, the longitudinal break being curved 
and slaty and the transverse uneven and splintery. 

1 White, David, The effect of oxygen in coal. U. S. Geol. Survey, Bull. 382, 1909. 

2 Vignon, Leo, Sur les dissolvants de la houille. Compt. Rend., Tome 158, pp. 1421- 
1424, 1914. 

3 Pishel, M. A., A practical test for coking coals. Econ. Geology, Vol. 3, pp. 265-275, 


The composition of bituminous coal, as it has been recognized by 
different writers in various countries is as follows: 

Variation Average 

Moisture 0.04-34.33 per cent 2 . 50 per cent 

Volatile matter 8.63-64.31 " 32.00 " 

Fixed carbon 26.49-80.60 55.00 

Ash 0.28-45.00 " 10.00 " 

Sulphur 0.0012-10.5 " 0.80 " 

Hydrogen 1.00-8.80 " 4.80 " 

Carbon 44.00-85.30 " 74.00 " 

Nitrogen 1.00-9.20 " 1.30 " 

Oxygen 0.95-46.90 " 7.00 " 

Calorific value 6840-15,169 B.t.u. 13,200 B.t.u. 

The specific gravity varies from 1.15 to 1.5, with an average of 1.3. 
A good average for the percentage composition and calorific value of 
the bituminous coals collected in the United States between the 
years 1904 and 19 lo 1 is as follows: 

Moisture 2 .00-10.00 per cent 

Volatile matter 25 .00-40.00 " 

Fixed carbon 45 . 00-65 " 

Ash 5.00-12.00 " 

Sulphur 0.50- 2.00 " 

Hydrogen 4 . 50- 6 . oo " 

Carbon 60. 00-80. oo " 

Nitrogen o. 80- 2 . oo " 

Oxygen 7 . 00-20 . oo " 

Calorific value 12,000-14,500 B.t.u. 

Cannel coal. 2 This coal was originally known as candle coal, but 
the term cannel was employed by the earliest mineralogists. Kirwin 3 
describes this coal, along with Kilkenny coal, as dull black in color 
and with conchoidal fracture when broken transversely. It burns 
with a bright lively flame and in some cases it may be kindled by the 
application of a match owing to the large percentage of highly volatile 
constituents which it contains. This property gave rise to the name 
candle coal. A variety of Scotch cannel which produces a marked 
crackling sound has been called parrot coal and Dana 4 mentions a 
variety from South Wales known as horn coal because, on burning, 
it emits an odor as of burning horn. 

1 U. S. Bur. of Mines, Bull. 22. 

2 Ashley, G. H., Cannel coal in the United States, U. S. Geol. Survey, Bull. 659, 1917. 

3 Kirwin, Richard, Elements of mineralogy. P. 215, 1784. 

4 Dana, E. S., A system of mineralogy. 6th ed., p. 1022, 1895. 


Cannel coal is generally described as a non-coking bituminous 
type, but it is just within the boundary of a special group, the mem- 
bers of which are char- 
acterized by a higher 
percentage of volatile 
oils and gases than that 
found in ordinary bitu- 
minous coal. To this 
group Rogers applied 
the term hydrogenous 
or gas coals, 1 while Po- 
tonie 2 considers most 
of them as sapropelic 
types. Cannel un- 
doubtedly consists 
chiefly of the spores of 
plants or canneloid 
and, as a result, differs 
FIG. 15. Photomicrograph of section of cannel markedly from ordin- 

coal consisting almost entirely of flattened spores. coal in the char 

(Photo by E. C. Jeffrey.) " 

acter of the materials 

which compose it. (Fig. 15.) Beginning, therefore, with a different 
type of vegetal matter it is possible to have it pass through the 
stages corresponding to brown and to bituminous coal, still retaining 
its canneloid character. Its average composition is illustrated by 
the following analysis of Kentucky cannel: 

Moisture 2.36 per cent 

Volatile matter 48 . 40 

Fixed carbon 38 . 75 

Ash 10. 49 

Sulphur i . 20 

Hydrogen 6 . 47 

Carbon 71-98 

Nitrogen i . 16 

Oxygen 8 . 70 

Calorific value i3>77 B -t.u. 

The specific gravity varies from 1.2 to 1.3. 

1 Rogers, H. D., Geology of Pennsylvania. Vol. 2, p. 990, 1883. 

2 Potoni6, H. ; Die Enstehung der Steinkohle und der Kaustobiolith iiberhaupt, wie 
des Torfes, der Baunkohle, des Petroleums, u.s.w., 5th ed. 1910. 


Torbanite: This is a variety of the boghead coals and it is named 
from Torbane Hill in Scotland where it has been mined for many 
years. It differs so much from ordinary coal that a prominent law- 
suit was carried through the Scottish courts about the middle of the 
last century to determine whether the mining of the rock was governed 
by the laws controlling mineral or coal deposits. The trial was 
settled in favor of the latter. Like the other bogheads it is charac- 
terized by a very high percentage of volatile constituents including 
illuminating and lubricating oils, paraffin, and large quantities of 
illuminating gases, running from 14,000 to 18,000 cubic feet per ton. 
There is a difference of opinion concerning its origin, some regarding 
it as derived from spores, others from algae, and it is often described 
as a variety of cannel coal. The evidence is strongly in favor of the 
origin from spores rather than from algae. It is closely related to the 
kerosene shales and bituminous schists. Its color is dark brown, its 
surface dull and lusterless. The fracture is irregular to subcon- 
choidal. According to Dana 1 the hardness is 2.25 and the specific 
gravity 1.17 to 1.2. Analyses quoted by the same authority show 
that the composition is approximately as follows, with ash excluded: 

Hydrogen n .48 per cent 

Carbon 81.15 " 

Nitrogen 1.37 ;< 

Oxygen 6 . oo ' 

The ash runs about 20 per cent. It is much higher in hydrogen than 
any ordinary type of coal. 

Byerite: This is a term applied by Mallett 2 to a so-called mineral 
coal, somewhat resembling Torbanite but differing from it in not 
crackling in the fire, in being heavier specific gravity 1.323 and 
in melting and intumescing when heated. It gives a large amount 
of gas and tarry oils, about 30 per cent more than English cannel. 
An analysis gave the following results moisture 6.02 per cent; 
volatile matter (gas and tarry oils) 39.95 per cent; fixed residue, 
consisting of coke and ash 54.03 per cent. The coke is a true coke 
but resembles the residue from the distillation of sugar and is too 
porous and crumbling to support a furnace burden. It is jet-black 
in color but gives a brown powder which does not color a potash solu- 
tion brown. It is insoluble in carbon bisulphide, ether, or turpentine. 

1 Op. cit., p. 1022. 

2 Mallett, E. J., On Middle Park mineral coal. Am. Jour, of Sci., Vol. 9, p. 146, 1875. 


Semibituminous coal. H. D. Rogers 1 adopted this term for coal 
containing from n to 18 per cent volatile matter and to include what 
has been called dry bituminous coal, as opposed to the group of fat 
coals including caking coal, cherry coal, and splint coal. This type is, 
caking and, non-caking. In spite of the fact that on heating it softens 
and swells into a coke, this coke does not always agglutinate or cohere. 
Although the term is quite widely used in the United States, it seems 
a little unfortunate in view of the fact that the prefix semi conveys the 
idea that it should be a little below bituminous coal in the ascending 
scale from peat to anthracite, and it does not harmonize with the use 
of the term semianthracite. The term superbituminous might have 
been suggested as a more appropriate one. Rogers did not give any 
detailed description of this type of coal but various analyses from 
fields throughout the United States 2 show the varying proportions 
of the following constituents and their average in a good quality of 
this variety of coal: 

Variation Average 

Moisture o . 78- 8 . 99 per cent 2 . oo- 4 . oo per cent 

Volatile matter 7 . 40-23 .84 14 . 00-18 . oo " 

Fixed carbon 57. 11-80.89 70.00-80.00 " 

Ash 1.80-34.15 4.00-8.00 " 

Sulphur o . 44- 6 . 47 o . 50- i . 20 " 

Hydrogen 3 .34-5.17 4.00-5.00 " 

Carbon 51.23-85.54 76.00-82.00 " 

Nitrogen 0.81-1.82 1.00-1.50 " 

Oxygen 3.38-13.70 4.50-6.50 

Calorific value 8386-14,814 B.t.u. 14,000-15,000 B.t.u. 

Semianthracite. This name was adopted by Rogers 3 at the same 
time as the term semibituminous, to cover the coal between 
semibituminous and anthracite. He describes it as possessing 
to a lesser degree the properties characteristic of anthracite. The 
conchoidal fracture is not so well developed as in anthracite, and the 
cleats are more numerous. It crumbles more readily in the fire and 
owing to a greater percentage of volatile matter it kindles more 
readily than anthracite and emits a small amount of yellow flame 
when ignited. Owing to more rapid consumption its efficiency is 
greater than that of anthracite for certain purposes. The volatile 

1 Rogers, H. D., Geology of Pennsylvania, pp. 988-990, 1858. 

2 Analyses of coals in the United States. Bur. of Mines, Bull. 22, 1912. 

3 Op. cit. 


FIG. i. Subbituminous coal showing irregular fracture. 

FIG. 2. Pennsylvania anthracite showing typical conchoidal fracture. 



matter varies from 6 to 1 1 per cent and averages from 7 to 8 per cent. 
The specific gravity is about 1.4. Analyses of this type of coal from 
the United States 1 indicate the following range in composition: 

Moisture i . 96- 7 . 94 per cent 

Volatile matter 6.81-32 .46 

Fixed carbon 58 . 24-82 . oo 

Asn 4.33-14.50 

Sulphur 0.57- 4 . 05 

Hydrogen 3.69- 4.81 

Carbon 72 . 43-80 . oo 

Nitrogen 0.51- 1.45 

Oxygen 5 . 46-10 . 02 

Calorific value 12,460-14,184 B.t.u. 

A proximate analysis of a good grade of this coal is represented by the 
following : 

Moisture i . 94 per cent 

Volatile matter 9 . 95 " 

Fixed carbon 79 . oo " 

Ash 8.80 " 

Sulphur o . 29 " 

Anthracite (Fr. Anthracite, Ger. Glanzkohle) . The first use of 
this term among mineralogists is ascribed to Hauy, 2 although An- 
thrazit may have been employed by Karst 3 ten years earlier. In 
America this coal is frequently known as hard coal, and in Wales as culm 
or stone coal. It is characterized by an iron-black color, and dull to 
brilliant, and even submetallic luster. It does not soil the fingers as 
bituminous coal does. It burns with a short, pale blue flame, emits 
little odor, and does not coke. It commonly breaks with conchoidal 
fracture and thus differs from bituminous coal which usually breaks 
into roughly rectangular fragments (Plate IV, Fig. 2). When very 
small fractures are numerous, the freshly broken surface shows 
small rounded or oval, eyelike forms and it has then been called 
"Bird's-eye" coal. 

The calorific value of anthracite is not as great as that of semi- 
bituminous or high grade bituminous coal because it does not develop 
a high temperature so rapidly. This is owing to the small amount of 
readily combustible material compared with the fixed carbon. It is 

1 Analyses of coals in the United States. Bur. of Mines, Bull. 22, 1912. 

2 Trait6 de mineralogie, Tome III, p. 307, 1807. 

3 Op. cit. 


much sought after for domestic use on account of its lack of soot and 
dust and because of the fact that it burns so much longer than other 
types of coal. 

Anthracite reaches the maximum hardness in coal. It varies from 
2 to 2.5 in Moh's scale. Certain varieties of this coal are capable 
of being cut and polished for ornamental purposes and some of that 
from the Hazleton and Summit Hill districts of Pennsylvania is 
used for this purpose. 

Like that of all other coals, the composition of anthracite as it has 
been mined in different regions varies greatly. The following figures 
show the variation in the analyses from various sources. 

Moisture o . 42- 5 . 61 per cent 

Volatile matter i . 72-10. 75 " 

Fixed carbon 73 . 71-90 . 90 " 

Ash 3.20-30.09 " 

Sulphur o . 17- 2 . 60 " 

Hydrogen i . 89- 5.61 " 

Carbon 78.41-83.89 " 

Nitrogen 0.63- i .57 " 

Oxygen 3 . 80-11 . 54 " 

Calorific value 9230-13,298 B.t.u. 

The specific gravity varies from 1.27 to 1.7. 

The anthracite from Rhode Island is not included in the above list. 
There the coal is in places graphitic, the moisture in the mine sample 
runs as high as 23 per cent and the fixed carbon as low as 49 per cent 
because of very high ash, although the volatile matter is as low as 
2.5 per cent. The ash may be over 30 per cent and the oxygen is 
high except in the dried samples. The nitrogen is usually below 0.5 
per cent. The pecific gravity of the Rhode Island anthracite varies 
from 1.43 to 2.2 1 

The following averages represent the percentage composition of 
good anthracite calculated on a moisture-free and ash-free basis: 

Volatile matter i . 50- 6 . 50 per cent 

Fixed carbon 93 . 00-98 . oo " 

Sulphur o. 50- i . 50 " 

Hydrogen i . 75- 4 . oo " 

Carbon 90.00-94.00 " 

Nitrogen 0.60- i . 25 " 

Oxygen 1.25-2.75 " 

Calorific value 14,500-15,000 B.t.u. 

1 Ashley, G. H., Rhode Island coal. U. S. Geol. Survey, Bull. 615, 1915 

9 6 


The moisture will run from 2.5 to 4 per cent and the ash from 1.5 
to 10 per cent. 

The specific gravity of Pennsylvania anthracite varies from 1.42 
to i. 65,* and of the Welsh anthracite from 1.29 to 1.45, averaging 
about 1.33. 


Table showing the relative percentage composition of wood, peat, and coals. 

Proximate analyses 

Ultimate analyses 

Calorific value 

Kind of Fuel 











i Cc/i 




rt -jg 










<5 o 








Peat a 













Do c 











Lignite a 




7 20 









Do ft 




4 74 






Subbituminous a . . 




3 25 





33 90 




Do b 



4- 74 



17 01 


_ o 

Bituminous a 










i. so 



Do b 










Cannel a 

I 70 







o. 40 


Do b 

J. . /U 








Semibituminous a . 























Semianthracite a . . 























Anthracite a 










i 50 



Do b 










(a) Sample as received. 

(b) Same sample calculated to an ash- and moisture-free basis. 

(c) Sample calculated to a moisture-free basis. 

Peacock coal. Peacock coal is not a distinct variety of coal but 
rather a condition in which either anthracite or bituminous coal may 
be found. It is of considerable interest in some localities because of 
its beauty and abundance. It has received its name from its irides- 
cent colors which resemble those o the peacock in their changing 
lights. This play of colors is similar to that produced by a film of 
oil or of iron oxide on water and is due to the same cause, viz., re- 
fraction and interference of the rays of light in passing through the 
film. This coal is found only in the upper levels of the mine, par- 
1 Stock, 22d Ann. Kept., U. S. Geol. Survey, p. 74, 1900-1901. 

JET 97 

ticularly where the seam and roof slate are much fractured, thus per- 
mitting surface waters to percolate through the fissures in the coal 
and to deposit thin films of iron oxide along the cracks. The film may 
in a few cases be due to traces of crude oil or to sulphur dioxide but 
the main cause is the iron oxide produced by the oxidation of iron 
pyrite near the surface where the oxygen of the air can attack the 
iron sulphide. That it might be due in some rare cases to sulphur 
dioxide gas, which may be set free in the weathering of iron sulphide, 
is suggested by the fact that a burning sulphur match brought close 
to a fragment of coal will often produce a similar iridescent film on the 
surface of the coal. 

Other Combustible Substances Entering Into the Composition 
of Some Coal Seams 

Jet (Fr. Jayet, Ger. Gagath, Greek, Gagates). This is a black, 
rather fibrous to compact substance capable of taking a good polish 
and used in Europe for the manufacture of ornaments, especially 
for those worn in mourning. Formerly an industry on a small scale 
was carried on in France at Sainte-Colombe sur THero, Departement 
de PAude. In Yorkshire, England, a few tons of this material have 
been produced and it is said to have been worth about a shilling a 
pound. The composition of jet is as follows: 1 

Volatile matter 37 . 90 per cent 

Ash 1.70 " 

Carbon 61 .40 " 

Its specific gravity varies from 1.26 to 1.3. 

Jet is generally described as a variety of lignite but Prestwich 2 
speaks of it as a wood converted into a sort of cannel coal. While 
jet may resemble cannel a little in physical character, from our present 
knowledge of cannel it is evident that it cannot resemble it in origin 
since all writers agree that jet is altered wood while cannel is made 
up almost entirely of plant spores. The jet found in the Jurassic 
rocks on the Yorkshire coast of England is believed from structure 
detected in thin sections to have been formed mainly from coniferous 
wood which was allied to the Araucarian pines. It is also considered 
that the trees drifted to their present position since the jet is now 

1 Descloizeaux, A., Manuel de mineralogie, Tome 2, p. 332, 1893. 

2 Prestwich, J., Chemical, physical, stratigraphic geology, p. 142. 

9 8 


found associated with Ammonites and other marine fossils. It oc- 
curs in Asia Minor, Spain and Bohemia as well as in England and 

Natural coke or carbonite. In certain cases where igneous rocks 
have intruded bituminous coal seams the coal has been transformed 
m - into natural coke more or less 

resembling artificial coke but 
usually differing from the latter 
chiefly in the percentage of the 
volatile constituents which it 
contains and in its more com- 
pact character. Taff 1 has sug- 
gested that the greater percentage 
of volatile constituents in the 
natural coke may be due to the 
lack of opportunity for the es- 
cape of these gases and to the 
possible accession of gases to the 
coke from the adjacent coal seam 
after it has cooled. The coke 
shows a typical columnar struc- 
ture varying in degree of perfec- 
tion of the columns (Fig. 16), 
and with the columns normal to 
the surface of contact between 
the igneous rock and the coal 
which has been coked. The ex- 
tent to which the coal is coked 

FIG. 16. Natural coke, or carbonite 

from Hesse (specimen in collection of 

Museum Nationale d'Histoire Naturelle, 


varies greatly. Other things 
being equal, there will be a fairly 
close relation between the thick- 
ness of the coked zone and that 
of the igneous rock, the former varying directly as the latter, but 
no definite rule can be established because cases have been noted 
where almost no observable coking has occurred, while in other cases 
the coal is coked out of all proportion to the size of the intruding 
rock. This condition is well understood when one considers that 

i Taff, J. A., Natural coke in the Wasatch Plateau. Science, N. S., Vol. 23, p. 696, 1906. 


igneous masses entering the coal seams at various times or in differ- 
ent places may vary greatly in temperature and in the amount of 
the hot vapors and gases which they carry. In some cases the 
latter may escape along the bedding planes in the coal deposits 
and conduct the heat some distance from the igneous rock. The 
basic igneous rocks, being more fluid than the acid are often capa- 
ble of intruding themselves into narrow fissures in ways in which 
the more viscous acid rocks cannot. 

In the United States natural coke is common in Colorado, Utah, 
and New Mexico, and it is also abundant in Mexico 1 and Alaska where 
the coals have been extensively intruded by igneous rocks. 

This coke has a regular fracture, is dark gray to iron-black in color, 
and its texture varies from distinctly porous to compact. The luster 
is graphitic to submetallic. It often grades into anthracite which in 
turn passes into the bituminous coal of the seam. In most places it 
makes excellent fuel. The following analyses indicate the per- 
centage composition of the coke, the adjacent coal, and a sample of 
artificial coke. 


Moisture 8.10 0.32 0.57 3.86 13.42 3.28 0.184 

Volatile matter 40.20 20.38 0.39 35.34 5.83 1.64 0.552 20.30 12.20 4.70 

Fixed carbon .45.91 65.90 78.24 53.28 61.50 89.14 88.726 79.70 87.80 95.30 


Sulphur. . 
Carbon. . 

5.76 13.10 20.80 7.52 19.25 9.22 9.993 8.29 9.73 45.96 
0.54 0.64 0.48 0.83 0.533 2.07 i. ii 0.15 

5-48 3-39 
72.66 61.55 

Nitrogen 1.17 0.81 

Oxygen 12.53 14.52 

Air-drying loss . 2 . 60 1 1 . 60 

B.t.u 13,068 9895 

I. Analysis quoted by Taff of coal in seam in Wasatch Plateau. 
II. Natural coke from same seam. 

III. Natural coke from Cokedale Mine, Colorado. U. S. Bur. of Mines, Bull. 22, pt. i, 

p. 69. 

IV. Coal taken i foot from natural coke and z\ feet from a dike. Walsen Mine, 

Colorado. Op. cit. under III, p. 65. 
V. Same locality as IV but close to small dike and coke. 
VI. Artificial coke. 

VII. Artificial coke from the coal of the Connelsville basin, Pa. U. S. Geol. Survey. 
VIII. Coal in the seam removed from the influence of the eruptive. 
IX. Coal 0.3 metres from the igneous rock. 
X. Coal in contact with the eruptive. 

* Analyses by G. von Rath. Contactverhaltnisse Zwischen Kohle und einem basischen 
Eruptivgestein bei Fiinf kirchen : Neues Jahrbuch, I, pp. 274-277, 1880. 

1 Durable, E. T., Natural coke of the Santa Clara Coal-Field, Sonora, Mexico. Trans. 
Am. Inst. Min. Eng., Vol. 29, pp. 546-549, 1899. 


The greater percentage of ash shown in the analyses of the coke 
than in the analyses of the coal from the same seam is often only rela- 
tive, but in some cases it is probable that silica and possibly other 
mineral constituents have been added to the seam by the igneous 
rock in its immediate vicinity. 

FIG. 17- Intrusion of diabase into a coal seam in Alaska, producing 
natural coke. (From a sketch by W. R. Crane.) 

Mineral charcoal or "mother of coal" (Fr. Fusain). In the 
different varieties of coal from lignite to anthracite there are dull 
laminae, lenses, and irregular bands of a black to dark-grey material 
which, on account of its resemblance to charcoal is known as 
" mineral charcoal" or among many of the miners as " mother of 
coal." It may take the form of an iron-gray, almost powdery 
material or it may show the outline of blackened fragments still 
retaining some of the original woody structure and fibers. In 
some cases even the most delicate structures of the leaf are pre- 
served. When cut with a knife it shows much the same consistency 


as wood charcoal but is more sooty and crumbling. It soils 
the fingers. Various explanations have been offered for its origin. 
Daubree 1 in 1844 ascribed it to forest fires started by lightning, burn- 
ing in the swamps where the coal vegetation was laid down. As early 
as 1858 Rogers 2 recognized that it was due to some alteration which 
the vegetation suffered before being buried and this explanation is 
supported by White, 3 who considers that the association of the various 
woody materials, the preservation of the rods, and the delicate 'fern- 
leaf fragments make the forest fire hypothesis untenable. He be- 
lieves that the charcoal has originated as a result of the greater amount 
of decomposition which the vegetation suffered before being buried in 
the bog. On the other hand, Jeffrey 4 still clings to the theory that 
the forest fire was the agent which produced the charcoal. 

A consideration of the actions of forest fires in our modern swamps 
and peat-bogs in the northern portions of the continent, in addition 
to the arguments put forth by White, oppose the forest fire hypothesis. 
It is seldom that the fire leaves the charred materials in such quan- 
tities in proportion to the ash and in such associations in relation to 
the coarse and fine fragments as that in which they must generally 
have been left to produce the deposits now found in coal. It is 
possible that an occasional mass of charcoal resulted from fire but 
improbable that the greater part of the mineral charcoal was produced 
in that way. The best explanation is found in the greater alteration 
of the vegetal matter in parts of the swamp exposed to dry rot where 
the water was low. 

It is evident that carbonite and mineral charcoal have at times 
been confused by some writers. 5 

Analyses show that mineral charcoal usually differs considerably 
in chemical composition from the other portions of the coal seam 
in which it occurs. The following analyses were made from a seam 
in which the charcoal occurs irregularly throughout the mine and is 
there known as " mother of coal." It is not found over 9 inches from 
the bottom of the seam and it always pinches out gradually. The 

1 Daubree, A., Compt. Rend., Vol. 19, p. 126, 1844. 

2 Rogers, H. D., Geology of Pennsylvania, Vol. 2, p. 993, 1858. 

3 White and Thiessen, The origin of coal. U. S. Bur. of Mines, Bull. 38, p. 33, 1913. 

4 Jeffrey, E. C., Jour, of Geology, Vol. 23, p. 218, 1915. 

6 Heinrich, O. J., The Mesozoic formation in Virginia. Trans. Am. Inst. of Min. 
Eng., Vol. 6, pp. 243-244, 1877-78. 


thickness of the charcoal varies from zero to 3 inches. There are 
usually very small bright streaks running through the dark gray, 
which always has a dull luster. The writer is indebted to Mr. H. B. 
Northrup for these analyses. 


Moisture o . 62 per cent o . 23 per cent 

Volatile matter 23 . 05 " 7.11 " 

Fixed carbon 68.86 " 90.99 " 

Ash 7.47 " 1.67 " 

Sulphur 1.19 " o . 23 " 

I. The coal from a seam in the Glenview Mine, Decatur Twp., Clearfield Co., Pa. 
II. Mineral charcoal from the same seam. 

Resinous substances. In addition to the substances described 
there are often found in coals, particularly in the younger and less 
altered coals such as the lignites, large and small masses of amber- 
like substances which represent the resins from various trees growing 
in the coal swamps. 1 To these the name Retinite is often applied in a 
general way. In the Tertiary lignites near Gore, New Zealand, 
masses of this retinite as large as a man's head may be seen and 
in some of the lignite of the western United States resins are found 
in considerable quantities. The following are examples of these 
resins from coal seams in various localities. 2 

Ambrite (C 4 oH 6 6O 5 approx.): A yellowish-gray, subtransparent, 
amorphous resin which breaks with a conchoidal fracture. The 
hardness is 2 and the specific gravity 1.034. The luster is greasy. 
It becomes strongly electrified when subjected to friction. An an- 
alysis by Maly shows: 

Ash o. 19 per cent 

Hydrogen 10 . 58 

Carbon 76.53 

Oxygen 12 . 70 " 

It burns with a yellow smoky flame. It is insoluble in ether, oil of 
turpentine, benzine, chloroform, and dilute acid. 

This resin is described by Hochstetter as occurring in large masses 
in several of the coal fields of New Zealand. It is so much like the 
Kauri gum of the North Island that it is sometimes exported with it. 

1 White, David, Resins in Paleozoic plants and in coals of high rank. U. S. Geol. 
Survey, Prof. Paper 85 E, 1914. 

2 For full description of these and related substances see Dana's System of mineralogy, 
pp. 1002-1014, 1892. Also, Descloizeaux, Manuel de mineralogie, Tome 2, p. 34, 1893. 


Bathmllite: This substance forms dull brown lumps in the Tor- 
banite in Scotland and since it usually occurs as a cavity filling it is 
not known whether it is a resin or a secretion from the Torbanite 
which it resembles in composition although containing less oxygen. 

Duxite: A dark brown, opaque resin from the lignite at Dux, 
Bohemia. Its specific gravity is given as 1.13 and its chemical com- 
position according to Fischer is as follows : 

Moisture 2.72 per cent 

Ash 1.94 " 

Sulphur o . 42 " 

Hydrogen 8 . 14 " 

Carbon 78 . 25 " 

Oxygen 13-19 " 

This is in general similar to Muckite and Walchowite except that 
they are lighter colored. Neudorfite from the coal beds at Neudorf, 
Moravia is very similar in composition. 

Middletonite: This substance, which was named by Johnston 1 
from the Middleton Collieries near Leeds, England, occurs about the 
middle of the main coal in little round masses. These masses are 
seldom larger than a pea and are generally in thin layers less than T \ 
inch in thickness between the layers of coal. It is hard and brittle, 
and its specific gravity is about 1.6. In color it is reddish-brown in 
reflected light and deep red in transmitted light. The luster is resin- 
ous. It blackens on exposure to the air and then cannot readily be 
distinguished from the coal except by its luster. It is unaffected by 
heat at 400 F. and it burns like resin. It is soluble in cold sulphuric 
acid but it is very slightly soluble in alcohol, ether and oil of turpentine. 
An analysis shows the following composition: 

Hydrogen 8 . 007 per cent 

Carbon 86.437 

Oxygen 5 . 563 " 

The formula suggested is (C 2 oHi + H 2 O) which resembles that for 
the hydrate of the oil of turpentine. 

Succinite: This substance is commonly known as amber. It is 
found in considerable quantities on the coast of the Baltic. It occurs 
as irregular masses which have a conchoidal fracture. The hardness 
is about the same as that of anthracite coal, 2-2.5, an d the specific 
gravity is 1.05 to 1.09. The color is yellow or reddish-brown and the 
luster resinous. It is negatively electrified by friction and it softens 

1 Johnston, F. W., The Phil. Mag., Vol. 12, p. 261, 1838. 


at 150 C. Its composition is represented by the following analysis 
by Schrotter: 

Hydrogen 10.22 per cent 

Carbon 78.82 " 

Oxygen 10 . 94 " 

There is usually a little sulphur present in the form of an organic 
compound. Succinite occurs in the bituminous coals of the southern 
part of France and in lignite in various localities. 

Wheelerite: In the Cretaceous lignite beds of New Mexico Loew 1 
found a yellowish resin filling fissures and interstratified with the 
coal. This was named Wheelerite after Lt. G. M. Wheeler. The 
composition is as follows: 

Hydrogen 7.31 per cent 

Carbon 73 . n " 

Oxygen 19 . 58 " 

It is almost entirely dissolved in alcohol or ether and is partially 
soluble in carbon bisulphide. It is soluble also in sulphuric acid, 
producing a brown solution, and with nitric acid it evolves nitrous 
fumes. It melts at 154 C. 

There are numerous other resins similar in many respects to those 
described above. Among these might be mentioned lonite from the 
lignite of lone Valley, California; Koflach from the Tertiary brown 
coals of Styria; Rosthornite, the brown to garnet-red material which 
forms lenticular masses in the coal of Carusthia; Schleretinite from 
the Coal Measures of Wigan, England; Tasmanite from the bituminous 
shales of Tasmania; Trinkerite which forms large amorphous masses 
of a hyacinth-red to chestnut-brown color in the brown coal near 
Albona, Istria. Pyroretinite which resembles the resin of Pinus 
abies is said to occur in masses from the size of a nut to that of a 
man's head in the brown coal near Ausseg, Bohemia. Its specific 
gravity runs from 1.05 to 1.18 and its hardness about 2.5. Rochled- 
erite occurs in large reddish-brown resin-like masses in the brown coal 
of Zweifelsruth in Eger, Bohemia. 

1 Loew, O., On wheelerite, a new fossil resin. Am. Jour. Sci. $d Series, Vol. 7, p. 571, 



There have been in use since the earliest days of the coal trade 
certain names which distinguish different varieties of coal, such as 
anthracite, bituminous, and lignite. These names, or their equiva- 
lents, are in general use almost throughout the world. As the im- 
portance of the coal trade increased, however, it was realized that some 
more definite means of classifying coals according to their composition 
and heating value was desired because the lines of distinction between 
the varieties used in the past were not sufficiently definite for prac- 
tical purposes. 

Frazer's Classification 

One of the first in this country to attempt a definite classification of 
coals on the basis of their composition and heating value was Persifor 
Frazer, Jr. 1 He based his classification on the ratio of the fixed car- 
bon to the volatile combustible matter (C : V.Hc). He states that 
as early as 1844 W. R. Johnson had used the same principle and had 
recognized the ratio of the volatile to fixed combustible matter as a 
logical basis for the classification of coals. After various attempts to 
make the fuel ratio of the different coals fit the descriptions of the 
varieties suggested by H. D. Rogers in 1858, Frazer concluded 
that it is only possible to classify the coals according to their fuel ratio 
within wide limits, and suggests the following divisions: 


Hard-dry anthracite 100-12 

Semianthracite 12-8 

Semibituminous 8-5 

Bituminous 5-0 

The table is deficient for modern use because it does not distinguish 

1 Frazer, Persifor, Jr., Classification of coals. Second Geol. Survey of Pennsylvania, 
Kept. M. M., pp. 128-144, 1879. Also Trans. Am. Inst. Min. Eng., Vol. 6, pp. 430-451, 
1877, and Vol. 36, p. 825, 1906 



subbituminous coal and lignite from bituminous coal and as stated 
by Frazer the ratio limits had to be arbitrarily chosen. The table 
represents, however, a considerable advance over any previous work 
and it sets forth a principle which has become deeply established in 
the coal trade. 

In discussing Frazer's classification, A. S. McCreeth 1 calls attention 
to the fact that the sulphur content of the coal should be taken into 
consideration since it is partly volatilized in coking, and he suggests 
that the portion volatilized should be subtracted from the volatile 
hydrocarbon percentage and added to that of the fixed carbon. 

Classification on basis of Moisture Content 

In 1903 Collier 2 suggested that all coals with a moisture content of 
10 per cent or more should be classed as lignite, and those with less 
than 10 per cent as bituminous, but his classification has proved en- 
tirely unsatisfactory. 

Campbell's Classification 

After extensive studies of coal for the purpose of obtaining a satis- 
factory classification Campbell 3 came to the following conclusions: 
(i) For the higher grades of coal the fuel ratio may be used as a satis- 
factory means of separation but it does not properly separate the 
lignites and bituminous coals. (2) The percentage of fixed carbon 
cannot be used as a satisfactory basis. (3) The calorific value cannot 
be used since many of the bituminous coals are of higher calorific 
value than the best grades of anthracite. It is, however, fairly satis- 
factory for the lignites and bituminous coals. (4) The percentage of 
hydrogen present is valueless as a basis of classification. (5) A classi- 
fication according to the carbon content is satisfactory in a general 
way as there is a fairly regular decrease in the carbon content from that 
of anthracite to that of lignite. The separation between anthracite 
and semibituminous is not marked and there are many exceptions 
to the rule. (6) The carbon-hydrogen ratio is regarded as the most 
satisfactory basis for classification. 

1 McCreeth, A. S., Second Geol. Survey of Pennsylvania, Rept. M. M., p. 157, 1879. 

2 Collier, A. J., Coal resources of the Yukon, Alaska; U. S. Geol. Survey, Bull. 218, 

3 Campbell, M. R., The classification of coals. Am. Inst. of Min. Eng., Vol. 36, p. 324, 
1906. Also, Report on the operation of the coal testing plant. U. S. Geol. Survey, 
Prof. Paper 48, pt. i, 1906. 



He then groups the coals as follows in a tentative classification, 
the ratios of the higher coals being rather indefinite owing to lack of 
ultimate anlyses. 

Carbon-Hydrogen Ratio. 

Group A (Graphite) oo-(?) 

Grouo B 
Group C 
Group D 
Group E 
Group F 
Group G 
Group H 
Group I 
Group J 
Group K 
Group L 

(Semianthracite) 26(?)-23(?) 

(Semibituminous) 23(?)-2o 


(Bituminous) I4 ' 


(Lignite) 11.2- 9.3 

(Peat) 9-3- (?) 

(Wood, Cellulose) 7.2 

Seyler' s Carbon-Hydrogen Classification 

Seyler 1 had previously published the following classification. It is 
based on the hydrogen and carbon in the pure coal. The genera, 
which are arranged vertically, are distinguished by their hydrogen 
content while the species are arranged horizontally and separated 
according to their percentage of carbon. This table is taken from 
Pollard. 2 

1 Seyler, C. A., Chemical classification of coal. Proc. S. Wales Inst. Eng., Vol. 21, 
p. 483 and Vol. 22, p. 112. Also, Colliery Guardian LXXX pp. 17-19, 80-82 and 134-136. 

2 Strahan, A., and Pollard, W., The coals of S. Wales. Mem. Geol. Survey of England 
and Wales, 2d ed., pp. 58-59, 1915. 











Meta. Ortho. 

over 93 . 3 





84-80 80-75 


over 5. 8 
per cent 





per cent 








per cent 









per cent 









under 4 
per cent 










Pollard shows that in the coals analysed from the Welsh field the 
hydrogen-carbon ratio falls fairly satisfactorily into Seyler's classi- 
fication. The carbon-hydrogen ratios given by the U. S. Geological 
Survey do not fit the Welsh anthracites very well as many of them 
have a ratio below 26. 



Grout's Classification based on Carbon Content 

In an article published the year after Campbell's classification 
appeared, Grout 1 criticizes the use of the carbon-hydrogen ratio as 
not being reliable and states that if total carbon in ash- and moisture- 
free coal had been considered the separation between lignite and 
bituminous coal would have been very satisfactory. The chief 
objection made to the carbon-hydrogen ratio is the fact that although 
the hydrogen content of lignite and bituminous coal is not so very 
different, the variation may amount to one-third of the total and thus 
give a large difference in ratio in coals which are not markedly differ- 
ent in other respects; on the other hand, it may throw two coals 
together which are unlike in many important respects. The diffi- 
culty in sampling the low grade coals so that all collectors may be 
able to get the same amount of moisture and therefore the same 
amount of hydrogen in the coal from the same seam is a further ob- 
jection to Campbell's carbon-hydrogen ratio since it is based on too 
variable a factor. 

The following is Grout's classification based on fixed carbon for 
those coals above bituminous, and on fixed carbon and total carbon 
for bituminous coals and those of lower grade. 

Graphite ............................... Fixed carbon over 99 per cent 

Anthracite .............................. Fixed carbon over 93 " 

Semianthracite .......................... Fixed carbon 83-93 " 

Semibituminous ......................... Fixed carbon 73-83 " 


grade ........................... 

Cannel / Fixed carbon 35~48 

....... I Total carbon 76.2- 


Peat and turf / Fixed carbon below 55 

Peat and turf ........................... ( Total carbon bdow 


Parr's Classification 

Parr, 2 in his classification, considers that the term volatile combus- 
tible as it has generally been used is incorrect since it includes some 

1 Grout, F. F., The composition of coals. Econ. Geology, Vol. 2, pp. 225-241, 1907. 

2 Parr, S. W., Illinois Geol. Survey, Bull. 3, 1906. Also, The classification of coals. 
Jour. Am. Chem. Soc., Vol. 28, p. 1425, 1906. 



hydrogen, oxygen, and nitrogen, which are non-combustible. The 
hydrogen present as hydrocarbons is combustible but that combined 
with oxygen in water is not. For example, in a Pocahontas coal with 
18.7 per cent volatile matter 14.5 per cent is combustible hydrocarbons 
and 4.2 per cent is non-combustible hydrogen, oxygen and nitrogen. 
This inert matter should be taken into consideration since it is not 
an asset to the fuel. 

In this classification total carbon (C) and fixed carbon (fc) are 
determined from analysis. The volatile carbon (vc) unassociated 
with hydrogen is obtained by subtracting the percentage of fixed 
carbon from that of total carbon (C fc = vc). The inert volatile 
matter is obtained by subtracting from 100 per cent the sum of total 
carbon + sulphur -f ash + water -f hydrogen, which is not united 
with oxygen in water and is, therefore, free to burn and produce heat. 
To reduce this remainder to a pure fuel basis it is divided by 100 less 
the sum of ash and water. The derived formula on which the fol- 

lowing table is based is vc 


This ratio serves to differentiate 

the coals above bituminous. In the bituminous and lower grades of 
coal the inert volatile matter, which is so much more abundant in 
these coals, is taken into consideration. The classification is as 
follows : 



Inert volatile 


Anthracites proper . 

. . . Below 4 

Anthracitic \ 

Semianthracites . . . 

. . . 4-8 



10 i^ 

A 20-32 



Bituminous proper 

B 20-27 
C 32-44 
D 27-44 


Black lignite 
Brown lignite 

27 up 
27 up 


In taking examples of the various analyses of coals tested by the 
U. S. Geological Survey at the St. Louis plant, Parr 1 shows that they 
readily follow this classification. 

1 U. S. Geol. Survey, Prof. Paper 48, 1906. 


A further formula is suggested for the purpose of determining what 
Parr chooses to call the " gross coal index," or the amount of any coal 
necessary to give 100 pounds of pure fuel. It is found by adding 
together the carbon, sulphur ,and combustible hydrogen, (these three 
constituents being regarded as the only true heat-producing factors 
in the coal) dividing the sum by 100, and 100 by the quotient. Thus 
a Dakota lignite contains: C 52.66 per cent; H 1.83 per cent; and 5 
2. 02 per cent = 56.51. The " gross coal index" for this coal would 

be = 177, or it would require 177 pounds of it to make 100 

pounds of pure fuel. 

Grout's classification resembles this one of Parr's in providing two 
factors for fixing the position of, the coal and it has the advantage of 
being simpler in its application. 

White's Classification based on Carbon Oxygen + Ash 


Another method of classifying coals has been suggested by White 1 
in making determinations of the anti-calorific influence of oxygen. 
As a result of an investigation of all available ultimate analyses it 
was found that ash and oxygen possess almost equal anti-calorific 
values, the former having slightly more than the latter. This was 
found to be true also for moisture-free coal. If two coals alternate 
in the percentages of ash and oxygen while the other constituents 
remain constant the calorific value changes very little. Since carbon 
is the principal calorific element in the fuel it seems appropriate that 
it should be taken as one factor and (oxygen -f ash) as the other in 
determining the calorific value. It is found, therefore, that the 
ratio C : (O + ash) gives a quotient which corresponds very closely 
to the determined calorific value of the coal, not varying more than 
i per cent, as a rule, from an efficiency curve. The sulphur, available 

hydrogen f H j and nitrogen seem to play a small part in con- 
trolling the calorific value of the fuel compared with that of the 
carbon, oxygen, and ash. The hydrogen is the most potent element 
of the three and its influence is shown in the special types of coal 
such as those of the boghead-cannel group. 

1 White, David, The effect of oxygen in coal. U. S. Geol. Survey, Bull. 382, 1909. 


It was found, further, that the relation of the ratio C : (O + ash) 
to the calorific value becomes much less distinct in coals undergoing 
anthracitization and having over 79 per cent fixed carbon in the pure 
fuel, or in those which have been weathered. 

This classification is of great scientific interest in its bearing on the 
calorific value of coals but it has little application in classifying coals 
according to the terms which are familiar in the coal trade. 

There is one strong objection, from a practical standpoint, to all 
the preceding classifications except that of Frazer in the fact that they 
require ultimate anlyses. If possible, the making of ultimate an- 
alyses for classification purposes should be avoided since they are 
always costly. Parr has met this objection to a considerable degree 
by devising an apparatus by means of which the total carbon may be 
readily determined and he has also prepared a curve from which the 
available hydrogen may be obtained. This curve is constructed on 
the principle that the available hydrogen is combined with volatile 
carbon in the form of hydrocarbons and that the percentage of avail- 
able hydrogen, therefore, bears a fairly definite relation to the per- 
centage of volatile carbon. Since the latter is easily obtained by sub- 
tracting the fixed carbon from the total carbon it is not difficult to 
obtain the available hydrogen from the curve. 

Dowling's Split Volatile Ratio Classification 

In order to avoid the necessity of making an ultimate analysis 
Dowling 1 has suggested a classification based on what he calls the 
" split volatile ratio" This system is adopted in order to take into 
account the volatile matter, which is available for the production of 
heat and that portion which is inert and therefore should be placed 
with the moisture as anti-calorific material. The formula used is, 

Fixed carbon -f i volatile combustible TT7 ~ , . ., 

.., . ^ . When the quotients result- 

Moisture + J volatile combustible 

ing from this ratio are compared with those obtained from the car- 
bon-hydrogen ratio they are found to be almost equally satisfactory. 
The various coals may be grouped according to this classification in 
the following order: 

1 Dowling, D. B., Classification of coals by the split volatile ratio. Can. Min. Joui. 
pp. 143-146, April 15, 1908. Also, Can. Geol. Survey, Rept., No. 1035, P- 43 


Anthracite 15 up 

Semianthracite 13-15 

Anthracite coal 10-13 

High carbon bituminous 6-10 

Bituminous 3 . 5-6 

Low carbon bituminous 3-3 . 5 

Lignitic coal 2 . 5-3 

Lignite 1-2-3.5 

This split volatile ratio was adopted in part of the following classi- 
fication of the coals of the world by the Twelfth International Geol- 
ogical Congress 1 and also in a later work by Bowling on the coal 
resources of Canada. 2 

Classification Adopted by the International Geological Congress 


(1) Burns with short, blue flame; gives off 3 to 5 per cent of volatile 
combustible matter. 

._ , . Fixed carbon 
Fuel ratio: . - = 12 and over. 
Volatile matter 

Calorific value, 8000 to 8330 calories, or, 14,500 to 15,000 B.t.u. 
Mean composition, 

Carbon 93 to 95 per cent 

Hydrogen 2 to 4 " 

Oxygen and nitrogen 3 to 5 " 

(2) Burns with slightly luminous, short flame and little smoke; 
does not coke, and yields from 7 to 12 per cent of volatile matter. 

Fuel ratio, 7 to 12. 

Calorific value generally 8300 to 8600 calories, or 15,000 to 15,500 
Mean composition, 

Carbon 90 to 93 per cent 

Hydrogen 4 to 4.5 " 

Oxygen and nitrogen 3 to 5.5 " 


(i) Burns with short, luminous flame and yields 12 to 15 per cent 
volatile matter; does not readily coke. 
Fuel ratio, 4 to 7. 

1 Coal resources of the world. Vol. i, Toronto, Canada, 1913. 

* Coal fields and coal resources of Canada. Can. Geol. Survey, Mem. 59, 1915. 


Calorific value generally 8400 to 8900 calories, or 15,200 to 16,000 
Mean composition, 

Carbon 80 to 90 per cent 

Hydrogen 4 5 to 5 

Oxygen and nitrogen 5 . 5 to 12 " 

(2) Burns with luminous flame and yields from 12 to 26 per cent 
volatile matter; generally cokes. 

Fuel ratio, 1.2 to 7. 

Calorific value 7700 to 8800 calories, or 14,000 to 16,000 B.t.u. 

Mean composition, 

Carbon 75 to 90 per cent 

Hydrogen 4. 5 to 5.5 " 

Oxygen and nitrogen 6 to 15 " 

(3) Burns freely with long flame; withstands weathering but frac- 
tures readily and occasionally has moisture content up to 6 per cent; 
volatile matter up to 35 per cent; makes porous, tender coke. 

Fixed carbon + \ volatile 

! * = 2 . C tO 3 . ^ 

Hygroscopic moisture + J volatile 

Calorific value 6600 to 7800 calories, or 12,000 to 14,000 B.t.u. 

Mean composition, 

Carbon 70 to 80 per cent 

Hydrogen 4-5 to 6 " 

Oxygen and nitrogen 18 to 20 


Burns with long, smoky flame; yields from 30 to 40 per cent vola- 
tile matter on distillation, leaving very porous coke. Fracture 
generally resinous. 

Calorific value 6600 to 8800 calories, or 12,000 to 16,000 B.t.u. 


Contains generally over 6 per cent of moisture; disintegrates on 
drying; streak brown or yellow; cleavage indistinct. 

(i) Moisture in fresh-mined, commercial output, up to 20 per cent. 
Fracture generally conchoidal. 
Drying-cracks irregular, curved lines. 
Color generally lustrous black, occasionally brown. 
Fixed carbon + volatile 

Hygroscopic moisture + \ volatile 

= 1.8 to 2.5 


Calorific value 5500 to 7200 calories, or 10,000 to 13,000 B.t.u. 
Average composition, 

Carbon 60 to 75 per cent 

Hydrogen 6 to 6 . 5 " 

Oxygen and nitrogen 20 to 30 

(2) Moisture in commercial output over 20 per cent. Fracture 
generally earthy and dull. 

Drying-cracks generally separate along bedding planes and often 
show fibrous (woody) structure. 

Color generally brown, sometimes black. 

Calorific value 4000 to 6000 calories, or 7000 to 11,000 B.t.u. 

Average composition, 

Carbon 45 to 65 per cent 

Hydrogen 6 to 6.8 

Oxygen and nitrogen 30 to 45 " 

In the above classification, letters are substituted for names. In 
a general way the classification conforms to the nomenclature used 
in America, as follows: 

AI = Anthracite coal. 

A z = Semianthracite coal. 

Bi Anthracitic coal and high carbon bituminous coal. 

B 2 = Bituminous coal. 

Bz = Low carbon bituminous coal. 

C = Cannel coal. 

DI = Lignitic or subbituminous coal. 

Dz = Lignite. 

Gruner's Classification 

In his classification of French coals Gruner 1 takes into consideration 
the fixed carbon and volatile matter as well as the constituents of the 
ultimate analysis. He also makes use of the ratio of hydrogen to 
(oxygen + nitrogen). No provision is made for lignite, subbitumi- 
nous coal, or cannel. The following table is a slightly abbreviated 
compilation of Gruner's tables. As previously mentioned the term 
"houille" in French corresponds to bituminous coal in America, and 
"charbon" is the general term used for coal. 

1 Gruner, E., and Bousquet, G., Atlas general des houilleres. Deuxieme partie, 
Texte p. 16, 1911. 



Class or type of coal 
and commercial 
name in France 

Proportion oi 
coke in 100 
parts of pure 

Proportion of 
volatile matter 
in loo parts of 
pure coal 

Nature and ap- 
pearance of 

Real calorific 

Industrial cal- 
orific power. 
Water at o 
vaporised at 
112 by i kgm. 
of pure coal 

Per cent 

Per cent 


Kgms. of water 

i. Houilles se- 
ches (dry) 
& longue 
Houilles flam- 



Powdery or 



2. Houilles 
grasses (fat) 
a longue 
Charbons a 



ated and 
very often 



3. Houilles 
grasses (fat) 
dites. Char- 
bons de forge 
et Houilles 



Fused and 
more or less 



4. Houilles 
trasses (fat) 
Charbons a 



Fused, com- 



5. Houilles 
maigres (lean) 
ou anthracit- 
euses char- 
bons demi- 
gras. Char- 
bons quart- 



fused, very 
often powd- 



6. Anthracites. 
maigre (lean) 



often de- 







Oxygen anc 

. + N 

Designation in 
(Ruhr Basin) 

Designation in 

Designation in 

Ratio H 

Per cent 
I. 70-80 

Per cent 




4 and 3 



Splint coal 

2. 80-85 



3 and 2 


gras ou 

Gas coal 

3- 84-89 



2 and i 


Caking coal 

4. 88-91 



Nearly i 


durs ou 

Steam coal 

5- 90-93 
6. 93-95 

4 . 0-2 . o 


Less than 









A number of experiments have shown that the lean (maigre) coals 
are almost insoluble in the ordinary solvents such as aniline while 
there is an increasing proportion of the fuel soluble, in passing from 
the lean to the fat (gras) coals. 

Ashley 's Use Classification 

A classification has recently been suggested by Ashley 1 which is 
intended primarily for the use of the person engaged in the coal 
business and which he designates as a "Use Classification." The 
main factors on which this classification are based are two ratios, 
the first being the ratio of the fixed carbon to volatile matter and moist- 

F c 

ure combined ' and the second the fuel ratio and the 
V.m. + rizU 

fixed-carbon-moisture ratio (F.c.m. ratio). A double ratio is thus 
made use of as in some of the previous classifications described. The 
higher-rank coals are distinguished by their fuel ratio and the lower 
ranks by the ratio of the moisture "as received" to fixed carbon. 
These ratios are chosen because in the higher ranks of coal the moist- 
ure changes little and the volatile matter much in relation to the 
fixed carbon when one rank of coal is changed to another higher in the 
scale by geological processes, while in the lower ranks there is a larger 
proportional change in the moisture than in the volatile matter with 
respect to the fixed carbon. The physical properties are also taken 
into consideration since they depend largely upon the genesis of the 
coal and must therefore be closely related to the chemical properties. 
For example cannel coal differs greatly from ordinary bituminous 
coal because of its different origin. The woody character of low- 
grade coals is also considered. 

A new departure in this classification is the adoption of locality 
names for certain ranks and grades of coal. The coal of a distinctive 
grade from a well-known mining locality takes the name of the lo- 
cality with the name changed so as to end in ite. As examples, 
Pocahontas coal would be known on the market as Pocahontite and 
Hocking Valley coal as Hockingite. In addition to the use of these 
terms for coal from those fields the names might be applied to the 
same grade of coal from other localities, thus adopting the use of 
locality names as they are used in mineralogy. 

1 Ashley, G. H., A use classification of Coal. Trans. Amer. Inst. Min. Met. Eng. 
LXIII, p. 782, 1920. 



The following tables show examples of the application of these 
ratios to the analyses of various typical coals throughout the country. 
The first table shows the ratio of fixed carbon to volatile matter and 
moisture combined, and the second the fuel ratio and fixed-carbon- 
moisture ratio. 


( ~ F ',' 1J 
\V.m. + H 





Anthracite . . 

IO 7 4- 

Saint Clair Co., 111. coal 

o 96 

Bernice coal 

6 8 

Sangamon Co., 111. coal 

o 84 

Brushy Mountain, Va. coal . . . 
Pocahontas coal . . 


7 .7 

Grundy Co., 111. coal 
Sheridan, Wyo. coal 


o 68 

Sewell, New River, coal 


Carney, Wyo. coal 

o 62 

Connellsville coal 

2 .O 

Gillette, Wyo. coal 

o. <c6 

Pittsburgh coal 


Wood Co., Tex. lignite 

O . cjO 

Beaver River, Pa. coal 

I .2 

Houston Co., Tex. lignite 


Gallatin Co., 111. coal 

I .09 

Williston, N. Dak. lignite 


(F.c.m. ratio.) 










Saint Clair Co., 111. . . 

1 .4- 

4 O-6 O 




Sangamon Co., 111. . . 

I .4- 

2 . "? 4 O 

Brushy Mountain, 

r 7 


Grundy Co , 111. 

I 4. 

2 O 2 ^ 

Pocahontas . 

j e- e 

IO+(24 O 

Sheridan, Wyo. 

I 4. 

I 72 O 


2 < 3 C 


Carney, Wyo. 

I 4 

I 4. I 7 


I 85-2 * 

IO-h(2T 5) 

Gillette, Wyo 

I 4- 

I O I 4. 


I .4-1.85 

io-}-(i9 .5) 

Wood Co., Tex 

T 4 

o 85-1 oo 

Beaver River, Pa. 
Gallatin Co., 111... 



6 .0-10.0 

Houston Co., Tex 
Williston, N. Dak.. .. 


o . 65-0 . 85 

0.5 -0.65 

From these tables it is seen that the lignites fall between 0.5 and 
i in the fixed-carbon-moisture ratio, most of the subbituminous 
coals between i and 2 and the bituminous coals between 2 and io+. 
Above this point the fuel ratio is used as a basis of separation. 

From a physical standpoint all coals are first divided into those 
of compact texture and those of woody, fibrous, or earthy texture. 
Those of compact texture are next divided into an anthracite class 
and a bitumite class. The anthracite class has a fuel ratio of 7+ and 


a non-luminous flame, and the bitumite class a fuel ratio of less than 
7 and a luminous flame. The latter class includes the bituminous 
and subbituminous coals. 

The anthracites are further divided into true, hard anthracites with 
conchoidal fracture, high specific gravity and submetallic luster 
and the soft anthracites with semi-cubic fracture and low specific 
gravity such as the so-called anthracite at Bernice, Sullivan Co., 
Pa. The dividing line between these two groups is a fuel ratio of 10. 

The bitumites are divided first into those with a B.t.u. value of 
over 14,300 and those with a value less than that when calculated on 
a coal free of moisture, ash and sulphur. The calculation is made 
from the following formula: 

B.t.u. (ash-, moisture-, B.t.u. (coal as received) 40 S. 

sulphur-free) 100 (moisture + ash + sulphur) 

The higher rank bitumites are divided into the Virginites, or so-called 
smokeless coals, having a fuel ratio between 2.5 and 7, and those 
with a fuel ratio below 2.5. The former have a short to medium flame 
and the latter a long flame. 

The Virginites are divided into three types having fuel ratios 
respectively between 5 and 7; between 3.5 and 5; and between 2.5 
and 3.5. The first type is a non-caking coal while the other two are 
caking coals. The Pocahontas type has a fuel ratio of 3.5-5 and the 
Sewell type a ratio of 2.5-3.5. The other group of the high grade 
bitumites is divided into the caking or steam coals and the non- 
caking or household coals. The caking, long-flamed coals are again 
divided into two groups based on a fuel ratio of i .4. Those above this 
figure are called the Pennsites from their abundance in Pennsylvania. 
The Pennsites are again divided into Connellsite with a fuel ratio of 
1.85 or more and Pittsite with a fuel ratio between 1.4 and 1.85. 
These names are taken from the Connellsville and Pittsburgh dis- 

Those coals with a fuel ratio below 1.4 and a fixed-carbon-moisture 
ratio of more than 6 are called Ohioites and those with a similar 
fuel ratio but with the other ratio less than 6, but still in the bitumite 
class, are called Illinoites. The Ohioites are again divided into the 
Belmontites with a fixed-carbon-moisture ratio of more than 10 
and Hockingites with a ratio between 6 and 10. The Illinoites which 
are high-moisture coals are also subdivided. 



The non-caking or household coals are divided into two groups, 
the splintites and the cannellites, wh ch are separated on a physical 
basis as their structure and fracture are quite different. The lower- 
rank bituminous coals with a fuel value of less than 14,300 B.t.u. 
on the ash-, moisture- and sulphur-free basis are divided into two 
groups according to their weather resisting properties. 

For the convenience of those persons who purchase coal by wire 
Ashley has suggested letters to designate the various ranks of coal 
and the grades in those ranks. The table of letter abbreviations for 
the grades is as follows : 

Ash per cent 

Sulphur per cent 

Fusibility of ash, degrees F. 

VI = very low 

0- 4 


Less than 2200 

/ = low 

4- 8 



m = medium 


i-5 -2.5 


h = high 


2-5 -4 


Vh = very high 


4 + 


The letters a, s, and / also stand for ash, sulphur and fusibility re- 
spectively. The fusibility of the ash is an important factor in the 
heating quality of the coal because of the effect it may have in clog- 
ging the grates, and it should be given serious consideration. 

This classification may appear complicated to the average man 
dealing in coal; there will be many exceptions to the classes made and 
people long accustomed to such terms as Pocahontas coal may at first 
object to the use of Pocahontite for coal from another region; yet 
there are a number of features in this classification wh'ch commend it. 
One important one is the fact that a proximate analysis furnishes the 
necessary data for making the computations 

After a review of all available classifications of coal it must be con- 
cluded that no one classification so far suggested meets with general 
approval. Some of the classifications are very satisfactory in com- 
bining the physical and chemical properties of certain of the coals so 
that they coincide with the names familiar to the public, and firmly 
established in the coal trade. Others are applicable to certain other 
coals and it seems probable that when the number of analyses has 
been greatly increased and our knowledge of the controlling chemical 
factors in coals has become somewhat more advanced it will be possible 
to formulate a classification which will be workable under most con- 


ditions at least. Some of the classifications may now be applied to 
certain regions with satisfactory results, but it is improbable that any 
one will ever be applicable to all kinds of coals from all districts, 
owing to the great diversity of physical and chemical characters 
resulting from the variations in the vegetal matter from which coals 
have been derived and in the variable geological conditions under 
which they have been developed. The classifications, therefore, 
which require more than two factors as a basis for determination of 
a type come nearer satisfying the fundamental requirements than 
those which are based on a ratio between only two constituents, and 
from a practical standpoint the making of ultimate analyses by the 
present chemical methods is to be avoided when possible. 



In the earlier days of geological science a few theorists, searching 
for some abstruse explanation for the origin of coal seams suggested 
that they were intruded into the enclosing strata as bituminous de- 
posits of igneous origin in the same manner that sills of igneous rock 
are injected between beds of sediments. Patrin regarded the seams 
as extrusions of bituminous matter on the sea bottom. So definite 
is the evidence, however, that all coal has resulted from the alteration 
of vegetal matter in some form, that a theory of origin based on any 
other premise may be dismissed without consideration. Any one 
questioning this conclusion has but to observe the transition from 
peat to lignite and from lignite to bituminous coal, with a gradual 
decrease in the distinctness of the plant remains in passing from the 
lower to the higher grades of coal, to be convinced regarding this 
matter. Many of even the hard coal seams contain remnants of 
trees completely changed to coal but retaining the markings of the 
bark and other woody structures. The modern application of the 
microscope to the study of those coals which show to the naked eye 
no evidence of plant remains reveals the spores, the fragments of 
resin and the modified woody tissue of the vegetation which formed 
the coal. 

Although it is almost universally agreed that all the varieties of 
coal originated from vegetal matter there is much difference of opinion 
regarding its mode of accumulation into such great bodies as those 
which gave rise to the coal seams. There is also a great divergence 
of opinion among geologists and paleobotanists regarding the proces- 
ses by means of which the vegetation has been brought into the form 
of brown coal, bituminous coal, or anthracite, in which it is now 



Theories for the Accumulation of the Vegetal Matter 1 

There are two main theories for the accumulation of the vegetal 
matter giving rise to coal seams, and there are two schools of geologists 
supporting these theories. One school contends that the plant 
remains accumulated in situ, that is, where the vegetation grew and 
fell, and the deposit is said to be autochthonous in origin. The other 
considers that the deposit is allochthonous , that it has accumulated as 
a result of the transportation of the vegetal matter by water. Ac- 
cording to the latter theory the fragments of plants have been carried 
by streams and deposited on the bottom of the sea or in lakes, in 
much the same manner as any other sediment would be carried, and 
allowed to settle to the bottom to build up strata which later become 
compressed into solid rock. 

The evidence favoring the in situ or autochthonous origin of the 
deposit may be summed up as follows: (i) There are large accumu- 
lations of vegetal matter forming in swamps at the present time, 
some of which are on a scale approaching those which gave rise to 
coal seams of considerable extent. (2) The purity of the coal, or 
its relative freedom from mineral matter, suggests the collection of 
the vegetation in swamps rather than in deposits where it has been 
transported with other sediments. The periods of high water when 
the greatest amount of vegetation is transported are also those when 
most mineral matter is carried. (3) Numerous tree trunks with 
their roots firmly embedded in the underlying clays occur in the coal 
seams and in some cases the rootlets pierce fragments of buried wood 
in the clays. (4) The topographic conditions under which the large 
coal fields formed were like that of a land surface near the critical level 
(that is, near sea level), and a slight sinking of the land would permit 
the sea to transgress over it or, in basins removed from the sea, per- 
mit sediment to be washed into the basin from adjoining lands. 
(5) Old soils on which the trees grew lie beneath the seams in some 
places. (6) Such an accumulation could not take place in the open 
sea and estuaries are not in very favorable locations because of the 
immense amount of mud usually carried into them. (7) The arrange- 
ment of various portions of plants with respect to one another is not, 
as a rule, that of transported material. (8) The lenses of cannel in 

1 For summary of theories see "The formation of coal beds," by J. J. Stevenson. 
Proc. Amer. Phil. Soc., Vol. 50, pp. 1-116, 1911. 


bituminous coal, or bands along the upper surface of bituminous coal 
seams, indicate patches of open water in swamps where spores would 
collect in great quantities rather than deposits forming part of an 
ordinary sedimentary formation. (9) The lenses and bands of " min- 
eral charcoal" suggest higher portions in the swamp exposed to weath- 
ering and more extensive rotting than that undergone by the remainder 
of the vegetation in the swamp. If this charcoal represents the 
remnant of burned wood transported to open water as some have 
suggested, it could scarcely have the distribution which it usually 
has in the coal seams. 

In favor of the transportation or allochthonous theory there are the 
following factors: (i) Enormous quantities of timber are rafted 
down streams in regions of virgin forest. (2) In some modern deltas 
beds of peat and brown coal have been found. (3) Coal beds are 
often associated with marine fossils which occur in the strata im- 
mediately above or below the seams of coal. (4) The rocks associ- 
ated with the coal are distinctly sedimentary and the seams appear 
to constitute a part of a regular sedimentary series, usually showing 
an increasing fineness in the particles of sediment in the rocks under- 
lying the seam as the seam is approached. (5) The fire-clay beds 
commonly found beneath coal seams are not necessarily clays on which 
forests grew, as formerly supposed, because similar clays have been 
found in marine formations unassociated with coal. (6) It is diffi- 
cult to determine in many cases whether a stump of a tree is located 
where it grew or whether it has been transported to its present lo- 
cation and gradually buried by clay or sand which settled around it, 
while resting upright on the bottom of the basin. (7) Trees have 
been found with their tops headed downward. (8) The large num- 
bers of spores grouped in the coal in some seams indicates their ability 
to float about freely and collect in masses. (9) The presence of 
fish remains in coal, especially the cannel coal of England, suggests 
considerable open water where the vegetation accumulated. (10) 
It would appear to be difficult for large trees to root in such an enor- 
mous depth of vegetal matter as that necessary to produce some of 
our thickest coal seams. 


Historical Sketch of the Development of the Theories for the 
Origin of Coal 

As early as the year 1778 Buffon 1 recognized the vegetal origin of 
coal and gave it the name charbon de terre, the term still frequently 
used in France. In the same year Von Beroldingen 2 very intelli- 
gently expounded the in situ origin of the vegetation in a peat-bog, 
its burial and its transformation from peat into the various types 
of coal. These writers were followed by many who had more or less 
hazy and highly theoretical views regarding the origin of coal. Even 
Darwin seemed to regard some of the coal beds as bituminous dis- 
tillations from vegetal matter capable of migration from one rock 
horizon to another. 

In the year 1831 MacCulloch published a work 3 in which he sup- 
ported the peat-to-coal theory. He pointed out that the plants 
forming the peat were of terrestrial type and that they grew in swamps. 
Three years later Marinnott recognized the prevalence of an under- 
day with coal seams but stated that there could be no genetic con- 
nection between the coal and the clay because he failed to find roots 
in the clay. A little later Buckland 4 described how the vegetal mat- 
ter was transported and he expounded the drift origin of the deposits. 
Although Witham 5 had probably made the first microscopic studies 
of coal in 1833 it remained for Link 6 to extend this work five years 
later and apply his results to the origin of coal. He concluded that 
coal was developed from peat because of the presence of various 
vegetal materials in it and that the vegetation accumulated in place. 
In 1841 Logan 7 stated that from his observations underclays were 

1 Buffon, L. de., Histoire natureJle, generate et particuliere Sonnini Edn. Tome 9 me, 

2 Von Beroldingen, Franz., Beobachtungen, zweifel und Fragen, die Mineralogie 
iiberhaupt und insbesondere ein natiirliches Mineral System betreffend; Erster Versuch, 
i 77 8. 

3 MacCulloch, J., A System of geology with a theory of the earth, Vol. II. 

4 Buckland, W., Geology and mineralogy considered with reference to natural theology, 
Phila. 1837. 

5 Witham, H., On the Internal structure of fossil vegetables found in the carboniferous 
and oolitic deposits of Great Britain, 1833. 

6 Link, F., Uber den Ursprung der Steinkohlen und Braunkohlen nach mikroskopischen 
Untersuchungen. Abhandlungen d. k. Preuss, Akad. Wiss. Berlin pp. 33-34, 1838. 

7 Logan, W. E., On the character of the beds of clay lying immediately below the coal 
seams of South Wales. Proc. Geol. Soc. London, Vol. Ill, 1841. 


characteristic of all coal seams and that from the presence of Stig- 
maria in these clays the vegetation must have consisted chiefly of 
this species which grew on these clays. Two years later Rogers 1 
published a very comprehensive statement of the results of his ob- 
servations. He concluded that the Pittsburgh seam extends over 
at least 14,000 square miles and that when isolated areas where it 
occurs are added the total area could not be far from 30,000 square 
miles. He stated that he failed to see how beds of such extent and 
purity could have been formed from drifted vegetation and he be- 
lieved that they were formed in swamps on great marginal plains 
subjected to gradual subsidence. He considered the underclays as 
very common and Stigmaria as almost always present in them, often 
preserving its fibrous processes. Another important point that he 
brought out was that the roof was different from the sole formation 
and that the roof sandstones showed evidence of strong currents. 

From a study of Russian coals Murchison 2 favored the drift theory 
but he also preferred the in situ theory for some of the English coal 
seams where the underclays represent old soils on which Sigillaria 
grew. Le Conte 3 favored the in situ theory because of the purity of 
the coal and the preservation of the delicate portions of the vegetal 
matter. He believed that the vegetation grew in bogs around the 
mouths of large rivers. Jukes 4 favored the drift theory because of 
the "rock faults" and frequent alternations of barren rock and coal. 
He believed that the materials were sorted on the basis of specific 
gravity. On the other hand Dawson concluded from a microscopic 
study of coal and an extensive investigation of the South Joggins 
area in Nova Scotia that the vegetation grew where it was accumul- 
ated because of the numerous examples of standing trunks, and the 
roots in place. He considered that the coal consisted chiefly of bark 
and similar materials with spores as a very minor constituent. He 
also regarded the irregularities in the floor of the seams as charac- 
teristic of the inequalities seen in swamps of the present day. Steven- 

1 Rogers, H. D., An inquiry into the origin of the appalachian coal strata, bituminous 
and anthracite, Repts. of Amer. Ass. of Geologists and Naturalists, Boston, 1843. 

2 Murchison, R. I., The geology of Russia in Europe and the Ural Mountains, Vol. 
I, p. 112, 1845. 

3 Le Conte, J., Lectures on coal. Ann. Rept, Smithsonian Inst., p. 131, 1858. 

4 Jukes, J. B., The South Staffordshire coal field. Memoirs Geol. Survey of Great 
Britain, 2 ed. London 1859. 


son, 1 Andrews, 2 and Newberry, 3 as a result of their studies in Penn- 
sylvania, Ohio and West Virginia strongly support the in situ theory. 
Dana considered that the coal was made up of all parts of the trees 
and that it accumulated in marshes. Mietzsch 4 was opposed to the 
transport theory and described the sunken forests near the coast off 
Rotterdam as illustrative of buried peat deposits found in situ. In 
1878 Lesley 5 described how cannel lenses occur in pools on the mass of 
vegetation which formed the coal seam and pointed out the significant 
fact that if the coal deposits were not formed in a continuously sub- 
siding area it would have been impossible for the many thousands of 
feet of shallow water deposits filling the Appalachian trough to have 
been laid down beneath the Coal Measures. He also believed that 
the underclays represented the finer particles of rock sorted out of 
the coarse sandstones and conglomerates and concluded that where 
underclays were thick they should therefore be associated with ex- 
tensive sandstone strata. Grand' Eury 6 seems to have favored a 
sort of combined in situ and drift theory as he believed the vegetation 
collected, suffered considerable decomposition, and was then washed 
from the land into the standing water where it was buried. He 
regarded the mineral charcoal as wood dried in the air. An objection 
was raised to the in situ theory because the roots of the trees do not 
penetrate the coal but spread out over it at the top of the seam in- 
dicating that they cannot exist in a mass of decomposing vegetal 
matter. It is well known, however, that this objection is overcome 
by observation of a modern peat-bog or swamp. Griiner 7 objected 
to the transportation of the vegetal matter chiefly because of the 
freedom of the coal from mineral sediment. He was strongly in 
favor of accumulation in place. 

In the year 1883 Von Gumbel 8 published an excellent discussion 

1 Stevenson, J. J., The upper coal measures west of the Allegheny Mountains. Ann 
Lye. Nat. Hist. N. Y., Vol. X, p. 226, 1873. 

Andrews, E. B., Geol. Survey of Ohio. Vol. I, Pt. I, 1873. 

Newberry, J. S., Geol. Survey of Ohio, Vol. II, Pt. I, 1874. 

Mietzsch, H., Geologic der Kohlenlager, 1875. 

Lesley, J. P., Second Geol. Survey of Pa., 1878. 

Grand'Eury, Memoire sur la formation de la houille. Ann. des Mines Ser. 8, Tome 
I, 1882. 

Griiner, L., Bassin houiller de la Loire, 1882. 

Von Gumbel, C. W., Bertrage zur Kenntniss der Texturverhaltnisse der Mineral- 
kohlen. Sitzungs d. Math. Phys. Klasse k. b. Akad. Wiss., Vol. 13, p. 113, 1883. 


of his microscopic and field observations. He treated fragments of 
coal with potassium chlorate, nitric acid and later with ammonia. 
He then washed them with absolute alcohol, thus employing a system 
very similar to that used in recent years. He showed that even the 
" stove" coal is made up of the various fragments of plant debris, 
some of which are much more easily decomposed and much less dur- 
able than others. He concluded that different varieties of coal may 
result because of differences in the kinds or parts of plants, because 
of differences in chemical and mechanical conditions, or in the ex- 
ternal conditions during transformation. He first used the terms 
allochthonous and autochthonous respectively to designate accumu- 
lation by transportation and accumulation in place. He regarded 
the interstratification of coal and distinct sediments as a strong 
factor in favor of those who support the drift theory but he felt that 
other evidence, especially the similarity between vegetation in 
modern coastal swamps, subject to submergence by the sea, and the 
peat deposits which gave rise to the coal, substantiated the autoch- 
thonous origin of the coal. 

As a champion of the drift theory probably no one man has pro- 
duced more convincing evidence in its favor than has Fayol, 1 a mining 
engineer, who made elaborate observations in the basin of Commentry 
in central France. He further supported some of his conclusions by 
laboratory experiments and as a result of his work a number of men 
were led to accept his opinions, among them the well-known French 
scientists, A. de Lapparent and B. Renault. He considered that the 
vegetation grew on high lands surrounding a deep lake and was washed 
into this body of water where it was deposited in a delta along with 
sandstones and conglomerates. The distinct delta deposits, the 
presence of abundant fish remains in associated shales, and the pres- 
ence of trees with their tops headed downward are all taken as dis- 
tinct evidences of the transportation of the vegetation. Many of 
these arguments are successfully refuted by Stevenson 2 who later 
studied the area and who claimed that nothing but a series of cloud- 
bursts could tear the vegetation from the surrounding lands if it were 
as dense as necessary to produce the coal seams under discussion in 

1 Fayol, H., Terrain houiller de Commentry. Saint-Etienne. Livre Premier, Lithol- 
ogie et Stratigraphie, 1887. 

2 Stevenson, J. J., The Coal basin of Commentry in Central France. Ann. N. Y. 
Acad. Sci. XIX, p. 161, 1910. 


the 17,000 years postulated by Fayol for this operation. Stevenson 
believed that the vegetation of this coal basin accumulated in situ. 

Gresley 1 regarded coal as of drift origin and based his conclusions 
largely upon observations in the Pittsburgh seam of the Appalachian 
province. He claimed that there are two slate partings in this seam 
from | to J inch thick separated by 3 to 4 inches of coal and occurring 
over about 15,000 square miles. These contain no Stigmaria and the 
underclay of this seam over large areas is a calcareous mud without 

One of the strongest supporters of the in situ theory was Potonie. 2 
He describes a core 750 meters long from the upper Silesian coal 
measures in which there are at least 27 beds of coal each with an un- 
derclay carrying Stigmaria. He also describes a fossil swamp in the 
Miocene formations near Senftenberg which has given rise to .brown 
coal and in which several generations of forests have grown and left 
their stumps rooted in the vegetal matter. His valuable observations 
on modern fresh-water swamps, such as those in Sumatra, have also 
helped a great deal in clarifying our ideas on ancient peat-producing 
swamps. He has suggested the following terms for organic deposits 3 : 
Kaustobioliths, or combustible rocks of organic origin, which are 
divided into Sapropelic deposits or those composed of animals and 
aquatic plants such as cannel coal and oil shales; and humus deposits 
which include all ordinary coals. 

In reviewing the literature on the subject of the accumulation of 
peat it is found that the majority of writers favor the autochthonous 
or in situ theory, but there are many scientists of note who favor the 
opposite view. Among living geologists the former theory is most 
generally accepted and it is particularly well demonstrated in the 
discussions of White 4 and his colleagues, although White accepts the 
drift theory for some lesser deposits. On the other hand, Jeffrey, 5 

1 Gresley, W. S., The slate binders of the Pittsburgh coal bed, Amer. Geologist, XIV, 
p. 356, 1894. 

2 Potoni6, H., Ueber Autochthonie von Carbonkohlen-Flotzen und des Senftenberger 
Braunkohlen-Flotzes Jarb. d. k. Preuss. Geolog. Landesanstalt, 1895. 

3 Potonie, H., Die Enstehung der Steinkohle und der.Kaustobiolithe iiberhaupt wie 
des Torfes der Braunkohle des Petroleums u. s. w. 5th ed., 1910. 

4 White, David, and Thiessen, R., The origin of coal. U. S. Bureau of Mines, Bull. 
38, 1913- 

6 Jeffrey, E. C, The mode of origin of coal. Jour, of Geol., Vol. XXIII, 1915, p. 218. 
Also, Petrified coals and their bearing on the problem of the origin of coals. Proc. Nat. 
Acad. Sciences, Vol. Ill, p. 206, 1917. 


the paleobotanist as a result of his extensive microscopic studies 
is a strong advocate of the drift theory, perhaps in a somewhat modi- 
fied form. His conclusions are based very largely on the abundance 
of spore remains, thus suggesting accumulation of the vegetal matter 
in open water, as in cannel coal. 

The writer believes that the majority of our coal seams are un- 
doubtedly autochthonous in origin as most of the evidence supports 
this theory. Owing, however, to the strong arguments advanced 
and supported by both schools on this subject he agrees that some of 
the less extensive deposits have been allocthonous, especially the 
lens-shaped seams of limited extent occurring in lacustrine and estuar- 
ine formations of the delta type. 

Discussion of the Theories of the Origin of Coal 

(1) The development of peat in bogs, marshes, and swamps. Peat- 
bogs. At the present day a vast amount of peat is being formed in 
small lakes and bogs, particularly in the cooler, wet climates and in 


FIG. 18. Diagram illustrating the formation of peat in a bog and the 
extension of the larger trees over the peat deposit. 

the regions which have been glaciated and where drainage is there- 
fore poor. 1 The depth of the peat may vary from a few inches to 
50 feet but the detached areas covered by it are comparatively small 
and while a peat-bog may serve to demonstrate how vegetal matter 
accumulates in considerable quantities it is in no way comparable in 
extent to the great bodies of vegetation which must have given rise 
to our important coal seams. These peat-bogs generally begin with 
a pond or a small lake varying from a few hundred feet up to a mile 
or more in diameter. The development of the peat begins with the 
growth and partial decay of a fringe of plants around the border of 
1 Davis, C. A., The origin of peat. U. S. Bur. of Mines, Bull. 38, pp. 165-186, 1913. 


the lake. The first plants to develop are usually the pond weeds and 
water lilies. These are followed by the bulrushes and beyond them 
the floating algae live in the deeper water where they do not reach 
the bottom. As this vegetation grows and dies, season after season, 
a deposit of peat develops along the shore and as it grows higher the 
plants mentioned gradually shift their relative position farther out 
from the shore and toward the center of the lake (Fig. 18). In the 
course of time a growth of sphagnum or "peat-moss," a large grayish- 
green or whitish moss, extends outwards over the peat deposit and 
this is followed by small trees of several species, chiefly the conifers; 
including the tamarack and spruce. As the peat becomes more and 
more firm, larger and larger trees will be supported and deciduous 
trees such as the white birch may partially replace the conifers. In 
time the lake may be completely filled up and the area overgrown by 
small timber. 

As the peat develops several zones may be observed in the deposit. 
A very dark, heavy, dense peat forms at the bottom and lighter- 
colored, more fibrous layers occur as the surface is approached. Scat- 
tered through these layers there may be trunks of trees more or less 
altered. These trees grew around the border of the lake and were 
killed at times of high water, or they may have been blown down or 
otherwise killed and they then became imbedded in the peat. In 
seasons when the water is low and the surface of the bog stands above 
the water-soaked level the vegetation may suffer considerably more 
decomposition, or dry rot, than in other seasons and all but the more 
resistant portions of the material will be destroyed. This may, if 
carried sufficiently far, give rise to mineral charcoal. In wet seasons 
when the water is high, a much smaller degree of decomposition occurs 
and a much greater proportion of the vegetation is preserved so that 
alternate bands with varying composition result. 

Marshes: In addition to the peat bogs there are in various parts 
of the world large areas without trees, where peat forms a shallow 
deposit covering a water-soaked land surface, but where standing 
water is not usually present except in the wet seasons. These areas 
are found chiefly in the frigid and terhperate zone, but they may also 
be found in the tropics. In the colder regions the peat consists mostly 
of sphagnum, but in some places rushes and grasses may form a con- 
siderable part of the plant growth. The Arctic tundra is one type of 



such deposit. In the warmer climates cane-brakes and "tuie" 
marshes represent this type of peat development. 

Fresh-water swamps: Interesting as the peat bogs and marshes 
may be in illustrating various ways in which peat may develop, they 
cannot be regarded as the sources of the peat which gave rise to im- 

FIG. 19. Cowhouse Run, Okefinokee Swamp, Ga. 
(Photo by Francis Harper.) 

portant deposits of coal. There is sufficient peat in the temperate 
regions of the world today to form large amounts of coal, if it were 
concentrated into coal seams, but no single bog or marsh known would 
supply sufficient peat to make a large coal seam, although Geikie 
states that one-seventh of Ireland is covered with peat bogs and in 
Allen alone, 238,500 acres are covered with peat to an average depth 
of 25 feet. 

There are, however, other deposits of peat forming at the present 
day in both temperate and tropical regions, which much more nearly 



represent the kind of accumulation of vegetation which gave rise to 
extensive coal seams. These deposits are forming in immense fresh- 
water swamps such as the Dismal Swamp of North Carolina and 
Virginia and the Sumatra swamp in the East Indies. Large swamps 
of similar character are believed to exist in tropical Africa and South 
America. From descriptions of these swamps it is apparent that the 
idea so commonly held that peat can scarcely form in warm climates 
and that modern deposits of peat are practically restricted to the 

FIG. 20. Scene in a cypress bay, Okefinokee Swamp, Ga 
(Photo by Francis Harper.) 

cooler regions of the earth is not correct. In fact there are deposits 
of peat in these swamps much more nearly approaching large coal 
seams in extent than anything found in the cooler regions. If there 
be an abundant rainfall on poorly drained land and a type of vege- 
tation capable of very rapid growth, the wastage of peat due to higher 



temperature may be offset by the greater rate of growth in tropical 
or sub-tropical climates. 

According to Shaler 1 the inundated portion of the Dismal Swamp 
is about 38 miles north and south by 25 miles east and west. The 

FIG. 21. Map of the Dismal Swamp. North Carolina and Virginia, showing 
the relation of the swamp to the coastal plain. (After Shaler, U. S. Geol. Survey.) 

swamp which was apparently extending its borders before man began 
to drain and cultivate portions of it is now considerably smaller than 

1 Shaler, N. S., Geology of the Dismal Swamp District of Virginia and North Carolina. 
U. S. Geol. Survey, Tenth Ann. Kept., Pt. i, pp. 313-339, 1888-9. 


it was originally. Osbon places the total area of this swamp originally 
at 2200 square miles with 700 now drained. 1 It lies on the coastal 
plain and represents the largest continuous swamp area of the many 
scattered over this plain between the Appalachian Mountains and the 
sea (Fig. 21). The rocks underlying the swamp are mostly strati- 
fied marine sands with some lime beds probably of Pliocene age. The 
surface is slightly rolling or billowy but the differences in elevation 
are small and on the whole the area approaches a level surface from 
5 to 25 feet above the sea. The geological events which have given 
rise to the present relief are outlined by Shaler as follows: (i) A 
subsidence leading to the formation of the Pliocene plateau. (2) 
Elevation permitting erosion of the plateau. (3) Subsidence permit- 
ting deposition of non-fossiliferous sands. (4) Elevation permitting 
carving of surface. (5) Subsidence and formation of the Nansemond 
escarpment. (6) Reelevation and development of valleys of streams 
to present depth. (7) Sinking now taking place. 

From this description it is seen that this swamp stands near the 
critical level in much the same way as the swamps of the coal measures 
must have been situated and that a slight change in elevation might 
produce dry land or a transgression of the sea. There are areas of 
open water in this swamp, such as Lake Drummond, which might 
represent the more extensive areas of open water in the coal measure 
swamps in which the spores collect and produce canneloid, thus 
giving rise to lenses of cannel coal. This lake is gradually filling up 
with peat by the encroachment of the vegetation. There are other 
areas which are never completely submerged and which are compara- 
tively dry during the greater part of the dry seasons. These exposed 
areas would illustrate those on which mineral charcoal would form 
because of more extensive rotting resulting from exposure (Fig. 22). 

The vegetation in this swamp varies with the amount of water 
present. The higher levels are usually occupied by pines such as the 
common southern pine. The lower levels are mainly occupied by 
three species of trees, the Taxodium, or bald cypress, the juniper, 
and the black gum. The juniper occurs on the land which becomes 
fairly well dried during the dry season. The other two may grow in 
areas continuously covered with water if the water does not rise too 

1 Osbon, C. C., Peat in the Dismal Swamp, Virginia and North Carolina. U. S. 
Geol. Survey, Bull. yn-C, 1919. 



high, as they develop knees, or arched roots to aid in keeping them- 
selves above water. 

The fallen trees, the spores, the leaves, and other plant debris are 
continually falling into the water in this swamp and building up a 
layer of peat which has been estimated at i to 20 feet in thickness. 
Osbon has estimated that 1500 square miles are covered to an average 

FIG. 22. Lake Drummond, Dismal Swamp. 
Geol. Survey.) 

(Photo by Shaler, U. S. 

depth of 7 feet and that the total available peat in this swamp is about 
672,000,000 tons. This peat if turned to coal would be sufficient to 
form a seam from about i inch to 20 inches in thickness and it would 
have many of the characteristics of coal seams as we are familiar with 
them today. The ash content is quite satisfactory. If the sinking 
of this area continued very slowly, the living vegetation would be 
destroyed and opportunities would be offered for the collection and 
preservation of a large amount of vegetation. It might become 
buried by the encroachment of the sea and the deposition of sediments 
over the vegetation. Submerged stumps in the valley of the Pamlico 
River, in this area, indicate that in comparatively recent time, geol- 


ogically speaking, submergence has occurred. On the other hand a 
slight uplift of the land surrounding this basin might cause large 
quantities of mud, sand, or gravel to be washed into the swamp and 
form partings in the resulting coal when a new swamp formed on top 
of this rock. 

The other large fresh-water swamp of which we have some definite 
knowledge is one on the island of Sumatra described by Potonie. 1 
It is said to cover about 312 square miles. The peat deposit reaches 
a thickness of 9 meters or nearly 30 feet in this swamp and it is made 
up of a mixture of logs and plant debris of all sorts. There is a stag- 
nant, tea-colored blanket of fresh-water over the peat, which makes 
an efficient preserving fluid for the materials which fall into it. The 
ash content of the dried peat is 6.39 per cent. This material if com- 
pressed into bituminous coal should produce a seam nearly 3 feet 
thick, as the lower layers of peat have already undergone considerable 
change and they are dense and compact. 

That many swamps and forests have become buried beneath mar- 
ine and fresh- water deposits is well demonstrated by Stevenson 2 in 
his article on " Buried Forests." An interesting example is also 
mentioned by Mietzsch 3 who says that off Rotterdam two bogs, 
5 meters and 6 meters thick, are separated by a bed of clay 4 meters 
in thickness. Some of the trees are still standing and they are of 
types which inhabited the adjacent lands centuries ago. Another 
of greater antiquity was described by Potonie from the Miocene and 
previously mentioned in this chapter. In these illustrations we seem 
to have abundant evidence of the efficacy of fresh-water swamps in 
producing coal deposits under proper climatic and topographic con- 

Mangrove swamps: There are also certain salt and brackish water 
swamps, which occur along the sea coasts and in which the trees are 
mostly mangroves. They are known as mangrove swamps. These 
are found in the tropical or semi-tropical regions and some of them 
are of considerable extent. They may be seen in northern New 
Zealand, Ceylon, Cuba, Florida, and many other countries (Fig. 26). 

1 Potonie, H., Die Entstehung der Steinkohle und der Kaustobiolithe iiberhaupt, 
5th ed., pp. 152-160, 1910. 

2 Stevenson, J. J., The formation of coal beds, Pt. II, Proc. Amer. Phil. Soc., Vol. 50, 
p. 626, 1911. 

3 Loc. cit. 



The long stilt-like roots raise the trunk above the water and among 
these roots the vegetal debris collects. They sometimes extend a 
short distance from the shore where the water is shallow and while 
considerable peat forms in such a swamp, so far as the writer's ob- 
servations go, there is always a large amount of sand mixed with the 
peat owing to the tidal currents and storm-waves which wash it into 
the swamp. This type of swamp never seemed very favorable for 

FIG. 23. Portion of Dismal Swamp in which peat is covered with water. (Photo by 
Shaler, U. S. Geol. Survey.) 

the formation of extensive bodies of peat. These trees may, however, 
grow farther back from the sea and even in fresh-water swamps where 
conditions are more favorable to the formation of purer peat deposits. 
(2) Drifted vegetation and delta deposits. The drift theory for 
the collection of vegetation giving rise to coal deposits has many sup- 
porters who naturally invoke processes now operative on the earth's 
surface to substantiate their arguments. They can point to a few 
cases where coal is being formed or has been formed in undoubted 
delta deposits in comparatively recent time considered from the 


geological standpoint. In an article describing briefly the artesian 
wells at Venice, Italy, Degousee 1 mentions lignite beds which were 
pierced in drilling for water. He states that the sea is very shallow 
in the Gulf of Venice for a long distance from the shore At a depth 
of 60 to 70 meters and above the real artesian bed ascending water is 
struck which is so charged with hydrogen carbide that the water is 
intermittently thrown above the surface with great violence. This 
gas is said to burn well but nothing is recorded regarding its relation 
to the lignite beds, fn all the wells bored several beds of lignite in 
sand and clay were passed through. Unfortunately we have no de- 
tailed data concerning the thickness or number of these seams. There 
were in the lignite fragments of wood sufficiently preserved to be 

Reference is frequently made in literature to the enormous amount 
of timber floating down the Mississippi River and the rafts of drift- 
wood, several miles in length, which years ago blocked the channel 
of the stream. Conditions as they are at present, in the cleared and 
cultivated valley of that river, make, however, a poor parallel to the 
conditions prevailing when the country was covered with virgin forest, 
as a vastly greater proportion of mineral matter is being carried than 
would have been carried then. A closer parallel to the conditions 
prevailing when coal was being formed may possibly be seen in some 
of the rivers in northern Canada where many streams flow through 
regions covered with virgin forests and peat bogs. One is impressed, 
for example, by the vast quantities of timber which descend the 
streams to James Bay every spring (Fig. 27). Owing, however, to 
the great variation in size of the fragments and the difference in the 
rate at which they become water-logged and sink, or float out to sea, 
there seems little opportunity for this material to collect into any 
extensive bodies of peat on the sea bottom. One of the main diffi- 
culties in the way of its producing coal is the fact that when most 
plant debris is carried in flood periods there is always more than the 
normal quota of mineral matter taken along. 

In an effort to obtain definite information regarding the proportion 
of plant debris carried by streams and thus support his arguments 

1 Degousee, M. J., Note sur les alluvions formant les lagunes venitiennes, et sur les 
puits artesiens de la ville de Venise. Bull, de la Societe Geologique 2 Serie, Tome 8, 
pp. 481-4, 1850. 



for the drift theory for the basin of Commentry, central France, 
Fayol 1 stretched a wire screen of one centimeter mesh across a stream 
known as the Baune. This was done in the month of January and 
it collected 502 grams in 2 minutes, or 1.5 grams for each cubic meter 
of water passed through. He also made certain laboratory exper- 
iments in a small body of water to determine the action of vegetal 
matter in sinking to the bottom and of mixing, or separating itself 

FIG. 24. Timber undergoing partial decay in the Dismal Swamp. (Photo by Shaler, 

U. S. Geol. Survey.) 

from the sediment which was carried into the body of standing water 
with the plant materials. He found that the roots were among the 
first materials to sink. Many stems remained in an upright or in- 
clined position on the bottom and the plant debris formed deposits 
varying from practically pure vegetal matter to those highly mixed 
with mineral matter. 
According to this writer, the basin at Commentry, in Carboniferous 

1 Fayol, Henri. Terraine houiller de Commentry, Livre Premier, fitudes sur le terrain 
houiller de Commentry, p. 397, 1887. 



time was occupied by a fresh-water lake surrounded by high lands. 
Streams entered the lake with sufficient gradient to move large 
boulders, some of granite in the conglomerate underlying the coal 
reaching a cubic meter in volume and suggesting for them a glacial 
origin. As a parting in the famous Grande Couche, a seam reaching 
a maximum thickness of 20 meters, there are 8 meters of conglomerate 
with some boulders half a meter in diameter. Another peculiar 



FIG. 25. Destruction of trees by high water in the Dismal Swamp. (Photo by 
Shaler, U. S. Geol. Survey.) 

feature of these coal deposits is the presence in the conglomerates of 
the Coal Measures of pebbles of coal and abundant grains of coal 
in the sandstones showing that older coal beds had been broken up 
by erosion. 

Some of the other evidences of the drift origin of the coal at Com- 
mentry are trees with their trunks in an inverted position, and the 
presence of abundant fossil fish in the associated rocks. The occur- 
rence of inverted tree trunks cannot, however, always be regarded as 
conclusive evidence of drift origin because one may often see trees in 
a swamp broken off by the wind and embedded, head down, in the 


peat. Their chances for preservation are, however, not great unless 
covered with clay or sand, since most of them project above the water- 
level. The presence of upright trunks and stumps on the other hand 
cannot be regarded in many cases as definite evidence of growth in 
place because a stump floating into a body of water will most likely 
settle to the bottom in an upright position, owing to the weight of the 
roots if they be present, or the greater weight of the big end of the 
trunk, when water-logged, if roots be absent. There are stumps 
in the Coal Measures at St. fitienne, France, with a number of roots 
penetrating the underlying rocks but it is impossible to determine 
whether the stumps are in place or whether they floated to their 
present position and became buried by sediment (Fig. 28) . If, how- 
ever, the unbroken rootlets are found in their proper position and 
roots are found piercing fragments of buried wood this would be 
regarded as proof of their growth in situ. Such conditions are found 
in many of the great coal fields. 

Some writers attach importance to the relative number of upright 
stumps and trunks in the coal and in the adjacent conglomerates, 
sandstones, and shales. This circumstance cannot carry any par- 
ticular weight in the argument because it is evident that these rocks 
are capable of supporting the trunks in this upright position and 
they were buried quickly; whereas the soft, yielding peat would 
permit them to be easily crushed down flat by the superincumbent 
load of rock or vegetal matter. Fayol observed that in the Commentry 
basin 99.5 per cent of the stems were flat in the coal and 0.5 per cent 
vertical or inclined. In the sandstones 70 per cent were flat and in 
the conglomerates 60 per cent. 

The fact that so much better plant remains are found in the shales 
and " coal balls" than in the coal itself is due to the soft, pliable peat, 
which gave rise to the coal, squeezing and creeping under the weight 
of the overlying rocks and to partial decomposition of the vegetal 
matter because of longer exposure destroying original structures. 
In many cases the tree will rot out in the sandstone or shale leaving 
perhaps traces of the bark and this space becomes filled later by sand 
or clay which is squeezed into it, thus giving a stone-cast of the tree. 
The rock in these casts often differs from the rock surrounding 
them because it has been squeezed up from a lower stratum 
or down from a higher stratum than the one holding the cast. In 



some of these casts, mineral matter from solution may be deposited 
where the wood has disappeared, giving more iron oxide, calcium car- 
bonate or similar mineral than is found in the surrounding rock. 

The sequence of conglomerate, sandstone, shale, and coal beds in 
varying succession argues strongly for the drift theory as it would 
appear that in so many cases there was almost complete assortment 
of sediments on the basis of specific gravity and rate of settling. 
Further, the accumulation of vegetation to such a tremendous depth 


FIG. 26. Mangrove swamp creeping out over the sea on coast of New Zealand. 
(Photo by E. S. Moore.) 

as that necessary to produce 50 or 60 feet of anthracite might seem to 
some most easily accounted for by supposing that the material was 
transported and dumped into a body of water because there would 
be little opportunity for trees growing in this mass to root in anything 
but peat. It has been shown, however, that many of the larger trees 
which occupied the swamps were specially equipped with roots 
adapted to an existence near the surface of wet peat deposits and they 
were no doubt supported by the extensive matting together and inter- 
locking of the roots of the forest trees. It is known that trees of 
considerable size can subsist at the present day on thick deposits of 
peat and it seems much easier to explain the accumulation of such 
great masses of peat, so free from mineral matter and requiring such 


long periods to form, in a swamp free from sediment than in open 
water where every season large quantities of mud or silt are likely to 
be carried and spread over it during floods. 

The Sargasso Sea: 1 One other phase of the drift theory may be 
mentioned. It has been suggested that the great mass of plankton 
floating on the ocean might segregate in the eddies in the ocean cur- 
rents and, sinking to the bottom, build up peat deposits which would 
be well preserved. This mass would be made up of great quantities 

FIG. 27. Drifted timber along the Metagami River, James Bay basin, Canada. 

(Photo by E. S. Moore.) 

of very small, low types of floating plants associated with sea-weed 
and other forms of plant life which would be carried about on the 
ocean surface. While it is true that some material is collecting in 
this way at the present time anyone familiar with ocean travel knows 
that coal beds were never formed in this way because there is not 
sufficient material being deposited. Deep-sea dredgings have failed 
to show any accumulation of plant material worth mentioning. Other 
convincing evidence opposing this theory is the presence of coarse 
littoral sediments so frequently interbedded with the coal seams, in- 
dicating that these sediments are shallow water or land formations 
and not deep-sea deposits. 

1 Mohr, F., Geschichte der Erde, 1886. 


Rate at which Peat Accumulates 

The rate at which peat forms in any given region will depend upon 
the rate of growth and proportional rate of decay. The nature of 
the vegetation will have a great influence on the rate of growth as 
some trees grow so much faster than others on an area partially or 
entirely covered with water, the condition essential for the preser- 
vation of the vegetation after it is grown. Coarse vegetation will 
naturally build faster than fine material but there are certain types 
of the finer plant debris which build at a fairly rapid rate owing to the 
fact that the proportional shrinkage is not so great as in the coarse 
debris and the material is being supplied to the bog every year. If 
we consider for example the spores of plants which fall every spring 
and float about in the open bodies of water until they sink we will 
find that a large amount of this material collects every year and goes 
to build up canneloid, which later forms cannel coal. The writer has 
seen, while traveling in the late spring through the northern woods 
of this continent, such quantities of spores and pollen grains from the 
birch, poplar, and related trees floating on the water of the small lakes 
and ponds that it was impossible to obtain water fit to drink. There 
are often so many of these green globules in the water that in places 
it becomes thick with them. They collect in bands and little ridges 
along the shore where washed up by the waves. It can be easily under- 
stood how vast quantities of these spores collecting in patches of 
open water in large swamps might produce lenses of cannel with the 
other coal. Modern microscopic investigations of coal tend to show 
that spores are very widely distributed through all coal and that owing 
to their resistance to decay they form a prominent constituent of the 
coal. Another constituent which resists decay and is prominent 
in many coals, especially those formed chiefly from coniferous trees, 
is resin. This has been observed in considerable proportions in micro- 
scopic studies. 

The soil will have some influence but after a thick layer of peat 
has developed the plants gather most of their sustenance from the 
air and water. It seems probable that the feldspathic rocks ob- 
served as so common in coal measures in various countries of the world 
may have furnished more than the average amount of potash to the 
vegetation, which was able to root in the soils of those days, and thus 
produced conditions favorable for growth. 


The climate plays a large role in the deposition of peat because a 
wet, uniform climate will produce much more vegetation in a given 
time, other things being equal, than a climate where growth and pres- 
ervation are limited to certain seasons of the year. The rate of de- 
cay in a warm climate will be greater but this is largely offset by a 
good water blanket for the fallen plants. The latter is possible only 
if the climate be uniformly wet throughout the year. If there be 
long, alternately wet and dry seasons, there will be little peat formed, 
unless the climate be cool, no matter how much rain falls. 

There is no satisfactory way of computing the rate at which peat 
accumulated in the coal-forming periods. We can only judge the 
rate approximately by considering the amount of peat which forms 
at the present day in a given time and it is only in a few areas that 
definite information can be obtained regarding the rate of formation 
of modern peat deposits. Where a forest is cut away or where peat 
grows over a road or other cultural feature whose age is known, 
quite accurate data may be obtained regarding its growth. Lesquer- 
eaux considers that in the Jura of Switzerland, peat has formed to a 
depth of 1 8 to 20 inches on an area which has been cut over within 
50 years. Geikie 1 gives quite a number of cases where the rate of 
growth is well established. In the valley of the Somme, 3 feet of 
peat has developed in 30 to 40 years, and on a moor in Hanover 4 
to 6 feet has grown in about 30 years. Near Lake Constance a layer 
3 to 4 feet thick has required only 24 years while among the Danish 
mosses 10 feet required 250 to 300 years for its deposition. 

In summing up the data concerning the rate of growth of peat 
Ashley 2 states that under the most favorable conditions i foot may 
form in 5 years, and that i foot in 10 years is a fair average maximum. 
In the larger and deeper basins the rate is slower and in any case the 
newly formed peat soon contracts to only a fraction of its original 
bulk. Lesquereaux considers that a foot of peat at the surface 
shrinks to f foot at depth in the bog. By taking into account the 
specific gravity of the peat at the surface and at depth, it is possible 
to arrive at an approximate figure for the amount of old peat formed 
from the surface layer. It is generally agreed that approximately 

1 Geikie, A., Text-book of geology, 2nd ed., p. 443, 1885. 

2 Ashley, G. H., The maximum rate of the deposition of coal. Econ. Geol. Vol. 2, 
PP- 34-47, 1907- 


i foot per century is a fair average rate for the development of old 
compressed peat. 

The Amount of Coal Derived from a Given Amount of Peat 

Having considered the rate at which peat forms we may take up 
the question of the approximate rate of the formation of coal. No 
definite figures can be obtained on this subject but a number of val- 
uable observations have been made. Renault 1 has decided after ob- 

FIG. 28. Upright trunk in Coal Measures at St. Etienne, France. Broken at base. 
(Photo by E. S. Moore.) 

serving carefully the shrinkage of stems of trees in passing from wood 
to coal that the loss is from eleven-twelfths to twenty-nine-thirtieths 
of the original. This is for the change to bituminous coal of the 
Commentry basin in France. Ashley 2 from calculations made on 
the relative specific gravity, and on the loss of moisture and other 
constituents, concludes that 3 feet of old peat would form i foot of 
bituminous coal such as that in the Pittsburgh seam, and, as a rule, 
about 20 feet of vegetal matter will form i foot of coal. In deducing 
his figures Ashley has also used other interesting examples such as the 
shrinkage in the vegetal matter which formerly filled a small, deep 
basin and now forms a thin lens-shaped layer of coal on the bot- 

1 Renault, B., Sur quelques microorganisms des combustibles fossiles, Bull, de la Soc. 
de 1'industrie min^rale, 3me serie Tome 13-14, 1899-190x5. 

2 Ashley. Loc. cit., p. 42. 


torn of the basin. He cites another case where two basins were 
connected over a low ridge and, considering that the basins were 
filled to a given level so that the peat could connect over the ridge, 
an approximation may be reached regarding the relative amount of 
coal formed on the ridge and in the basins from a mass of peat reach- 
ing a given level. 

If a foot of old, compact peat forms in a century and it requires 
3 feet of this peat to form a foot of bituminous coal it will require 
three centuries to form a foot of coal and three thousand years to 
form a seam 10 feet thick. 

Various attempts have been made to express the change from wood 
to coal by chemical formulae but they are "unsatisfactory because the 
formula given for cellulose will not represent the chemical composition 
of all the material entering peat, and it is difficult to write a chemical 
formula properly expressing the composition of a coal seam. There 
is almost no end to the formulae which might be written. Renault 1 
gives the following to illustrate the change from wood of Cordaites 
to homogeneous coal: 

(C 6 H 10 5 ) 4 = C 9 H 6 + 7 CH 4 + 8C0 2 + 3 H 2 O 

Cellulose Bituminous Marsh gas Carbon dioxide Water 

Parr's formulae 2 for lignite and bituminous coal are: 

(1) 5(C 6 H 10 5 ) = C 20 H 22 4 + 3CH 4 + 8H 2 O + 6CO 2 + CO 

Cellulose Lignite Marsh gas Water Carbon Carbon 

dioxide monoxide 

(2) 6(C 6 H 10 5 ) = C 22 H 20 + 5CH 4 + ioH 2 O + 8CO 2 + CO 


These formulae are valuable in showing the relative proportions 
of the various constituents of the wood which are supposed by these 
investigators to be lost but they cannot be taken too literally as 
representing the changes which have taken place. 

1 Renault, Loc. cit., p. 299 

2 Parr, S. W., Illinois Geol. Survey, Bull. 3, 1906. 


The Topographic Conditions Prevailing During Coal- 
forming Periods 

On examining the topography of any of the continents as they 
existed prior to and during the deposition of the vegetation giving rise 
to the great coal deposits, it is found that extensive, low swampy 
areas were very characteristic. The coal-forming periods invariably 
followed periods when shallow, continental seas, which were gradually 
filling: up, had spread over considerable areas of the continent. These 

FIG. 29. Section at Treve, France showing numerous stumps in Coal Measures. 

(After Grand 'Eury.) 

seas gradually retreated leaving great expanses of low land, poorly 
drained and ideal for the development of swamps on a large scale. 
The conditions must have been closely parallel to those now found 
on our great coastal plains along the Atlantic Ocean and the Gulf 
of Mexico. In the eastern part of North America the deposition had 
been predominantly marine previous to the Carboniferous period. 
During this period the land over most of this part of the continent 
began to emerge finally from the sea, never again to become an area 
of extensive marine deposition, although the western portion of the 
present continent continued to be covered with the sea. With the 
emergence of this great area there was a differential rise of the area 
bordering on the Atlantic and lying between the Atlantic as it then 
existed, and a long northeast-southwest sound on its westward 
side, known as the Appalachian trough. This trough was being filled 
with sediments from the land masses forming Appalachia on the east, 


the pre-Cambrian areas to the north, and the Cincinnati arch to the 
northwest. These land masses continued to be the source of clastic 
sediments, for the area occupying the old Appalachian trough became 
practically filled with sediments at the beginning of the Carboniferous 
period, presenting the aspect of an extensive coastal plain. This 
great flat area was subject to very gentle warpings, probably the 
forerunners of the larger buckling movements which later produced 
the Appalachian Mountains at the close of the coal-forming period. 
This area was so near sea level that a slight rise brought it into the 
condition of dry land or a small subsidence put it below the ocean 
just as minor changes cause the Atlantic coastal plain of the present 
day to rise above or fall below the sea. 

In the larger of the depressions formed by warping of the strata 
the swamps giving rise to the more extensive coal seams such, for 
example, as the Pittsburgh seam originated. In many of the depres- 
sions slow subsidence was constantly going on as these basins were 
being filled up with vegetal matter and sediment but it seems probable 
that the conditions can be best accounted for by frequent small 
elevations of the surrounding land and consequent relative sinking 
of the low areas. In some cases the conditions even permitted en- 
croachment of the sea, the destruction of forests, and the deposition 
of limestones and other marine deposits over the accumulated vegetal 
matter. Much of the sediment found associated with coal seams 
consists of feldspathic sands indicating incomplete decomposition, as 
if the materials composing the rock had been swept off a land surface 
where rocks were disintegrating. These products of disintegration 
might have been carried off to the basins owing to change of climate, 
or elevation of the land on which they were lying, causing greater 
activity of water. These materials could be derived from the dis- 
integration of granitic rocks and they could be rapidly transported 
to an area of deposition without being completely sorted or water- 
worn if streams became very active owing to increase in velocity due 
to increase in gradient or volume of water. 

The general absence of extensive erosional features in the measures 
during Carboniferous time indicates that there was a general sub- 
sidence in progress and that the swampy areas were seldom raised 
sufficiently above the sea to permit much erosion of the formations 
carrying the coal. They were areas of deposition rather than erosion. 



The red beds of the later Permian indicate a drier climate than that 
which had prevailed during the Carboniferous and the coal-forming 
process had practically ceased when the larger movements producing 
the Appalachian Mountains occurred. 

An examination of the conditions in the western part of the con- 
tinent at a later period shows that the conditions found in the east 
during the Carboniferous, (Mississippian and Pennsylvanian) were 

FIG. 30. Upright trunk in Coal Measures showing roots descending into rock to 
right of the hammer. (Photo by E. S. Moore.) 

practically duplicated in the west during the Jurassic and Cretaceous 
periods. During the former period a large shallow sea extended over 
the region now occupied by the Cretaceous and Tertiary coal deposits. 
This sea gradually withdrew from the land and conditions became 
favorable for extensive swamp development. The coal-forming proc- 
esses ended with the elevation of the Rocky Mountains as it did in the 
east with the rise of the Appalachians. An examination of other 
continents will reveal a similar close relation between the topographic 
conditions and the development of extensive coal-bearing formations. 
The essential features are base-leveling of the higher areas with a 
consequent aggrading and leveling up of the lower ones, and a general 
slow subsidence of the areas of peat deposition. 


The Origin of Underclays 

Various names have been applied to the clays underlying coal 
seams such as the "sole," "seatearth," and "mur." Some seams 
have no distinct underclay and some even lie on granite, schist or 
other igneous or metamorphic rocks. Beneath others the floor of 
the seam is conglomerate or coarse sandstone, and limestone under- 
lies a few beds. In many seams the change from coal to barren rock 
is abrupt while in others there is carbonaceous shale or black slate 
lying next to the coal indicating a gradual transition from the coal 
to the rocks free from vegetal matter. The shales, being less porous, 
are more likely to have partly preserved vegetation in them than the 
sandstones are, because the latter permit access of oxidizing water 
which decomposes the vegetal matter and leaves no carbonaceous 
deposit. The change thus appears more abrupt at the contact with 
sandstone than it really was. 

Underclays are so abundant in certain coal fields that some early 
writers, like Logan, regarded them as a universal accompaniment of 
coal seams. They are almost everywhere present under the seams of 
some of the English and American fields of Carboniferous age and 
they have been regarded by some writers as inseparably connected 
genetically with the seams. Many of these clays are fireclays and 
they are of great economic importance. They seldom show good 
stratification which may be at least partly explained by their plastic 
property, permitting them to be squeezed and kneaded under pressure 
until the bedding was lost. It is also observed that a layer of rock 
which has been penetrated by innumerable roots usually loses its 
laminated character. 

The unstratified character, the bleached appearance, and the 
common occurrence of Stigmaria, or roots in these clays has led many 
observers to regard them as old soils on which the vegetation forming 
the coal seams grew. It is well known from observation that the 
roots of plants will bleach the rocks they penetrate and these under- 
clays bear a certain resemblance to the muds under some modern 
peat-bogs and swamps. It is also well known, however, that modern 
peat does not grow only on such soils but it may be found on sands, 
marls, or almost any kind of rock. It is therefore evident that under- 
clays are not essential to the growth of luxuriant vegetation and the 
question may then be asked whether the vegetation is essential to 


the development of the underclays. Some writers have gone so far 
as to claim that where coal is not found above the fireclay it has been 
removed by erosion, but such a sweeping statement does not seem to 
be justified because fireclays have been found in marine deposits 
unassociated with coal deposits of any kind. Most of those clays 
are, however, stratified and laminated. 

If the drift theory were to be accepted for the accumulation of the 
vegetal matter these clays should represent a deposit of the finest 
and most completely assorted mineral sediment deposited in quiet 
water just before the lighter vegetal matter settled to the bottom. 
In that case, however, they should show more stratification than 
they do. Arber 1 suggests that they are marine and brackish water 
oozes deposited in estuaries like the black oozes of the nipa and man- 
grove swamps of the present day. If this be so, it is hard to under- 
stand why they are found only in their present position with reference 
to the coal. If coal be deposited in accordance with the in situ theory 
then these clays may have been the finer material which filled the 
basin in which the swamp occurred and the lack of stratification re- 
sulted from the growth of the plants upon it and later movements in 
a semi-plastic mass. 

There is one other possibility. If the statement of Mietzsch holds 
good that living Lycopodiaceae have from 22 to 26 per cent of clayey 
matter in their ash and the ancient types of these plants had a similar 
proportion, may not the decay of vast quantities of such plants on 
the floor of a swamp, before there was sufficient water over the vege- 
tal matter to prevent decay, have produced a deposit such as the 
underclay? Some efforts have been made to compare the composi- 
tion of the ash of the coal with that of the fireclay but this has not 
proved to be an entirely satisfactory means of settling the question. 
The clay in any case is mineral matter and there is always more or 
less of this in coal, carried in by wind and water from surrounding 
lands, and while it may be similar to that in the plants it is independ- 
ent of the composition of the ash of the wood. It is probable that 
some clays are at least partly chemical sediments. 

There is much need of further information regarding these inter- 
esting and valuable rocks. It seems very probable that the clays 
were deposited as part of a normal series of sediments and that 

1 Arber, E. A. N., The natural history of coal, p. 91, 1912. 


the growth of plants helped to destroy the stratification and to 
extract certain of the soluble salts; but the plants were not abso- 
lutely necessary for the formation of the clay nor was that kind of 
clay necessary for the growth of the vegetation as demonstrated by 
modern swamps and peat-bogs. 

Climatic Conditions 

Concerning the climate of the coal-forming periods there is some 
difference of opinion among paleobotanists. They are our chief 
judges in this discussion because we are dependent mainly upon the 
plants of those periods for indications of climatic conditions. There 
is one feature, however, concerning which there is unanimity among 
all the best authorities, and that is that the climate was uniform over 
great areas of the earth's surface. This is demonstrated by the 
fact that the same genera and some of the same species of plants of 
Carboniferous age are found distributed over both hemispheres from 
the tropical to the polar regions. A similar condition prevailed again 
in Jurassic and Cretaceous times. As to the cause of this uniformity 
little is definitely known. It has been suggested by some geologists 
and botanists that this condition was due to a greater amount of 
carbon dioxide in the air than there is in normal times and Cham- 
berlin 1 has described in detail how its presence might be brought 
about. Other factors which might aid in producing this uniform 
condition are the relation between sun and earth in position and dis- 
tance and changes in the distribution of land masses in the sea, per- 
mitting warm ocean currents to reach the polar regions and melt 
the ice. 

There is also little doubt concerning the humidity of the atmosphere 
during the coal- forming periods. This is necessary for the growth 
of such enormous quantities of plants in order that they may give 
rise to coal. Humidity and uniformity in climate are rather closely 
related. Further, if we accept the in situ theory for the origin of 
coal, sufficient water to cover the fallen vegetation is essential for 
its preservation and the warmer the climate the more the water re- 

As to whether the climate in the Carboniferous and other great 
periods of peat formation was hot is a debated question among paleo- 

1 Chamberlin and Salisbury. Geology, Vol. Ill, p. 432, 1906. 


botanists. Arber 1 claims that there is nothing in the Carboniferous 
flora so far as known to prove that it was tropical in character, as 
luxuriant forests may be found today in temperate regions and the 
large cells of the plants do not necessarily indicate tropical conditions. 
White 2 believes that the climate was humid, uniform and mild, being 
generally either tropical or sub-tropical. Some evidences of these 
conditions are the similarity in character between many of the plants 
now found in tropical swamps and those found in coal formations. 
The absence of growth rings in the trees indicates uniformity in seasons 
and the wide distribution of almost identical floras indicates uniform- 
ity in climate over wide areas of the globe. The large leaves and 
fronds, and the large cells with thin walls indicate rapid growth. The 
stomata are protected in grooves on the under sides of leaves of many 
plants and subaerial roots are found on many species. The seeds 
show provision for flotation and delayed fertilization. The presence 
of tree ferns, palms, and cinnamon trees in the Tertiary coal deposits 
suggests tropical, or at least sub-tropical conditions. 

There is one rather peculiar association of plants known as the 
Gangamopteris, or Glossopteris flora, which in Permian time spread 
widely over the Southern Hemisphere. It is different from the 
other coal-formation floras because of its close association with glacia- 
tion. It is found in Australia, India, South Africa, South America, 
and to some extent in Russia, where Glossopteris and Gangamop- 
teris are abundant in the vicinity of Moscow. 

In Australia the Permo-Carboniferous, or possibly more strictly, 
the Permian system, forms a very thick group of rocks containing 
extensive coal seams, which are of fresh- water origin and which in 
most cases show evidences of autochthonous origin by the presence of 
roots in the underlying clays. This group also contains thick beds 
of tillite showing that glacial conditions were prevalent at that time 
and that there were at least two great interglacial periods. A con- 
densed description of these rocks taken from David's work is as 
follows: 3 

1 Arber, E. A. N., The natural history of coal, Cambridge University Press, p. 70, 1912. 

2 White, David, The origin of coal, U. S. Bur. of Mines, Bull. 38, p. 68, 1913. 

3 David, T. W. E., British Ass. Adv. Sci. Handbook for Australia, p. 257, 1914. See 
also Siissmilch, C. A. An introduction to the Geology of New South Wales, p. 93, Sydney, 



1. Acid granites of New England 

2. Upper or Newcastle coal measures; with 35 to 40 feet of workable 

coal. Glossopteris predominates over Gangamopteris. Dadoxy- 

lon abundant 1500 

3. Dempsey Series; Barren fresh- water shale 2200 

4. Middle coal measures; with 20 feet of workable coal 500-1800 

5. Upper Marine Series; with marine fossils and glacial erratics ... 6400 

6. Lower or Greta coal measures; with about 20 feet of workable coal. 

Gangamopteris predominates over Glossopteris 100-300 

7. Lower Marine Series; with marine fossils. Basalts and tuffs. 

Glacial beds 300 feet thick at base 4800 

At Bacchus Marsh, Victoria, there are four beds of tillite in a for- 
mation 2000 feet thick. These glacial beds have been correlated with 
the Dwyka conglomerates of South Africa. In one place Ganga- 
mopteris occurs with a local coal seam in the upper part of the Lower 
Marine series, in fresh-water deposits. 

So far as known the Glossopteris flora does not occur in the typically 
Carboniferous strata which reach 20,000 feet in thickness in Australia, 
nor is Lepidodendron found in the Permo-Carboniferous although 
prevalent in the Carboniferous and upper Devonian. No doubt the 
great change in climate was too severe a test for Lepidodendron and 
related plants and they disappeared during the glacial conditions. 

Although there were two glacial periods associated with the coal 
seams of the Permian, there is no evidence that there was a sudden 
change in climate and that the Glossopteris and Gangamopteris 
flora lived under frigid conditions. These glacial epochs were separ- 
ated by long periods of time and when it is considered that during 
the apparently much shorter interglacial periods of the Pleistocene 
in America such trees as the pawpaw (Asiminia triloba) and the osage 
orange (Madura arantiaca), now found only considerably farther 
south, grew at Toronto, Canada, 1 it seems probable that Australia 
may still have had a reasonably mild climate during the formation 
of the important coal seams of Permian age. 

The Transformation of Vegetal Matter into Coal 

It is generally recognized that when vegetation changes to coal it 
passes through two stages, the first being known as the biochemical 
and the second as the dynamochemical stage. As these terms indicate, 

1 Coleman, A. P., Interglacial fossils from the Don Valley, Toronto. Amer. Geol. 
Vol. XII, p. 86, 1894. 



the first process is due chiefly to the action of bacteria and other low 
forms of life and the second to geological forces capable of produc- 
ing chemical and physical changes in the vegetal matter. 

The biochemical process, or the first stage in coal formation. 
When plants in a bog or swamp cease to grow, and fall, they are 
subject to attacks from bacteria and other low organisms. The 
most extensive investigations on this subject have been carried on 
by Renault, 1 the French scientist, who spent most of his later years 

I J 

FIG. 31. Bacteria in the cuticle of bothrodendron from the "paper coal" (x 800) (a) 
Bacillus exiguees (b) Isolated micrococcus (c) Micrococcus in process of division (d) Micro- 
coccus in colonies (e) Spores of bacilli. (After Renault.) 

in studying and identifying new species of bacteria in the coals. It 
is unfortunate that when Renault did such excellent work on this 
subject he should have permitted himself to go to extremes in his 
ideas of the prevalence and importance of these fossil organisms in 
the coal. Having had the privilege of examining his original slides 
the writer is convinced that many objects taken for bacteria were 
specks of mineral matter and in some cases, at least, crystallized or- 
ganic matter. Similar conclusions have been reached by others 
who have investigated this subject. Renault has shown, however, 

1 Renault, B., Loc. cit. Also du role de quelques bacteriace'es fossiles au point de 
vue geologique. Congres Geologique International, pp. 646-663, 1900. 



that a great many bacteria have been sufficiently well preserved to be 
recognized and to show that they undoubtedly did a great deal to 
macerate the vegetal matter (Figs. 31 and 32). There have been 
recognized representatives of the living forms such as Micrococcus 
and Streptococcus in ad- r miTTim 

dition to many others. 
These forms were most 
active in the upper 
layers of the peat be- 
cause the lower portions 
of the bog were so 
charged with organic 
solutions of ulmic, crenic 
and other acids resulting 
from chemical action 
that the bacteria could 
scarcely exist. Although 
no quantitative study 
has been made of this 
subject it is believed 
that their action extends 
to comparatively shallow 

In addition to the 
bacteria there are many 


FIG. 32. Chains of bacilli in coal of arthropitus 
(x 1200) (a) Chainlet of bacilli mostly diplospores 
(b) Group of arthrospores (c) Chain beginning to 
ramify. (After Renault.) 

larger plants, especially 
the fungi, which help to 
produce chemical 
changes and aid in the 
maceration of the plant debris. Among these, mushrooms and related 
plants probably play an important role. The action in all cases 
seems to result in a change from the production of oxygenated hy- 
drocarbon compounds of the living plant to a breaking up of these 
into such simple compounds as the oxides of carbon. When the 
latter compounds are formed the hydrogen must then be free to form 
simple compounds with carbon and with oxygen such as methane, and 
In addition to the bacterial action being halted by acid compounds 


resulting from their own action, it may be stopped by burial of the 
peat under layers of sediment or by mineral matter, deposited from 
solution, surrounding the plant debris. The latter action is well 
illustrated by the concretions commonly called "coal balls" found 
in many seams, or in the rocks overlying them. These bodies fre- 
quently contain perfectly preserved plant remains showing that the 
mineral matter must have sealed them up almost immediately after 
they fell. 

The second stage in codification: It seems to be generally admitted 
that biochemical processes are responsible for the early stages in the 
alteration of the plant debris as it changes to coal of any kind or even 
to old compact peat. There is a much greater divergence of opinion, 
however, regarding the processes which continue the alteration until 
different varieties of coal result. Since the greater number of ob- 
servers consider that the second stage is produced almost entirely 
by dynamochemical action this stage in the process is very frequently 
discussed as if the dynamochemical were the only factor to be taken 
into consideration, but several other hypotheses have been advanced 
in opposition to the dynamochemical theory. 

The various suggestions to account for the development of different 
varieties of coal from vegetal matter may be summed up as follows: 
(i) Differences in kinds of vegetation and differences in climates in 
different regions. (2) The length of time during which the vegetation 
has been exposed before burial by sediments. (3) Length of time; 
since burial of the vegetation. (4) The depth of burial of the vege- 
tation. (5) Action of heat from compression or from intrusions of 
igneous rocks. (6) Possibility of escape of volatile constituents after 
burial beneath sediments because of fractures or pores in the over- 
lying rocks, and jointage in the coal seams. (7) The pressure re- 
sulting from compression of the seam during dynamic changes in the 
enclosing rocks. 

1. Different kinds of vegetation and different climates. An 
examination of the different varieties of coal, omitting special types 
like cannel, will show that they differ very little in their physical 
composition. They all, whether lignite or anthracite, contain light 
and dark bands, fragments of resin, spores, fragments of bark and 
other plant debris. This seems to indicate that they may have been 
derived from the same type of vegetation. Anthracite has not been 



shown to contain a greater proportion of spores, resin or other portions 
of the plant than bituminous coal. It is well demonstrated that in 
an anthracite region a seam will be anthracite throughout and not 
in patches only like the cannel in bituminous coal seams. The fol- 
lowing analyses will show that various types of trees are so nearly 
alike in chemical composition that it would be impossible to put 
them through the same geological processes and expect to get different 
kinds of coal from them. 


















o. 50 


6. 20 





6. ii 
























*' o 


Table by Gottlieb. 

From Cellulose, by Cross and Be van. Longmans, Green 






i. Lycopodium dendroideum 
3. Lycopodium complanatum . . . . 
5 Equisetum hyemale 


41 Q4 


?Q .23 



. 12 

II .82 

7. Asidium marginale 

44 77 

c no 

41 .97 


9. Cyathea camculata 

4? . ?o 

6. II 


. 12 


n. Cyathea caniculata 






Analyses by G. W. Hawes. 1 Nos. 1,3,5 and 7 are average samples of the part 
of the plant above ground, including spores. Nos. 9 and n are tree ferns from 
Tahiti. No. 9 is an analysis of a section of the stem and No. n of the cortical 

Analyses of coal derived from different genera of Carboniferous 
trees were made by Carnot and it can be seen that the differences in 
composition in coal from Lepidodendron, Cordaites or Ptychopteris 
are negligible, the maximum difference in carbon being only 2.66 
per cent and in hydrogen 0.03 per cent. 

The plant fossils were identified by Renault and carefully selected 

1 Hawes, G. W., On the chemical composition of the wood of acrogens. Amer. Jour. 
Sci. ( 3 rd Series) Vol. 7, p. 585, 1874. 


to obtain any differences in the coal which might be due to differences 
in the original vegetation. 

It can be concluded that different types of plants cannot produce 
any material difference in the nature of the coal formed and that they 
have no particular bearing on the origin of anthracite. It is recog- 
nized, however, that different portions of the plant such as spores 
or resin, the latter of which may contain over 80 per cent of carbon, 
may form different types of coal if separated from the other plant 
debris and segregated in sufficiently large masses. There is, how- 
ever, no evidence whatever that such has been the case in the for- 
mation of anthracite. 

As for differences in climate producing any marked variation in 
the coal of different regions, there is no ground for accepting such a 
theory as all vegetation must be covered with water to preserve it. 
There is no great difference in the peat formed from trees in the 
tropical and temperate zones. 

2. Exposure before burial. It is a recognized fact that if wood be 
exposed to the air certain portions will decompose before other por- 
tions and there will be a relative increase in carbon and a decrease in 
hydrogen and oxygen. The wood usually decomposes first and leaves 
the more resistant bark and related tissues. To illustrate the change 
which occurs, the following analyses are quoted from Fayol's work. 1 

Carbon in bark of oak, 29.65 per cent; in sound wood 21.95 to 22.82 
per cent; in the same tree, slightly decomposed, 24.75; mor e decom- 
posed, 27.60; and rotten, 31.00 per cent. Analyses by Pollard of 
dark and bright coal from a seam in Wales show carbon in bright 
band 63.96, and in dull powder 77.17 per cent, and since the dull 
layers of mineral charcoal are generally thought to have originated 
through extensive rotting of the vegetation before burial these figures 
show that there undoubtedly may be considerable difference produced 
in the composition of the resulting material by more prolonged ex- 
posure before burial. When one attempts to employ this as a means 
of explaining the origin of the great deposits of anthracite it is useless, 
however, because these dull layers are present in bituminous coal also, 
and they are distributed throughout the anthracite seams in such a 
way as to indicate that they have no bearing on the anthracitic char- 
acter of the seam taken as a whole. 

1 Fayol, H. Loc. cit, p. 171. 


It has been suggested that the anthracite field of Pennsylvania 
owes its origin to longer exposure of vegetation laid down in the east- 
ern part of the state than that deposited in the west because of a 
gradual migration westward of the coastal plain on which the plants 
grew. This assumption scarcely seems justified because it is probable 
that the swamp or swamps which gave rise to the Pennsylvanian coal 
deposits were spread pretty uniformly over the anthracite and bitumi- 
nous areas at the same time. Further, the anthracite region being 
closer to Appalachia, the main source of supply for clastic sediments, 
it is probable that the vegetation was buried early in the history of 
these deposits In their studies of the South Wales anthracite de- 
posits Strahan and Pollard state that no definite relation exists be- 
tween the position of the anthracitized beds and the old shore- 

3. Length of time since burial. A general impression exists among 
many people interested in coal that the ag of the coal has an impor- 
tant bearing on its quality. To a certain degree this assumption is 
correct, because, other things being equal, the older coals will be 
higher in the peat-to-anthracite scale than the younger ones, not 
simply because the vegetation was formed in any particular geologic 
period, but because the metamorphosing processes have had longer 
to work and the older rocks have as a rule been more deeply buried 
and subjected to greater pressures than the younger rocks. There 
are many examples on record where seams of Carboniferous age are 
still in the form of brown coal or lignite. Such a case is found in 
Western Australia where a small area of Permo- Carboniferous meas- 
ures was faulted up and preserved from intense pressure. The coal 
is still brown coal, although practically all other Penno-Carbonifer- 
ous coal in Australia is bituminous or anthracite In Russia brown 
coal occurs in the Mississippian, or Lower Carboniferous, while in the 
western states and Canada and in many other countries the Cretaceous 
and Tertiary coals, which are more typically lignite, have been altered 
to high-grade bituminous coal or even anthracite in local areas. 

In connection with this discussion on the length of time since 
burial of the vegetal matter, the question of the length of time a bed 
of vegetation must be buried before it is changed to coal may be con- 
sidered. We have very little definite information on this subject 
but there is a clue in the occurrence of coal pebbles in the rocks asso- 


dated with coal beds. Renault and Fayol 1 have discussed the coal 
grains and pebbles in the Coal Measures in the Commentry basin in 
France. That these are water-borne fragments of coal and not frag- 
ments of wood buried in the sandstones and conglomerates and later 
transformed into coal is indicated by the fact that they have not 
shrunk nor have they been deformed in shape as they would have 
been had they consisted of wood and been turned into coal after their 
burial. They must represent fragments of a deposit lower in the 
Carboniferous which had already changed to coal and been broken up 
by erosion. 

In England there are also pebbles of coal high up in the Coal Meas- 
ures which Strahan considers as distinct fragments of coal derived 
from an eroded coal seam lying a few feet below the Pennant grit 
which carries the pebbles. There is no older coal formation in the 
region which could urnish these pebbles. These examples indicate 
that coal must form quite, rapidly from the vegetation. 

As modern examples of wood changing to coal in very short 
spaces of time, a case occurring in the vicinity of Scranton, Penn- 
sylvania, is cited by Moffat. 2 

A mine prop left standing and surrounded by mine refuse was sub- 
jected for about 30 years to high pressure from the roof and to high 
temperature from a mine fire, although the fire did not actually reach 
the prop. Different parts of the prop suffered varying degrees of 
alteration The lower portion was well preserved wood; about half- 
way up it was a little charred externally and above this it was turned 
into friable, soft charcoal. The upper part and especially the cap 
wedge, which had suffered from great compression and had been 
crushed down, was greatly altered and had a conchoidal fracture like 
anthracite coal, a jet black color, a bright glossy luster, and a specific 
gravity of 1.38. It burned with a feeble flame. Analyses showed 
that it contained: Moisture at 100, 5.65; Volatile Matter, 43.05; 
Fixed Carbon, 51.00; and Ash, 0.30 per cent. It would appear that 
although heat aided this change the pressure was necessary to produce 
the coaly character, as distinguished from charcoal. The wood in 
this prop and wedge retained its structure very well. 

1 Op. cit. 

2 Moffat, E. S., Note on the formation of coal from mine timber, Trans. Amer. Inst. 
Min. Eng., Vol. 15, p. 819, 1886. 



1 1 

^ I 

. .9 



Daubree 1 and Fremy have produced materials resembling coal 
from various woody constituents at temperatures from 200 to 300 C. 
It was found that woody fibers, as vasculose and cellulose, became 
black and brittle but retained their organization and did not fuse; 
while such substances as starch, sugar, gums, and chlorophyll became, 
when subjected to heat and pressure, black, brilliant, and insoluble 
like coal. The latter substances will also leave a coke. This may 
account for some of the differences between lignite and black lignite, 
or subbituminous coal, the one originally having more woody material 
than the other. 

From all available evidence it would appear that coal may form in 
a very short time, geologically speaking, if conditions be favorable. 
The chief factors producing the change are heat and pressure. 

4. Depth of burial. The depth of burial is so closely related to 
the compression resulting from crustal movements that these two 
factors may be considered together. It should be pointed out, how- 
ever, that there are few, if any, cases where it can be shown that the 
depth of burial alone was sufficient to produce anthracite, although 
it is such a generally recognized principle that the fixed carbon in- 
creases and the volatile matter decreases with depth in a series of seams 
that this principle is commonly known as the Law of Hill, after the 
man who expounded it. It has been stated by some writers that 
there is a definite relation between the depth of the seams and the 
anthracitization of the coal in the basin of Commentry in France, 
but this statement will not hold in all cases. Strahan 2 has pointed 
out that in the South Wales field the cover of not only the Palaeozoic 
rocks but also of the later rocks over the bituminous field is much 
thicker than that over the anthracite field. He states further, how- 
ever, that in general the conclusion of De la Becke and Joseph that 
the lower seams in the anthracite field were more anthracitic than the 
upper was correct but this will not hold for all seams throughout the 
field. The chart of iso-anthracitic lines (Figs. 33 and 34) brings out 
clearly the relation between the various seams in this field. White 3 

1 Daubree, fitudes et experiences synthetiques sur le metamorphisme et sur le for- 
mation des roches crystallines, p. 72, 1860. 

2 Strahan, A., and Pollard, W., The coals of South Wales, with special reference to 
the origin and distribution of anthracite. Memoirs Geol. Survey, England and Wales, 
2nd Ed., pp. 73 and 74, 1915. 

White, D., Op. cit., p. 126. 



has pointed out that of 20 cases where two or more of these seams were 
vertically 100 feet or more apart the analyses show only one case 
where there was a downward increase of volatile matter. Two cases 
show no difference and the others show an average loss per 100 feet 
of descent of 0.6 per cent volatile matter. In American seams, out of 
thirty-four cases twenty-nine show an average decrease of 0.38 per 
cent volatile matter per 100 feet descent. Quoting from Van der 
Gracht, White states that at Helenaveen the decrease in the gas coal 
is about 0.53 per cent; at Helden in the coking coal about 0.8 per 
cent; at Baarlo about 0.62 per cent; and in Westphalia, 0.51 per 

FIG. 34. Relation between depth and the carbon-hydrogen ratios in three seams 
in the South Wales coal field. (After Strahan and Pollard.) 

cent for gas coal and 0.71 per cent for coking coal per 100 feet. In 
Pennsylvania the depth of the anthracite seams cannot be taken as 
a criterion for the alteration which the coal has undergone but in 
some of the semianthracite areas of China there seems to be a more 
marked connection between the depth at which the seams lie and the 
degree of anthracitization There must, however, also be taken into 
consideration the factor of thrust, a subject which will be discussed 


5. Effects of heat. That heat from igneous rocks aided by the pres- 
sure which must be an accompaniment of intrusions can produce an- 
thracite from bituminous coal has been proven beyond a doubt. In 
Colorado, Alaska, New Mexico, and in numerous countries, natural 
coke, anthracite, and other types of coal have been produced from 
bituminous coal by igneous rocks. The effects of igneous intrusions 
are, however, quite local and they have not been responsible for the 
anthracite in the great fields of South Wales and Pennsylvania. In 
the Cerrillos Coal Field of New Mexico, considerable anthracite, 
mostly of secondary grade, has been produced as a result of the in- 
trusion of a great sill about 400 feet thick along the surface of a coal 
seam, but the effects extend only a comparatively short distance from 
the sill. As a rule there is some relation between the width of a dike 
or thickness of a sill and the width of the zone of coal affected, but 
this varies greatly. Usually the coal is not affected much beyond 
the width of the dike. It should be remembered in this connection 
that an igneous rock intruding coal will affect it much as it does other 
rocks which it intrudes. In some cases a dike or sill will scarcely 
metamorphose the adjacent rocks due to the fact it was almost cooled 
when it reached them or it may have had little hot gas or water to 
give off to attack the adjacent rocks. Some intruding rocks were 
hot and, carrying much hot gas and water, were capable of profoundly 
altering the surrounding rocks. As a rule acid rocks, such as granites 
and rhyolites, are capable of existing in the liquid condition at lower 
temperatures than the basic rocks like gabbros and basalts or traps, 
but they usually carry more liquids and gases and are, therefore, 
capable of producing more metamorphism at the temperature of 
intrusion than are rocks without these agents. 

In 1869 Bevan 1 attempted to explain the origin of the South Wales 
anthracite as due to trap rocks but it has been shown that these 
igneous rocks were earlier than the coal seams. The formation of 
Pennsylvania anthracite has also been assigned to the heat of igneous 
intrusions but there are no intrusions worth mentioning in this coal 
field and those intrusions which do occur are Triassic in age and much 
later than the coal. Intrusions of the same age and character occur 
also in the bituminous field of Pennsylvania without appreciably 
affecting the bituminous character of the coal. It must be admitted 
1 Bevan, J. P., The geologist, Vol. II, p. 75, 1869. 


that the influence of igneous rocks is very limited although neverthe- 
less real. 

6. Escape of volatile constituents through fractures and pores. 
In order to explain the lack of anthracitization of coal in areas of 
intense folding and even where the temperature has been rather high, 
Campbell 1 has suggested that fractures such as joints or cleavage 
in the coal and adjacent rocks have been responsible for this process. 
He assumed that the transformation of one type of coal to another, 
higher in fixed carbon, was primarily due to heat although not neces- 
sarily to a high temperature and that time was a very important 
factor in connection with the results derived from heating. Pressure 
may be important in producing heat by compression and in aiding 
the driving off of the volatile constituents but unless there be a means 
of escape for these there cannot be much change in the coal either 
from compression or heating. The process may operate if the en- 
closing rocks be porous, and overlying coarse sandstones would be 
much more favorable than shales for the escape of volatile constituents. 
In support of this principle he cites the graphitic coal of Rhode Island 
as an example of coal carried to the extreme condition of carbon- 
ization because of extensive fracturing permitting escape of volatile 
constituents. The anthracite of Pennsylvania is more fractured than 
the bituminous coal, and the lignites of North Dakota and Texas are 
overlain by impervious clays. This hypothesis is said to apply 
equally well to all the coal fields studied in the United States. 

Since there is no doubt that the coal changes to a higher carbon 
type by loss of gases Campbell's principle is perfectly logical but 
there are some limitations which should be kept in mind, and this 
may explain why some highly fractured coal has not been altered to 
a high carbon type. The extensive fracturing of a rock is evidence of 
yielding to stress, and the pressure which would have been exerted on 
the coal, if the rock had not been broken, is relieved by fracturing, 
with the result that both heat and pressure are lost. There is ap- 
parently a proper balance between the length of time the coal suffers 
pressure and the fracturing, because if the fracturing occurs too early 
in the process insufficient pressure may be exerted. 

There are many coal seams which contain an abundance of gas 

1 Campbell, M. R., Hypothesis to account for the transformation of vegetable matter 
into the different grades of coal. Econ. Geology, Vol. I, p. 26, 1905. 


which escapes by blowers or by oozing out during the mining oper- 
ations. This coal is not necessarily lower in fixed carbon than other 
coal which does not give off so much gas during mining, because it 
has absorbed the gas in its pores. If the pressure be sufficiently great, 
the gas will be compressed and will remain in the coal, but in all 
cases where it cannot escape an equilibrium will be established be- 
tween the volatile constituents attempting to escape and the com- 
pressed gas already given off. It is evident, however, that other 
conditions being equal less pressure will be required to raise the coal 
to a higher type if the gas can escape. 

7. Effect of pressure. Although there may appear to be many 
exceptions to the rule it must be generally recognized that anthracite 
and other high-carbon coals are characteristically found in regions of 
crustal disturbance the world over. Anyone reading the descriptions 
of coal fields will find that if any country contains anthracite it is 
invariably found in its mountains or disturbed areas, and this con- 
dition goes a long way towards establishing the thrust-pressure hy- 
pothesis for the origin of anthracite. This hypothesis has in recent 
years been worked out in great detail by White 1 for the United States, 
and he has shown that this is the most logical explanation for the 
devolatilization of coal in its second stage of development. 

There are certain geological factors entering into a consider- 
ation of such a hypothesis which have not always been given due 
consideration. In almost any coal field there will be found a series 
of sediments made up of heavy, strong beds, such as sandstones or 
conglomerates, known as the competent beds; and others, such as 
coal and shale, which comprise the incompetent beds. When pressure 
is applied to these strata the incompetent beds yield and adapt them- 
selves to the movements of the competent beds which are sufficiently 
strong to resist buckling. If the beds always lay perfectly horizontal, 
or the thrusts were always applied parallel to the bed and equally to 
all the competent beds there would be no important result. In such 
a heterogeneous column of strata, however, there are oblique thrusts 
and therefore movements of one rock over another in various direc- 
tions, with the result that great pressures are exerted on the coal and 
the shale but the adjacent competent rocks have suffered very little 

1 White, D., Op. cit., p. 105; and, Some problems of the formation of coal. Econ. 
Geol., Vol. 3, p. 292, 1908. 


deformation. This condition is well illustrated in Figure 63, where 
one formation is highly contorted but the rocks above and below show 
no effects of the pressure. Coal acts as a plastic mass in the early 
stages of its development from vegetal matter as illustrated by Figure 
74, and it is then capable of accommodating itself to almost any 
shaped space without showing any trace of the movement. These 
structural principles may offer an explanation of the flat-lying an- 
thracite seams in the Wyoming basin in Pennsylvania and in the coal 
fields of China. A highly fractured stratum is not always evidence 
of excessive pressure having been applied in that area but it is evidence 
that the pressure was relieved. It may not have done more than a 
small fraction of the work in devolatilizing the coal which it would 
have done had it been applied to a competent bed capable of with- 
standing that pressure and of transmitting it to the coal seam. A 
small amount of heat thus generated and held there for a long period 
of time, would devolatilize the coal. 

If this principle be applied to the well-known anthracite fields of 
Pennsylvania and South Wales it is believed that it will explain most 
of the features. The Pennsylvania field lies in a highly disturbed 
area along the main limb of the anticlinorium forming the Appal- 
achian Mountains to the southeast and the synclinorium forming the 
Appalachian Valley to the west of this field. There is, when con- 
sidered on its broader lines, a marked difference between the com- 
plicated structure of this region and that of the comparatively simple 
structure of the bituminous field farther west. It is probable that 
this area suffered an unusual amount of compression where the mount- 
ains were developed and the fact that there are small, comparatively 
undisturbed areas within this region is no evidence that they did 
not suffer from intense thrust pressure. The thickness of the whole 
series of strata concerned in the great crustal movements must have 
also affected the pressure exerted on the coal seams although the seams 
lie near the top of the series. The strata were very thick, probably 
upwards of 25,000 feet in that region. The accompanying map of 
Pennsylvania showing the fuel ratios of the coal in various parts of 
the state illustrates the relation between the anthracite and bitu- 
minous areas and shows the gradation from one to the other (Fig. 

Turning to the South Wales anthracite field, so well described by 







Strahan and Pollard, 1 a gradual change from an T 
thracite to bituminous coal is found, but with 
the peculiar condition that there is a marked 
increase in the ash in the latter, a condition 
which would not be expected if part of the bi- 
tuminous coal gave rise to anthracite by de- 
volatilization. The ash content as indicated by 
all analyses available varies from about i per 
cent at the anthracite end to 6 per cent at the 
bituminous end. (Fig. 36.) Various explana- 
tions have been offered to explain this, such as 
differences in the original vegetation and differ- 
ences in the extent of decomposition before 
burial of the vegetation. These are not satis- 
factory because there is no evidence that the 
vegetation in these areas was different and if 
it were it would require that practically all the 
coal in the bituminous area be derived from 
Equisetum or some such plant to give rise to so 
much ash. If the same plants underwent diff- 
erent degrees of decomposition, this would tend 
toward higher carbonization and therefore an- 
thracitization but it certainly would not reduce 
the relative ash content in the anthracite. It 
would appear that the only explanation is found 
in the addition of more mineral matter to the 
vegetation while it was accumulating, or later 
by action of ground water percolating through 
the rocks. 

It has been clearly shown that the anthra- 
citization was not the result of igneous intru- 
sions, nor does there seem in all parts of the 
field to be any relation between the lines of 
iso-anthracitization, and the original outline of 
the basin in which the coal was deposited, or the 
present outline of the basin. Strahan and Poll- 
ard have shown that there is with few excep- 

1 Strahan, A., and Pollard, W., Op. cit., p. 80. 


tions a regular increase in anthracitization with depth and also in going 
westward from the eastern border of the basin, but they conclude that 
there is for them no satisfactory explanation for the origin of the an- 
thracite. Differences in original vegetation are not satisfactory; nor is 
the metamorphism by pressure hypothesis substantiated as the iso-an- 
thracitic lines do not correspond with the lines of disturbance, and 
the faulting which has so profoundly affected the region was later 
than the formation of the anthracite and has had little influence on it. 
Although the carbon-hydrogen ratio increases with depth there seems 
to be little or no difference between the coal in the anticlines and that 
in the synclines. 

White considers that the isovols, or lines of equal volatile matter, 
in this field follow closely lines normal to the thrusts and that if the 
area were worked out on this basis the thrust-pressure hypothesis 
would explain the anthracitization. In the writer's opinion this is 
the only explanation, and the composite chart in Figure 33 indicates 
that the iso-anthracitic lines follow the outlines of the basin except 
for variations which would be the logical result of thrusting. An 
example of this may be seen on the chart in the Rhonda No. 2 

The best hypothesis so far offered for the origin of anthracite and 
the one which it is believed will explain its origin in all the fields so 
far studied, if logically applied, is the thrust-pressure hypothesis. 

The Origin of Cannel and Boghead 

As early as 1833 Hutton 1 examined cannel coal under the micro- 
scope and found small " cells " which he said were of a resinous 
nature and contained a wine-yellow " liquid." This seems to have 
been the first time that the spores of cannel coal had been noticed. 
Balfour, Huxley, Dawson, Bertrand, Renault, and Jeffrey have 
since that time, in turn, studied these spores in detail and added much 
to our knowledge concerning them. There is now no doubt but that 
cannel consists almost entirely of spores and spore exines with some 
of the other more resistant portions of the vegetal matter. These 
bodies collect in open water and form layers usually of lens-shape, 
in the other types of coal. 

1 Hutton, W. Observations on coal. London and Edinburgh Phil. Mag. and Jour, 
of Sci., Vol. II, p. 302, 1833. 



Cannel bears certain resemblances to the bogheads, including the 
varieties Torbanite, oil shales, kerosene shales, and bituminous schists. 
There seems to be little 
doubt that the organic 
matter of the latter 
rocks is a step nearer 
petroleum and natural 
gas than that of the or- 
dinary coals and in this 
way petroleum is related 
to all coals through these 
types high in volatile 
constituents, especially 
the lighter hydrocar- 
bons, and lower in the 
carbohydrates. The best 
known deposits of these 
rocks are the Torbanite 
of Scotland, the bitu- 
minous schists of Autun, 
France, and the kerosene 
shale of New South 
Wales, Australia. 

Largely as a result of 
the work of C. E. Bert- 
rand and B. Renault 1 it 
became generally accep- 
ted that these bogheads 
were formed from gela- 
tinous algae. The rocks 
were studied micro- 
scopically and certain 

FIG. 37. (a) Horizontal section through the bog- 
head of Autun showing Pila bibractensis (x 17), (6) 
Vertical section of same (x 38). (After C. E. Bert- 

minute bodies were recognized as the thalli of algae (Fig. 37). 

1 Renault, B., and Bertrand, C. E., Note sur la formation schisteuse et le boghead 
d' Autun. Bull. Soc. 1'industrie minerale, Tome 7, 3me Ser., p. 499, 1893. Also, Pila 
bibractensis et le boghead d'Autun. Soc. d'Histoire Naturelle d'Autun, Bull. 5, p. 159, 
1892. Also, Reinchia Australis et Premieres Remarques sur le Kerosene Shale de la 
Nouvelle-Galles du Sud. Soc. d'Histoire Naturelle d'Autun, Bull. 6, p. 321, 1893. 


Bertrand 1 describes the algae as occurring as a hollow, compressed 
sack lying in a brown jelly, which is known as the fundamental jelly 
and which is said to carry many bacterial bodies. Between the 
thalli there are spores and grains of pollen forming thin laminae of 
orange or reddish-brown color. It is stated that the algae carry 
solid material to the extent of 0.015 to 0.030 of their volume. 

Various names were applied to the supposed algae from different 
regions. Those from the boghead of Autun were known as Pila 
bibractensis and those from the kerosene shale of New South Wales 
as Reinschia australis. As Thiessen 2 has pointed out, however, there 
are many unsatisfactory features in Bertrand's explanation of the 
source of the bituminous matter which formed the fundamental jelly. 
Jeffrey 3 has attacked the works of Renault and Bertrand and has 
shown by means of modern section-making methods that these sup- 
posed algae are not thalli of algae but spores of vascular cryptogams. 
The openings in the supposed thalli are the tri-radiate lines on the 
spores. He explains the difference between cannel coals and boghead 
as due to the fact that the latter are composed of larger spores than 
the cannels, i.e., they consist chiefly of macrospores. The fact that 
oil shales derive their oils and gases from spores has been verified by 
other investigators. 

Jeffrey's conclusions have been generally accepted but one writer 
claims that he has obtained very strong evidence in support of the 
algal theory in some recent deposits in Russian lakes. M. D. Zalessky 4 
states that he was inclined to agree with Jeffrey until he saw well 
preserved, silicified specimens of Pila from Autun and he has recently 
examined algal deposits which are now forming. In the brackish, 
shallow lake, Ala-Kool which lies at the southern extremity of the 
fresh- water lake known as Balkhash and which is overgrown with 
aquatic plants there lives the oleaginous alga, Botryococcus braunii 

1 Bertrand, C. E., Charbons gelosique et charbons humique. Compte Rendu VIII, 
Congres Geologique International, p. 458, 1900. 

2 White, D., and Thiessen, R., The origin of coal. U. S. Bureau of Mines, Bull. 38, 
pp. 198-199, 1913- 

3 Jeffrey, E. C., The nature of some supposed algal coals. Proc. Amer. Acad. Arts 
and Sciences, Vol. XL VI, p. 273, 1910. 

4 Zalessky, M. D., On the nature of pila, the yellow bodies of boghead and on sapropel 
of the Ala-Kool Gulf of Lake Balkhash; Extrait du tome XXXIII des Bulletins du 
Comite" Geologique, St. Petersburgh, No. 248, 1914. 


in such superabundance that it would appear that sapropel might 
form from it on the lake bottom as in the case of the bogheads in 
Permian and Carboniferous time. The plankton algae come to the 
surface and they have been analysed by S. L. Ivanov, who obtained 
the following: Oil, 3.5 per cent; number of free fatty acids, 12; 
ether number 16; saponification number 28; iodine number 55.4. 
The sapropelic crust formed along the edge of the lake was also ana- 
lyzed and with ether yielded 25 per cent of its substance. The ether 
was then evaporated and a hard, wax-like mass remained. This 
mass gave acid number 93.5 per cent; ether number 46.7; saponi- 
fication number 140.2; iodine number 31.5; nitrogen, 0.4003 per cent. 
Oleinic acid was believed to be present. 

A hydrogen sulphide fermentation takes place in the mass and when 
it is exposed to the air it changes from a green, movable body into a 
yellow-brown solid, elastic and reminding one of a mass of rubber, 
which can be cut with a knife. Thin sections show some preserved 
cellular structure of algae, the cavities of the swollen cells being 
represented by roundish pores. Zalessky claims that these are very 
similar to the structures seen in the silicified bogheads of Autun 
prepared as suggested by Jeffrey and he considers that Pila and 
Botryococcus are strikingly alike. The mud of Ala-Kool consists 
almost exclusively of algae of this type with a few other green algae 
and some diatoms. 

The liquid product of B. brunni reminds one of tar with a slight 
benzine smell. There are solids like vaseline and other lubricants, 
and since Engler obtained artificial petroleum from oleaginous algae 
there would appear to be a possible source of petroleum in this type 
of plant. 

These observations of Zalessky are very interesting as throwing 
new light on this subject, but it is doubtful whether he will con- 
vince most observers that algae were the source of the bogheads. 
It is peculiar that if these algae were so abundant during the for- 
mation of the coal measures they have not been more frequently 
recognized in coal deposits, while on the other hand it might naturally 
be expected that in the open waters of almost every swamp a con- 
siderable amount of such plant material should be laid down. 




Plants are the source of all coal and therefore the types which 
formed it and their distribution are matters of vital interest to all 
who study the origin of coal deposits. The climatic conditions 
existing during the coal-forming periods and the question as to whether 
the plants of those periods were similar to those now living on the 
earth are also subjects for special consideration. The fossil plants 
are our best geologic thermometers and hygrometers and we are largely 
dependent upon them for our information regarding the earth's 
early climates. 

In searching for plant fossils one seldom finds distinct forms in 
the higher grade coal itself unless they are enclosed in " coal balls " 
where they are almost hermetically sealed. The soft, semi-plastic 
vegetal matter which forms the coal is partially destroyed by bac- 
terial action and oxidation and then is squeezed so that little sign 
of the original plants remains evident to the naked eye except that 
in some cases a large fragment of a tree trunk may resist complete 
destruction. In the coal balls the most delicate plant structures 
may be preserved and aside from them the best fossils occur in the 
shales and slates of the partings or in the roof or floor of the seam. 
Delicate structures are sometimes preserved in these rocks, which, 
being originally muds, have formed good coverings for the plants as 
they have sealed them very tightly. In the coarser sandstones and 
conglomerates only casts of the larger fragments of plants are pre- 
served, due to two reasons, one the ready access of air and water to 
the plant fragment, causing it to decay without leaving a good im- 
print, and the other the coarseness of the material surrounding the 
plant. This prevents the various particles of the plant from being 
held in their proper position for the production of perfect impressions 
of its structure. 

A study of fossil plants satisfies us that, in many respects, the 




vegetation existing during the coal-forming periods was similar to 
that now found upon the globe. The changes from the earliest 
land vegetation to the modern types have, on the whole, been gradual 
although a few sudden and marked changes have occurred. The 
first great development of land plants, which made the formation of 
coal possible, occurred in the Devonian period, and from Upper Dev- 
onian time until the Pleistocene there was not a period in the earth's 

FIG. 38. Lepidodendron lycopodivides, (Sternberg) showing branches 
and leaves. (After Zeiller.) 

history when coal was not fo ming somewhere on the earth. This 
indicates that the formation or non-formation of coal during any period 
since the first appearance of land plants has been fundamentally de- 
pendent upon the topographic and climatic conditions then existing 
on the globe rather than on the lack of plants or of any particular 
kind of plant. There seems always to have been a flora ready to 


populate any region where conditions were suitable for development. 
Everything points to the fact that it matters little what kind of plant 
enters into the constitution of coal, but the physical and chemical 
changes which the vegetation later undergoes produce the profound 
differences in the different types of coal derived from it. 

The Rise of the Land Plants 

The two outstanding features in the evolution of the earth's 
vegetation are the great development of the Pteridophytes, known 
to many as the Vascular Cryptogams, in the early days of land plants, 
and the advent of the flowering plants comparatively late in the 
earth's history. 

The Pteridophytes include the Filicales, or ferns; the Equise- 
tales, or horsetails; the Lycopodiales, or lycopods, and the Spheno- 
phy Hales. All of these were present in the Devonian and they reached 
an extraordinary degree of perfection in the Carboniferous. The 
ferns have continued to flourish through all the periods to the present 
day, with the disappearance of many genera and the appearance of 
new ones. The horsetails had representatives in the Carboniferous 
which were good-sized trees, and they continued as such until the 
end of the Jurassic when the last great trees of this type disappeared 
and the group degenerated until it is now represented only by the 
insignificant Equisetum. 

The lycopods of the genera, Lepidodendron and Sigillaria formed 
giant trees which were dominant in many of the coal basins. They 
disappeared very early in the history of land plants, Lepidodendron 
not even reaching the Permian and only a few species of Sigillaria 
existing in the lower portion of that system. For the sudden ending 
of these great genera in the Northern Hemisphere there is not much 
explanation because there seems to be little evidence of a sudden 
change in climate, although the prevalence of red beds and the pres- 
ence of annual rings of growth in trees indicate approaching aridity 
and more distinctly marked seasons. In the Southern Hemisphere 
their extinction is more readily understood as it corresponds closely 
with the inception of glacial conditions which practically wiped out the 
previously existing flora and introduced the Gangamopteris flora 
containing, as common forms, Gangamopteris, Glossopteris and 
Rhacopteris. The latter flora has been an accompaniment of inter- 



A group of grains, cones, spores, and seeds from the Coal Measures of France. 
Figs, i, 2, Male floral organs of cordaites; Fig. 3, Grains of pollen; Figs. 4, 5, 6, 
7, Cordaianthus gemmifer; Figs. 8, 9, 10, n, 12, 13, 14, 15, Cordaianthus bacci- 
fer; Figs. 16, 17, 18, Cordaicarpus major, ventricosus, vellavus; Figs. 19, 20, 21, 
C. Guthbieri, ovatus, congruens; Fig. 22, Cordaicarpus punctatus, Gr.; Figs. 23, 
24, 25, C. drupacens, expansus, reniformis; Fig. 26, C. eximius; Fig. 27, Diplotesta 
Grand'Euryana (Brong.); Fig. 28, Carpolithes avellanus. (After Grand'Eury.) 


glacial periods in Australia, India, South Africa, and South America. 
All of these countries were more or less closely linked up in the Per- 
mo-Carboniferous by land connections. This flora has also been found 
to a limited extent in the Northern Hemisphere as, for example, in 
European Russia which could be easily reached from India since the 
Himalaya Mountains were not then in existence. 

This change in the vegetation of the Southern and to a lesser 
extent in that of the Northern Hemisphere is the most sudden change 
in the history of plant life on the earth. In the coal fields of America 
there was a great change in the vegetation during the Permian, as 
every species, but not every genus, of the Coal Measure plants dis- 
appeared early in that period. The increasing dryness and the ele- 
vation of the Appalachian Mountain system had a profound influence 
on the flora of the eastern part of the continent, which was the only 
great land area at that time as most of the western portion of the 
continent was under the sea. Many genera and some families ceased 
to exist, and when the Triassic period opened the Gymnosperms 
had become the dominant type of vegetation in place of the Pteri- 
dophytes, or Vascular Cryptogams. 

The Gymnosperms, or " naked-seed " plants were represented in 
the Devonian by the Cycadofilicales, a group of seed plants which 
strongly resembled some of the ferns in appearance but which bore 
seeds and were similar to the cycads in some other respects. These 
plants occupied a very prominent position in the Carboniferous period 
and were for a long time mistaken for ferns. The Gymnosperms 
were also represented by the conifers which appeared in the Devonian 
and which left some traces in the Carboniferous. In the Permian, 
Walchia and Voltzia were typical examples of this group, which be- 
came much more prominent in the Triassic than it had been previously. 
During the Jurassic some of our more modern types of conifers, like 
the pine and the cypress, appeared and continued to flourish. 

Another great Gymnosperm group was the Cordaitales which 
appeared in the latter part of the Devonian period, became very 
abundant in the Carboniferous and gradually died out before the 
close of the Paleozoic. These plants were probably the ancestors of 
the Gingkoales. The latter became abundant in the middle of the 
Mesozoic era and then gradually declined until the group is now 
represented by the single species, Gingko biloba. The cycads were 




Lepidodendron aculeatum (Sternberg) showing the leaf scars and the varying ap- 
pearance of these when portions of the bark are removed, i A is an enlargement of 
one of the leaf cushions, and 7 illustrates the bark of an old tree. (After Zeiller.) 


represented in the Coal Measures and they gradually developed to a 
climax in the Jurassic. They have since declined in relative im- 

From the Triassic, which seems to have marked the beginning of 
the dominance of the more modern vegetation over that of the Pale- 
ozoic, the flora has become more and more like that with which we 
are now familiar. There were periods of adversity for the plants 
and there were periods like the Jurassic and early Tertiary when the 
climate seems to have been fairly uniform from the equator to the 
poles. During these periods the tropical and subtropical species 
spread far to the north and south as they did in the Carboniferous, 
and the remains of plants like the cycads, which we now think of as 
tropical and subtropical lie beneath the Arctic snows. 

In the Triassic 1 the Gymnosperms were dominant but the flora 
on the whole was not luxuriant as in the Carboniferous. The horse- 
tails were large and abundant. There were many ferns and conifers. 
The cycads were beginning to be numerous. 

The Jurassic period showed a much greater development of modern 
genera than did any previous period. The cycads reached their 
climax and the period has been called the " Age of Cycads." Mod- 
ern conifers like pines, arbor vitae, and cypresses appeared. 

With the opening of the Lower Cretaceous, or the Comanchean of 
America, an important event in the evo ution of plants occurred. 
This was the appearance of the Angiosperms, or " enclosed-seed " 
plants. These flowering plants, apparently originating in the north- 
eastern part of the continent, soon spread all over it, and many modern 
genera of eucalypti, figs, magnolias, cinnamon, and others well known 
today, made their appearance and have contrived to flourish to the 
present time. In the Upper Cretaceous the beech, birch, oak, wal- 
nut, breadfruit, and holly were all present and the flora had assumed 
quite a modern aspect. 

Classification of Plan 

In a classification of plants which includes foss'l types it should be 
pointed out that the fossil plants must be divided into genera which 
are founded on a basis different from that used in a classification of 

1 Fontaine, W. M., Older Mesozoic flora of Virginia. U. S. Geol. Survey, Monograph 
VI, 1883. 



living plants. This is owing to the incompleteness of the fossils 
since parts of the plant may be separated from each other or entirely 
destroyed. It is necessary to classify them into what may be called 
" form " genera, based on the form of the fragment. For example, 
the genus Lepidodendron includes the stem of a tree and Stigmaria 
the root of the same tree. Such an arrangement of genera is not 
found in the classification of living plants. 


FIG. 39. Group of grains representing the seeds of various plants in the Coal Meas- 
ures of France A, B, Trigonocarpus (Brong.); C, Polylophospermum (Brong.); D, E, F, 
Polypterocarpus; G, H, Codonospermum (Brong.); I, Carpolithes sulcatus (Prest.); 
J, K, L, M, Rhabdocarpus (Gopp and Berg). (After F. C. Grand'Eury, Flore Carbon- 
ifere du Departement de la Loire.) 

Many botanists have divided all plants into two large groups, the 
Cryptogams or spore-bearing plants, and the Phanerogams, or flower- 
ing plants. The former supposedly included all those in which the 
sexual reproduction is concealed, thus embracing all the lower types. 
In the Phanerogams the reproduction was thought to be exposed in 
the stamens and pistils which were mistaken for sexual organs. In 
this division were placed all the seed plants. 

In more recent classifications, however, the seed plants are known 
as Spermatophytes and they are divided into the Gymnosperms and 
Angiosperms, the former comprising the primitive seed types and 
the latter the more highly developed and more modern flowering 
plants. As might be expected, the older fossil seed plants all belong 


to the Gymnosperm group as do also many of the later fossils, and our 
discussion of the coal flora will be confined largely to a discussion 
of this group, as the Angiosperms did not appear on the earth, so 
far as known, before the Cretaceous period. In a modern classi- 
fication 1 of plants the following divisions are recognized: (i) Thal- 
lophytes, (2) Bryophytes, (3) Pteridophytes, and (4) Spermatophytes. 


The Thallophytes are plants of the simplest form and they get 
their name from the fact that with few exceptions they consist only 
of thalli. The thallus is an undifferentiated vegetal body which in 
its lowest form, like the animal amoeba, does not have a division of 
functions. In such forms the jelly-like mass of protoplasm can push 
out legs, or pseudopodia for purposes of locomotion and these may 
surround particles of food which become engulfed in the mass and are 
absorbed. The processes of reproduction are simple. In some 
cases there is simple division, in others a spore is produced which 
gives rise to the new plant. Some of the higher forms possess multi- 
cellular sex organs. 

There are two important divisions of the Thallophytes including 
(i) Algae and (2) Fungi. The Algae are subdivided according to 
color into the " Blue-Green," the " Green," the " Brown " and the 
" Red " Algae. 

The Fungi are subdivided into at least four groups which contain 
respectively, the water moulds and the mildews; rusts and smuts; 
the toadstools, mushrooms and puffballs; the bacteria and the lichens. 

The Algae vary in size from microscopic organisms to the large 
seaweeds, and many of the Fungi are so minute that they cannot be 
seen with the naked eye. 

From a palaeontological standpoint the Algae existed in pre- 
Cambrian time and they have been abundant in certain geological 
periods, although it is doubted whether they played any important 
part in the formation of coal. Bacteria have also been in existence 
since early geological time and their influence in coal formation has 
been discussed in connection with the biochemical processes in the 
origin of coal. It is believed that fungi such as mushrooms have also 

1 Coulter. J. M., Barnes, C. R., and Cowles, H. C. A textbook of botany, Vol. I, 


I8 7 


i 4, Sigillaria elegans (Sternberg); 5 10, Sigillaria mamillaris (Brongniart). 
These figures illustrate the different appearance of the specimens when portions of 
the bark have been removed, i and 5 show the scars of the organs of fructification 
as well as the leaf scars; 4 and 6 show the posterior side of the bark; 10 is from a young 
tree. (After Zeiller.) 


been instrumental in producing biochemical changes in peat as far 
back as the Carboniferous period. Any evidence of fossil Thallo- 
phytes, so far as known, can be seen only by aid of the microscope and 
therefore these plants do not concern the average person collecting 
plant fossils. 


The Bryophytes are a large group of plants showing a distinct 
advance over the Thallophytes in structure. They show a definite 
alternation of generations and are characterized by sexual and sexless 
individuals. The gametophyte produces the sex organs and the 
sporophyte produces the spores. The members of the group possess 
an archegonium which is characteristic of higher plants, and they thus 
show their relation to these higher forms. They possess a multi- 
cellular antheridium much more highly developed than that of the 

This group is divided into two main divisions (i) Hepaticae or 
liverworts and (2) Musci, or mosses, including the Sphagnales or 
" bog mosses "; the Andreaeales; and the Bryales, or " true mosses." 
The Bryophytes, or Bryinae are regarded by Land and others as of 
recent origin although it has been claimed that barren forms of this 
group have been found in the Carboniferous of France. They are of 
little interest from the palaeontological standpoint but the Sphag- 
nales, comprising the genus Sphagnum, are of much interest at the 
present time because of the importance of this genus in the formation 
of peat in the cooler climates. 


The group of Pteridophytes contains many important fossil species 
in addition to numerous well-known living forms, such as ferns, horse- 
tails and club-mosses. They are characterized by a vascular system, 
or series of vessels for conducting material from one part of the plant 
to another, and from this character they are frequently known as the 
Vascular Cryptogams. This vascular system serves to separate the 
Pteridophytes very sharply from the Bryophytes and Thallophytes, 
but it is found in the Spermatophytes and shows the relation of the 
Pteridophytes to these higher seed plants. The gametophyte, known 
as the prothallium, and the sporophyte are independent of each other. 



The pro thallium develops from a spore and on it the oo spore develops 
in the archegonium, giving rise to the sporophyte, the full-fledged 

FIG. 40. i Sigillariostrobus goldenbergi. (O. Feistmantel.) ; 2 S. tieghemi (Zeiller); 
4 S. goldenbergi (Zeiller); i, 2, 2 A and 4 show cones of fructification; 2 B and 4 A are 
macrospores enlarged. (After Zeiller.) 

plant, bearing spores in the sporangia. Most people are familiar 
with the dark spots on the under side of fern leaves. Each of these 
spots is a group of sporangia known as a sorus. It is considered that 


the Pteridophytes have been developed from a liverwort-like an- 

This group has been subdivided by Coulter, Barnes, and Cowles 1 
into six groups as follows: (i) Lycopodiales or club-mosses, (2) 
Psilotales, (3) Sphenophyllales, including only the fossil genus Spheno- 
phyllum, (4) Equisetales, or " horsetails," (5) Ophioglossales, in- 
cluding the common adder's tongue and moonwort, and (6) Filicales, 
or ferns, including the Filicineae or " true ferns " (homos porous) and 
Hydroteridineae, or " water ferns " (heteros porous). 

Zeiller 2 makes the following four divisions (i) Filicineae, or ferns, 
(2) Rhizocarpeae, or Hydropterides, often placed as a sub-class under 
the Filicineae, (3) Equisetineae and (4) Lycopodineae. Of these 
(i), (3) and (4) are well represented among the Coal Measure fossils, 
but (2) is absent unless Sphenophyllam be put in that class as some 
have placed it, although it is more nearly related to the Lycopodineae. 
It has no living representative. 

(1) The Lycopodiales. There are several living and many ex- 
tinct genera in this group. Lycopodium, which is the best known, 
has been characterized by Coulter as possibly the best living repre- 
sentative of the earliest forms of vascular plants. Some have re- 
garded Phylloglossum, an Australian species, as the most primitive 

In Lycopodium the plant, or sporophyte, is a branching stem cov- 
ered with many small leaves and on each of these there is a spo- 
rangium on the upper side. The term sporophyll is applied to these 
spore-bearing leaves and when grouped together they form a strobilus. 
There is a tendency in some of these plants for the lower leaves to be- 
come sterile and cease to bear sporangia, while this function is carried 
on entirely by stalk-like sporophylls rising above the foliage leaves. 

The stem shows two zones, an outer one of cells known as the cor- 
tex and an inner one known as the stele in which the vascular system 
is found. From the vascular cylinder, strands extend through the 
cortex to form the leaf traces on the exterior. 

The Lycopodiales, although now represented only by the humble 
club-mosses, were in Carboniferous time among the large trees and 
their fossil forms are as a rule arborescent. 

1 Op. cit., p. 122. 

2 Zeiller, R., Bassin houiller de Valenciennes, Description de la Flore Fossile, Text 
and Atlas. Paris, 1888. 



Two well-known families, Lepidodendrae and Sigillariae, are found 
widely distributed in later Paleozoic rocks. Under the Lepidodendrae 
several genera have been recognized: Lepidodendron (Sternberg), 
Lepidopholios (Sternberg), Halonia (Lindley and Button), Bothro- 
dendron (Lindley and Hutton), Lepidostrobus (Brongniart), Lyco- 

FIG. 41. i Stigmaria ficoides (Brongniart) showing main roots and attached rootlets; 
2 and 3, Scars where rootlets have been attached. (After Lesquereaux, Pa. Geol. Survey.) 

podites (Brong.), Lepidophyllum (Brong.). Of these Lepidodendron 
is best known and it will be described as a type. 

Lepidodendron (Sternberg): Plants of this genus formed trees in 
Paleozoic time which according to Grand 'Eury 1 reached a meter in 
diameter and 30 meters in height, with leaves in some cases a meter 
long. They and the Sigillariae are so abundant in the Coal Measures 
and their stems are so characteristic that they have always attracted 
a great deal of attention among miners and others collecting plant 
fossils. Sigillaria is recognized by the parallel vertical lines of leaf 

1 Grand'Eury, F. C, Flora carbonifere du Departement de la Loire et du Centre de 
la France; Paris, p. 148. 1877. 


cushions on the bark while Lepidodendron is distinguished from it by 
its spirally arranged lines of leaf scars. 

The leaves of Lepidodendron are generally acicular, and very long 
on the stems, but much shorter on the branches; they diminish in 
size with each bifurcation of the axis. On the stem they are attached 
to elongated-rhomboidal to pointed-oval cushions, (Fig. 38). When 
the epidermis is present these cushions show three bodies making up 
one structure roughly oval in outline and sharply tapering at one end. 
The other end is capped by a small rhomb with three small dots. 
Above this rhomb, close to the end of the cushion, is a small scar 
representing the leaf-detachment scar. The small dots are re- 
garded by most writers as leaf-bundle traces, although some think 
that only the middle one is of this origin. If the outer bark be re- 
moved, a new condition is presented and each cushion shows only 
one scar at the top. (Plate VI.) 

The cushions are in contact with one another except that in some 
specimens they are separated by sharp furrows and in others by broad 
flat strips. According to Stur 1 who has given detailed descriptions 
of these fossils, the former are older plants than the latter. 

As to the reproduction of the arborescent fossil Lycopods, Zeiller 2 
says that they appear to have been heterosporous. The greater 
part of the cones of fructification in which the structure has been 
studied seem to carry the macrosporangia on the lower and the micro- 
sporangia on the upper bracts. He still feels, however, that the 
matter has not been fully settled. 

Geologic and geographic distribution: .Lepidodendron was widely 
distributed over the earth in Carboniferous and sub- Carboniferous 
time. It seems to have been found in every country where coal was 
forming at that time, reaching its maximum development in the 
lower and middle Coal Measures and then declining. In Australia 
no trace of it is found even in the Permo-Carboniferous deposits 
as it had died out before they were laid down, and in Europe it barely 
extends into the Permian. In North America it has not extended 

1 Stur, D., Die Culmflora der Ostrauer und Waldenburger Schichten. Abh. d. k. k. 
Geol. Reichsanstalt zu Wien, Vol. 8, Heft II, also Die Culmflora des mahrisch-schlesis- 
chen Dachschiefers, Heft I, 1877. Quoted by Solms-Laubach in Fossil Botany, Rev. 
Trans, by Balfour, I. B., 1891. 

* Zeiller, R., Op. cit. 



into the Permian. 1 It is confined, therefore, to the Paleozoic. The 
earliest appearance of the genus is reported to be in the Lower Dev- 
onian beds of Wieda and Hartz. 2 It is widely distributed in America. 

FIG. 42. 1-2 aa, Annularia longifolia (Brongniart); 2 b, 2 bb, A. inflata (Les- 
quereaux); j, 30, Asterophyllites equisetiformis (Brong.); 4-50,, A. gracilis (Lesq.); 
6, 7, Sphenophyllum schlotherinne (Brong.); 8, 9, Annularia sphenophylloides (Zenk.); 
10, loa, Sphenophyllum bifurcatum. (After Lesquereaux, Pa. Geol. Survey). 

Europe, and Australia in the Upper Devonian and the Mississippian, 
or Sub-Carboniferous. 

Sigillariaea: Under the family Sigillariaea have been described 
the genera Sigillaria (Brongniart) 3 , Sigillariostrobus (Schimper), and 
Stigmaria (Brong.). It has been known, however, since the work 
of Binney that Stigmaria is not a genus but simply the root of 
Sigillaria and Lepidodendron. 

1 Solms-Laubach, Fossil botany. Rev. Trans, by Balfour, I. B., p. 194, 1891. 

2 Fontaine, W. M., and White, I. C., Permian flora. 2nd Geol. Survey Pa., Pt. PP, 
p. 114, 1880. 

8 Solms-Laubach, Op. cit 



Of the others, Sigillaria (Brong.) 1 is by far the best-known genus. 
As already stated, it may be distinguished from Lepidodendron by 
the fact that the leaf scars are arranged in vertical, parallel bands 
rather than in spirals. Our knowledge of the leaves and many other 
features is not as great as it is of those of Lepidodendron. 

FIG. 43. Calamites suckowi (Brongniart) with articulations and secondary branches. 
Coal Measures of France. (After Zeiller.) 

The leaf cushions are roughly polygonal in outline and they may 
be compressed vertically so as to give a transversely elongated six- 
sided figure with the two horizontal sides considerably longer than 
the other four, which are approximately equal. (Plate VII.) When 
of this form they are compressed together so that they form vertical 
ribs of scars alternating in adjacent rows. 

Along the upper side of the cushion there are three small marks. 
The middle is punctiform or somewhat elongated transversely, while 
the others are short, thin marks diverging from it. These marks 
represent the leaf traces. 

1 Brongniart, A., Observations sur la structure interieure du Sigillaria elegans com- 
pare"e a celle des Lepidodendron et des Stigmaria et a celle des vegetaux vivants. Ar- 
chives du Museum d'Hist. Nat. Vol. I, 1839. 



There is a good deal of uncertainty about the leaves of Sigillaria, 
but leaves which are believed to be from these trees have been de- 
scribed by a number of botanists. They are long and have a keel 
resulting from the projection of the 
median nerve. White 1 has found 
leaves in the Missouri Coal Meas- 
ures which he describes as probably 
belonging to Sigillaria. They were 
broad, rather thin, but seldom 
flattened. Some fragments were 
20 cm. long and 5 to n cm. in 
width. They tapered very grad- 
ually and, from the appearance of 
certain fragments, the entire leaf 
must have been 40 to 50 cm. in 
length before being broken. The 
upper surface showed a strongly 
marked furrow 2 to 2\ mm. in 
width. The lower surface of the 
leaf was marked by a carene about 
2 mm. wide and on either side of 
this there was a well-defined crease, 
probably the stomatiferous crease 
previously described by Renault. 

Dichotomous branching has been 
found in this genus but stems are 
frequently single. 

In the matter of reproductive 
organs it has been observed that 
the regular bands of leaf scars are 
frequently curved or irregular and 
that lying between them there are other scars which are rounded or 
angular and which differ considerably from the leaf scars. These 
are supposed to be the scars left by the organs of fructification. Much 
interest has been attached to Zeiller's 2 discovery of Sigillarian cones 

1 White, D., Flora of the outlying carboniferous basins of Southwestern Missouri. 
U. S. Geol. Survey, Bull. 98, p. 103, 1893. 

2 Zeiller, R., Cones de fructification des Sigillaires. Ann. des Sci. Nat., Ser. 6, Tome 
19, 1884. 

FIG. 44. Calamites cistii (Urong- 
(After Lesquereaux Pa. Geol. 


on long stalks with the leaves bearing sporangia standing out from 
the stem. Since he could only find macrospores he considers either 
that these trees were homosporous, or that the two types of spores 
were produced on different cones and the macrospore cones were not 
found. The discovery of these cones has led some botanists, such as 
Renault, to regard some of the Sigillariae as closely related to the 
cycads, but such relation has not been substantiated. 

Geologic and geographic distribution: Sigillaria did not make its 
appearance in Europe before the beginning of the Carboniferous, and 
very few specimens are found in the Millstone Grit. It seems to 
have reached a climax about the middle of the Coal Measures and 
then declined. The Rothliegende is probably the latest formation 
in which remains are found. This family is not mentioned as oc- 
curring in Australia or New Zealand and it seems to be considerably 
more restricted geologically and geographically than Lepidodendron. 
In North America only two species reach the Permian and they dis- 
appear early in that period. 

Stigmaria ficoides (Brongniart) : x The fossils known as Stigmaria 
were in early days thought to be a genus of plants. They are ex- 
tremely abundant in the " sea tear th " under the coal seams of many 
fields, and the finding in England of these bodies actually attached to 
stumps of Sigillaria and Lepidodendron has settled their derivation. 
They are probably the roots of a few other genera also and it is in- 
teresting to see how similar are the roots of so many of these trees. 
The scars on the roots are the markings of the rhizomes or rootlets, 
and specimens have been found with dichotomous branches (Fig. 41). 
Very often these roots when broken open exhibit a cylindrical body 
which readily separates from the exterior coating and which seems 
to be a cast of the central cylinder. 

(2) Sphenophyllales. The Sphenophyllales are not represented 
by a living species. The only genus is Sphenophyllum (Brongniart) 2 
which is well represented by fossils in the Coal Measures. There 
has been much difference of opinion regarding its relations. Some 

1 Renault, B., et Grand'Eury, Etude sur les Stigmaria, rhizomes et racines de Sigil- 
laries. Annales des Sciences geologiques, Tome 12, 1881. 

2 White, D., Op. cit., p. 35; Coemans, E. et Kick, J. J., Monographic des Sphenophyl- 
lum d'Europe, Bull, de 1'Acad. Roy. d. Belgique, 2me Ser., Tome 18, p. 134, 1864; also 
Newberry, J. S., The Genus Sphenophyllum. Jour. Cincinnati Soc. Nat. Inst. XIII, 
p. 212, 1891. 



botanists consider it as most closely related to the Lycopodiaceae 
while others regard it as being more nearly related to Calamariae. 
Members of this genus are herbaceous, the stems are simple or branched, 
and the surface is canaled. The leaves are in verticils on the strongly 
marked articulations and in groups of three. The leaves are sessile 
as a rule but they may occur on pedicles. Those on the stipe are 
different from those on the habetas. 

FIG. 45. i, ia Sphenopteris subalata (Gein); 2, 2b, S. brittsii sp. nov.; 3-40,, 
S. goniopteroides sp. nov.; 5, 50, S. hoeninghausi (Brongniart); 6, 6a, S. elegans (Brong.) ; 
7, fa, S. larischi (Stur); 8-pa, S. tridactylites (Brong.). (After Lesquereaux, Pa. 

Geol. Survey.) 

The center of the stem consists of a triangular axis made up of three 
vascular bundles. Exterior to these is a ring of large aqueous tubes 
with lateral tangential growth. 

The bark is thin, lacuneous and generally poorly preserved. The 
branches are single on articulations. The roots are cylindrical and 
the arrangement of the wood in them is much like that of the stem. 

The sporangia are borne on the bracts at some distance from the 


axis and are marked at the point of attachment by a small circular 
umbilical depression. 1 

Geologic and geographic distribution: In Europe Sphenophyllum 
extends from the Culm to the lower Rothliegende and was a very 
prominent genus in the middle and upper Coal Measures. 2 It is not 
mentioned as occurring in Australia. In North America this genus 
occurs from the lower Coal Measures to the Permian. 

(3) Equisetales. The Equisetales, or horsetails, include the 
order Equisetineae, which in turn includes the family Calamarieae. 
This group, which formed a great arborescent flora in the Paleozoic, 
is now represented by the single genus Equisetum, a genus of small, 
insignificant plants preserving many of the characteristics of the 
fossil trees and commonly known as scouring rushes. 

Of the Calamarieae Renault states that these include all fossil 
plants, either Cryptogams or Phanerogams, which present a cala- 
mi toid stem, i.e., a stem of which the central part is occupied by a 
relatively voluminous pith, its length being divided into a series of 
similar articulations which may or may not be related to the articul- 
ations of the sheath. 3 He would then divide the Calamarieae into 
two divisions, the Equisetinees and the Calamodendrees. The first 
would include the articulated plants containing only primary wood, 
some of which reproduce by simple spores, i.e., are isosporous, like 
the modern Equisetum, while others carry both microspores and 
macrospores. As examples the genera Annularia and Asterophyl- 
lites are cited, (Fig. 42). Catamites apparently belongs here also. 
The second division includes those which have the secondary 
wood more or less well developed and which in their organs of fructi- 
fication more nearly approach the phanerogamic plants than do those 
of the other division. Of the family Calamarieae, Calamites (Suc- 
kow) (Fig. 43), and Annularia (Sternberg) are the best known genera. 
Other genera are Pinnularia, Asterophyllites, and C alamo phyllites. 

In these plants the surface of the stems, the roots and their branches 
are marked by ribs and longitudinal furrows. The bark appears 
smooth but little furrows may be found. In some species the furrows 

1 Renault, B., Bassin houiller et Permian d'Autun et d'Epinac. Flore Fossile, Text 
and Atlas, Fasc. IV. 

2 Solms-Laubach. Op. cit., p. 343. 
8 Renault, B., Op. cit., p. 60. 




Pecopteris (Asterotheca) abbreviata (Brongniart.) i, Illustrating the gradual 
dividing of the pinnules near the inner end of the frond; j, 4 Fertile pinnules; 4 B 
Spores enlarged 40 times. Coal Measures of northern France. (After Zeiller.) 



alternate at the joints and in some they do not. The roots have an 
organization similar to that of the stem and frequently the aerial 
stems rise from articulations of the roots. The racines and leaves are 
arranged in verticils at each node on the root, stem, or branch. The 
leaves are simple and uninerved, sometimes free and sometimes in a 
collarette along the stem and branches. Sporangiae, attached to the 
borders of transformed leaves, are generally disposed in numerous 
verticils connected and forming the cone. 

FIG. 46. i Odontopteris alata (Lesquereaux) ; 2 O. brardii? (Brongniart) ; 3, 4 O. 
sphenopteroides sp. nov.; 5, 6 O. subcrenulata sp. nov.; 7, ?a O. abbreviata sp. nov.; 
8 O. aequalis (Lesq.) (After Lesquereaux, Pa. Geol. Survey.) 

These plants are believed to be isosporous like the modern represent- 
atives of this group. 

Geologic and geographic distribution: Calamites and Annularia 
seem to have made their appearance with the Carboniferous rocks, 
although members of the Equisetales were present in the Devonian 
formation and extended through that system and into the Permian. 
They were extremely important in the Carboniferous and representa- 



tives of the Equisetales have continued to flourish through the geologi- 
cal periods to the present day. They continued to form large trees 
until the end of the Jurassic period, but in the Cretaceous they de- 
generated into small plants. As well as having extensive geological 
distribution these plants were. widely distributed in Australia, Asia, 
Europe, and America 

FIG. 47. Neuropteris heterophylla (Brongniart) showing the development of primary 
and secondary pinnules. Coal Measures of France. (After Zeiller.) 

(4) Filicales, or Ferns. As previously intimated, the Filicales 
are divided into two groups, the Filicineae or " true ferns " which 
are homos porous, and the Hydropteridineae or " water ferns," which 
are heterosporous. The true ferns include such types as the royal 
ferns, tree ferns, filmy ferns and ringless ferns. The members of the 
group extend from the Devonian period to the present and some 
of them were very prominent in the coal measures of various periods. 



They may be arborescent or herbaceous, the height of some of the 
arborescent varieties being as much as 20 meters. 

The classification of the living ferns is based chiefly on the nature 
of the sporangia. Zeiller 1 states that on this basis ferns may be 
divided into two large groups, Leptosporangiae or the ferns proper, 
and Eusporangiae or Marattiadiae. In the former group each spo- 
rangium springs from only one epidermic cell and when it is ripe the 

FIG. 48. i, 4, 5, 7, 9, 12 Neuropteris hirsuta (Lesquereaux) ; 2, 5, 6, 8, 10, n, N. 
angustifolia (Brongniart). (After Lesquereaux Pa. Geol. Survey.) 

walls are formed of only one layer of cells. In the latter sub-class 
each sporangium proceeds from a subepidermal cell, and when mature 
the walls are relatively thick since they are constituted of several 
layers of cells. 

In the case of fossil ferns it is generally necessary to follow Brong- 
niart's system 2 and classify them according to the nature of the fronds 

1 Zeiller, R., Bassin houiller et Permien d'Autun et d'Epinac. fitudes des gites 
mine'raux de la France. Fasc. II, Pt. I, Flore Fossile, (FougSres) 1890. 
* Brongniart, A., Histoire des vegetaux fossiles, 1828. 


and the nervation since the organs of fructification are infrequently 
preserved. One of the striking features of all ferns is the highly 
divided character of the leaves. The method of division has been 
used as a means of classification by Brongniart and others, but that 
system is not very satisfactory. The organs of fructification, or 
sporangia, where preserved, are found on the under side of leaves and 
form little globular sacs containing a considerable number of spores 
which are set free by rupture of the wall of the sporangium. The 
spores give rise to the prothallium, a vegetative apparatus which 
carries both the male and female organs. 

On the basis of the manner of attachment of the pinnules and the 
nervation the ferns may be divided into the following six groups: 1 

1. Sphenopteridae, in which the frond is finely divided and the 

pinnules are small; 

2. Pecopteridae with pinnules attached to the rachis for all their 


3. Odontopteridae with pinnules equally fixed to the rachis for 

all their width but without the distinct median nerve; 

4. Neuropteridae with pinnules generally quite large, rounded, 

and often notched in the center of their base, attached at 
only one point; 

5. Teniopteridae with simple fronds, ribboned, much longer than 

wide, the edges entire or feebly crenulated; 

6. Dictyopteridae, including all forms in which the nervation 

anastomoses and forms a more or less complex network in- 
stead of remaining separate. 

In cases where the organs of fructification have been found, a more 
logical and genetic arrangement may be made, but the classification 
has never been satisfactory. 

Following unsatisfactory attempts to classify the ferns thus, re- 
cent work by Grand'Eury, White, Kidston, Oliver and Scott has 
shown that many of these plants are not ferns and that they should 
be placed with the Gymnosperms as the most primitive of these 
plants. For those plants which bear seeds and which had formerly 
been called Cycadofilices because they combined in the stem the 

1 Zeiller, R., Op. cit. 



characters of ferns and cycads, Oliver and Scott 1 have proposed the 
name Pteridospermae. In this group Zeiller 2 considers that there 
should be placed several of the Sphenopteridae, some Pecopteridae 
such as Pecopteris fluckeneti and Pecopteris sterzeli, probably all the 
Alethopteridae comprising probably Callipteridium and Callipteris, 
also all the Odontopteridae and Neuropteridae. He considers that 
it would be easy to change the two last-named families but there is 
much uncertainty about many of the others such as the Alethopteridae, 

FIG. 49. Taeniopteris Newberriana sp. nov. From the Permian. (After Fontaine 

and White, Pa. Geol. Survey.) 

and that three groups might be made, including the Filicineae, the 
uncertain forms and the Pteridosperms. In this division Zeiller 
would leave with the ferns those plants whose fronds carried the fili- 
coid fructifications but whose male apparatus is like that of the Pteri- 

Geologic and geographic distribution: The ferns made their ap- 
pearance in the early Devonian and reached a fairly high state of 

1 Oliver, F. W., and Scott, D. H., On Lagenostoma Lomaxi, the seed of Lyginodendron. 
Proc. Roy. Soc. London LXXI, p. 477, 1903. LXXIII, p. 4, 1904; also On the structure 
of the Paleozoic seed Lagenostoma Lomaxi. Phil. Trans. Roy. Soc. London, Ser. B., 
Vol. 197, p. 193, Pis. 4 to 10, 1904. 

2 Zeiller, R., Bassin houiller et Permien de Blanzy et du Creusot, Etudes des gftes 
MinSreaux de la France, Fasc. II, Flore Fossile, Text et Atlas. 



development in that period. They increased in numbers 01 species 
and in individuals in the Carboniferous and while none of the typical 

FIG. 50. i Alethopteris serli (Brongniart) ; j, A. decurrens (Artes). These forms 
illustrate the different forms of the pinnules in this genus. (After Zeiller.) 

Carboniferous species extended beyond the Permian other species 
of the same genera have occupied a prominent position in the world's 
flora during the Triassic and Jurassic periods and still others have 



carried the succession to the present time. They have been found 
in probably every country in which plant remains are abundant 


The Spermatophytes include the two great groups of highly organ- 
ized seed plants, the Gymnosperms and the Angiosperms. They are 
often called Phanerogams or " flowering plants." 


The Gymnosperms include a great variety of plants, from shrubs 
to large trees, and they have had representatives from middle Paleo- 
zoic time to the present. They are characterized by their naked seeds 

FIG. 51. Lonchopteris bricei (Brongniart) showing the terminal pinnules and the 
changes occurring in the pinnules with maturity. From the Coal Measures of France. 
(After Zeiller.) 

in contrast to the Angiosperms which have the seeds enclosed. The 
main groups of. Gymnosperms are (i) Cycadofilicales , (2) Bennettitales , 
(3) Cycadales, (4) Cordaitales, (5) Gingkoales, (6) Coniferales, and 
(7) Gnetales. Of these groups the Cycadofilicales, the Bennettitales, 
and the Cordaitales are all extinct. 

(i) Cycadofilicales: As already mentioned in the discussion on 


ferns, there have been found during this century numerous plants 
which were formerly thought from their frond character to be ferns 
but which have been grouped together to form the Pteridosperms 
because of the discovery of their seeds. They are believed to be the 
most primitive of the seed plants, and from them the modern Gym- 
nosperms developed. They show a transition between the ferns 
and cycads and they differ from the ferns in having secondary wood. 
This secondary wood is still a Pteridophyte character in some groups 
although it is also a characteristic of the Gymnosperms. The micro- 
sporangia are similar to those of the ferns but the macros porangia are 
very different since an ovule is developed. As the members of this 
group have been differentiated so recently and as there is so much 
uncertainty about which genera and species should be placed with 
the Pteridosperms and which with the ferns, it is impossible to state 
definitely their geological range. They appeared at least as early as 
the Upper Devonian, became extremely abundant in the Carbonifer- 
ous, extended into the Permian and probably into the Mesozoic. 

(2) Bennettitales and (3) Cycadales: Bennettitales is the name 
applied by some botanists to a group of extinct Mesozoic plants which 
are regarded as the ancestors of the living cycads. In his monograph 
on the fossil cycads, Wieland 1 stated that in the opinion of Scott and 
Zeiller the Bennettitales should not be regarded as a separate class 
and that his work has verified the opinion of these botanists and his 
own earlier expressed opinion. He had formerly believed that Cycad- 
ales should include the existing families Cycadeae and Zamiae form- 
ing the order Cycadaceae, and the extinct family Bennettiteae which 
might have the rank of an order. 

The living forms of cycads are tropical plants and they occur in 
both the Eastern and Western Hemispheres. Common genera are 
Cycas and Zamia. 

The family Cycadeoideae or the Bennettiteae have been reported 
from the Triassic, the Jurassic, and lower Cretaceous of America 
and they have a similar range in Europe and Asia. 

The representatives, such as Zamites, of the living families of 
cycads have been found as far back as the Coal Measures. 2 They 

1 Wieland, G. R., American fossil cycads, Carnegie Inst. of Washington, p. 236, 1906. 

2 Renault, B., et Zeiller, R. Sur quelques cycadees houilleres. Comptes rendus de 
Pacad. de Paris, 1886. 



increased in numbers through the Permian and reached a maximum 
development in the Jurassic which is often spoken of as the " Age of 
Cycads." They have had a very wide geographical distribution. 
(4) Cordaitales: The Cordaitales formed the main portion of the 
arborescent Gymnosperm vegetation of the later Paleozoic. They 
comprised rather slender trees which were of uniform size for 10 or 
15 meters, but reached upwards of 30 meters in height and were 
crowned by numerous branches. The genus Cordaites (Unger) may 

FIG. 52. Cycadeoidea marshiana showing stages in fruit production as shown in 
branching species. (After Wieland, American Fossil Cycads.) 

be taken as the typical representative of the group. The leaves are 
simple and are characterized by distinct parallel nervation, often 
becoming complex. They resemble those of the Cycads in exhibiting 
the characteristic mesophyll, and those of the Coniferae in the form 
of the leaf, which is long, usually rounded at the outer end and narrow- 
ing towards the base. 

The stem and branches are provided with a large medullar sheath 
cut by transverse diaphragms of the pith. There is a thick cylinder 
of secondary wood. 

In the structure of the ovule and the swimming sperms they re- 
semble the Cycads and Gingkos which are the only living plants 



with these sperms. Their structure has been studied in detail by 
Grand'Eury, and Renault, and to them chiefly we owe our knowledge 
of the reproductive organs. 

Geologic and geographic distribution: The Cordaiteae appeared in 
the Devonian in America, 1 Europe and Australia. It seems possible 

FIG. 53. Cordaites showing the leaves and organs of fructification. (After Grand' 
Eury. Flore Carbonifere du Departement de la Loire.) 

that they may have lived as early as the Middle Devonian. They 
were abundant in the upper Coal Measures and continued into the 

1 Dawson, J. W., On Fossil Plants from the Devonian Rocks of Canada. Quart. 
Jour. Geol. Soc. of London, Vol. 15, 1859. 



Permian, but it is not believed that they survived the close of the 

(5) Gingkoales: This order of Gymnosperms is represented by a 
single living species, Gingko biloba, found wild in China and culti- 
vated by the Chinese and Japanese. The fossil forms of this group 

FIG. 54. Walchia frondosa (B. Renault) showing small cones. From the Permian of 
France. (After B. Renault, Bassin Houiller et Permien, Etudes des Gltes Min6raux 
de la France.) 

have frequently gone under the name of the Salisburias. They have 
probably been derived from the Cordaitae and they were abundant 
in the Mesozoic, being mentioned as occurring in the Oolite and the 
Chalk of Europe, and in the Triassic and Jurassic of Australia. 1 

1 Siissmilch, C. A., An introduction to the geology of New South Wales, pp. 164 and 
175, 1914. 



(6) Coniferales: This group of plants is so well known at the 
present day that they scarcely need a detailed description. They 
are characterized primarily by their cones although other plants, 
such as some of the Pteridophytes, may have cones of a certain kind. 
Most of these trees are evergreens, as the pines, hemlocks, spruces, 
and cedars but some, like the tamarack, are deciduous. Most of 
them have needle leaves which are specially adapted to the rigors of 
northern climates. The stem is a single, central stalk extending to 
the top of the tree. 

There are two families (i) Taxaceae and (2) Pinaceae. The mem- 
bers of the former family usually have fleshy seeds and ovules freely 

FIG. 55. Leaves of plants from the Glossopteris flora. 
(6) Glossopteris. (c) Rhacopteris. 

(a) Gangamopteris. 

exposed and those of the latter family have dry seeds and ovules 
concealed by scales. 

The Pinaceae may again be divided into four groups well repre- 
sented by living forms: (i) Abietineae, including pines, spruces, 
hemlocks, firs, cedars, and larches; (2) Taxodineae, including Sequoia 
and Taxodium (bald cypress common in our southern swamps); 
(3) Cupressineae, including the arbor vitae, and the juniper; (4) 
Araucarineae, including the Araucarian pines so frequently seen in 
New Zealand. 

Representatives of the Coniferae extend back into Devonian beds, 
but it is not always easy to place the fossil forms in the groups men- 
tioned above and, furthermore, the wood of the Coniferae may in 

FIG. 56. Leaves illustrating the development of the modern types of plants in the 
later geological periods, a, Macro taenopteris magnifolia (Rogers), Triassic coal 
beds of Virginia (Fontaine); b, Gingko digitata (Herr), Jurassic; c, Cinnamomum 
Lesperium (Knowlton); d, Aralia veatchii and e, Rhamnus? Williardi (Knowlton), Upper 
Cretaceous; /, Fagara, catahoulensis major (Berry) and g, Ulmus floridana (Berry), 
Oligocene; h, Quercus chapmanifolis (Berry), Miocene (U. S. Geol. Survey.) 212 


some cases be confused with that of the Cordaites as there is a close 
relationship between the groups, Cordaites and Coniferae. The 
Taxaceae do not seem to have extended backward beyond the Jurassic. 
The Cupressineae have been found as far back as the Jurassic. The 
well-known extinct genus Voltzia probably belonged to the Araucar- 
ineae and extended back into the Permian. Walchia is a conifer from 
the Permian. The Sequoias have been found from the early Cret- 
aceous onward and were abundant in the early Tertiary. Taxodium 
probably extended from the Oligocene to the present. The Coniferae 
have been widely distributed over the globe. 


This great group of plants, representing the climax in plant evol- 
ution, was ushered in with the Cretaceous period. They have de- 
veloped so rapidly and they now occupy such an important and com- 
mon place in the living vegetation that any attempt to describe them 
here would be futile. Their representatives are found in every 
formation where plant fossils occur since the beginning of the Lower 
Cretaceous period, and they now outnumber the Gymnosperms several 
hundred times. The common trees, outside of the Conifers, belong 
to this group, as do the grasses and the other common flowering plants 
with which everyone is so familiar. 


Thickness of Seams 

Coal beds vary from a fraction of an inch to the enormous thickness 
of 266 feet. At Morwell, Victoria, Australia, there are three seams 
of brown coal which are 266, 227, and 166 feet respectively, in thick- 
ness. They are the thickest so far known in the world. A drill 
hole 1010 feet deep passed through 780 feet of coal. Other notable 
beds are the Grande Couche of Commentry, central France, which is 
60 feet thick, and the Mammoth seam of the anthracite region of 
Pennsylvania, which in the Southern Field reaches 50 feet in thick- 
ness. Seams in Styria and Manchuria exceed 100 feet in places. 
Most seams vary rather rapidly in thickness from place to place, the 
Pittsburgh bed of the Appalachian province being probably the most 
remarkable exception to this rule. This seam has been traced over 
an area of more than 2100 square miles with an average thickness of 
over 7 feet. Its total original area has been estimated at about 
30,000 square miles. The irregularities in the thickness of seams are 
due chiefly to the structures known as " partings," " pinches " or 
"squeezes/' " swells," " horsebacks," "rolls," "clay veins" and 
" cut-outs " and to igneous intrusions. 

Partings. A seam may be divided into several thinner seams or 
" splits " by partings of clay, shale, slate, or sandstone, (Fig. 57). 
For example, the Mammoth seam, which reaches a thickness of 50 
feet in the eastern part of the Southern Field is divided into three 
splits at the western end, averaging about 10, 12 and 15 feet respec- 
tively, in thickness, with partings of slate between them running from 
10 to 30 feet in thickness. These splits would be regarded as indi- 
vidual seams were it not for the fact that they can be traced into the 
main seam to the eastward. Other seams are known in which the 
number of splits is very much larger than in the case cited. 

The splits are due to the fact that while the vegetal matter is being 
laid down in the swamp or open body of water there are periods 



when clay or sand is brought in by water from the surrounding lands 
and carried out over the vegetal matter. The deposit of sediment 
grows thinner as it extends away from the dry land and some distance 
from the edge of the basin the deposition of vegetal matter goes on 
without interruption so that a continuous coal seam results, whereas 
closer to the edge the seam is interrupted by these bands of sediment. 
The number of partings will depend upon the rate of change in level 
between the surrounding land and the basin, or upon the variations 
in climate. A sinking of the basin where the vegetal matter is being 
deposited or a rise of the surrounding land will cause sediment to be 

FIG. 57. Diagram illustrating: C, cut-out; H, horsebacks; P, parting; R, roll; 

S, split; V, clay vein. 

carried out by streams farther from the edge of the swamp or other 
basin than it was formerly, while a change to a wetter climate may 
also cause greater erosion of the land and consequently a more ex- 
tended deposition of sediment over the vegetal matter in the swamp. 
" Pinches " or " squeezes," and " swells." These are terms 
applied to sections in the seam where it has become constricted by 
the squeezing in, or extended by the bulging out of the overlying or 
underlying rocks. They are due to pressure applied to the seam during 
the folding and other movements of the enclosing strata and they 
may accompany the formation of " horsebacks " and similar struc- 



" Cut-outs." This is a term applied by miners to any place in 
the seam where the coal ends abruptly on account of faulting, squeez- 
ing, or erosion. It may be used in a more restricted sense for the 
case where part of the bed has been removed by erosion, (Fig. 57). 
It often happens that a coal-bearing formation suffers erosion and a 
stream cuts a ravine through one or more beds of coal. This ravine 
may be filled later by sand or clay carried in by the stream, or a 
glacier passing over it may fill it with drift consisting of a mixture 
of clay, sand and boulders. A fine example of the latter phenomenon 
is found in the Anthracite Field of Pennsylvania. Before the glacier 
appeared in this district the Susquehanna River flowed in a channel 

FIG. 58. Gorge of Des Moines River at city of Des Moines illustrating how a cut- 
out may develop. (From Iowa Geol. Survey.) 

between Nanticoke and Pittston. During Pleistocene time the 
glacier moved southward across this channel, which became filled 
with glacial drift. The river was thus forced to carve out a new 
channel for itself after the glacier melted away. It has also been 
suggested that this abandoned channel might have been gouged 
out by the glacier as fiords are deepened. The old channel has 
been well outlined as it has caused much trouble in mining, owing 
particularly to the large amount of water contained in the sand and 
gravel and the bad condition of the rocks along its edges. 

" Horsebacks," ' 'rolls," and "clay veins." All of these 
names have been used more or less loosely for the same structures 
in coal mines in different localities. The term " horseback " among 
the coal miners is used to indicate some foreign body in the coal 
seam in much the same general way as " horse " is used among the 
metal miners to indicate a mass of rock in the lode. It probably 


arose from the general rounded form, which is more or less charac- 
teristic of these structures and which suggests the arched back of a 
horse. The German miners use the word " horst " in much the same 
way as " horse " is used among the miners in this country. 

The names " rolls " and " swells " are very appropriate terms for 
these structures because in some mines these masses of rock resemble 
nothing more closely than the waves on the sea when running as a 
ground-swell. The reason for confusing the " clay vein " with the 
horseback is doubtless due to the fact that the former in many places 
is an offshoot from a rounded mass of clay similar to a typical horse- 
back, (Fig. 57). 

Several theories have been offered to explain the origin of horse- 
backs and it is possible they have been formed in at least two ways. 
One theory, advanced by mining men in some coal fields, is that 
they were formed by streams flowing into the swamps where the 
vegetation giving rise to the coal was being laid down. 1 These 
streams would bring in clay or sand and build up long narrow ridges 
of sediment which would become buried under vegetal matter as 
the formation of the coal bed progressed. The rolls in the roof are 
explained as due to a stream cutting a channel down into the coal 
seam, this channel later becoming filled with sediment. While this 
explanation may account for a few of these structures it will not 
account for the great majority of horsebacks, as they are undoubt- 
edly due to compression of the seam and enclosing rocks, which pro- 
duces small folds in either the roof or floor of the seam or in both. 
When pressure is applied to the floor it buckles up into the coal, which 
is less resistant than the bottom rock and, in the early stages of its 
development, much more plastic than the underlying rocks. Like- 
wise when pressure causes the draw slate to buckle in the roof of the 
seam it bends down into the coal (Fig. 57). A very fine illustration 
of the occurrence of these structures is seen in the Pittsburgh seam 
in the vicinity of Connellsville, Pennsylvania. 2 They rise from 6 
inches to as many feet above the general level of the floor of the seam 
and resemble waves spread over the floor of the mine (Plate IX). 
The seam is everywhere constricted above them except in one or two 

1 J. F. Blandy, On evidence of streams during the deposition of the coal, (horse- 
backs). Trans. Amer. Inst. Min. Eng., Vol. 4, p. 113, 1875. 

2 Moore, E. S., "Horsebacks" in Oliver No. 3 Mine. Coal Age, Vol. 3, p. 566, 1913. 


places noted, where the roof slate is bowed up above the elevation 
in the floor. The rolls often show lamination in the sediments where 
the beds have been bent and in many of these there are bunches of 
pyrite crystals which have collected there because the structure direc- 
ted the circulating, iron-bearing waters into these little anticlines. 

The horsebacks are not uniformly distributed over the floor of the 
mine because the rocks are not uniformly resistant and therefore they 
buckle in some areas and resist buckling in others. Where there is 
one roll there are usually two or more adjoining it, as in the case of 
waves on water, due to the fact that a large anticline should normally 
have small ones on either side where it dies out. These smaller folds 
result from irregularities in the strength of the bed and from the differ- 
ent angles at which the force is applied as the larger fold develops. 
That these structures are not deposits made by streams is proven 
by the fact that they often occur entirely away from the border of 
the swamp in which the coal vegetation was laid down. 

The coal basins as they now exist are not identical in size or shape 
with the original basins but have resulted from the folding of the coal 
measures into anticlines, where there were originally small elevations, 
and synclines, where there were originally small depressions in the 
strata. With subsequent erosion of the anticlines the synclinal basins 
have been separated from each other. Thus it will be seen that one 
of these basins may be near the center of the great swamp in which 
the vegetal matter was originally laid down and the horseback may 
show no connection with the land at the border of the original basin. 

It is evident that a direct relation may be found between the orient- 
ation of the horsebacks and the direction of the main structures of 
the basin. Following the general principles of structural geology it 
is known that if a small fold occurs on the flank, in the trough, or on 
the crest of a larger fold the axis of the minor fold will be in the same 
direction as the strike of the rocks at that particular point in the larger 
fold. It was found to be true at Oliver No. 3 mine, mentioned above, 
that the axes of the horsebacks follow the strike of the rocks forming 
the larger basin at the point where they occur, and inquiries in various 
other mining regions where horsebacks are common elicited answers 
which go to strengthen this assumption for the arrangement of these 
structures in all fields. According to this principle the long axes of 
the horsebacks in a pitching synclinal basin would form, if plotted on 


a map of the basin, an elliptical zone around the deepest point in the 
basin. As the center of the basin is approached the arrangement of 
the structures will become much less regular owing to the confusion 
of forces which are acting from various directions on the rocks in the 
center of the basin. The establishing of this relationship between the 
direction of the horsebacks and the larger folds in the coal basins has 
a practical bearing. It should become possible, as our knowledge of 
these structures increases, to predict the general direction in which 
the long axes of the horsebacks will lie and, when the arrangement of 
these is known, the entries and butts in the mine may be planned in 
such a way as to avoid as much as possible the cutting of these ridges. 
If one must be cut it may be cut along its shorter axis. 

A " clay vein " is a body of clay which fills a crevice in a coal seam, 
(Fig. 57). It is usually roughly tabular like an ore vein, but in 
many cases it branches in an extremely complex manner, sending 
stringers out in all directions through the coal. It originates where 
the pressure on the floor or roof of the seam, or on both, is sufficiently 
great to force plastic clay into small fissures and in many cases en- 
large them. The clay often rises as a mound on the floor of the seam 
so that it resembles a horseback and if there be a crack in the overlying 
coal it rises from the mound as a vein. In some localities the miners 
use the word " spar " for a small clay vein. 

"Bell," "pot," "kettle." The terms "bell," "pot," and "kettle" 
are often used for a roughly cone-shaped or rounded mass of slicken- 
sided rock which falls from the roof of a seam, sometimes causing 
serious accidents to the miners. These bodies are also known as 
" camel-backs " and " tortoises." They are, in most cases, con- 
cretionary structures containing pyrite, iron oxide, iron carbonate or 
calcite mixed with clay or slate and they separate rather freely from 
the roof slate. This ready separation is apparently often due to 
previous movement in the strata as the bodies frequently show 
slickensided surfaces indicating that there has been slipping of the 
surrounding rocks over the concretionary masses. In addition to 
the concretionary bodies which form these structures in the roof there 
are certain harder or denser patches of clay or sandstone, which 
separate from the adjacent rocks and fall from the roof, (Fig. 59). 
Rounded masses of igneous rock and casts of trees occur in the upper 
part of the coal bed in some regions and they fall freely from the roof. 



These structures may all go under the names mentioned above if 
their shape, in the opinion of the miner, happens to correspond to 
that of any of the above-named bodies. 

FIG. 59. Small coal stringer, Paradise Mine Duquoin, 111. (From Bull, of the 111. 
Geol. Survey, University of 111. and U. S. Bur. of Mines.) 

Folding in Coal Beds 

In any study or discussion of folds two terms, dip and strike, are 
much used. The dip is the angle which the bed makes with a hori- 
zontal plane, or in other words the inclination of the bed to a hori- 

FIG. 60. 

zontal plane. The strike is, in general terms, the direction of the 
outcrop, but in many cases a more accurate and concrete definition 
is necessary for practical purposes since the strike must sometimes 



be determined in the bottom of a mine shaft or elsewhere where only 
a very small area of the stratum is exposed. In such cases the strike 
is represented by a horizontal line on the face of the bed or in other 
words the strike is the line along which the bed intersects a horizontal 
plane. This line may be found by using a clinometer or level and its 
direction may be determined with a compass. The direction of 
dip is always at right angles to the direction of strike, (Fig. 60). 
The pitch is the inclination of the axis of a fold to a horizontal line. 
The pitch and dip correspond at the extreme ends of a pitching anti- 
cline or syncline, but in no other portion of the fold. Among miners 
the term pitch usually refers to the inclination in the opposite direction 
from that of the dip. It may be expressed as " up the dip." 

Outcrop of Coal Seam 

FIG. 61. Stereogram of a pitching syncline showing the relation between pitch and 

dip in the coal seam. 

A fold is a flexure in rocks, and it usually consists of two sections, 
the anticline, or crest, and the syncline, or trough, of the wave-like 
structure. The axis or the central line of the anticline or syncline is 
never horizontal for great distances but bows down at the ends in the 
anticline and up at the ends in the syncline, giving pitching anticlines 
and synclines, (Fig. 61). This explains why a coal bed " cropping " 
around the edge of a basin forms a sort of ellipse. Folds may be 
closed or open. In an open fold the limbs, or the beds on the sides 
of the flexure, are not squeezed together, while in the closed fold they 
are. An isoclinal fold is one in which the limbs are parallel to each 
other. An overthrust fold is one in which the beds are bent beyond the 
vertical position and such a fold may grade into a thrust fault where 
the compression becomes sufficiently great to break the rocks and 
push them along the fracture. A monoclinal fold is one in which 



the beds dip in one direction only within a given area. When 
a number of small, or secondary anticlines occur on a large anti- 
cline the structure is known as an anticlinorium, and if small 
synclines occur on a large syncline the resulting structure is a syn- 

Folding has a great influence on coal seams, in pinching them off 
as in horsebacks, bulging them out, and squeezing them so that in 
some cases they are partly turned into graphitic carbon. The pres- 
sure is less in the crest of an anticline than in the sides, therefore the 
coal and soft rocks like clay are crowded into the anticline and the 

FIG. 62. A sketch by W. R. Crane of an anticline in Alaska, in which the coal seam 
has been pinched off on the limbs of the fold and crowded into the crest of the anti- 
cline where the pressure is least. 

seam becomes thicker in the crest but thinner on the limbs, (Fig. 
62). Where the folding is intense there is always considerable 
slipping of beds over one another, and the folds pass over into faults 
if the movement becomes intensive. It is the heavy, strong beds or 
so-called competent beds in a formation, which always control the 
folding as they compel the softer and weaker beds to fold themselves 
into such forms as they may under the circumstances. Cases are 
even known where a certain bed has been highly folded although it 
lies between other beds which show very little evidence of folding. 
The latter beds must have slipped over each other and thus relieved 



the pressure without crumpling, while the former was compelled to 
wrinkle up to accommodate itself to the new conditions. An inter- 
esting example of this in the English coal fields is pointed out by 
Strahan (Fig. 63). This may have a bearing on the origin of an- 
thracite in showing that the lack of crumpling in the strata adjacent 
to the coal does not always prove the absence of great compressive 
stress in the coal. 


FIG. 63. Contortion in a parting between two coal seams leaving the beds above 
and below apparently unaffected. Tir-bach. (After Strahan, Geol. Survey of England 
and Wales.) 


A fault is a fracture in the earth's crust along which the rocks on 
one side have moved relatively to those on the other side. There are 
three relative movements which may occur: (i) The rocks on one 
side of the fracture may remain stationary and those on the other 
side move up or down. (2) Those on one side may move up and the 
others down. (3) The rocks on both sides may move in the same 
direction but those on one side must move more than those on the 
other before a fault results. The movement may also be along hori- 
zontal or oblique rather than along vertical lines. 



Certain names are used to designate the various real and apparent 
motions in a fault. The fracture along which the slipping occurs is 
usually called the fault-plane but the term fault surface is a better 
word because the fracture in many faults departs widely from a plane 
and it is sometimes a regular curved surface. The term displacement 
is used in a general way to describe the relative movement of the 
rocks on this surface whether the movement 
be in a horizontal, a vertical, or an oblique 
direction. In Fig. 64, EF is the displacement. 
The vertical distance ED the beds are dis- 
placed, is called the throw, the horizontal 
distance FD the heave. The angle FED, 
which the fracture makes with the vertical is 
the hade. When the rocks on the upthrow 
side of the fracture project above those on 
the downthrow side this projection AC is known as the fault scarp. 
During the movement on the fault surface the rocks are often smoothed 
and polished. This smooth surface is a slickenside and when clay 
results from the grinding up of the rocks during movement it is called 
gouge, or selvage. If the rocks along the fracture are broken up into 
angular fragments the resulting material is known as a fault breccia. 

There are two main types of faults: (a) the gravity or normal 
fault, and (b) the thrust fault. In the former the overhanging side 

FIG. 64. Diagram illus- 
trating a thrust fault and 
fault nomenclature. 

FIG. 65. Sketch of faults in main entry near parting. Southern Coal, Coke and 
Mining Co., Mine No. 7, New Baden, Clinton County, 111. (From Bull, of the 111. 
Geol. Survey, University of 111. and U. S. Bur. of Mines.) 

or hanging wall side has moved downward towards the center of 
the earth as a result of tension or stretching in the earth's crust, and 
in the latter the overhanging side has moved upward relatively to 
the other side as a result of compressive force. Igneous activity 
may sometimes exert an upward pressure and produce thrust faults. 
Figure 65 is an example of a normal fault and Figure 64 of a thrust 



fault. There are also various names used by the miners to indicate 
the nature of faults such as " shove " fault and " slip " fault. In 
the former, one body of rock has been pushed into another and the 
latter term is frequently used for a fault which lies nearly parallel 
to the bedding. 

In many coal fields faults are a source of great difficulty to the 
miner, but other fields are almost entirely free from them. In some 
faults the seam is only thrown a few feet but in others the displace- 
ment may be several thousand feet. Thrust faults show the greater 
maximum displacement and this may reach many miles in the large 
mountains. It may be considered a general rule that the faults in 
any particular basin will be practically all normal or all thrust unless 
it can be shown that they have originated during at least two distinct 
periods of faulting. 


FIG. 66. Diagrams showing how in (A) a drill hole may pass through the same coal 
seam twice because of thrust faulting and in (B) it may miss the seam entirely in the 
gap resulting from normal faulting. 

The effects of faulting on prospecting are very great. A concealed 
seam may be brought to the surface or a seam at one time exposed 
may be faulted and eroded so that it no longer comes to the surface. 
A seam may be duplicated by faulting so that a drill hole will pass 
through it twice, (Fig. 66 (A)) or a gap may be produced so a drill will 
pass between the two portions of the seam without indicating its pres- 
ence, (Fig. 66 (B)). If a fault cuts transversely through a syncline the 
outcrops of the seam on the sides of the syncline after erosion has 
occurred will be closer together on the upthrow side of the fault than 
on the downthrow side, while the opposite will be the case if the fault 
cuts an anticline. 

It should be borne in mind that the older rocks will always be ex- 
posed on the upthrow side of the fault if the area has been eroded since 
faulting. In very few cases are faults so recent that the faulted rocks 



have not suffered erosion and in most cases all evidence of the fault 
scarp has been removed. There is usually, therefore, little evidence 
of the presence of the fault on the surface unless there be a marked 

FIG. 67. A large fault in the Coal Measures near St. Etienne, France. (Photo by 

E. S. Moore.) 

difference in the rocks on opposite sides of the fracture. In some 
places a sandstone may be brought opposite a shale, a shale opposite 
a limestone or a non-fossiliferous rock may be brought into juxta- 
position to a fossiliferous rock, or 
a sedimentary rock to an igneous 
rock. There are many features 
which may be used by the geologist 
to distinguish the rocks on opposite 
sides of a fault and thus detect its 

FIG. 68. Diagram illustrating a great 
unconformity by folding, erosion and 
subsequent deposition. 


An unconformity is an interrup- 
tion in the continuous deposition 
of sediments in any locality. The 

presence of this hiatus, or break may be indicated by one or more of 
a number of factors among which are the following: (i) A sudden 
change in the character of the fossils found above or below the 



horizon where the unconformity occurs; (2) Folding or faulting of 
the rocks below the unconformity while those above remain un- 
disturbed; (3) Erosion of the underlying rocks before the later rocks 
were laid down upon them. This is illustrated in Figure 57 where the 
cut-out occurs. In Figure 68, the effect of both folding and erosion 
is seen, as the coal-bearing formation was folded and eroded before 
the later formation was laid down. 

Igneous Intrusions 

In regions of igneous activity such as those of the western states, 
Alaska, parts of Great Britain and some other countries, the coal 
seams have been cut by igneous intrusions of many forms. The 

FIG. 69. Diagram illustrating the different forms which igneous rocks may assume 
in intruding coal measures. B, a portion of a batholith; D, dike; L, laccolith; and 
S, sill. Such intrusions produce natural coke and otherwise alter the coal adjacent 
to them. 

different forms which these intrusions take are illustrated in Figure 69. 
If a fracture becomes filled with liquid rock it is known as a dike', if 
the liquid spreads out along a bedding plane in the sediments and 
solidifies as a tabular mass of great areal extent compared with its 
thickness it is known as a sill. If it forms a lens-shaped body and 
arches up the overlying strata it is a laccolith, while a large, irregular 
mass is a batholith. Other bodies which have great vertical dimensions 
compared with their lateral, are known as bosses, necks or plugs and 



if the liquid rock reaches the earth's surface and flows out over the- 
surface it is a lava flow, or sheet. 

Some of the intrusions in coal seams are extremely complex in form. 
A good example is that figured by Jukes from the South Staffordshire 
Coal Field in England, (Fig. 70). Intrusions of less complexity may 
be seen in the Newcastle Field of Australia and in some of the western 
states. As a rule the dark basic rocks, such as traps, are capable of 
producing more complex intrusions than are the lighter-colored, acid 
rocks like granites because the liquid is less viscous and it more readily 
enters intricate fractures. 

T = Trap ; C = Coal ; S = Sandstone ; 


FIG. 70. Complex intrusion in coal seam. (After Jukes, Geol. Survey of 

England and Wales.) 

The most important effects of igneous intrusions outside of the 
difficulties they often create in mining operations is the coking of the 
coal. (For a discussion of this subject see Carbonite or Natural 
coke.) A dike usually affects a very limited area but a large sill 
or laccolith may extend for a long distance parallel to a seam, con- 
verting practically the whole bed into coke, as some of the sills have 
done in Colorado and New Mexico. There is usually a relation be- 
tween the thickness of the igneous body and the thickness of the coked 
zone, one being directly proportional to the other, but this relation 
will not always hold any more than it does in the case of the width of 
the metamorphosed zone adjoining intrusions in other rocks. The 
temperature of the molten rock, its gas content and other physical 
conditions at the time it reaches the coal have great influence on its 
coking effects. 

Concretionary Bodies in Coal Seams 

The concretionary bodies found in coal and in the adjacent rocks 
commonly go under the names of " coal apples," " coal balls," and 


" sulphur balls." The coal apples, or coal balls consist chiefly of 
calcium carbonate, magnesium carbonate, iron carbonate, or iron 
oxide, with varying amounts of clay, shale or sand. Small amounts 
of calcium phosphate, carbonate of manganese and other constituents 
are often present. The sulphur balls consist of iron sulphide (FeS 2 ) 
in the form of pyrite often known as " fool's gold " or marcasite, 
mixed with clay or sand in different proportions. In some cases a 
little free sulphur occurs as a coating owing to oxidation of the pyrite. 
All these bodies are concretions in the strict sense of the term. They 
have grown up as a result of the chemical deposition of these various 
substances around some central point and they show a concentric 
arrangement of the material varying very greatly in degree of perfec- 
tion. They are irregularly distributed through the coal seam, or the 
shales above and below the coal, or they project from the coal into 
the adjacent rocks. 

In addition to these concretions there are other bodies consisting 
of coal, which strongly resemble concretions in appearance but which 
are not true concretions since the material composing them has not 
been precipitated from solution around a nuclear point. They re- 
semble somewhat the so-called " physical " concretions of some writers 
as distinguished from chemical concretions, and they are believed to 
have been formed as a result of fracturing and movement in the bed. 
This type is common in Colorado where the coal is known as " nigger- 
head " coal. 

Calcareous concretions. These bodies are abundant in the Coal 
Measures where limestones are associated with the coal-bearing for- 
mations. They have been described in detail by S topes and Watson 1 
for the coal fields of England and some of the Continental fields. 
They occur in large numbers in those coal seams, the roofs of which 
contain a marine fauna consisting of goniatites and lamellabranchs. 
The waters in which the vegetal matter forming the seams was laid 
down were rich in salts of calcium and magnesium. The roof shales 
contain plant remains which differ considerably from those in the coal 
seams, thus suggesting that the vegetal matter in the overlying rocks 
was drifted to its present location while that which composed the seam 

1 Slopes, M. C., and Watson, D. M. S., On the present distribution and origin of the 
calcareous concretions in coal seams known as "coal balls." Phil. Trans. Roy. Soc. 
London. Series B, Vol. 200, pp. 167-218, 1909. 



FIG. 71. Vertical dike in Coal Measures, Australia. (Photo by E. S. Moore.) 

FIG. 72. Peculiar effects of shearing in coal. Specimen in Museum National d' 
Histoire Naturelle, Paris From Northern France. 




100 metres North of Shaft No.l 


Section North of 
Shaft No. 1 


400 metres East and 

100 metres South of 

Shaft No.l 

FIG. 73. Very complicated structures resulting from faulting and squeezing in the 
coal seams of Northern France. The dark areas are sections of the seams. (From 
the Publications du Service des Topographies Souterraines; Bassin Houiller du 


grew in place. This might be the result of the deposition of plant 
remains in brackish water along the sea coast followed by a trans- 
gression of the sea over this material with the deposition of marine 
fossils in calcareous strata. Jeffrey 1 considers that the coal balls 
indicate that the vegetal matter enclosed in them was transported 
rather than developed in situ because he has found fragments of char- 
coal associated with other remains of plants in the same concretion. 
The material in the concretions differs from ordinary coal in the ab- 
sence of the large proportion of spores which are found in the latter. 

These " coal balls " almost everywhere contain remarkably well- 
preserved plant remains, indicating that they were formed about the 
time the plants settled to the bottom of the body of water and before 
they had an opportunity to decompose and become macerated. It is 
not necessary, as some writers have suggested, to invoke the preserva- 
tive properties of saline water to account for their preservation. The 
perfect sealing conditions provided by the accumulation of mineral 
matter above the plant have been responsible for their complete 
preservation, and the finer structures of the plants may often be rec- 
ognized in these concretions when they are not preserved at all in the 
adjacent coal. In some cases a plant stem may extend out into the 
surrounding coal. A concretion may be partly in the coal and partly 
in the roof slate, and laminations of the roof slate may pass through 
some of the concretions. 

Another evidence that the concretions have formed early in the 
history of the coal seam, in addition to the preservation of the plant 
structures, is that the vegetal matter has been squeezed down around 
the balls while they have been scarcely compressed. They must have 
been in existence before the compression of the vegetal matter occurred, 
and the presence of slickensides shows that the coal and accompanying 
rocks were squeezed around them. It is only reasonable to suppose 
that these concretions were formed on the bottom of the marsh in 
which the vegetal matter grew and that they may have originated 
by the action of algae or other low forms of plants causing precipitation 
of calcium carbonate, as many calcareous concretions originate at the 
present day. As they grew, fragments of plants came in contact with 
them and were enclosed. In the case of the iron-carbonate concre- 

1 Jeffrey, E. C., Petrified coals and their bearing on the problem of the origin of coals. 
Proc. Nat. Acad. Sci., Vol. 3, pp. 206-211, 1917. 



tions it is possible that they resulted from the reaction of ferrous sul- 
phate and calcium carbonate in the presence of carbon dioxide. If 
the supply of carbon dioxide were insufficient, limonite would have 

FIG. 74. Coal stringer, Brilliant Coal and Coke Co. Horn Mine Duquoin, 111. 
(From the Bull. 111. Geol. Survey, University of 111. and U. S. Bur. of Mines.) 

formed instead of siderite and in the presence .of hydrogen sulphide 
iron pyrite would have been precipitated to form sulphur balls. As 
to the agent causing precipitation of the iron compounds the iron 

1 1 


1 1 

, i 

1 1 1 1 1 

1 1 


1 1 


''. ; v. '. : ' ''...'..:''..'.-.' /. :.':.'.''''.'..'.'. ' -'..'-'"-'.' ''.' 

1 1 1 1 

1 1 


1 1 

, / 

^^^^v^.^^ : :^ : .VvV:^VV^^V;V-vV^X^:V:^^'^'v;:^\V: : :^y.'. /.''.'.'. 

1 1 1 1 1 

1 I 


1 1 

i / 

'' :''..':'.:':.''.' .^': :: :::'.'-'-'-'-'-:'--'.--::-'.-'.-'-'. - y-'.--':- ''.'.-: 

1 1 1 1 

1 f 



vU-::HU'--:-}:l : .Ov/;^nastQiiB:^-vv;^::-:;i-:-;:i:v 

ll.imhsvni'ie 1 

1 1 


1 1 1 1 


ni e 1 

**/.' ' ' '."' Y"'\ ' * 

1 1 1 1 I 

i ' r 

1 ' 1 ' 

T ' 1 ' 





, 1 , 1 , 1 , 1 , 



I _ 

(T~l 2 5 4 5 

FIG. 75. Roll in roof, Madison Coal Corporation Mine No. 6, Divernon, 111. (From 
Bull. 111. Geol. Survey, University of 111. and U. S. Bur. of Mines.) 

bacteria may have played a part or the balls may be replacements of 
calcareous nodules. 

In size these balls may vary from minute nodules, less than an inch 
in diameter, to bodies several feet in diameter. One ball about 4 


feet in diameter and estimated to be of about 2 tons weight was found 
in a mine at Shore, England, and it almost completely cut out the coal 
seam. The balls are usually roughly spherical and some large ones 
are made up of several smaller concretionary centers cemented to- 
gether by carbonate and carbonaceous matter. 

The analysis of the calcareous nodules according to S topes and 
Watson showed calcium carbonate (CaC0 3 ) as high as 91.09 and as 
low as 49.35 per cent, and magnesium carbonate (MgCO 3 ) reaching 
42.82 per cent, thus indicating that some of them consist almost en- 
tirely of dolomite. Iron pyrite was found as high as 3.27 per cent, and 
other constituents, as ferrous carbonate, ferric oxide, manganese 
carbonate and calcium phosphate occurred in small amounts. 

The studies of Zalessky 1 in the Donetz Basin of Russia showed that 
the calcareous balls occurred there under conditions almost identical 
with those described for England and northern France. The coal 
seam and the shales carrying abundant concretions lay between two 
limestones and the same types of plant remains were preserved in 
much the same way. 

" Niggerhead " coal. In the Walsenburg district of Colorado and 
in the coal fields of Washington State and Alaska certain seams of coal 
have been intruded with igneous rocks and a great deal of natural 
coke occurs. In some of these seams most of the coal is made up of 
roughly spherical masses called " niggerheads," varying from an inch 
or less to a foot or more in diameter. They resemble somewhat the 
form taken by diabase or other basic rocks on disintegrating by 
spheroidal weathering. The laminations in the coal are still distinct 
in most of the balls, and in many of them portions of flat sides indicate 
the original joint cracks, but the corners are rounded off and some of 
the balls are almost spheres, (Fig. 77). 

It might be thought that these bodies owe their form to a sort of 
concretionary development as a result of silicification or other form 
of mineralization of the coal when it was intruded by the igneous 
rock, but the following analyses show that it is not high in ash and it 
is considered a very good quality of coal in the Rocky Mountain 

1 Zalessky, M. D., On the discovery of the calcareous concretions known as coal balls 
in one of the coal seams of the Carboniferous strata of the Donetz Basin. Bull, de 1'ac- 
ademie Imperiale des Sciences de St. Petersburg, VI Series, pp. 477-480, 1910. 


The subspherical form is apparently due to the coal being heated 
to a high temperature with the driving off of certain volatile matter. 

FIG. 76. A sharp syncline near Hazelton, Pa., from which the anthracite has been 
removed by open-cut mining. (Photo by E. S. Moore.) 

FIG. 77. "Niggerhead" coal from Colorado. 

It then contracted so that it scales off concentrically in the same 
manner as any other rock which has been heated and allowed to cool. 







Fixed. carbon 

Per cent 

"?3 OQ 

Per cent 

ff 2O 

Per cent 

ri e;i 

Per cent 

rA gl 

Volatile matter . . 

27 CQ 

57 78 

31 QO 

?r Si 


2 06 

2 22 

** * 

2 D3 






Ash . . 

7 3^ 


q 8s 

6 7C 

Sp. gr. ... . . 


i . 300 

I 324 

I 312 

B.t.u. (dry). 





1 Analyses furnished through kindness of D. A. Stout. From Huerfano County, 
Colorado. I, Cameron seam, II and III, Walsen seam and IV, Robinson seam. 

There is also evidence in the smooth surfaces of the balls that consid- 
erable movement has occurred between them and the adjacent coal. 
This may have resulted from the great pressure exerted when the 
intrusion entered the coal seam and adjacent rocks and it probably 
aided in forming the rounded bodies. The spherical structure was 
apparently formed after the coal was jointed into blocks since rem- 
nants of the joint planes may still be seen in most of the balls. These 
joint fractures in all probability aided in the distribution of the heat 
from the igneous rocks and in the irregular cooling of the coal when the 
volcanic activity had subsided 

The only other specimen of coal resembling these " niggerheads " 
from Colorado, which the writer has seen was found in a seam in the 
Newcastle district of Australia. That seam had also been intruded 
by igneous rock and a spherical mass found gave unmistakable evi- 
dence of having suffered from great pressure and some shearing. It 
was thought at the time to have been the result of pressure squeezing 
the more plastic coal around harder lumps of the vegetal matter in 
the seam, but it is probable that the heating of the coal may also have 
had an influence in producing the concretion-like body. A few speci- 
mens of these bodies have been reported from the Anthracite field 
of Pennsylvania apparently formed by pressure on the coal. 

The nature of the origin of these peculiar bodies does not seem to be 
fully understood by mining men and more extensive observations re- 
garding them are needed. 




Prospecting for coal may be considered as two operations. One 
of these is the search for coal in regions where it has not already been 
found and the other the testing of geological formations already 
known to contain at least some coal. 


Laws governing operations. According to the laws of the United 
States, coal lands are classed as Mineral Lands and unoccupied coal 
lands may be obtained through the government departments. The 
legal conditions controlling the purchase of lands already occupied are 
quite different. The Land Office Regulations relating to entry on 
vacant coal lands in the Public Land States and Territories and the 
district of Alaska are as given below, (Sees. 2347 and 2348). These 
were issued April 12, 1907 and they abrogate all previous rules and 
regulations relating to coal lands, 1 (Sec. 2347). 

Every person above the age of twenty-one years who is a citizen 
of the United States, or who has declared his intention to become such, 
or any association of persons severally qualified as above, shall, upon 
application to the register of the proper land office, have the right to 
enter by legal subdivisions, any quantity of vacant coal lands of the 
United States not otherwise appropriated or reserved by competent 
authority, not exceeding 160 acres to such individual person, or 320 
acres to such association, upon payment to the receiver of not less than 
ten dollars per acre for such lands, where the same shall be situated 
more than 15 miles from any completed railroad (one constructed, 
equipped, and operating on date of entry), and not less than twenty 

1 Charles Shamel, Mining, mineral, and geological Law. Hill Pub. Co., 1907. 



dollars per acre for such lands as shall be within 15 miles of such road. 
This statute was authorized March 3, 1873, and is still applicable. 
The lands which may be entered must be surveyed and legally sub- 
divided, they must contain workable coal deposits, but they must not 
contain valuable deposits of gold, silver, or copper. 

Coal lands may also be entered according to the following statute 
(Sec. 2348) on the basis of a preference right to purchase: Any 
person or association of persons severally qualified (as provided in 
Sec. 2347), who have opened and improved, or shall hereafter open 
and improve, any coal mine or mines upon the public lands and shall 
be in actual possession of the same, shall be entitled to a preference 
right of entry under the preceding section (Sec. 2347) of the mines 
so opened and improved : Provided, that when any association of not 
less than four persons severally qualified as above provided shall have 
expended not less than five thousand dollars in working and im- 
proving any such mine or mines, such association may enter not ex- 
ceeding 640 acres, including such mining improvements. To preserve 
a preference right the person or association must present to the register 
of the proper land district, within sixty days from the date of actual 
possession and commencement of improvements a declaratory state- 
ment therefor, in all cases when the township plot has been filed. 

An individual or the several individuals of an association are en- 
titled to but a single entry on coal lands. No one can operate or 
work a coal mine for profit upon the public lands without having 
made the proper entry. 

Those desiring information regarding public coal lands should 
apply to the register of a land district, who is furnished from time to 
time with schedules and maps. These maps show three types of 
lands: (i) Those lands known to lie outside of ascertained coal areas 
and open to entry under the general land laws. (2) Those lands 
known to contain workable deposits of coal, whereon prices will be 
fixed upon information derived from field examination. (3) Those 
lands containing coal of such character as may from their location 
with reference to transportation lines, be sold at the minimum price 
fixed by statute. The lands of the first and third types are entered 
at minimum prices as stated above and those of the second type at 
prices fixed in the schedules. 


Entry on coal lands in Alaska: To make entry on unreserved 
coal lands in Alaska 1 the same individual and personal qualifications 
are necessary as in the United States but entry may be made on un- 
surveyed coal lands. In unsurveyed tracts the lands upon which a 
mine or mines are situated must be located in rectangular tracts of 
40, 80, or 1 60 acres with north and south boundary lines run accord- 
ing to the true meridian and marked by permanent monuments. 
All locators shall within one year of making a location file a notice 
with the register of the land district. 

To obtain a patent an application for such must be filed with the 
register and receiver of the land district within three years. A patent 
gives control of the land to the patentee and his heirs. 

The regulations governing the control of coal deposits in lands 
other than the Public Lands of the United States vary with different 
states. In many states the person holding land in fee also holds the 
minerals lying beneath the surface unless they have been expressly 
reserved in the deed. In others, such as Wyoming and Colorado, 
the coal land is leased only on a royalty basis. 

The recent leasing law for coal lands: On February 25, 1920, the 
President of the United States signed an act known as an " Act to 
promote the mining of coal, phosphate, oil, oil shale, gas and sodium 
on the public domain." This bill places the development of these 
lands, not including those of Alaska, under the control of the Secretary 
of the Interior and it throws open millions of acres of coal and oil 
lands in the West for leasing purposes. The law refers to lands 
classified or unclassified but it does not include : (a) Lands in .National 
parks; (b) Lands controlled by the Appalachian Forest Reserve Act; 
(c) Lands in military or naval reservations; (d) Indian reservations; 
(e) Ceded or restored Indian lands the proceeds of which are credited 
to the Indians. 

According to this act coal lands may be leased to citizens, asso- 
ciations of citizens, corporations, and municipalities in tracts of 40 
acres or multiples thereof up to 2560 acres by one applicant. The 
tracts are to be contiguous if possible for them to be so. Railroads 
may work for their own use for railroad purposes only one grant for 

1 Regulations governing Coal Land Leases in the Territory of Alaska. Dept. of the 
Interior, Washington, May 18, 1916. 


each 200 miles of road. There is to be paid to the Government a 
royalty on coal leases of not less than 5 cents a ton (2000 Ibs.) and a 
yearly rental of not less than 25 cents an acre for the first year, not 
less than 50 cents an acre for the second to the fifth year inclusive, 
and not less than $1.00 an acre for the remainder of the term of the 
lease. Leases are for indeterminate periods not to exceed twenty 
years but renewable to a like extent. In an emergency individuals or 
associations may be allowed to mine coal for their own domestic use 
without payment of rent or royalty. This privilege is restricted to an 
area of 40 acres and a license of two years duration. Municipalities 
may lease coal lands for their own use without the payment of rent 
or royalty under the following special conditions: The coal must 
be used for domestic purposes only, which means household purposes; 
a municipality of less than 100,000 population is limited to an area 
not exceeding 320 acres, one of 100,000 to 150,000 population to an 
area not exceeding 1280 acres and one of a population of over 150,000 
is limited to an area not exceeding 2560 acres. The special lease 
granting this privilege is limited to four years. 

No person, association or corporation, except as provided, shall 
have more than one coal, phosphate or sodium lease during the life 
of such lease in any one state. " No person or corporation shall take 
or hold any interest or interests as a member of an association or 
associations or as a stockholder of a corporation or corporations hold- 
ing a lease under the provisions of this bill which together with the 
area embraced in any direct holding of a lease under this Act or which 
together with any other interest or interests as a member of an associa- 
tion or associations or as a stockholder of a corporation or corporations 
holding a lease under the provisions hereof, for any kind of mineral 
leased hereunder, exceeds in the aggregate an amount equivalent to the 
maximum number of acres of the respective kinds of minerals allowed 
to any one lessee under this Act. Any interests held in violation of 
this Act are forfeited to the United States." 

Permits, known as coal prospecting permits may be granted, which 
gives the holder the exclusive right to prospect unclaimed and un- 
developed lands where exploratory work is necessary to determine 
the existence or workability of coal deposits. These permits cover 
a maximum area of 2560 acres and they are good for two years. 




In looking for new seams of coal there are certain conditions which 
should govern the prospector's operations. A seam may outcrop 
at the surface but if the adjacent rocks have suffered much disin- 
tegration very little definite evidence of the coal may be found with- 
out excavating. There may often be found a black band, or area, 
known as the " smut " or " blossom " which indicates the position 
of the seam. In some cases the presence of a seam which is covered 
with clay or sand wash may only be inferred by finding minute frag- 
ments of the coal mixed with the sediment carried down grade by 
water or transported in a certain direction by a glacier. Outcrops 
are most frequently found in gullies and ravines and quite frequently 
seepages or springs of water in the bank indicate the position of seams 
of coal. 

In prospecting it should be observed that coal is only found in 
stratified rocks, and it is absolutely useless to search for it in those 
of igneous origin. Further, of the stratified rocks, there are usually 
certain types which carry the coal. These are shales, or slates de- 
rived from the shales, and sandstones. Black shales are the most 
favorable. Although coal has been found in limestones, it is very 
rarely indeed that it is found in a limestone formation in which there 
is not also considerable shale or sandstone, and there is no chance 
of finding it in quantities in distinct limestone formations. Regard- 
ing sandstones and conglomerates, the latter rarely carry coal except 
along shaly and sandy bands. Clean sandstones are poor coal- 
bearers as most of the coal in sandy rocks is found in impure sand- 
stone containing clay or in feldspathic sandstones known as arkoses. 

Although shales and impure sandstones are favorable rocks for the 
occurrence of coal not all of them carry it. In America no coal has 
been found in rocks older than those of the Mississippian, or Lower 
Carboniferous series, but in Europe a little has been found in rocks 
as old as the Devonian. Carbonaceous shales may be found as low as 
the Archean rocks, but the geological and botanical conditions had 
not become favorable for the formation of coal before the periods 
mentioned above. There are many examples of people spending 
large sums of money in drilling in these older formations, as for ex- 


ample, in the Ordovician black shales, where there is no possibility 
of finding coal. There is good evidence to show that the great groups 
of land plants which gave rise to the coal had not developed before 
the Devonian period, and in America as well as in some of the other 
continents the sea covered so much of the continent that there was 
little opportunity for coal to form in the Devonian. 

The coal-bearing formations are found principally in the Carbon- 
iferous, Cretaceous, and Tertiary systems. There is a little coal in 
the Jurassic in Alaska, and outside of America the Jurassic and Tri- 
assic coals are important. In dividing these systems of rocks into 
smaller divisions so that certain seams of coal may be located or a 
seam may be traced from one basin to another the different plant 
fossils may be used to correlate beds, and animal fossils in the ad- 
jacent rocks often serve to identify the seams. Thiessen claims to 
have discovered from his microscopic studies that the plant spores 
found in any coal seam have characters distinct from those of spores 
in other seams, and may be used as a determinative factor in recog- 
nizing the seam in various localities. This new evidence of the dif- 
ference in the spores from different seams is likely to be of considerable 
practical value in the future in correlating seams. 

In addition to the fossils there are often other features which 
locally distinguish one seam from another, such as the presence of 
" sulphur balls " or other concretions in some seams and their ab- 
sence in others, the fracture of the coal, the presence of streaks of 
cannel or mineral charcoal, the nature of the adjacent rocks and 
similar features. The adjacent rock may be a fire clay, a calcareous 
rock or some distinctive sandstone which can be recognized wherever 

Testing coal-bearing formations to determine the extent of the 
seams. A coal seam may vary greatly in thickness within very 
short distances or it may, like the Pittsburgh seam of the Appalachian 
province, extend with a fairly uniform thickness over several thous- 
and square miles. Shallow seams may be tested with tunnels, pits, 
or shafts, but where they lie much below the surface prospecting is 
usually done with a core drill. The diamond drill is most commonly 
used, although a rotary calyx drill has also been employed. The 
advantage in using drills of this type is in the core which is obtained. 

As few coal seams lie horizontally the length of the section of coal 


in the drill core from any seam will depend upon the angle at which 
the hole perforates the seam and will vary inversely as the acute angle 
for a vertical hole. If the hole be vertical, the angle will be found by 
subtracting the angle of dip of the bed from 90, that is, the angle 
will be the complement of the angle of dip. In case the hole is not 
vertical but is still in a plane normal to the strike, the angle which it 
makes with the seam can be found by subtracting the angle of dip 
from 90 and then adding the angle the hole makes with the vertical, 
if it be inclined in the opposite direction to the seam, or subtracting 
it, if it be inclined in the same direction. These figures may be easily 
obtained by use of a clinometer. 

If the hole is driven so that it departs from the vertical in a plane 
which is parallel to the strike and therefore normal to the dip, the 
difference between the true thickness of the seam and the thickness 
shown in the core will increase as the angle which the hole makes with 
the vertical increases. 

In the case of holes drilled at an angle to the vertical and lying in 
any other plane than the plane parallel to the direction of strike of 
the seam or in the plane normal to the strike, as 
mentioned above, the conditions become quite com- 
plicated and must be worked out for each individual 

In all the cases mentioned above, the true thickness 
of the seam may be determined from the thickness 
of coal in the core by a solution of the triangles in- 
] D volved, but the simplest method and one sufficiently 
accurate for all practical purposes is to solve the 
]B problem graphically. This is done as follows: In 
FIG. 78. Graphic Figure 78 let A B be a drill core containing a band 
method of deter- o f coa i CD. Carefully project the coal seam, keeping 
mining the thick- ^ inclination, and draw a line from A per- 

ness of a coal seam 

from the drill core, pendicular to the projected seam. The distance EF 
will bear the same relation to the distance CD 
(which is already known) that the true thickness of the seam does 
to the thickness of the coal in the core since they are drawn to the 
same scale. If CD be 10 feet and EF scales half as much as CD 
the true thickness of the seam will therefore be 5 feet. 


Determination of thickness of ccal formations. There are several 
means of determining the thickness of an outcropping coal seam or 
of a formation containing one or more seams, without the use of the 
drill. The method employed depends upon the circumstances, (i) 
If the beds lie flat and are exposed in a cliff (a) the vertical height of 
the cliff will be the thickness. (2) If the beds dip there may be sev- 
eral different conditions: the surface may be level where the for- 
mation outcrops (b) ; the rocks may outcrop in a slope, which is inclined 
in a direction opposite to the direction of the dip of the strata (c) ; 
the rocks may outcrop in a slope which is inclined in the same direction 
as the dip of the strata, (d) (Fig. 79). The thickness of the formation 

FIG. 79. Determination of the thickness of a formation under varying conditions. 

is found by solving the triangles in the three cases, (b), (c), and (d) 
as follows: (b) Since the angle of dip ACB and the distance CA may 
be measured, the distance AB is easily found from the formula. 

Sin ACB = , or AB = CA Sin ACB, (c) AB = CA Sin (ACD -f 


DCB). The slope distance and angle of dip are measured and the 
angle of slope ACD may either be measured or found from its sine, 
computed from the length of the slope and the difference in elevation. 
(d) AB = CA sin (DCB - DC A). 

As the angle of dip increases the horizontal distances normal to the 
strike approach more nearly the thickness of the formation until the 
dip becomes 90, or vertical, and the two are then equal. 

Graphic method: The thickness of a series may be very conveniently 
and rapidly determined by the graphic method when the angle of dip 
and the horizontal distance across the outcrop are known, (Fig. 80). 
In this diagram the numbers on the left hand side of the diagram repre- 
sent various dip angles and each vertical space corresponds to any 
chosen unit of measurement. To determine the thickness find the 
number corresponding to the number of degrees in the dip angle and 
follow the horizontal line to the right for as many units as there are 



in the distance across the outcrop. Then follow the curved line (or 
an imaginary curved line between two of the curved lines if the point 
falls between two lines) to the top of the figure and count the number 
of units between the point reached and the left margin. The vertical 
spaces may each be taken as equal to 5, 10, 20, 100, 1000, or any other 
number of feet, the same scale being used in all parts of the diagram 


FIG. 80. Diagram employed in the graphic determination of the thickness of geological 
formations. (After Hayes.) 

in any one calculation. To illustrate its use: Let a formation out- 
cropping on a level surface dip 30 and the distance across its outcrop 
normal to the strike be 1000 feet. Its thickness is found by following 
the horizontal line from 30 to the right and if each vertical space be 
considered equal to 100 feet, the point corresponding to 1000 feet will 
fall on the fifth curved line. If this line be followed to the top of the 
diagram and the same scale be used, it will be found that the distance 
to the left margin is 500 feet. Instead of considering each space 


equivalent to 100 feet another scale might have been used, for example 
200 feet or 50 feet per space. It is best in all cases to use as small a 
number of feet to a space as the diagram will permit in order to 
minimize the error in computing the thickness. In this connection 
it is sometimes wise to use a certain fraction of the distance across the 
outcrop to obtain the thickness of that fraction of the formation, and 
then to find the total thickness from this fraction. For example the 
total distance across the outcrop of the formation is 2000 feet. In 
order to use a large scale on the diagram find the thickness corre- 
sponding to a distance of 200 feet and multiply this by 10, to find the 
thickness for the whole formation. 

In addition to the methods suggested above, the thickness of a 
formation may be determined graphically by simply drawing to scale 
diagrams like those in Figure 79, and scaling off the distance repre- 
senting the thickness. If this is done carefully and on a fairly large 
scale the results will be satisfactory for most purposes since in most 
cases thicknesses and dips are subject to considerable variation within 
short distances. 

Determination of the depth of a coal seam at different points. - 
If an outcropping seam lies flat its depth below the surface at any 
point can readily be found from the topographic map. On many 
geological maps structural contour lines are drawn on one important 
seam in a coal-bearing formation and all points on any one of these 
lines have the same elevation above sea level. These contours bring 
out the subterranean topography and the structural features of the 
seam and when they are placed on a topographic map the depth of 
the seam at any point is quickly found by taking the difference be- 
tween the elevation of the surface at that point as shown on the top- 
ographic map and the contour line on the seam lying beneath this 
point, (Fig. 81). 

When an outcropping seam dips it may be desired to find its depth 
at certain points at various distances, and in various directions from 
some point on the outcrop. For convenience in discussion, the 
depth of a seam in three directions from a point on the outcrop and 
at varying distances from that point will be considered. The con- 
ditions are illustrated by Fig. 82. Let A BCD represent a section 
of a seam outcropping along AB. The direction of strike is parallel 
to AB and the direction of dip normal to AB and parallel to PM. 




FIG. 81. Relation between surface contours and structural contours drawn on the 
surface of a coal seam underground. The former are the light lines and the latter 
the heavy ones. 

/ M 

/'I,' JM X 

j / \ 1 


'' i 


\ ( 

/ \ 


, \ 


;X \ 




/ \ 


, \ 




FIG. 82. Diagram illustrating the determination of the depth of a coal seam at 
varying distances and in different directions from a point on the outcrop. 



(i) In the first case consider the depth of the seam below various 
points L, O, and M, along a line parallel to the dip. The angle of 
dip, MPN and the distances PL, PO, or PM being measured, the 
depth is found from the tangent of the angle of dip. It is seen that 
the depth at any point will be directly proportional to the distance 
from the point P, and the following table shows the depth of a seam 
at points 10 feet from a point on the outcrop when measured on a 
horizontal surface, supposing the seam dips at various angles from 5 
to 85. At 90 the bed is vertical. To find the depth of the seam 
beneath any other point along this line multiply the number given in 
the table by the distance in feet and divide the result by 10. 




Angle of dip 

10 feet from outcrop 

Angle of dip 

10 feet from outcrop 


.8749 feet 


11.918 feet 































(2) In the second case consider the depth at various points along 
a line 45 from the direction of dip. Or in the diagram (Fig. 82) 
let the direction of the dip be south, the strike east and west, and the 
direction (PH) under consideration, southeast. On this line, PH 
the depth at any points such as E, F, and H, will be found by first 
measuring the distance PE, PF, or PH, then drawing a line from 
this point normal to the line PM meeting PM at the point K. The 
triangle PFK thus formed is solved, PK is found and the problem 
then becomes the same as that described above for the first case con- 
sidered. The following table shows the depth of a seam at points 
10 feet from a point on the outcrop, measured for various dips of 
5-85 in a direction 45 from the direction of dip. 

To obtain the figures for any other point, multiply by the distance 
in feet and divide by 10. 

2 5 





Angle of dip 

10 feet from outcrop 

Angle of dip 

10 feet from outcrop 


.61855 feet 


8.42602 feet 


i . 24665 




























7 .07110 

The formula for determining the depth D at a point C feet from the 
outcrop and in a direction at A to the direction oi dip, if the angle 
of dip be B, is 

D = Tan. B x C cos A. 

An instrument known as Brunton's slope chart is a convenient ap- 
paratus for determining the apparent dip of the bed at any angle 
of divergence from the true dip. It is for the purpose of mechanic- 
ally solving the formula Tan C = Sin A Tan B, where A is the angle 
of divergence from the true dip, B the true dip, and C the apparent 
dip. Thus, after the angle C has been found, the depth at any point 
is found just as in the case where the measurement is taken along the 
true dip by finding the tangent of C and using the table given for the 
first case. 

(3) In the third case it should be observed that any point along the 
line of strike of a coal seam will be at the same depth as every other 
point on that line whether the seam be considered at the surface or 
at the bottom of a mine shaft. This is evident since the strike is the 
line along which the seam intersects a horizontal plane. 

The Valuation of Coal Lands 

Factors governing the value. The chief factors which influence 
the value of coal lands are : (a) the proximity of the coal to an impor- 
tant market center; (b) the transportation facilities; (c) the abundance 
or scarcity of coal in the district; (d) the nature of the coal; (e) the 
depth at which it occurs; (/) the thickness of the seam; and (g) the 


other geological conditions which affect mining operations, such as 
folded or faulted strata, abundance of water and the character of 
the floor and roof of the seam. -The nearness of coal deposits to a 
good market may be offset by labor difficulties and poor quality of the 
coal or the difficulty of mining it, while the handicap of being a con- 
siderable distance from the market may be overcome by good trans- 
portation facilities, especially by water, and the favorable condition 
of most of the other factors mentioned. If there be little fuel in the 
vicinity of a large city the lower grades of coal, such as lignite, may 
bring a good price whereas they would scarcely be used if there were 
plenty of good bituminous coal or anthracite in the region. Good 
gas coal is in demand, especially around cities, and high-grade coking 
coal is much sought after for metallurgical purposes. If it occurs in 
large amounts, industrial centers may grow up in areas where it is 


The depth of coal mine shafts in the United States. In the 

United States it is customary to regard any coal lying below 3000 
feet as negligible in estimating the value of the land, because industrial 
conditions make it impossible at present to mine the coal profitably 
at a greater depth. It is the consensus of opinion, however, that the 
time is not far distant when the maximum depth for profitable mining 
will be extended to at least 4000 feet, as this depth is almost attained 
in Belgium at the present time, and in England for almost half a century 
all seams less than 4000 feet deep have been figured in the reserves. 
There are no mechanical impediments to mining at that depth or 
even at a much greater depth; but the abundance of coal, the high 
cost of labor and the low price which usually prevails in the United 
States when compared with prices in those countries where deep min- 
ing is carried on make it impossible to mine coal profitably at these 
great depths in this country. 

The maximum depths at which coal is mined at the present time 
in the various fields of this country are approximately as follows: 1 
The deepest mining is in the anthracite region of Pennsylvania, and 
it reaches about 2200 feet although the deepest shaft is only 1850 feet. 

1 Fisher, C. A., Depth and minimum thickness of coal beds as limiting factors in valu- 
ation of coal lands. U. S. Geol. Survey, Bull. 424, p. 48, 1910. 


This depth does not indicate the maximum depth of the coal in the 
anthracite region as the depth of a few of the basins has not yet been 
determined and from every indication it is very great. In the not 
far distant future it is probable that coal will be mined from the 
Southern Field at a depth of at least 3500 feet. In the Schuylkill 
section the coal probably reaches 4500 feet or more in depth. 

In the bituminous fields of the Appalachian province the coal does 
not lie at great depths in many places, the deepest so far known being 
in Alabama where some of it exceeds 3000 feet. The deepest shafts 
are not over 1000 feet in the states of Pennsylvania, Ohio, West 
Virginia, eastern Kentucky, Tennessee, and Alabama, and there are 
large areas where all shafts are less than 200 feet in depth. 

In the Eastern Interior field, including Illinois, Indiana, and western 
Kentucky, the greatest depth reached is at a mine in Illinois, which 
is slightly over 1000 feet, but most of the coal in these states is com- 
paratively shallow. In Michigan the seams lie very close to the sur- 
face and the shafts are seldom, if ever, more than 200 feet deep. 

In the Western Interior field the depth reached in Iowa, Missouri, 
and northeastern Kansas scarcely exceeds 300 feet, while in eastern 
Kansas, Oklahoma, and western Arkansas the depth is considerably 
greater. A test shaft 1 1 70 feet deep was sunk near Atchison, Kansas, 
but it has not been regularly operated. With the exception of this 
one the deepest shaft is about 800 feet and is found in the McAlester 
district of Oklahoma. In Arkansas the deepest shaft is about 500 
feet and in Texas the shafts are comparatively shallow. 

In the northern Great Plains province mining has not been carried 
beyond about 500 feet. A shaft 480 feet deep has been reported 
from the Judith Basin region and there are some less than 400 feet 
near Sheridan, in the Fort Union region. In the Black Hills region 
the maximum depth is not over 400 feet and in the Assinniboine 
region of northern Montana not over 300 feet. 

In the Rocky Mountain province, owing to more intense folding 
and faulting, the depth of the mines is considerably greater than in 
the Great Plains or the Interior province. In Wyoming, at Rock 
Springs, there is a shaft about 2000 feet deep and in the Hams Fork 
region there is one which is reported to be over 1600 feet. At Coke- 
dale, Montana, a mine was worked at a depth of 1300 feet and near 
Carbondale, Colorado, the Spring Gulch mine is down about 1500 


feet. In southern Colorado and northern New Mexico there are some 
mines working at a depth of over noo feet, and in the vicinity of 
Glenwood Springs, and at Canon City, Colorado, shafts are about 
1000 feet deep. Elsewhere in the Rocky Mountain province the 
mines are generally less than 600 feet deep. In the Pacific Coast 
province the deepest mines are found in Washington. The Roslyn 
mine is said to be over 700 feet deep. In the Coos Bay field of Oregon 
the coals lie under 500 feet of strata and in central California the depth 
is about 300 feet. 

The maximum depth of coal mines in foreign countries. The 
deepest shaft in the world is in Belgium and the latest figures avail- 
able give its depth as 3937 feet. Other mines in the Mons district 
of that country run from 2500 to over 3000 feet. The average through- 
out Belgium is placed at 1444 feet by E. Loze. 

In England the Rams mine at Manchester is not far short of the 
depth of the Belgian shaft, being over 3480 feet; a seam 2 to 6 feet 
in thickness is worked at this mine. In the same district there are 
two other mines each over 3300 feet in depth, but these are not classed 
as shafts. A number of mines in other fields run from 2000 feet to 
over 3000 feet. In South Wales the Ocean Collieries reach 2700 feet. 1 
In Scotland the deepest workings are near Edinburgh and they are 
down to 2700 feet. The deepest shaft in Great Britain is said to be 
2820 feet, but some of the collieries mentioned above are considerably 
deeper than this shaft. In France some mines reach 3000 feet and 
in Germany mining has been carried to over 3100 feet. In the Rhen- 
ish- Westphalian district the average depth of the mines is said to be 
about 1 700 feet. 

Australia has a shaft 2937 feet deep near Sydney Harbor, New 
South Wales. This shaft was sunk to a 3-foot bed of coal which out- 
crops at Newcastle and dips southward towards Sydney. 


There are several factors which govern the minimum thickness at 
which coal seams may be worked. The most important of these 
factors are: the market for, and the character of, the coal; the 
nature of the enclosing rocks; the association of a thin seam with 
other seams; the depth of the seam; and the training of the miners. 
1 Report of the Royal Commission on Coal Supplies, 1871 and 1901-1905. 



So far, much thinner beds are worked in some foreign countries than 
in the United States. The cost of mining thin seams usually increases 
rapidly as most miners demand a bonus or refuse to work the seam if 
it be less than a certain thickness. A mine manager in New Zealand 
stated that the labor conditions there prohibit the working of any 
seam less than 4 feet thick and the contract price for mining at one 
mine visited by the writer was 2 shillings 8 pence for a seam 4 feet 
to 4 feet 6 inches thick down to 2 shillings 4 pence for a seam 5 feet 
thick or over, showing a decrease in cost of mining of 4 pence per ton 
for an increase in thickness of 6 inches or more. 

Thin seams mined in the United States. Owing to the high 
quality of certain thin seams of coal or their chance location near a 
large city or important industrial center, the working of them is not 
confined to any particular part of the country. The following table 
compiled from the work by Fisher 1 shows the thickness of the thinnest 
seams reported as worked in the various states. 



Thickness of Seam 


22-24 inches. 
14 inches. From a stripping. 

18-42 inches. From a drift. 
18-84 inches. From a drift. 
20 inches. From a slope. 
17 inches. From a drift. 
22 inches. 
14-18 inches. From a shaft 230 feet. 
15-18 inches. From a shaft. 
24 inches. 
30 inches. 
24 inches. 
12 inches. From a shaft 44 feet. 
12 inches. From a drift. 
30 inches . 
7-15 inches. 
26 inches. 
22 inches. 

1 8 inches. 
17-48 inches. 
22 inches. 
19 inches. From a shaft. 
20-24 and 24-36 inches. 
16 inches. 















New Mexico 



Anthracite field 

Western Clearfi eld district . . 


West Virginia 

Wyoming . . 

Op. cit., p. 69. 


Many of the thin seams in this table are mined for local use and 
nearly all of them are comparatively shallow. Some are from drifts 
and some from strippings, so that on the whole their thickness is 
rather below a good minimum for ordinary mining operations, 
although the official regulations governing coal lands of the United 
States place the minimum limit of thickness for a workable seam at 
14 inches. 

Thin seams mined in other countries. Some very thin seams of 
coal of special quality have been worked in foreign countries. A 
bed of cannel 8 inches thick has been mined in Lancashire, England, 
and this probably represents the thinnest seam on record. Many 
beds ranging from 10 inches to 20 inches and consisting of various 
types of bituminous coal have been mined in different parts of England 
and Wales, while in Scotland beds ranging from 15 inches upward 
in thickness have been worked. 

In Belgium several seams not more than n inches thick have been 
worked, and other seams 13-15 inches thick are regularly mined where 
the coal is of high grade. 


The price of coal at the mine and the cost of mining. The value 
of an acre of coal land in the United States before the war varied all 
the way from $10 to $2000. The latter figure is that stated by 
Ashley 1 for some of the land in the Connellsville district of Pennsyl- 
vania. There are, however, some areas which are held at a much 
higher figure than this. 

In attempting to arrive at the value of the coal in the ground the 
price per ton at the mine and the possible fluctuations in price are 
taken as a basis. The figures given below represent the price of 
coal at the mine in various states for the years 1912, 1913, and 1914? 
and they may be taken as an indication of the prevailing prices in 
different parts of the country although it must be remembered that 
the price varies with the demand, and the location will have a great 
influence upon the local price. For example, small outputs of coal 
have sold as high as $4.10 per ton at the mine in Idaho even in normal 

1 Ashley, G. H., The valuation of public coal lands. U. S. Geol. Survey, Bull. 424, 

2 Mineral Resources, U. S. Geol. Survey, 1914. 

2 5 6 


years, and recently during a period of scarcity reports have been re- 
ceived of coal selling for $10.00 and $11.00 a ton at some mines in 






Alabama $ .29 

Arkansas .71 

California a .33 

Colorado .49 

Georgia .49 

Illinois .17 

Indiana .14 

Iowa .80 

Kansas .62 

Kentucky .02 

Maryland .18 

Michigan .99 

Missouri .76 

Montana .82 

New Mexico .42 

North Dakota .53 

Ohio .07 

Oklahoma .14 

Oregon .60 

Pennsylvania Bituminous .05 

Anthracite .11 

South Dakota 

Tennessee .14 

Texas .67 

Utah .67 

Virginia o . 96 

Washington 2 .39 

West Virginia o . 94 

Wyoming i . 58 

Average Bituminous 1.15 

Average Anthracite of Pennsylvania 2.11 




















a Includes Alaska. 

b Includes Idaho and Nevada. 

After a consideration of many fields Findlay 1 concludes that the 
cost of mining bituminous coal, including operating and related ex- 
penses amounts on the average to about 96 per cent of the sale price. 
The average cost per short ton to the Pittsburgh Coal Company from 
a large number of mines for five years was 89 cents and to the Mononga- 
hela River Consolidated Coal and Coke Company for nine years, 
91 cents. 

1 J. R. Findlay, The cost of mining, Eng. and Min. Jour., Vol. 87, p. 948, 1909. 



In Pennsylvania, the cost of mining anthracite is considerably 
higher than that of mining bituminous coal. The following figures 
show the cost per long ton to three large companies in 1905.* 

The Delaware, Lacka wanna and Western $i . 80 

The Delaware and Hudson 2 . 09 

The Lehigh Coal and Navigation Company 2 . 02 

Between the years 1902 and 1908 the costs to the Philadelphia and 
Reading Coal and Iron Company varied from $i .85 to $2 .00 per short ton. 

The reports published by the committee of the Federal Trade 
Commission 2 show the following figures for the cost of producing coal 
in the several states mentioned, during recent years. 




Total Cost 
f.o.b. mine 

1913-1918, inclusive 








Total cost f.o.b. mine 

Margin realized 

1916 $0.82 
1917-18 $0.88-1.38 

1916 $0.92 
1917-18 $1.12-1.73 
Illinois, 5 districts. 
1916 $0.74-1.48 
i 917-1 8 $0.83-2.26 
Ohio, 8 districts. 
1916 $o 781 19 

S. W. field. 


Central field 




$1.35-$!. 94 



$1 OO I 4.4 




$O . 2O-O . 80 

IQI7 $O Q8 I 6^ 

$1 1<\ 2 21 


1918 $1 252 24 

$1 732 Q6 


Indiana, 2 districts. 
1916 $o. 871 .52 

$1 . OQ I . QQ 

1917 $1.081.73 

$i .372 . 16 

1 ., 

1918 $i .422 . 25 

$i . 8^2 . 77 

} $0.45-0. 51 

1916 $1.58 


1917 $1.95 

$2 -55 

1 *, .. 

1918 $2 52 

$3 38 


Alabama, 3 districts. 
1918 $i 532 oo 

$2 17-2 ^8 

Tennessee, 3 districts. 
1918 $i .302 . 14 

Si .772 84 

Kentucky, 4 districts. 
1918 $1.25-1.61 

$1 . 74-2 . 28 

1 Chance, H. M., The cost of mining coal, Eng. and Min. Jour., Vol. 87, p. 1099, 1909. 

2 Reports of the Federal Trade Commission on Coal, June 30, 1919. 


The general expense increased gradually during the six years, but 
the lowest labor cost as well as the lowest total cost was in the period 
April to August, 1915. 

The margin realized on the mining operations from 1913-1918 
was as follows : 1913,10.31-0.44; 1914,10.22-0.50; 1915, $0.90-0.50; 
1916, $0.38-0.57; 1917, $0.54-0.72; 1918, $0.35-0.39. 

Weight of coal in a foot-acre. The amount of coal under a given 
area is estimated by the foot-acre and it is directly related to the 
specific gravity of a solid mass of the coal. A cubic foot of water 
weighs 62.5 pounds. A cubic foot of coal with a specific gravity of 1.3, 
a good average for bituminous coal, will, therefore, weigh 81.25 pounds. 
This gives 24.6 cubic feet per short ton and 27.5 cubic feet for a long 
ton of 2240 pounds. It is often assumed that 0.9 cubic yard of 
bituminous coal equals one ton. This is equivalent to 24.3 cubic 
feet per short ton and corresponds very well with the figure given 
above. Good Pennsylvania anthracite will weigh in the block about 
92 pounds and in lump 57 pounds to the cubic foot. 

An acre contains 43,560 square feet and a foot-acre that number 
of cubic feet. This would yield about 1770 short tons providing it 
could all be extracted in mining. The percentage recoverable in 
mining will vary greatly according to conditions, such as the thickness 
of the seam, its freedom from partings and irregularities, the condition 
of the roof and other things, such for example as location beneath a 
town or city. Some companies under favorable conditions recover 
97 to 98 per cent of the coal while others do not take out more than 
50 per cent or about 880 tons per foot-acre. A fair average might be 
80 per cent recovered, which gives about 1400 tons per foot-acre. 
A 5-foot seam would therefore yield on this basis about 7000 tons 
per acre. It should be borne in mind that it may be impossible to 
mine, by present methods, more than a small portion of a bed which is 
more than 30 feet thick, and an allowance must be made for this 

Estimate of coal in seams of varying thickness. It almost in- 
variably happens that when a geologist examines a coal property he 
must estimate the coal in a number of seams of varying thickness 
lying one above another. The best procedure is first to secure a map 
of the property outlined on cross-section paper, and then proceed to 
divide the property into areas beneath each of which the average 


thickness of the coal is estimated, from all the available data, to be a 
certain figure. The whole property is divided up in this way, and the 
sum of the tonnages computed for the various areas will give the 
total tonnage for the property. The larger the number of areas into 
which the property is divided, the greater the probability of securing 
an accurate estimate, in most cases. The seams may be lettered or 
numbered and then treated separately in dividing the property into 
the various areas. 

Royalties paid on leases. The royalty paid on coal -lands varies 
greatly in different fields. The variation is very much greater than 
in the price of coal at the mine in the different fields, and the differ- 
ence in royalty demanded does not always correspond to the differ- 
ence in the price per acre, which might be demanded for land in 
different areas. This is because the rate at which the coal is mined 
has an important bearing on the relative income from the royalty and 
that from the sale of the land, since the interest on the money and the 
taxes amount to a considerable item if the time required for mining the 
coal be long. According to Ashley 1 the royalties paid in the Anthracite 
region of Pennsylvania previous to 1910 ran up to 50 cents or locally 
to $1.00 a ton, and the writer has obtained similar figures for this 
field in more recent years, with some running as high as $1.40 a ton. 
In the bituminous fields of the state the royalties varied from 5 to 
30 cents except in a few cases in which they went up to $1.00 or more 
in the Connellsville field. The average for the state was perhaps 10 
cents a ton. In Ohio the royalty varied from 8 cents to 15 cents. 
In Illinois 2 cents to 25 cents has been paid, and in Indiana 2 cents to 
10 cents. The West Virginia royalties which have been reported run 
from 8 to 24 cents, the latter in the coke regions. In Kentucky, 
Tennessee and Alabama the figures are from 3 cents to 12 J cents and 
in Arkansas and Oklahoma 3 to 8 cents. In Colorado, state lands 
pay 10 cents and other lands from 8 to 27 cents. On account of the 
great local demand for coal in limited areas in Wyoming some roy- 
alties have been reported as high as $1.00 a ton, but they usually run 
from 3 to 10 cents. Montana royalties are about 15 cents so far as 
known, and in Utah some local mines have paid as high as 75 cents. 
All these figures have changed rapidly during the last few years of 
inflated prices. 

1 Op. cit., pp. 9 and 10. 


In many of the fields where the royalties mentioned above are paid 
there is also a bonus and in most cases a minimum yearly royalty is 
demanded in the contract. In some states the royalty decreases as 
the output increases and in Kentucky it fluctuates with the thickness 
of the seam. 


The " Regulations on the Classification and Valuation of Coal 
Lands," adopted by the Secretary of the Interior on April 10, 1909, 
contain the following clauses: 

I. For purposes of classification and valuation, coal deposits shall 

be divided into four classes. 

A, Anthracite, semianthracite, coking and blacksmi thing coals. 

B, High-grade bituminous, non-coking coals having a fuel value 

of not less than 12,000 B.t.u. on an unweathered, air-dried 

C, Bituminous coals having a fuel value of less than 12,000 B.t.u. 

on an unweathered, air-dried sample, and high-grade sub- 
bituminous coals having a fuel value of more than 9500 
B.t.u. on an unweathered, air-dried sample. 
Z), Low-grade subbituminous coals having a fuel value below 
9500 B.t.u. on an unweathered, air-dried sample, and all 
lignite coals. 

II. Lands underlain by coal beds, none of which contain 14 inches 
or over of coal, exclusive of partings, of Class A, B, or C, or 
over 36 inches of Class D, shall be classified as non-coal land. 

III. Lands containing coals of classes A and B of any thickness 
at depths greater than 3000 feet shall be classified as non-coal 
lands, except where the rocks are practically horizontal and 
the coal lies within 2 miles of the outcrop or point at which it 
can be reached by a 30oo-foot shaft. 

IV. Lands containing coals of class C of any thickness at a depth 
greater than 2000 feet shall be classed as non-coal lands, ex- 
cept where the rocks are practically horizontal and the coal 
lies within 2 miles of the outcrop or point at which it can be 
reached by a 2000-foot shaft. 


V. Lands containing coals of Class D of any thickness at a depth 

greater than 500 feet shall be classed as non-coal lands, except 
where the rocks are practically horizontal and the coal lies 
within i mile of the outcrop or point at which it can be reached 
by a 500 foot shaft. 

VI. The prices of coal lands of Classes A, B, and C shall be de- 
termined on the basis of estimated tonnage at the rate of one- 
half cent to i cent per estimated ton for Class C, i to 2 cents 
per estimated ton for Class B, 2 to 3 cents per estimated ton 
for Class A, when the lands are within 15 miles of a completed 
railroad and half that much when at a greater distance; but 
the price shall in no case exceed $300 per acre, except in dis- 
tricts which contain large coal mines where the character and 
extent of the coal are well known to the purchaser. When, 
however, topographic conditions affect the accessibility of the 
coal the land within the 1 5-mile limit may be given a lower 
valuation, but in no case shall it be placed at less than the 
minimum, and a graded allowance may be made for increasing 
depth, with the same restriction. 

VII. The rates per ton in the preceding paragraph are based on 
the assumption that only one bed is present. If more than one 
bed occurs in any tract of land in such relationship that the 
mining of one will not necessarily disturb the other, then for 
the second bed there shall be added to the price of the first 
bed 60 per cent of the value of the second bed according to the 
schedule, 40 per cent of the value of the third bed, and 30 per 
cent of the value of each additional bed; but the estimated 
price for coal shall in no case exceed $300 per acre, except in 
districts which contain large coal mines where the character 
and extent of the coal deposits are well known to the purchaser. 
Where a bed is over 15 feet thick, the normal value shall be 
placed only on 15 feet; the next 15 feet or part thereof shall 
be valued at 60 per cent of the normal; the next 15 feet or 
part thereof at 40 per cent of the normal and the rest of the 
bed at 30 per cent of the normal. 

VIII. The tonnage shall be estimated for the purpose of valuation 
on the basis of 1000 tons recovery per acre-foot. 


IX. The price of lands of Class D shall be the minimum provided 
by law, $20 per acre when within 15 miles of a railroad and 
$10 per acre when at a greater distance. 

X. In all valuations of coal lands any special conditions enhanc- 
ing the value of the land for coal-mining purposes shall be 
taken into consideration. 

XI. When only a part of a smallest legal subdivision is underlain 
by coal the price per acre shall be fixed by dividing the total 
estimated coal values by the number of acres in the sub- 
division, but in no case shall this be less than the minimum 
provided by law. 

XII. When lands which were at the time of classification more 
than 15 miles from a railroad are brought within the 1 5-mile 
limit by the beginning of operation of a new road all values 
given in the original classification shall be doubled by the 
register and receiver. 

XIII. Except in case of entries now pending or entries made prior 
to classification, review of classification or valuation may be 
had only upon application therefor to the Secretary accompa- 
nied by a showing clearly and specifically setting forth condi- 
tions not existing or known at time of examination. 1 

In formulating these regulations it was desired that the price should 
be such that it would discourage private citizens from buying coal 
lands for speculation with a view to holding them for future favorable 
conditions, but at the same time that it should not retard the business 
of legitimate coal mining. The royalty rate taken as a rough standard 
in figuring the price per ton was 10 cents, since it was believed to be 
a fair average for the whole country. On the adoption of the above 
regulations much land was withdrawn from entry in order that it 
should be classified and valued by the Geological Survey. The amount 
of land withdrawn from coal entry on November i of that year in the 
nine states, Wyoming, Washington, Utah, Oregon, Montana, New 
Mexico, Colorado, South Dakota, and North Dakota, amounted to 
31,872,171 acres. The area withdrawn from all entry in the same 
states on that date was 11,862,576 acres, and the amount of classi- 
fied land restored to entry was 35,915,255 acres. 

1 Ashley, Op. cit., pp. 37 and 42. 


There has been a growing feeling among government officials and 
others interested in coal lands that the public coal lands should be 
leased for the purpose of mining only and the title to the land should 
rest with the State. 1 Colorado has had for many years a leasing 
system on a royalty basis of 10 cents a short ton run-of-mine, less one- 
twelfth of the minimum annual royalty which shall have been paid 
at the beginning of the year. This minimum royalty is paid whether 
any coal is mined or not. Wyoming also adopted the leasing system 
in 1907 and in that state an " advance royalty " is paid and is applied 
on a royalty of 6 cents on all coal mined, and sold up to 25,000 tons, 
5 cents if amount is between 25,000 and 50,000 tons, 4 cents if it falls 
between 50,000 and 100,000, and 3 cents if it exceeds 100,000 tons per 
annum. The lessee must spend not less than $200 on development 
work. As indicated above, Congress has also recently passed a leas- 
ing bill which permits the leasing of public coal lands from the 

1 Bain, H. F., Leasing the Federal Coal Lands, Min. and Sci. Press, Vol. 96, p. 73, 1908. 
The value of Coal Land. Mines and Minerals, Vol. 29, p. 366. 




The process or mining coal has become a highly developed art and 
a detailed description of all methods employed would embrace a very 
extensive literature. In this chapter only the main methods employed 
are described and reference is made to a few of the larger works in 
which the details of the various operations are found. 1 With the 
introduction of labor-saving machinery, resulting especially from the 
more extensive use of electricity in mines, rapid changes in methods 
are taking place and before long the bulk of all coal mined under favor- 
able conditions, in the more advanced countries will be cut, broken 
and loaded by machinery. The development of large steam shovels 
has made it possible to strip many coal seams formerly out of reach 
in open pit mining and to mine them on the surface, while the 
working out of the thicker seams underground necessitates the mining 
of thinner seams. In this work the use of mechanical conveyors 
and other labor-saving devices is becoming more common. 

Mining Methods 

The main methods employed in coal mining may be classed as (i) 
Open work and (2) Underground, or dosed work. The first is fre- 
quently known as stripping or open-pit mining. The underground 
methods may be divided into Room-and-pillar and Longwall methods, 
and there are several modifications of each of these. 


In areas where a good seam of coal underlies a thin overburden 
it pays to strip off the covering. The depth to which this stripping 
may be profitably carried depends upon many factors. It has been 

1 Coal miner's pocketbook, McGraw Hill, 1916. Peele's Handbook for mining en- 
gineers, John Wiley & Sons, Inc., 1918. Practical coal mining by W. S. Boulton, London, 
1907. Vols. 1-6. Colliery working and management, Bulman and Redmayne, 1912. 




considered in the past that a foot of overburden could be removed 
by hand for each foot of coal obtained. Most stripping is done at 
the present day, however, by the large steam shovel of ordinary type, 
the rotary shovel or the dragline excavator. In Illinois hydraulic 
means are employed to some extent in stripping. The proportion 
of overburden to coal which may be profitably removed has therefore 
increased to from 3 to 6 times the figure stated. The proportion will 
vary greatly according to the grade and the price of the coal and the 
nature of the overlying rock. A heavy, little-jointed sandstone or 
limestone which requires blasting, or a loose rock which is full of water 
and runs readily may increase to a large degree the relative cost of 

FIG. 83. Stripping on the Mammoth Seam near Hazleton, Pa. (Photo by E. S. 


In the anthracite region of Pennsylvania extensive stripping oper- 
ations are carried on, especially in the district around Hazleton where 
the Mammoth seam is thick, (Figs. 76 and 83). In some places this 
seam runs from 50 feet up to 100 feet or more, where it is duplicated by 
folding, and an overburden up to 90 feet in thickness has been removed, 
while some of the projected strippings will require the removal of 
nearly 200 feet of overburden as, for example at Locust Mountain. 
A great deal of coal is obtained by this method which could not be 
obtained by underground mining, especially in those areas where 


the early mining operations left much coal in the ground and a 
great deal of it in such condition that underground mining is very 
difficult, dangerous or even impossible. 

In some of the bituminous fields of the United States open cuts are 
extensively worked, particularly in Alabama, Missouri, Kansas, In- 
diana, Ohio, Pennsylvania, Illinois and Oklahoma. In Missouri over 
one million tons, or 21.6 per cent of the coal mined in that state in 
1916 was mined in this way. Over 12 per cent of the coal mined in 
Indiana and a considerable amount of that raised in Alabama is worked 
by this method. 

After the stripping is done the coal is usually dug by steam shovels 
of special type, known as rotary shovels, but in a few cases it is dug 
by hand. 

The main advantages of the stripping method are in the absence 
of squeezes, falls of roof and dangerous gases with accompanying 
explosions. There is no necessity for timbering or lighting, and the 
work may be more easily directed. Experienced men are not neces- 
sary except for the management of the steam shovels, and in case of 
closing down operations the damage by flooding of the pit is not 
usually so great as the damage suffered by an idle mine. The dis- 
advantages are the necessity of ceasing work in very stormy weather 
and the collection in the open pits of so much water, and, in the colder 
climates, of snow. It is difficult to dispose of the overburden in some 
regions and the abandoned pits are objectionable, but probably not 
much more so than a surface area which is extensively caved after the 
mining of shallow seams. 



In order to reach the coal which lies too deep for stripping oper- 
ations a tunnel or drift is driven, or a slope or shaft is sunk. A tunnel 
is typically open at both ends but the term is often applied to an 
opening driven horizontally or nearly so across the measures. In 
coal mining, a drift is usually regarded as an opening driven from the 
surface in the seam but the term is also used in some cases where the 
opening does not reach the surface. A shaft is a vertical mine opening 
driven from the surface. If it is driven from one seam to another it 


. i 

is known as a blind shaft. A slope is an inclined opening usually 
driven on the coal seam and used as a haulage or other roadway. 

Shafts. A shaft should be placed where it will best serve the 
maximum portion of the area to be mined and it should be kept away 
as much as possible from areas which are faulted, highly squeezed 
or subject to flooding. A shaft may be timbered, bricked, concreted 
or lined with metal. Timber is commonly employed but many of 
the modern shafts in large mines are concrete lined while brick is used 
in many mines, especially in Europe. The advantage of brick or 
concrete over timber is in their greater durability, in the absence of 
danger from fire, and, in the case of air shafts, in the fact that they 
offer much less friction to the air currents since the timbers tend to 
create local eddies in the current and thus increase resistance to 

The shape of the shaft varies with the conditions. A timbered 
shaft is, as a rule, rectangular while a brick or concrete shaft is usually 
made circular or elliptical. The size depends chiefly upon the pro- 
posed output of the mine, the size of the mine car to be employed 
and the possibility of the formation of ice in the compartments in 
winter. The width of the cross section may be from 5 feet to more 
than double that width, and the length may exceed 50 feet where 
there are a large number of compartments used in hoisting a big 

In most shafts there is a compartment set apart for pipes and 
ladders while the others are used for hoisting. 

In sinking a shaft the same methods are employed in coal mining 
as in metal mining and include the blasting of the rock and its re- 
moval by hoisting with windlass or steam hoist. Where the rock 
is not firm or where quicksand or other running ground is encoun- 
tered special methods such as piling, freezing or cementing must be 
employed. A shield may be used in some cases to protect the work- 
men from falling rock. 

The laws of most states require at least two separate openings to 
all coal mines so that in case of accident men may have a means of 


Entries, headings, or gangways. As the term implies this method 
consists in working out rooms, chambers or breasts, in the seam, leaving 




portions of the coal between these rooms in the form of pillars to sup- 
port the roof. The portion of the seam which is to be mined from a 
certain shaft or slope is first split up into a number of sections by 
driving passages from the shaft bottom or from the slope as the case 
may be, (Fig. 84). These passages are known as main entries or 
main headings in the bituminous mines and as gangways in the an- 
thracite mines of America, and they usually run to the border of the 
property. They are as straight as possible so as to avoid turns in 
track or sudden changes in direction of the air currents, and where 
used for air courses the perimeter should be as small as possible in 
proportion to the area so as to reduce friction of air current to a mini- 
mum. The nearer a square is approached the less the perimeter for 
the area enclosed. They are about 6 feet high and from 6 to 21 feet 
wide, according to the thickness of the seam, the nature of the bottom 
and roof of the seam, the amount of output from the mine and other 
factors. If the roof and bottom are bad it is more difficult to carry 
a wide entry and if the seam is too thin so that the roof must be 
brushed down by taking down a lot of draw slate there must be an 
entry wide enough to furnish some storage space for the waste rock. 
It usually costs much more to drive narrow entries than wide ones 
in proportion to the coal taken out as the former operation is classed 
as narrow work and a higher charge is made for all work so classed. 
The size of the area mined from one shaft where the seam is flat 
will run from several hundred to two thousand acres or more depend- 
ing upon conditions, and some main entries are, therefore, of great 
length. They are timbered, bricked or concreted where necessary 
to properly support the sides and roof. Timber is more commonly 
used but concrete is now being extensively adopted in the larger 
mines for at least the part of the entry near the shaft or slope. 

In driving main entries they are usually driven on the dip of the 
seam, if the seam is inclined, and if it be nearly flat such factors as 
drainage, direction of horsebacks, direction of joints in the coal or its 
cleat, and direction of fractures in the roof of the entries affect the 
direction. From the main entries cross entries, cross headings, or 
butts are driven, usually at right angles to the main passages. There 
are some important considerations in laying out the cross entries or 
butt headings. They must drain properly to the main headings and 
if possible any grade should be used to advantage in hauling the coal. 


In case a syncline or " swamp " occurs in the mine the headings 
should be run so that the rooms may be driven on the rise from the 
entry and the coal thus worked down grade to the main haulage lines. 
In inclined seams the headings are driven so that they follow closely 
the strike of the seam, allowing for drainage, and each section of the 
mine in which one or more of these headings is driven off the slope is 
known as a lift or level. This term includes all the workings lying 
at approximately the same level and connected with the slope or shaft 
at the same elevation. 

Entry systems: The number of entries varies greatly in the mines 
of different regions. There are single, double, triple, quadruple, and 
even sextuple-entry systems. The first is seldom used and is not 
applicable to a large mine. In it a single entry is driven and it serves 
as the haulageway and intake air course. It is inefficient because an 
accident in the entry may cut off the circulation of air, the haulage, 
and the escape of men from the mine. 

The double-entry system is very commonly used in America and as 
indicated by the name the main and cross entries are all driven in 
pairs. This increases the efficiency of the mine as a double track 
increases that of a railroad. If one entry becomes blocked the air 
current and the haulage may be shifted to the other, (Fig. 84 and 
Plate IX). 

The triple-entry system is also frequently used and it has an ad- 
vantage in that the central passage may be used as the main haulage 
route and at the same time the intake air course. The other two 
entries are the return air courses for their respective sides of the mine. 

In the four-entry system there are four entries driven side by side; 
this system is frequently adopted, especially for gaseous mines and 
those with a large output (Fig. 84). For those mines where endless 
rope haulage is used it has an advantage as one entry may serve as a 
haulage road for loaded cars and the other for empties, while the 
other two are the return air courses. Several different arrangements 
are possible as one entry may be used for a manway and intake air 
course, one as a haulage road and intake and the other two as return 
air courses, or they may be divided so that the four entries are oper- 
ated as pairs. 

In all these systems where two or more entries are used the entries 
are connected by cut-throughs , break-throughs or cross cuts, which 


are openings about the same width as the entries and driven at right 
angles to the entries, through the pillars separating them. When 
one of these openings is driven at an inclination less than 90 to the 
entry it is known in some localities as a shoofly, (Fig. 84). The 
distance between these openings varies with the law requirements of 
the region, the gaseous nature of the mine and other local conditions. 
In the entries, spaces must be provided for the temporary storage of 
cars where they are collected from the working places and made up 
into trips. These track areas are known as sidings, partings or lyes, 
and where single track is used for haulage the siding where the cars 
turn out to pass is known as a turn-out or pass-by. 

Rooms, chambers, or breasts. The rooms, chambers or breasts 
are openings in the seam turned off the cross-entries and separated 
by pillars, (Fig. 84). These rooms are laid out according to a definite 
system and at stated intervals. The end of the room where the coal 

FIG. 85. Rooms driven at inclination to the entry in double entry mine. 

is being mined is known as the face or working face and the side of the 
room or entry along a pillar is the rib. The terms inby and outby 
serve to indicate the direction in the room, the former meaning toward 
the face and away from the entry and the latter the opposite direction. 
When a room is begun an opening known as the neck or mouth is 
made from the entry and about the same width as the entry. This 
is usually at right angles to the entry in flat or steeply pitching seams, 
but in gently inclined seams the rooms may be inclined less than 90 


to the entry and thus secure a more gradual rise for hauling cars to 
the face, (Fig. 85). Where the rooms are driven at such an angle 
their necks must be longer in order to leave sufficient coal in pillars 
to protect the entry. The direction of the room may also be influ- 
enced by the fractures in the roof and by the cleat in the coal. There 
are several terms describing the relation between the direction of 
these joints and the direction of the room. When the face is parallel 
to the main, or face cleat, and the rib at right angles to it the position 
is known as face on. The opposite to face on is end on, the position 

in which the face is at right 
angles to the face cleat and 
parallel to the butt cleats. 
Half on is the term used where 
the face of the room makes an 
angle of 45 with the face cleats 
and short horn where it makes 
an angle of more than 45. In 
driving long horn the face of the 
room lies at an angle less than 
45 to the face cleats. These 

FIG. 86. - Double room and break-throughs. vari US Psitions have their ad- 

vantages under different con- 
ditions because the coal breaks more readily and leaves more lump 
if mined from a certain direction with relation to the cleats. The gas 
may escape from the coal more gradually if the face lies across the di- 
rection of the main joints rather than parallel to them. 

When the neck of a room has been driven a sufficient distance from 
the entry, varying from 6 to 25 feet, the room is widened out on one 
side of the neck at an angle of 90 or less, usually less, (Fig. 84). 
This side is known as the gob side because the waste rock is usually 
stored in it and the track is laid along the opposite side. The width 
of the room will depend upon such factors as the weight of overlying 
strata, the. character of the roof and bottom and the thickness of the 
seam. A common width is about 20 feet, but it may run from 12 
feet up to 40 feet or more. The length of the room usually lies be- 
tween 150 and 300 feet although rooms are sometimes as much as 
600 feet in length. A common length is 250 feet. The presence of 
gas will usually affect the length of the room to some extent and tend 


to shorten it. The rooms are connected by cut-throughs , or break- 
throughs, to permit the circulation of air and the movement of the 
workmen, and in some cases a series of these in line may serve as a 
haulage road. The more gaseous the mine the more numerous the 
break-throughs should be. In many fields their number is fixed by 
law. In the bituminous region of Pennsylvania they cannot be more 
than 35 yards nor less than 16 yards apart. 

In some mines double rooms are driven, leaving a pillar of coal be- 
tween the double necks, (Fig. 86). The main advantage of the 
double room is in the more extensive working face provided. If 
there be much waste rock it may be gobbed along the center of the 
room leaving the tracks along the ribs on either side. 

Pillars. The several types of pillars in a coal mine comprise : 
the ordinary pillars left between entries and between rooms or breasts; 
chain pillars; shaft or slope pillars; and barrier pillars. A chain 
pillar is a long wide pillar left along an entry or gangway from which 
rooms are being driven to protect that opening, and it may be cut 
through by a number of break-throughs. A shaft pillar or slope 
pillar is left around a shaft or slope in each coal seam through which 
the shaft or slope passes, to protect the shaft or slope and the build- 
ings or other structures on the surface from damage. A barrier pillar 
is left along the border of a property to protect adjacent lands on 
either side of a property line from caving and from water or gas. 
The term is also applied to a pillar left in a mine to protect a certain 
portion of the mine from gas or water or to separate for some other 
reason this portion from the remainder of the mine. 

Size of pillars: The size of any of these pillars depends upon vari- 
ous conditions and can only be determined from experience in the 
region being worked. The greater the inclination, depth and thick- 
ness of the seam, the greater the quantity of water present, the weaker 
the roof and bottom, the more friable the coal, the more faulted the 
overlying strata, and the longer the pillars must stand, the larger 
they must be, other things being equal. The approximate weight 
of the overlying strata may be figured by averaging the specific gravity 
of the rock and computing the weight of the column of rock of the 
proper size and depth, but even then the effects of arching or bridging 
of the heavy beds in the series will not be taken into account. The 
average specific gravity of sandstone may be taken as 2.3 and that of 






shale as 2.5, which makes a cubic foot of sandstone weigh about 140 
pounds and a cubic foot of shale approximately 160 pounds. 

The distance between entries is usually made from 20 to 60 feet. 
Under certain conditions it is necessary to leave extra entry pillars 
to protect the entry, and these may be very wide, sometimes exceed- 
ing 100 feet. The room pillars vary from 6 to 90 feet in width in 
various mines, depending upon conditions and the methods adopted 
in these mines. The pillars are much wider at the stump, which lies 
between the necks of the rooms than elsewhere. A common width is 
20 to 30 feet for these pillars. 

The width of barrier pillars, like that of all others, varies with the 
conditions, the three main ones being the inclination and depth of 
the seam and the amount of water in the adjacent workings. A rule 
generally used as a guide by inspectors and engineers in the anthracite 
region of Pennsylvania is as follows: Multiply the thickness of the 
deposit in feet by i per cent of the depth below drainage level and add 
to this 5 times the thickness of the bed. In the bituminous region of 
Pennsylvania the mine law fixes the width of the pillar according to 
the conditions relating to water pressure. 

In some of the steeply pitching anthracite seams it is probably 
impractical to attempt to leave a barrier pillar which will be capable 
of supporting the load and holding back the water in deep basins, 
when the seams have been extensively mined. The oxidation of 
the coal where circulating water comes in contact with it tends to 
weaken the pillar in time. 

There are many rules for establishing the size of shaft pillars. As 
in the cases of the other pillars mentioned it is necessary to leave a 
large margin of safety as it is extremely important to protect the shaft 
bottom and the structures on the surface from any damage. Among 
the rules for the size of shaft pillars which are most generally ac- 
cepted is Dron's, which allows for a good factor of safety. Dron's 
Rule is as follows: Draw a line enclosing all surface buildings that 
should be protected by the shaft pillar. Make the pillar of such a size 
that solid coal will be left over the whole area enclosed by this line and 
for a distance beyond the line equal to one-third the depth of the shaft. 
The formula for computing the diameter of the shaft pillar by this 

rule is as follows: D = s -\ , where 5 is the diameter of the circle 



or square enclosing the structure on the surface and d is the depth of 
the shaft, in the same units of measurement. 

Some of the other rules employed are as follows: 

Andre's Rule : Minimum diameter of circular pillar or side of square 
pillar should be 35 yards to a depth of 150 yards. Add 5 yards for each 
25 yards of additional depth. 

D = 35 + 5 

Mining Engineering Rule: Radius of circular pillar or half side 
of square pillar, in yards is equal to 20 yards plus one-tenth of the prod- 
uct obtained by multiplying the depth of shaft, in yards, by the square 
root of the thickness of the seam in yards. 

^ ( , d x Vt\ 

D = 2 [ 20 H ) = 

V 10 / 

d x Vt\ . d x Vt 
40 + 

where d = depth of shaft and t the thickness of the seam. 

Foster's Rule : Radius of circular pillar, or half side of square pillar 
in feet, is equal to 3 times the square root of the product of the depth of 
cover, in feet, and the thickness of the seam in feet. 

Hughes Rule: For the diameter of a circular pillar or the side of 
a square pillar allow i yard for each yard in depth. 

Central Coal Basin Rule: Leave 100 square feet of coal for each 
foot that the shaft is deep, a main entry of average width being driven 
through this pillar. If the bottom is soft the result is increased by one- 

D = Vioo d 

Modifications of The Room-and-Pillar Method 

The pillar-and-stall system. This system is also known in some 
places as bord-and-pillar and post-and-pillar, although the systems 
are not the same in all respects. The pillar-and-stall system differs 
from the method already described in the smaller size of the rooms in 
proportion to the size of the pillars. The stalls are narrow rooms 
usually 10 to 15 feet wide with pillars about the same size in some 
cases. In other cases the rooms are driven about 10 feet wide on 
loo-foot centers and the pillars are then split a great number of times. 
In some cases double stalls corresponding to double rooms are driven. 


This system is used to advantage in some seams with bad draw slate 
and a bottom rock inclined to heave. In some places the stalls are 
driven full width from the entry without a neck. One form of this 
system is used in the Connellsville region of Pennsylvania. 

The panel system. The principle adopted in the panel system is 
to divide the area to be mined into square or rectangular blocks by 
entries driven at right angles to each other, (Fig. 87). These blocks 
are subdivided into a large number of smaller blocks and thus the 

FIG. 87. The panel system. 

original section is worked out as a unit. A large solid pillar is usually 
left surrounding the panel on three sides, serving as a barrier in case 
of fire or accident and controlling the air circulation. The system 
has the disadvantage of much narrow work but the advantage of 
giving complete control of the ventilation in that section of the mine 
and of permitting the block to be handled as a separate unit in case 
of accident. 

Anthracite mining in Pennsylvania. Since special methods must 
be employed in seams dipping more than 10 a description of some of 
the methods employed in the anthracite region of Pennsylvania will 
serve to illustrate the main variations from those employed in flat- 
lying seams. In general the room-and-pillar method is used, but the 
rooms are known as breasts or chambers and the entries as headings 

2 7 8 


or gangways. The breasts are driven to the rise and nearly up to the 
next higher gangway, (Fig. 88). 

One of the main problems confronting the miner in inclined seams 
is that of transporting the coal in the breast from the face to the gang- 
way. The following methods are employed: If the seam does not 
pitch more than 10 or 12 and the breasts are driven at an inclination 

to the pitch the car may 
be taken to the face and 
lowered by hand, by 
mule or motor. These 
means cannot be em- 
ployed in a seam pitch- 
ing more than 5 or 6 if 
the breast be driven on 
the full pitch. If the 
breast be driven on the 
full pitch the car may 
be lowered by windlass 
up to 10 or 12 inclina- 
tion. Jig roads are also 
used under similar con- 

The buggy system. 
The buggy system is 
often used in thick 
seams where there is 
plenty of head room. 
This system consists in 

the use of a small car which can be taken to the face by hand or by 
aid of a windlass where the seam pitches from 10 to 18. The coal 
is loaded on the buggy, taken down the breast and dumped on a 
platform, from which it is shoveled into the mine car in the gang- 
way. In some cases two buggies are used and the coal is trans- 
ferred from one to the other and thus lowered by stages. This 
method is costly in labor and coal broken. 

Chutes. In seams dipping between 1 5 and 30 the coal is 
usually sent down sheet-iron chutes to the gangway. These chutes 
are laid in the center of the breast with a row of props along either 

FIG. 88. Mining anthracite in Pennsylvania in 
steeply dipping seam. (After H. H. Stock, U. S. 
Geol. Survey.) 


2 79 

side and the gob is stored between these props and the ribs. The 
men travel along the chute. When the seam dips more than 30 
the coal will usually slide of its own weight and it is necessary 
to place an obstruction at the bottom of the chute in the neck of the 
chamber to hold the coal back. The structure employed is known 
as a battery, and a breast with such an arrangement as a battery breast, 
(Fig. 89): The coal is drawn out through the battery at such a 
rate that plenty of broken coal remains in the breast to permit the 
men to stand upon it and work at the face. This avoids the necessity 
of building a timber stage on which to work. In some cases the 
breasts are driven with double necks and two batteries are then 

constructed, (Fig. 90). This arrange- 
ment has the advantage where the seam 
is steeply inclined, of leaving a large 
pillar in the center of the lower end of 

FIG. 89. Single battery breast in FIG. 90. Double battery breast, 

anthracite mine. 

the breast to support the weight on the battery. In the battery 
breasts a manway must be provided as a separate opening driven 
through the coal or as an opening through the battery. In the 
breasts the men travel along the chute which is lined with posts 
securely set into the floor and roof of the seam. 

In the working of contiguous seams or of seams lying parallel and 



close together but separated by more than about 3 feet of rock, the 
coal in the upper seam is carried to the gangways in the lower seam 
through rock chutes, (Fig. 91). If there be less than about 3 feet of 
rock separating the seams they are usually worked as one seam with 
a parting, and the rock is mined out. Where contiguous seams are 
worked the working of the upper seam is usually completed first and 
the pillars robbed before the underlying seam is worked beyond the 
driving of gangways and airways. 

FIG. 91. Method of working contiguous seams through a horizontal rock tunnel. 
(After H. H. Stock, U. S. Geol. Survey.) 

Pillar Drawing 

During the first mining a large portion of the coal is left in the 
pillars and it must be extracted later. The process of removing the 
coal in the pillars is known as robbing pillars or pillar drawing. 
It is one of the more hazardous features of mining operations and 


the work should be attempted only by the more experienced 
miners. The percentage of coal left in the pillars after the first work- 
ing varies from 30 to 65 per cent of that originally in the seam, and 
in some cases where the thickness of the seam is favorable, the gas 
not excessive, and the roof and bottom good, as much as 98 per cent 
has been removed by final working. 

There are several systems of robbing pillars and the one adopted 
depends largely upon the local conditions. In some cases a break- 
through is made at the inby end of the pillar and the pillar is gradually 
removed until only the stump is left near the entry. Props are used 
to partially support the roof as the coal is removed and as the work 
advances the props are recovered and the roof allowed to cave. Care 
must be exercised in supporting the roof so as to keep sufficient pres- 
sure on the coal to help break it but not enough to crush the pillar. 
The roof should be broken at the stumps if possible, so as to relieve 
the weight on the entry pillars. Gas should not be allowed to collect 
in the gob for an indefinite period as it may escape into the workings 
or take fire. Another method of robbing pillars consists in splitting 
the pillars one or more times and then drawing them back as described 

In some mines the pillars are drawn out in panels and in others 
the workings are driven to the edge of the property and the pillars 
drawn back on a retreating system. In any case the ends of the 
pillars being drawn back should be kept in a nearly straight line so 
as to keep the roof supported and also to let it cave in a systematic 
manner, (Fig. 84). This lessens the danger to the miners and avoids 
the loss of coal. 


There are two main systems in longwall mining and several modi- 
fications of these systems to suit particular conditions. The systems 
are known as the advancing and retreating systems. In the former 
the workings are advanced from the shaft pillar toward the border 
of the property and in the latter the main entries are driven to the 
border of the property and the workings are then carried back toward 
the main shaft. The main features of the longwall method are the re- 
moval of practically all of the coal as the face advances and the main- 
taining of a continuous working face around the workings, (Fig. 92). 
The waste rock is used to fill up the space from which the coal has been 


removed and the roadways are maintained by pack-walls on either 
side of them, made of waste rock. These piles of rock are known as 
the road packs and those in the areas between the roads as gob packs. 
The main roads run diagonally from the shaft pillar like the spokes of 
a wheel, and the intervening areas are subdivided into smaller and 
smaller sectors by subsidiary roads. 

Overcasts shown thus: X 
Curtains shown thus ; 

FIG. 92. Plan of a longwall mine showing direction of ventilating current. (After 
Swift; from Bull. 13, III. Geol. Survey, University of 111. and U. S. Bur. of Mines.) 

In this method little of the coal is blasted from the face, the roof 
pressure being used to break it down after the coal is undercut. It 
is necessary therefore that the face be advanced uniformly and con- 

This method is particularly adapted to thin seams where the roof 
settles and the bottom tends to heave, since the waste rock is used 
for packing and the coal can all be removed in the first working. 
It also leaves the surface in better condition than the room-and- 



pillar method because the strata settle more uniformly. A larger 
percentage of the coal can be extracted in most cases than with the 
other system. Less timber is needed for roadways than in other 
methods and as a rule this method brings quicker return for capital 
and labor. 

FIG. 93. Plan of longwall mine with auxiliary permanent entries. (After S. O. Andros.) 

The disadvantages of the longwall method lie in the fact that more 
experienced miners are needed to operate the mine successfully. A 
section of the mine cannot be controlled as with the other methods 
and the mine suffers more from idleness or from irregular work of 
men at the face. It is more difficult to get into operation and a great 
deal of trouble is often encountered in getting the roof to break prop- 
erly around the shaft pillar or at the limits of the property as the case 
may be. It is only successful where there is plenty of waste rock, 
although in France it is employed where rock must be brought in 



from the surface in great quantities. There are immense quarries 
in central France from which the rock is taken for this purpose, 
(Fig. 96). This increases the expense considerably. In the United 
States the longwall method is used comparatively little. There are 
a good many longwall mines in Colorado and some of the other west- 
ern states, a number in Illinois and a few in some of the eastern 
states. Certain modified systems used in the anthracite region of 
Pennsylvania are known as the chamber longwall, lateral longwall and 
block longwall systems. These are operated on a rectangular or sort 
of panel arrangement, (Figs. 94 and 95). 



) r^ it ^ i ) r )( i i ic 


Airway in Coal Only |_ 




Pillar i 






It B - 





* <5 ** i 

p DH 

si .? 


ra @ 



Pillar Left in Place 





i B ij 

f ill * !? 

Bl .1 = f. 

T I 1 S g 1 i 

t Mr* if 

S 5' '"fl 

i II 1 i j, 

F |- | . A 





1 H S @ 





i @ e 



p a 



J I If 1 ( 

f " "^ 

( J 1 


Airway in Coal Only 

FIG. 94. Block longwall system. (By courtesy of the D. & H. Company, 

Scranton, Pa.) 

Mining in thick seams. When seams are very thick it is neces- 
sary to mine them in benches or with some sort of shrinkage stope 
system. The system which has been most successful is a modified 
form of the longwall in which the seam is worked in benches and the 
open spaces packed full of waste rock, (Fig. 97). 

Breaking the Coal at the Face 

Several methods are employed in breaking the coal at the face. 
When the longwall method of mining is adopted the coal is undercut 


by a longwall machine and the roof is allowed to settle gradually so 
as to break down the coal. In the room-and-pillar method the coal 
is undercut by a coal cutting machine or by miners' picks and is blasted 
or wedged down, (Fig. 98). In many cases the coal is sheared as 
well as undercut. Shearing consists in making a vertical cut along 
the side of the room or entry as the case may be in order to keep the 
wall straight and uniform. Some of the latest machines will not 

FIG. 95. Development of a longwall operation in the anthracite region. 
(By courtesy of the D. & H. Company, Scran ton, Pa.) 

only undercut the coal but also shear it, and it is expected that in the 
near future they will be so constructed that they will also success- 
fully break down the coal. The depth of the channel which is cut 
along the bottom of the seam, or along a parting in the coal as the 
case may be, may reach 6 feet or more, but it depends somewhat upon 
the nature of the coal and roof pressure. When it is done by hand it 
must be wide enough to permit a man to lie in it on his side and work 


a pick, the seam above him being kept from closing down by a short 
prop. After the coal is undercut it is shot down or wedged down. 
In some cases coal is shot from the solid, and fhis is necessary in 
many anthracite mines. This method has the disadvantage of 
breaking the coal up so that much more slack and less lump coal 
results. There is also more danger in firing owing to the heavy 
charges necessary to blow the coal down. The production of a 
greater percentage of slack does not matter so much if it is to be 
used for coking but it lowers the value of the coal very greatly for 
domestic and steaming purposes. A great deal of care and judg- 
ment is necessary in placing the holes which are made by augers or 
hammer drills, as their depth and arrangement affect the amount of 
coal shot down, the conditions in which the broken coal occurs and 
the safety of the miners, especially when black powder is used. 

Mining Machines 

There has been a rapid development in coal mining machines in 
recent years. The latest coal-cutter has been so developed that it can 
undercut and shear the seam, can cut out a sulphur band or a parting 
in the seam and can be operated much more readily than the earlier 
types. There are also loading machines which apparently work 
quite successfully under certain conditions. The tendency has been 
to get away from the pick machines, or punchers and adopt the con- 
tinuous cutting types. The application of electricity has been re- 
sponsible for a great development in mining machines and it is now 
possible to use electric machines in gaseous mines. According to the 
latest report of the Department of Mines of Pennsylvania, the per- 
centage of bituminous coal mined in this state by compressed air 
machines in the year 1899 was 21.22, and in 1917 it was 9.03. In the 
same years the percentages mined by electrical machines were 18.38 
and 45.14 respectively. In the same years the percentages mined by 
hand were 60.40 and 45.83. 

The use of cutting machines in the anthracite region has developed 
more slowly than in the bituminous region of Pennsylvania, owing 
to the difficulty in cutting the harder coal and in moving the machines 
on the steep pitches, but the machines are now successfully used in 
parts of the region. 



It seems probable that we will see a machine in the not far distant 
future which will undercut, shear, break down and load the coal 
where the conditions are favorable. 

Mining Methods in Foreign Countries 

Europe. The longwall method is much more generally used in 
Europe than in America, and on the European continent it is used 
almost entirely. According to G. S. Rice 1 the typical American room- 
and-pillar method is not used in Europe except in a few places in 
Wales, where it is known as the pillar-and- (single) -stall method, and 

FIG. 96. Open cut at Commentry, France, from which coal has been mined and most 
of the rock used to fill the mines. (Photo by E. S. Moore.) 

in Upper Silesia where it was formerly used rather extensively but is 
now largely abandoned for the longwall method. The pillar-and- 
double-stall method was formerly used to some extent in Scotland 
and in Wales but it has also been nearly abandoned for the longwall 
method. In South Staffordshire a method known as the square- 
chamber method has been used in the Ten Yard seam. In this method 
the coal is worked by chambers 46 yards wide and up to 200 feet long 
with thick pillars between them. Four to six coal pillars are left 
standing in rows through the chamber. 

1 Rice, G. S., Coal-pillar drawing methods in Europe. Trans. Amer. Inst. Min. 
Met. Eng., New York Meeting, Feb. 1921. 


The bord-and-pillar or stoop-and-room method is common in the 
north of England, in Scotland and to a lesser extent in Wales. In 
Upper Silesia it is used in a modified form where the hydraulic sand 
filling system is in use in the thick seams. The writer has visited 
mines near St. Etienne, France, where the modified longwall method 
was being used and the waste rock of the mine was supplemented by 
rock brought in from the surface so that the space mined out could 
be completely filled up as fast as the coal was removed, (Fig. 96). 

Australia. 1 On this continent the pillar-and-bord system is very 
largely used although the longwall method is found in a number of 
mines. In several places both methods are used in the same mine. 


FIG. 97. Bench working in thick seams, with stone packs. 



In some mines one method is used in one seam and the other method 
in an underlying seam, depending upon the thickness of the coal, the 
abundance of waste rock and other factors. 

Mine Haulage 

Haulage in mines is performed by animals, electric motors, com- 
pressed air locomotives, steam locomotives and cables. There are ad- 
vantages in all these sources of power under certain conditions. Some 
companies have successfully taken the cars to and from the face with 
a motor while others have found it uneconomical to use a motor for 
other purposes than hauling trains of mine cars considerable dis- 
tances. In the latter case a mule is used for gathering the cars into 
trains. Whether a motor may be used successfully in gathering seems 
to depend very largely upon the thickness of the seam and the ease 
with which the tracks are kept open and in good condition. 

Rope or cable haulage is of two types, endless and tail. In the 

1 Power, F, Danvers, Coalfields and collieries of Australia. 1912. 


former type the cable runs continuously and the car is arranged 
so as to grip the cable. This works successfully in some mines but 
unsuccessfully in others. The straightness and regularity of the 
entries has a good deal of influence on this system. With the tail 
rope the cars are hauled in opposite directions by separate ropes. 

Conveyors are now being used successfully in some mines, espe- 
cially in some of the thin seams in the anthracite region of Pennsyl- 
vania. Scrapers have also been used to some extent in gathering 

FIG. 98. Sullivan Ironclad alternating current mining machine in operation 
undercutting a seam. (By courtesy of the Sullivan Machinery Co.) 

coal. A remarkable conveyor, about eight miles in length is being 
installed by the H. C. Frick Company for transporting to the river 
the coal from several mines. It runs underground and the great belt 
is driven by a series of motors connected with each other by auto- 
matic control systems. It may revolutionize this type of trans- 


Hoisting of coal is usually accomplished by raising the mine car to 
the tipple and dumping it. Some mines, however, have operated 

2 go 


lo-ton skips very successfully. 1 Some of the advantages claimed for 
skip hoisting over a self-dumping cage are: a larger capacity for 
coal and rock; smaller shaft necessary; lower rope speed and power 
consumption; and fewer men. Some of the objections commonly 
made to skip hoisting are: the greater breakage of coal, although 
this does not appear to be necessary; excessive dust raised by dumping 
at bottom of shaft; necessity of a cage for hoisting men and materials; 
difficulty in docking and inspecting the coal; and difficulties in hand- 
ling waste rock on the surface. 

FIG. 99. Electric haulage. A trip leaving the mine of the Ebensburg Coal Company. 
(Photo, by courtesy of J. F. Macklin, Pres. Ebensburg Coal Co.) 

Mine Gases 2 

Ordinary pure air contains about 20.93 P er cen t by volume of 
oxygen, 79.04 per cent nitrogen, 3 parts in 10,000 of carbon dioxide 
and small amounts of argon, helium and other gases. Water vapor is 
present in varying amounts depending upon temperature and pressure 
and the presence of water in the neighborhood. The oxygen is the 
most active chemical agent in the atmosphere and it unites with 

1 Allen, A., and Garcia, J. A., Skip hoisting for coal mines. Trans. Amer. Inst. 
Min. and Met. Eng., New York Meeting, Feb. 1921. 

2 Beard, J. T., Mine gases and explosions. John Wiley & Sons, Inc., 1908. 


metals causing them to deteriorate, as in the case of iron rusting. 
Oxygen is given off by plants, but when animals breathe slow com- 
bustion occurs as in a fire and the carbon in their systems unites with 
the oxygen to produce carbon dioxide. Nitrogen is an inert gas and 
serves the purpose of diluting the oxygen of the air. 

In some mines the air is fairly pure and an open light may be 
carried without danger. In others there is an abundance of methane 
and carbon dioxide and dangerous quantities of carbon monoxide 
and hydrogen sulphide, making it unsafe to enter the mine at all 
with an open light and dangerous to enter it with a closed light unless 
the ventilation is good. 

Carbon dioxide. Carbon dioxide (CO 2 ) has a molecular weight 
of 44 and a specific gravity of 1.529. Being heavier than air it natur- 
ally settles to lower levels when with lighter gas, and this explains 
why animals may be overcome in low places where this gas has col- 
lected while at higher points in the same region they may be quite 
safe. It should be borne in mind, however, that this may not always 
be true for the location of the gas in mines since the air currents and 
the source of the gas may have some influence on its gathering point. 
It is a product of combustion from fire and the lungs of animals. It 
may also be given off during the decay of vegetal matter and this 
explains the presence of a considerable amount of it in the mines where 
oxidation of the coal is in progress and where it has been imprisoned 
in the coal seam since its formation from the altering vegetal matter. 
A certain amount is given off by the breathing of the men and the 
horses or mules in the mine and by the burning of the lamps. 

Black damp or choke damp is a mixture consisting chiefly of nitro- 
gen and carbon dioxide with a little oxygen. 1 It is not explosive or 
poisonous but its danger lies in the fact that it excludes the oxygen 
so that a sufficient quantity does not reach the lungs of animals. 
According to W. G. Duncan, average black damp contains 85 to 95 
per cent nitrogen and the remainder is chiefly carbon dioxide. The 
average composition of the mixture is about 90 per cent nitrogen 
and 10 per cent carbon dioxide. It is, therefore, impossible for an 
animal to live or a light to burn in this gas. 

The presence of carbon dioxide may be detected by an ordinary 

1 Burrell, G. A., Robertson, I. W., and Oberfell, G. G., Black damp in mines. U. S. 
Bur. Mines, Bull. 105, 1916. 



lamp or candle which requires 17 per cent of oxygen, but an acety- 
lene lamp is not extinguished until the oxygen is reduced to about 12 
per cent. When 3 to 4 per cent of the dioxide is present most people 
begin to feel its effects in headaches or other derangements, and real 
distress may be caused by 5 to 6 per cent of the gas in the air. Where 
carbon dioxide is present owing to exhalation of animals it is not only 
this gas which causes the trouble but also the deficiency in the oxy- 
gen which has been removed by breathing. 

FIG. ioo. Shaft bottom of Jerome Shaft No. 2. Hillman Coal and Coke Co. 
(By courtesy of the Hillman Coal and Coke Co.) 

Carbon monoxide. Carbon monoxide (CO) is an odorless, color- 
less gas with a molecular weight of 28, a density of 14, and a specific 
gravity 0.967. It is, therefore, slightly lighter than air. Its rate of 
diffusion compared with air is 1.0149 an d its ignition point 650 C. 
When mixed with air in any proportions it forms white damp. Un- 
like carbon dioxide it is a deadly poison, the effects in some cases being 
sudden, in other cases delayed. It requires only about T V of i per 



cent of this gas in air to cause dizziness, headache, shortness of breath 
or other effects, and T \ may be dangerous, while T \ of it is almost sure 
to be fatal. The gas attacks the haemoglobin of the blood and 60 
to 70 per cent saturation of the blood is fatal. It usually takes from 
5 to 6 hours to free the blood after a serious case of poisoning. The 
effect on the blood is to turn it a pink color. The best treatment is to 
remove the patient into pure air and apply heat to the body by wrap- 
ping up in warm blankets or applying hot-water bottles. In serious 
cases of poisoning it may be necessary to use pure oxygen mixed with 
10 per cent CC>2. To test mine gas for the presence of CO a small 
animal such as a mouse or canary bird is used, the latter being the best 
indicator. Experiments by the United States Bureau of Mines 1 have 
shown that in air containing carbon monoxide canaries and mice be- 
haved as follows: 


in air 





Guinea pigs 


No. tested 8; 
i affected in 
12 min., 2 
slightly af- 
fected in 4 

No. tested 7; 
i distressed 
in 30 min., 6 
showed no 
distress in 2\ 

No. tested i; 
no effect in 
2\ hours. 


No. tested 4; 
affected in 5 
to 30 min. 

No. tested i; 
affected in 
45 min. 

No. tested i; 
no distress in 
45 min. 


No. tested 12; 
i distressed 
in 35 min., n 
in 2 to 6 min. 

No. tested 6; 
i distressed 
in 40 min., 5 
in 6 to 1 2 min. 

No. tested 4; 
distressed in 
10 to 45 min. 

No. tested i; 
in 5 min. 


No. tested 2; 
i distressed 
in i min., i 
in 2 min. 

No. tested 2; 
i distressed 
in 2 min., i 
in 3 min. 

No. tested i; 
in 4 to 9 


No. tested 8; 
in 2 to 9 

It is evident that all animals of the same species are not affected to 
the same degree. If an animal becomes accustomed to small amounts 

1 Burrell, G. A., Seibert, F. M., and Robertson, I. W., Effects of carbon monoxide on 
small animals. U. S. Bur. of Mines, Tech. Paper 62, 1914. 


of the gas it is more resistant to future attacks. Small animals are 
more readily affected than human beings but not in proportion to 
their weight. The flame of a safety lamp is not affected by less than 
i J per cent of this gas and about 2 per cent is necessary to show a cap. 
This cap is similar to that of marsh gas. An instrument known as 
the M-S-A Carbon Monoxide Detector has recently been put on the 
market; it is very sensitive to this gas and is supposed to indicate 
within ten seconds any percentage of the gas from 0.05 to i. Car- 
bon monoxide is explosive when mixed with air in proportions of about 
I 5-5 to 75 per cent, but the presence of carbon dioxide and marsh 
gas affects these limits by respectively raising and lowering them. 

Carbon monoxide is formed by incomplete combustion of carbon 
in a fire when the oxygen supply is deficient, by the explosion of some 
types of blasting powder such as those deficient in saltpetre and by 
the partial oxidation of organic material. The first process is the 
most important producer of the gas. 

Methane. This gas is also known as marsh gas (CH 4 ), and when 
mixed with air it forms fire damp. Its molecular weight is 16 and its 
specific gravity 0.53. It is thus much lighter than air. It is non- 
poisonous, tasteless, odorless and colorless. It will not support com- 
bustion but it will burn with oxygen, producing water and carbon 
dioxide, when the proportions of the gas vary from i volume of gas 
to between 3.5 and 30 volumes of air, the greatest explosive intensity 
being reached when the proportions are i volume of methane to 9.5 
volumes of air. The cap produced on the flame of a safety lamp is 
the means usually employed in detecting the presence of the gas and 
the following table shows how the cap develops with the varying per- 
centages of the gas present in the air : 

Percentage of methane Height of cap and flame 

i Base of cap forming 

1 2 iinch 

2 f to 2 inch 

25 | inch and slightly luminous top 

2 f finch 

3 i j inches 

35 15 to if inches 

3f Up in gauze 

An increase in moisture lowers the explosibility of fire damp and a 
mixture of i part of carbon dioxide with 7 parts of an explosive mixture 


of air and marsh gas makes it non-explosive, or i part of nitrogen to 
6 parts of a similar mixture produces the same result. 

Marsh gas is abundant in some mines but almost entirely absent 
in others. It is given off by the coal and it results from the alter- 
ation of the vegetal matter in forming coal as indicated in a general 
way in the following equation: 

C 57 H 56 10 - (3H 2 + C0 2 + 2CH 4 ) = C^A 

Lignite Bituminous coal 

As previously mentioned, one mine in the anthracite region of Penn- 
sylvania has produced as much as 2400 cubic feet of methane per 
minute. (For further notes see discussion of gases under the Chemi- 
cal Properties of Coal, Chapter II.) 

Hydrogen Sulphide. Hydrogen sulphide, or sulphuretted hy- 
drogen (H 2 S) occurs in mines in small amounts and when it is mixed 
with air the mixture is known as stink damp or stone damp since it 
has a very strong and disagreeable odor. It results in very small 
amounts from blasting, especially where black powder is used and 
it is also set free through the decay of organic matter. The odor of 
rotten eggs is largely due to the presence of this gas. It may also 
be generated by the action of acids on sulphur compounds. The gas 
will not support combustion but it burns in air with a pale blue flame, 
the temperature of ignition being 333.3 C. or at red heat. When 
mixed with one-half times its own volume of air it burns with ex- 
plosive force and with 7 volumes of air it explodes violently. It 
produces headache, nausea and the loss of the sense of smell, and if 
inhaled in sufficient quantities results are fatal. The amount neces- 
sary to produce death in a human being is about i part by volume to 
200 parts of air. Canary birds are sensitive to about .05 per cent in air. 
Treatment consists in removal to a plentiful supply of fresh air, and in 
severe cases a little chlorine gas may be administered to aid recovery. 

Hydrogen. This gas may be formed in small amounts in mines as 
a result of incomplete combustion in mine fires or in explosions, but 
it seldom occurs in noticeable quantities. Other rarer gases, including 
some of the paraffin series, occur in very small quantities in mines. 

Safety Lamps 

Various methods have been devised for the lighting of mines, from 
the torch and the flint mill which generated sparks by contact of a 


steel wheel with a piece of flint, to the high candle power electric light 
of the present day. In gaseous mines it is necessary to have a closed 
light and this gave rise to the safety lamp which is now found in such 
great variety. The structure of the safety lamp is based on the prin- 
ciple of a protecting envelope through which air will pass but which 
will prevent the gases outside of the lamp from becoming heated to 
the temperature of ignition. The first safety lamp was invented by 
Clanney in 1813 and air was forced into it through a water seal by 
means of a bellows. The Davy safety lamp was invented by Sir 
William Davy two years later and had a wire gauze around the flame 
to conduct the heat away so that the gases outside of the lamp would 
not take fire. Credit is also due to George Stephenson for discovering 
the principle of the bonnet 'the same year. The modern lamps are 
safely locked so that a miner cannot unlock them in the mine but must 
take them to a safe place to be unlocked by a key or an electrical 
device. Most of them have a self-lighting device inside which in- 
sures greater safety to the men. Oil is the fuel mostly used. The 
light is much better in the modern lamp than in the older types since 
it has a glass envelope or chimney and the air enters near the base of 
the lamp. 

The electric cap lamp has made its appearance in the mines during 
the last seven years and it gives promise of being very largely used 
because of its greater convenience and its efficiency in producing light. 1 
It has one serious objection to the miner used to the other safety lamps, 
and that is the fact that it does not indicate the presence of harmful 

For open lights in non-gaseous mines acetylene generated from 
calcium carbide in contact with water produces a very efficient light 
and acetylene lights are very commonly used. 

Mine Ventilation 

Since a coal mine is certain to contain more or less foul air it is 
essential that it be well ventilated. There are two means of ven- 
tilating a mine: by a furnace and by a fan. A furnace may be used 
in the smaller mines which are not gaseous. It is built of brick at 
the foot of a shaft on the main airway, so as to create a strong upward 

1 Clark, H. H., Permissible electric lamps for mines. U. S. Bur. of Mines. Tech. 
Paper 75, 1914. 


draft by convection currents generated by a fire which is kept burning 
all the time men are at work in the mine. 

Mine fans are of many types. They may be constructed as the disc 
fan where the blades are arranged as they are on a windmill or as the 
centrifugal type in which the blades are normal to the plane of revo- 
lution. The fans are usually run so that they propel the air through 
the airways and to all the working places in the mine, but in some 
cases the fan may be run as an exhaust fan. It is considered neces- 
sary to so ventilate a mine that every man may have a minimum of 
150 cubic feet of air per minute if the mine be non-gaseous and 200 
cubic feet if it be gaseous. The velocity of the current of air in the 
mine workings is measured by an anemometer and the pressure by a 
water gage. If the anemometer reading were 1800 feet in three 
minutes and the size of the airway 6 feet by 10 feet the volume of air 

passing through would be found in the following way: 6 x 10 X - 


= 36,000 cubic feet per minute. Fans are as much as 35 feet in diam- 
eter and they are capable of delivering from a few thousand up to over 
400,000 cubic feet of air per minute, depending upon the size and type 
of the fan, the rate at which it is run, and the mine resistance. 

In ventilating a mine the foul air and explosive gases are driven out, 
but the fresh supply of oxygen tends to oxidize the coal and to set 
methane free, sometimes at a rapid rate. The air entering the mine 
becomes warmed and the presence of air with the increased tempera- 
ture aids the absorption of moisture which is carried out with the air 
current, leaving the mine dry and in some cases dusty. The fine coal 
dust becomes distributed through the air and acts much the same 
as an explosive gas when ignited. 1 It has been shown that the dust 
is capable of producing tremendous explosions and it is particularly 
dangerous when mixed with gas as this increases the possibility 
of igniting the dust by lamps or blasts. The discovery of the ready 
explosibility of coal dust has aided greatly in avoiding many bad ac- 
cidents. The danger of explosions may be greatly lessened by 
sprinkling the mine, and taking other precautions against trouble 
such as regulating the use of certain explosives, like black powder 
which generates a long flame on firing. There are certain explosives 

1 Rice, G. S., and others, Explosibility of coal dust. U. S. Geol. Survey, Bull. 20, 1911. 


designated as permissible explosives 1 for coal mines and the use of 
these has aided in reducing accidents although they are not always 
the most suitable from the practical standpoint for producing the best 
type of coal for the market. Great strides have been made in recent 
years in the direction of greater protection for life and property in coal 
mining and the percentage of accidents has been greatly reduced. 
Mining has become a relatively safe occupation. 

Mine Fires 

Mine fires are one of the great causes of trouble in coal mines and 
they start by lamps firing gas, timbers or coal, or from blasts or spon- 
taneous combustion. If they are taken in their incipient stages they 
can as a rule be put out although the safest practice is to take all 
precautions against letting them get started. When small they may 
be put out with water or a chemical extinguisher but when once well 
started they must be flooded or smothered out. In some cases it 
may be necessary to flood the whole mine, while in others dams of con- 
crete, masonry or wood may be built and the spaces behind them 
flooded. In smothering a fire the mine shaft may have to be sealed 
up or a portion of the mine may be walled off and sealed so tightly 
that the fire dies out for want of oxygen. The sealing is done by walls 
of rock and clay, masonry or concrete. Sometimes a wooden wall is 
built, and clay, sand or other suitable material is filled in behind it. 
The waste or " slush " from a breaker or washery may in some cases 
be turned into the mine to seal up the fire. It is often extremely 
difficult to seal the area so tightly that no oxygen can enter and 
there are some fires which have burned for over half a century 
baffling all attempts to extinguish them. When sealed the area may 
retain its heat for years, and in some mines the fire which was sup- 
posed to be dead has broken out as soon as air was admitted. Great 
care must therefore be exercised in reopening a sealed mine or local 
area in a mine. 

In some cases fires have been extinguished by mining out the seam 
around the fire, thus isolating it. 

1 Howell, S. P., Permissible explosives tested prior to Mar. i, 1915. U. S. Bur. of 
Mines, Tech. Paper 100, 1915. 



A glance at the statistics of distribution of coal mined in the United 
States shows the manner in which the coals of various ranks are di- 
vided for consumption. 1 In 1917 the distribution of approximately 
80 million tons of Pennsylvania anthracite was as follows: nearly 51 
million tons were of domestic sizes; 18 million tons of steam sizes; 
6 million tons were used by railroads and over 4 million tons exported. 
For the same year about 366 million short tons of bituminous coal, 
mined and distributed in this country, were divided as follows: 

Used at mines for steam and heat 12,117,159 tons 

" in manufacture of beehive coke 52,246,612 

" in manufacture of by-product coke S^SQS^SQ 

" in manufacture of coal gas ........ 4,959,697 

" by electrical utilities 31,692,722 

" for domestic purposes 57,104,000 

" for industrial purposes 176,365,939 

In addition to the coal included in these figures about 153 million tons 
were used by the railroads and over 10 million tons were loaded at 
seaports for bunker purposes. Approximately 23 million tons were 

For industrial purposes and for the use of the railroads, the two 
largest items of consumption, a great variety of coals and grades of 
coal may be used. The same holds true for the electrical utilities, 
mine consumption and to a certain degree for domestic purposes. 
For certain types of industrial operations where special coals are 
required as, for example, in smithing, there were 255,000 tons used. 
For coking purposes certain limits may be placed on the grade and 
ranks of coal used, as low sulphur coals and coking varieties must be 

For domestic purposes the distinctions made lie more in the prep- 
aration of the coal for use than in the rank or grade of the coals, since 
all ranks from lignite to anthracite are extensively used and some 
of the coals are of very low grade. For gas manufacture particular 
types of fairly high volatile coals are best. 

1 U. S. Geol. Survey, Mineral Resources of the United States, 1917. 


3 oo 


Preparation of Coal for Domestic Purposes 

Anthracite. On account of its high heating, low smoke-producing 
and long-burning qualities, and its freedom from dirt and dust, 
anthracite has long been a favorite domestic fuel. The operation of 
preparing it for market has become quite a highly developed me- 
chanic art. 

FIG. 101. Slate pickers in an anthracite breaker. (Photo by courtesy of R. P. Hutch- 
inson of the Bethlehem Fabricators Inc.) 

There are two main objects in view in breaking and separating 
anthracite, one being that of getting it into uniform sizes so that it 
will readily burn in a grate and the other that of cleaning the coal 
by washing out the small particles of mineral matter and by removing 
the larger fragments of slate by hand or with mechanical separators. 
According to Sterling 1 the methods of preparation may be grouped 
under three classes, as follows: (i) Dry preparation, used for 
lump coal which comes from the mine dry and which readily 

1 Sterling, Paul, The preparation of anthracite. Trans. Amer. Inst. Min. Eng., Vol. 
42, p. 264, 1912. Also Peele's Handbook for Mining Engineers, p. 1842. 



separates from the waste rock; (2) Combination of dry and wet 
preparation employed when the run-of-mine contains a high per- 
centage of impurities, perhaps up to 55 per cent, but also consid- 
erable lump coal which can be handled as in (i); (3) Wet prepara- 
tion, when the run-of-mine is high in impurities and is discolored 
with iron or clay. This type of coal occurs near the surface and in 
disturbed zones in the mine. 

The coal is taken from the mine mouth to the breaker in the mine 
cars or by conveyors, depending upon the relative position of the pit 
mouth and the top of the breaker. It is first passed over a sizing screen, 
sometimes known as a bull shaker, which sorts the lump from the 
smaller material, the former going to a picking table and the latter, 
which is often called the mud-screen product, moving along to be 
treated by the wet process, (Fig. 101). On the picking table pieces 
of rock are removed by hand. If coal and rock adhere the lumps are 
removed to a special table where they are broken by hand and the 
rock sent to the rock pile. 

The cleaned lump goes to a pocket for shipment as lump or to the 
rolls to be broken, depending upon the demand for the different 
sizes. The rolls, which are furnished with teeth, break the coal into 
the sizes indicated by the following table: 


Size of coal 

Punched plate 

Woven wire 








Through , 





J P 
















1 3 

T 6 












Egg. . 







Buckwheat No. 4 

3 02 


The percentages of each size allowable in the other sizes and the 
percentage of slate and bone allowable in the various sizes is shown 
in the following table: 


May contain 









Of slate 









Of bone 






Of next size 









Of next size 








2 5 



After screening, the steamboat size is either sent to a pocket and 
shipped or sent to other rolls and further crushed, according to the 
condition of the market for various sizes. This process is continued 
until the whole operation is complete except that certain portions of 
the coal are put through the wet process to clean it if necessary. The 
course followed is clearly outlined by Ashmead 1 in the accompanying 
diagram, (Fig. 102). 

The screens used in recent years are largely of the shaker type 
rather than the oscillating or gyratory screens. The advantages of 
the shaker type, according to Sterling, are: low first cost; ease with 
which it may be repaired and maintained; good sizing of smaller 
sizes; large capacity; ability to size material not over 150 pounds 
in weight in going to the picking room. The revolving screen does 
not vibrate the breaker as much as a shaker screen and it performs 
exact screening and sizing. It has smaller capacity, however, and 
requires more space than shaking screens of the same capacity. Only 
about one-eighth of the surface is in contact with the coal at one 
time. The first cost and maintenance are high. 

There have been some recent developments in the use of jigs, es- 
pecially of the plunger type, for separating the slate from the coal, 
and mechanical pickers are used a great deal for the same purpose 
in dry preparation. Where hand picking is done the moving table 

1 Ashmead, D. C., Modernized breaker with hand pickers, spirals, jigs and concen- 
trators. Coal Age, Vol. 18, p. 585, 1920. 





is found to be an advantage. In the automatic mechanical pickers 
the moving table is so arranged as to give it a pitch in two directions, 
first transverse to the table, and second along the center line. This 
requires the moving material to travel up hill and the coal is separ- 
ated from the rock, owing to difference in specific gravity and friction 

FIG. 103. Cross-section of Alliance Breaker, showing loading method. (After Ash- 
mead: Reproduced by courtesy of Coal Age.) 

of the coal and slate on the table. The rock discharges at one point 
and the coal at another. With the increased efficiency of the cleaning 
equipment in the modern breakers it is now possible to save a much 
larger percentage of the coal than formerly and some of the culm 
banks can be reworked. Several large Pennsylvania anthracite 
companies have quite recently installed tables of the Deister-Over- 
strom type for washing the barley and smaller sizes of coal. There 



seems to be a good future in the Anthracite region for the application 
of some of the devices so long used for ores, and adopted in some of 
the western fields for coal washing and separation. 

Bituminous coal. It is becoming more and more a custom to 
wash and size bituminous and semibituminous coal for domestic pur- 
poses. A cleaner coal and a coal which will burn better and stand 
storage better is produced in this way, and mining operations are 
aided because some labor in sorting coal and rock underground is 
saved. At many mines simple bar screens are used while at others 
modern shaker screens have been adopted. The coal is sorted into 
various sizes somewhat like anthracite but on a less perfectly devel- 
oped plan. The state of Illinois has probably been the most advanced 
of the states of the Union in the systematic preparation of bituminous 
coal, and now only about 20 per cent of her output is sold as run-of- 
mine, the remainder being treated before shipment is made. 1 This 
remarkable development in washing and sizing operations in Illinois 
is partly due, however, to the fact that very little of the coal in the 
state is of coking quality. This is a type which does not need sizing for 
market, although it is customary to wash a great deal of coking coal to 
reduce the sulphur content. At mines where the coal is only passed 
over shaking screens and then sold, four sizes are commonly made; 
these are known by the following names: 


Size in inches 

Per cent of total output 


Over 6 

T (J 


Over 3^ through 6 


No. i nut 

Over if through 3^ 


No. 2 nut 

Over i through if 


No. 3 nut 

Over f through i 


No. 4 nut 

Over j through f 


No. 5 nut 

Through j 


The sizes for these different types vary somewhat in different fields. 
In some areas the lump sizes run through 8 grades of lump, from 8- 
inch lump to ij-inch lump and on down through chunk, egg, nut, pea 
and screenings. At some mines mechanical pickers, as well as men 
and boys, are employed and some companies wash the coal in addition 

1 Andros, S. O., Coal mining in Illinois. Illinois Coal Mining Investigations. Bull. 
13, p. 202. Urbana, 1914. 

3 6 


to screening it. Washing tends to remove clay, slate and iron pyrite 
and this is quite an advantage for high sulphur coals for coking. 
An elaborate washery was put into operation at the United States 
Fuel Company's mine at Benton, Franklin County, Illinois in the 
fall of 1918. l It has been the hope of mining men that the greater 
part of the sulphur could be removed from coal by washing out the 
pyrite. Unfortunately, as previously pointed out in this text, it is 
impossible to wash out the sulphur in organic compounds, or the 
finely divided pyrite which is almost always present. 

FIG. 104. The Loree Breaker. (Photo by courtesy of R. P. 
Hutchinson, Bethlehem Fabricators, Inc.) 


The storing of coal is a very important item in many industries. 
If it is not stored at times when it is plentiful and transportation 
facilities are good, plants may be tied up owing to break-downs in 
traffic or mining operations, resulting from storms, strikes or other 
causes. Another advantage in storing coal is that it distributes the 
demand more uniformly over the whole year and the peak load does 

1 Campbell, J. R., Mechanical separation of sulphur minerals from coal. Trans. Amer. 
Inst. Min. and Met. Eng., Vol. LXIII, p. 683, 1920. Also, Frazer, Thomas and Yancey, 
H. J., Some factors that affect the washability of a coal, p. 768. 


not always fall in the winter when most coal is likely to be needed. 
According to Stock the coal should be stored as near the place where 
it will be used as possible, although it is practical to store at the mines 
temporarily when the car supply is short. The main objections to 
storage of coal in large amounts are the breakage, the cost of re- 
handling, danger of fire from spontaneous combustion or other causes, 
the deterioration from weathering, the difficulty in securing adequate 
storage facilities in large cities where the coal may be stored near 
the plant in which it is to be used, and the possibility of a sudden 
and considerable drop in price. 1 

Spontaneous combustion. The cause of spontaneous combustion 
is heating of the coal by oxidation and other agencies. Oxidation is 
continually going on in coal exposed to the air and there is a general 
impression that sulphur in the form of pyrite is responsible for much 
of the trouble. This is not the real cause although it may aid the 
chemical processes producing the heat. Sulphuric acid is developed 
to a certain extent in the weathering of iron pyrite and since it is such 
a strong oxidizing agent and generates so much heat on coming in 
contact with water the presence of pyrite will naturally have an effect 
on chemical action. It should be borne in mind, however, that the 
condition in which the pyrite occurs in the coal, whether finely divided, 
or coarsely crystallized, will have some influence on its rate of weather- 
ing and it is found that the rate varies greatly. Specimens of pyrite 
in a collection in a laboratory show great differences in the rate of 
alteration. Some will break down in the course of a few years while 
others will remain perfectly bright for an indefinite period. 

In a recent paper some English writers 2 have claimed that fusain, 
(mother-of-coal or mineral charcoal) probably aids spontaneous com- 
bustion owing to the ease with which it crumbles to powder and takes 
fire. It smoulders in many cases without any evidence of flame. 
These writers have also found, as previously mentioned in this work, 
that mineral charcoal contains a higher percentage of ash and fixed 
carbon than the coal in which it occurs and that it is deleterious to the 
production of good coke. It seems possible to the writer, in view of 

1 Norris, R. V., The storage of anthracite. Trans. Amer. Inst. Min. Eng., Vol. XLII, 
p. 314, 1912. (Full discussion of systems of storage and handling.) 

2 Sinnatt, F. S., Stern, H., and Bayley, F., Does fusain cause mine and bin fires, spoil 
coke and aid explosions? Coal Age. Vol. 18, p. 384, 1920. 


the great absorptive quality of wood charcoal, that mineral charcoal 
may have the power of occluding within its walls more gases than or- 
dinary coal, and the presence of these gases would influence spon- 
taneous combustion. This would be a very interesting field for in- 

An investigation of the causes of spontaneous combustion with 
special reference to Illinois coals was carried out by Parr and Kress- 
mann 1 and their conclusions were that the following factors entered 
into a consideration of the subject: (i) kind of coal with regard to 
its volatile matter; (2) purity of the coal; (3) presence of pyrite and 
other sulphur compounds; (4) temperature of the coal; (5) size of 
the fragments; (6) presence of occluded gases; (7) presence of mois- 
ture; (8) accessibility of oxygen; (9) pressure on the coal. 

Regarding the kind of coal, it is found that those high, or fairly high, 
in volatile matter such as lignites, subbituminous, bituminous and 
semibituminous coal are the only ones which are likely to take fire. 
The anthracitic coals have too high an ignition temperature and they 
weather too slowly to take fire readily. According to Fayol lignite 
as fine dust takes fire at 150 C., gas coal at 200 C., coke at 250 C. 
and anthracite at 300 C. or above. He also found that coal absorbed 
oxygen about twice as fast as did pyrite. 

The pure coals seem to oxidize more rapidly than those with more 
foreign matter. The effect of pyrite has already been described above. 
The size of the coal is an important factor as fine coal is a much more 
rapid absorbent of oxygen than lump and is dangerous in storage. 

Occluded gases of an inflammable type, such as methane, no doubt 
favor spontaneous combustion, but to what extent is unknown. 

Moisture under certain conditions aids the process since it influ- 
ences the oxidation of pyrite and coal. Accessibility of oxygen is 
without question an important factor. 

Pressure is believed to be an important factor in aiding the devel- 
opment of heat in coal, but to what extent and in what manner is not 
very fully understood. 

Some of the remedies suggested for spontaneous combustion are: 
storage under water to eliminate oxidation; exclusion of fine coal by 
screening, or its regular distribution throughout the pile; keeping 

1 Parr, S. W., and Kressmann, F. W., The spontaneous combustion of coal, Illinois 
Experiment Station, Bull. 46, 1910. 


the piles low, only a few feet hign; keeping the coal away from ex- 
ternal sources of heat such as boilers, pipes or the sun's rays; keeping 
it dry unless completely submerged; and elimination of high sulphur 

The deterioration of coal in storage. From the researches of 
David White, previously mentioned, it is shown that oxygen in coal 
is practically equivalent to ash in its anti-calorific properties. The 
oxidation of coal therefore decreases its heating value. Regarding 
the deterioration in storage Parr 1 concludes that very little loss is 
suffered if the temperature is not allowed to rise above 180 F. as there 
is no appreciable evolution of CO 2 below 200 F. The loss per pound 
in heat value is due largely to an increase in weight per unit mass of 
coal on account of the absorption of oxygen, and Parr claims that 
the weathered coal gave just as satisfactory results in firing, if care 
were taken in controlling the fire, as the unweathered coal. In an 
earlier article Parr and Hamilton 2 present the following conclusions, 
in addition to those previously set forth: Submerged coal does not 
lose appreciably in heat value while outdoor exposure results in a loss 
in heating value of from 2 to 10 per cent. In some cases the losses 
appear to be complete at the end of five months. From the seventh 
to the ninth month the loss is not appreciable. Similar results were 
obtained by Porter and Ovitz 3 in experiments on Sheridan, Wyoming 
coal. They found that this coal lost 3 to 5.5 per cent of its heating 
value in about three years in storage, 70 to 80 per cent of the loss oc- 
curring within the first nine months. They also found that storage 
in air-tight bottom bins had a distinct advantage over covering the 
surface of the coal. The slacking of the coal is one of the important 
factors in weathering as it tends to destroy its firing qualities. 

Briquetting 4 

The process of briquetting coal has developed considerably in re- 
cent years. It is applied to fuels which are dusty, such as peat, lig- 

1 Parr, S. W., Effects of storage upon the properties of coal. University of Illinois, 
Bull. No. 39, Vol. XIV, 1917. 

2 Parr, S. W., and Hamilton, N. D., The weathering of coal. University of Illinois, 
Bull. No. 33, 1907. 

3 Porter, H. C., and Ovitz, F. K., Deterioration in the heating value of coal during 
storage. U. S. Bur. of Mines, Bull. 136, 1917. 

4 Franke, G., A handbook of briquetting. Translated by F. Lantsberry, Charles 
Griffin and J. B. Lippincott, 1917. 


nite, fine slack, and culm. It consists of compressing the powdered 
fuel into briquets or little bricks, using pitch as a bond to hold the 
particles together. The pressing is done at rather high temperatures. 

In recent years much material from the culm banks of the anthra- 
cite region of Pennsylvania has been recovered, washed, dried, and 
briquetted. Many of the old culm piles contain the coal which is now 
sold as barley and buckwheat sizes. According to Dorrance, 1 at the 
Lehigh Coal and Navigation Company's plant the culm is loaded into 
gondolas of ioo,ooo-pound capacity and taken to a track hopper at 
the briquetting plant. It is elevated to the drying plant and passed 
through Vulcan rotary kiln driers which are heated by gases from the 
furnace. It is screened on vibrating screens of Newago type, the 
material passing through the finest screen going to the refuse conveyor. 
The refuse from this and later screenings is sent to the mines at Sum- 
mit Hill for slushing the mine fire burning there. Commercially- 
sized coal separated is sent to the drier building for feeding the fur- 
naces. The material from the screens is sent to Damon air separators 
and the coal retained from them is sent to the bins and from there to 
the mixing-house. Solid coal-tar pitch is used as a binder and it is 
fed into rolls and cracked to " pea " and " dust" sizes. This is then 
elevated to the pitch-measuring apparatus which feeds the right pro- 
portion of pitch to a squirrel-cage pulverizer which in turn feeds it 
into a screw conveyor with a measured amount of culm material. 
These materials then pass to the briquetting-house and are sent 
through the mixers to the presses. In the mixers the material is 
heated with superheated steam to about 400 then cooled by a cooling 
fan and pressed into briquets. Briquets are used by the railroads and 
industrial concerns, while the little balls known as boulets are sold 
for domestic use since the larger size does not seem to burn as well 
in domestic heaters as the smaller balls. 

Experiments have shown that a great number of binders may be 
used for briquetting, but some of them cost a prohibitive sum. 2 The 
nearness to the source of supply influences to quite a large extent 
the choice of the type of binder. The following binders have proven 
satisfactory and they are available in many localities: (i) Asphalt, 

1 Dorrance, Charles, Jr., Anthracite culm briquets. Trans. Amer. Inst. Min. Eng., 
Vol. XLII, p. 365, 1912. 

2 Mills, James E., Binders for coal briquets. U. S. Bur. of Mines, Bull. No. 24, 1911. 


the heavy residuum from petroleum, costing about 45 to 60 cents per 
ton of briquets and used in proportion of 4 in 100. (2) Water-gas 
tar pitch costing 50 to 60 cents; 5 or 6 per cent is used. (3) Coal- 
tar pitch; 6.5 to 8 per cent is used per ton and the cost per ton of 
briquets runs 65 to 90 cents for binder. Other substances which 
might be used are starch, sulphite and magnesia. 

The results of the tests made on briquets by the Bureau of Mines 1 
indicate that there is considerable difficulty in burning them in do- 
mestic heaters where low temperatures prevail so much of the time, 
as the binder either tends to produce a deposit on the interior walls 
of the furnace and the pipes which clogs them, or it burns off too 
rapidly when the temperature rises quickly. The briquets ignite 
readily unless an inorganic binder is used or there is too much im- 
purity in the slack from which they are made, and they produce a 
large amount of smoke if not properly fired. Their relative efficiency 
is high, they are clean and they weather very well. It is concluded, 
however, that there is no justification for briquetting lump coal 
and the main advantage in the process lies in consolidating coal which 
is in too fine a condition or is dusty. Lignite and fine coal, which 
does not coke may be profitably briquetted in many cases. Coking 
coals are more easily handled without briquetting than non-coking 
types since they are not readily lost by running through the grates. 
The average cost of briquetting a ton of fuel has been placed at about 
$1.00 to $1.80. Recent developments in the briquetting of partially 
devolatilized coal, or carbo-coal, indicate that there is probably a more 
promising future along that line than in the briquetting of the raw 

Coals Used in Gas Manufacture 

Producer gas. Coals which are used in gas manufacture may 
vary greatly in quality and it is difficult to fix limits as to their prop- 
erties. Fuels from peat to anthracite have been used for the manu- 
facture of producer gas, which is coal gas diluted with air and often 
mixed with water-gas. They should, however, be comparatively low 
in sulphur and ash and the fusibility of the ash is an important fac- 
tor. It should not be low. The size of the coal also has an impor- 

1 Wright, C. L., Fuel briquetting investigations. U. S. Bur. of Mines, Bull. 58, p. 191, 


tant bearing as coarse run-of-mine is not good material. Egg and nut 
sizes are desirable and screenings may be used. 1 

Illuminating gas. For illuminating gas a coal must be high in 
volatile matter so as to yield per short ton at least 10,000 cubic feet 
of gas at 60 F. and 30 inches mercury pressure, and the gas should 
test 1 6 to 1 8 standard candle power. Cannel coal has long been 
recognized as probably the most desirable coal for this purpose. 
The quality of the volatile constituents is important as well as the 
quantity. The coal should also yield a good proportion of coke. 
The sulphur must be low, not above ij and preferably below i per 
cent, although coals have been used in some cases which run up to 
about 2 per cent. The sulphur unites with hydrogen to produce 
hydrogen sulphide H 2 S and with carbon to produce carbon disul- 
phide (082). The former is an evil-smelling, poisonous gas and the 
latter under certain conditions has a horrible odor. Both of these 
gases burn to sulphur dioxide (802) and this gas is not only suffo- 
cating and objectionable to man but it aids in tarnishing metal house- 
furnishings. The sulphur gases can be removed from the illumin- 
ating gas at a rather high and in many cases prohibitive cost. 2 

The following figures indicate the general chemical composition of 
coals which have been used and are well adapted for gas making : 

Cannel Bituminous gas coal 

Moisture i . 30- 4 . 50 per cent i . oo- 4 . oo per cent 

Volatile matter 30.00-39.00 " 28.00-37.00 " 

Fixed carbon 50.00-60.00 " 54.00-61.00 " 

Ash 2.20-6.00 " 3.50-10.00 " 

Sulphur 0.50-1.05 " 0.80-1.32 " 

B.t.u 13,000-14,500 13,200-14,600 

Water gas. Water gas is a commercial gas consisting very largely 
of carbon monoxide and hydrogen and it is made by dissociating 
steam into hydrogen and oxygen, thus permitting the latter to unite 
with carbon to form carbon monoxide (CO). Anthracite and coke 
have been most generally used for this purpose but non-coking bitu- 
minous coals might also be used. 

1 Brooks, G. S., and Nitchie, C. C., Gas producer practice in western zinc plants. 
Trans. Amer. Inst. Min. and Met. Eng., Vol. LXIII, p. 846, 1920. 

2 Odell, W. W., and Dunkley, W. A., Removal of sulphur from illuminating gas. 
Trans. Amer. Inst. Min. and Met. Eng., Vol. LIII, p. 660, 1920. 


Smithing Coals 

No very definite limits have been fixed for the quality of smithing 
coals. Semibituminous or " smokeless " coals have been generally 
used although anthracite and semianthracite coal have also been 
used. Some of the requirements for a first-class coal of this type are 
low sulphur, less than i per cent; high calorific value; low ash; and 
sufficient coking quality to seal over and retain the fire when articles 
are not being inserted or withdrawn. 

Coals for Cement and Tile Burning 

For a cement-burning coal the requirements are a high calorific 
value, 12,000 B.t.u. and upward, and a high volatile content. For 
burning brick and pottery, coals of high volatile content and non- 
coking qualities are desirable. 

For burning porcelain and the finer grades of ceramic materials 
low sulphur is essential and low ash desirable. According to Par- 
melee 1 the English pottery practice requires a coal which comes near 
the following figures: Total sulphur, 1.20 per cent; sulphur in ash 
o.i i per cent; and volatile sulphur 1.09 per cent. The practice in 
America is about as follows: 

For Sanitary ware: Maximum i.o per cent; 0.5 per cent desirable. 

For Sewer pipe: As high as 3.10 per cent has been used but 1.2 per 
cent should be the maximum and i.i per cent is about present run. 

Terra Cotta: i.o per cent is approximate and 0.5 per cent is basis 
of contract. 

Pottery: i.o per cent contract basis and 1.5 per cent probable 

Enameled brick: 1.3 per cent maximum. 

Powdered Fuel 

Powdered fuel must be ground exceedingly fine and then be blown 
into the furnaces with a supply of air adequate to completely con- 
sume it. For ordinary steam purposes the sulphur and a reasonable 
amount of ash do not greatly affect the qualifications, but for use in 
the steel plants the sulphur and ash must be low. The same rules 
should govern the proportions of sulphur in such fuel as in coke. The 

1 Parmelee, C. W., Effect of sulphur in coal used in ceramic industries. Trans. Amer. 
Inst. Min. and Met. Eng v Vol. LXIII, p. 727, 1920. 


volatile matter should be over 30 per cent and the greater the pro- 
portion of combustible gas in the volatile matter the better the quality, 
other things being equal. 

There is an interesting new development in the use of coal as a 
colloidal fuel. 1 The use of this type of fuel is largely in the experi- 
mental stage but there may be a large future for it. The colloidal 
fuel in which coal has been concerned is very finely powdered coal 
suspended in fuel oil. Several types of coal have been used and the 
calorific power developed has been high. There seems to be a pos- 
sibility of not only suspending the fine coal in the liquid as a mechani- 
cal mixture but also of dissolving certain parts of it so that it actually 
goes into a liquid condition. 

Steam Coals 

Coals used in the production of steam include especially those 
used on ships, in locomotives and under stationary boilers and they 
embrace a wide range in ranks and grades. The ideal steaming coal 
is one combining high calorific power with small smoke- and clinker- 
producing, as well as fairly long-burning qualities. It should also be 
sufficiently high in volatile matter to permit a rapid response to 
stimulated firing, as a fireman on a locomotive, for example, may 
need a fire which responds rather quickly when heavy grades are 
approached. The coal must also be capable of standing storage, 
especially when employed for bunkering purposes. The presence 
of sulphur will influence its qualities for storing as well as the clink- 
ering of the ash since sulphur, especially in the form of mineral sul- 
phides, seems to show a marked influence in lowering the temperature 
of fusion of the ash if present in quantities over about 2 per cent. 
The character of the ash and the methods of firing will also influence 
the results to a marked degree. The iron of the pyrite unites with 
other elements and produces more fusible compounds. The sulphur 
compounds also break up and form new compounds some of which 
corrode the furnaces. 

Semibituminous, or so-called " smokeless," coal has long been rec- 
ognized in America and abroad as the finest type of steam coal. 

1 Sheppard, S. E., Colloidal fuels, their preparation and properties. Jour, of Ind. 
and Eng. Chem. Vol. 13, p. 37, 1921. 


It has the highest calorific value of any coal and it contains sufficient 
volatile matter to make it ignite a little more readily than anthracite. 

Some of the best steam coals in America are the semibituminous 
coals of Virginia, West Virginia, Maryland, Central Pennsylvania, 
Arkansas, and Alberta, Canada. The steam coals of South Wales 
have long been famous. 

Analyses showing the limits in composition of some of the well- 
known types of semibituminous coals in the United States are as 
follows i 1 




West Virginia 

Volatile matter 
Fixed carbon. . . . 

0.85- 3.50 
II .40-16.60 
7 4OI2 OO 

0.38- 3.40 
4 20 18 so 

0.57- 4.50 
15 .80-27.20 
2 4012 2O 

0.30- 3.40 
13 .IO-22.OO 
2 OO I I 2O 


1.30- 2.8o 

0.80- 4.70 


0.50- 2.IO 
1 3,400 IA, 6 SO 

0.50- 2.50 
14. OOO 14. Q2O 

An analysis of high-grade Pocahontas coal would be illustrated by 
the following figures: Moisture, 1.31; Volatile matter, 16.30; Fixed 
carbon, 77.06; Ash, 5.33; Sulphur, 0.67; and B.t.u. 14,746. 


The coking of coals for the purpose of securing metallurgical coke 
is a process which has long been in vogue and it has attained a place 
of great importance in our industrial operations. There are, however, 
some new phases of this process which bid fair to become of much 
more widespread interest than that of simply securing metallurgical 
coke. They are the saving of the volatile products from the coal and 
the production of solid fuels which will be better suited than coal for 
domestic use and for some industrial purposes. 

Coke. Coke is the hard residue obtained from heating coals in 
the absence of air. It has a dull to submetallic luster, is dark 
gray to silvery gray in color and is very porous, or vesicular. There 
is sometimes a great variation in the strength of coke made from the 
same coal seam. Some of it will support the largest blast furnace 

1 Analyses from the Coal Catalog, Zern, E. N., Editor, Keystone Publishing Co., 
Pittsburgh, 1918. This work contains analyses of practically all coal seams in the 


charges while other portions will not. The percentage of coke which 
may be derived from coal varies from about 50 to 80 per cent, but a 
profitable coking coal should yield on the average at least from 65 
to 70 per cent coke. 

Coking coals. The question of what physical and chemical 
properties determine the quality of a coking or caking coal has not 
been fully decided. It is known that certain portions of a coking 
coal are soluble in such solvents as aniline, phenol, or pyridine, and 
that these soluble constituents constitute the better coking ingredients. 
As previously stated in the discussion on coking coal it has been 
found by Pishel that coking coals tend to adhere to the sides of an 
agate mortar when rubbed with a pestle while non-coking coals do not. 
White also shows that there is some relation between the oxygen and 


hydrogen ratio and the coking quality. When > 58 the coal 


generally cokes; when > 55 < 58 the coal may coke; when -- > 

5 < 55 the coal is not likely to coke satisfactorily. Exceptions 
must be made for weathered coals. A test which is often used, es- 
pecially in Europe, to determine the coking qualities of a coal con- 
sists in mixing the powdered coal with sand and heating the mixture. 
The coking quality is judged from the ability of the coal to cause the 
and grains to stick together in a coherent mass, and the greater the 
amount of sand the coal can cement the better its coking qualities. 
The relative qualities of the various coals are fixed by a scale made 
for that purpose. All coals leave a residue but in many cases it is 
powdery and incoherent and of no value unless it is briquetted. It 
is assumed that a good coking coal should run over 30 per cent vola- 
tile matter and have not more than i J per cent sulphur and 0.02 per 
cent phosphorous. 

The requirements of the American Society for Testing Materials, 
for standard foundry coke are that the dry coke shall not exceed the 
following limits in chemical composition : 

Volatile matter not over 2 . o per cent 

Fixed carbon not under 86.0 " 

Ash not over 12.0 " 

Sulphur not over i . o " 

Sulphur in coke. Owing to the fact that the mineral constit- 
uents in the coal mostly enter the coke with the ash some of the sulphur 


is carried into the coke. The statement is frequently made that 
approximately one-half of the sulphur of the coal is driven off and the 
other half remains in the coke. This assumption has been largely 
verified by the recent work of Powell 1 although some factors not always 
considered must be taken into consideration in dealing with this 
subject. Sulphur in the coal may be in three forms: mineral sul- 
phides, as pyrite and related minerals; organic sulphur, in some un- 
determined form; and sulphates, in small amounts. The organic 
type occurs in quantities ranging from 0.5 to 2.0 per cent and the 
quantity is nearly uniform for a seam or locality. Apparently this 
uniformity is due to the nature of the plants which grew in that 
locality and to the bacteriological and other conditions existing at 
that time. Pure pyrite is completely decomposed at 1000 C. and 
the resulting products are ferrous sulphide and free sulphur, the 
latter uniting with hydrogen if this element be available to form hydro- 
gen sulphide. A negligible amount of the sulphur remains in the 
ferrous sulphide in the form of a solid solution known as pyrrhotite, 
or magnetic sulphide of iron. The sulphur is thus practically equally 
divided between the volatile and residual constituents. From his 
tests on the carbonization of coals Powell concludes as follows: (i) 
At 300 C. decomposition of the pyrite begins with the formation of 
pyrrhotite and hydrogen sulphide. The reaction is complete at 600 C. 
and reaches its maximum between 400 and 500 C. (2) At 600 C. 
the reduction of sulphates to sulphides is complete. (3) Decomposi- 
tion of J to J of the organic sulphur takes place to form hydrogen 
sulphide. Most of this reaction occurs below 500 C. (4) A small 
part of the organic sulphur decomposes to form volatile, organic 
sulphur compounds most of which enter the tar. This reaction takes 
place chiefly at the lower temperatures of the process. (5) A portion 
of the pyrrhotite disappears and the sulphur apparently enters into 
combination with carbon. This reaction is most active at 500 or 
more. Between 400 and 500 C. the organic sulphur not accounted 
for above undergoes decided changes and ceases to resemble the 
original sulphur in the coal. It appears therefore that the percentage 
of sulphur originally in the coal rather than the form of the sulphur 
will be the prevailing factor to be considered. Some carbon bisul- 

1 Powell, A. R., Some factors affecting the sulphur content of coke and gas in the 
carbonization of coal. Jour. Ind. and Eng. Chem. Vol. 13, p. 33, 1921. 


phide is formed from hydrogen sulphide where it passes over red-hot 
coke. If hydrogen is passed through coke at a temperature above 
600 C. a marked evolution of hydrogen sulphide occurs although the 
coke had ceased to evolve hydrogen sulphide at about 600 C. The 
effect of the hydrogen is to aid the decomposition of iron pyrite at a 
temperature below 500 C. and the decomposition of organic sulphur 
compounds at temperatures above 500 C. Hydrogen over a coke 
containing 1.2 per cent sulphur was saturated, when it contained 
about 0.25 pounds of sulphur per 1000 cubic feet with the coke at 
900 C. Hydrogen can therefore scarcely be regarded as an agent 
which could be profitably employed to remove sulphur from coke. 

Apparently the gases given off in the coking process play an active 
part in removing the sulphur from the coke if they can be relieved of 
their load of sulphur and returned over the coke. Less sulphur was 
found in the by-product coke when the gases were returned in contact 
with the coking mass than in the coke where the gases were drawn 
entirely away from the mass. One may predict therefore, that some 
method may be devised to eliminate to quite an extent the sulphur in 
the coke. 

Beehive coking. The earliest forms of beehive ovens, which 
get their names from their shape, were built of clay but the modern 
ovens are standardized in size and form and are constructed of mas- 
onry, brick and tile. Fire brick is used for lining and the space between 
the lining and outside walls is filled with waste brick and other ma- 
terial to prevent, as far as possible, the loss of heat to the exterior. 
The ovens, which are usually 12.5 feet long by about 7 feet high 
internally, are arranged in a double row and connected with a com- 
mon flue, the opening to which is controlled by a damper. In some 
places the hot waste gases are used for producing steam in the power 
plant or for heating purposes. The cost of an individual oven in nor- 
mal times runs from about $450 . oo to $500 . oo. 

The oven is started at first with a wood fire and coal is added grad- 
ually for from two to four days to prevent cracking the brickwork. 
A small charge may then be added and the front door bricked up, 
leaving holes for air. The burning of this charge, which does not 
give good coke, is performed to heat the oven and the resulting ma- 
terial may be rejected or used to heat other ovens. When the oven 
is hot a charge is loaded in after the front door has been bricked up 



about two- thirds of the distance to the top. The charge for a stand- 
ard oven is about 5 tons. The proportionate swelling of the coal on 
heating varies with different coals. 

In many places the coal is crushed to about \ mesh before charging, 
unless it be finely divided when it comes from the mine. The charge 
is carefully leveled with a leveling bar and the door bricked and 

FIG. 105. Beehive ovens at the Isabella plant of the Hecla Coal and Coke Co. 
courtesy of the Hillman Coal and Coke Company, Pittsburgh, Pa.) 


sealed up within about ij inches of the top, or far enough to admit 
just about the right amount of air to burn the gas above the charge. 
During the latter part of the process the oven is sealed tightly to 
prevent entrance of air, which causes loss of coke by combustion. 
The length of time the coke is burned depends upon the purpose to 
which it is to be put. The best foundry coke is burned for about 
seventy hours but about forty-five hours is the time many ovens are 
run for other types of coke. 


When the charge is burned the " coke-puller " places a sort of 
iron sprinkler with comparatively large orifices, in the oven and 
quenches the coke, applying upwards of 1000 gallons of water to each 
oven. Care should be exercised so that the lower part of the oven 
will not be so cooled with excess water that it will not start the fresh 
charge when it is added. The coke is then drawn either by hand or 
with a drawing machine and is loaded with a fork so that the fines 
are separated. 

The Coppee type of oven. In an effort to exclude all direct access 
of air to the coking chamber Coppee introduced a retort type of oven 
in 1 86 1. 1 The oven consists of narrow rectangular chambers about 
30 feet long and 3^ feet high. They are built with a slight taper 
towards one end to lessen the friction of discharging. The ovens 
are charged at the top and the gases pass into a series of vertical flues 
into which enough air is admitted to permit the combustion of the 
gases. The hot gases move downwards into a sole flue and after 
passing under the whole length of the oven they return to a chimney 
by the sole flue of the adjoining oven. They pass over boilers to 
utilize the heat and then up a chimney. The oven is discharged by 
a pusher and the coke is quenched outside the oven. The advan- 
tages claimed for this type over the ordinary beehive oven are: greater 
yield because of exclusion of air from the coking chamber; shorter 
coking period, because hot gases are utilized; saving in oven heat, 
because of external quenching and use of mechanical appliances. 

By-product coking. The beehive oven has long been recognized 
as an extremely wasteful apparatus and the time is rapidly coming 
when it will be entirely superseded by the by-product type which will 
save all of the volatile constituents as well as the coke. It was thought 
for a long time by metallurgists that the coke made in by-product 
ovens was inferior to that made in beehive ovens, but the by-product 
coke has become quite popular and it has been found that in regular 
operation the consumption of by-product coke per ton of pig iron 
manufactured is from 100 to 300 pounds less than of beehive coke, 
in the same operation. 2 Further, the energy used in coking a ton of 

1 Byrom, T. H., and Christopher, J. E., Modern coking practice. Crosby, Lockwood 
and Son, 1910. 

2 Sperr, F. W. Jr., and Bird, E. H Bv-product coking. Jour. Ind. and Eng. Chem., 
Vol. 13, p. 26, 1921. 



coal in a beehive oven is 9,388,000 B.t.u., the equivalent of 671 
pounds of coal, or 33.5 per cent of the heating value of the coal, while 
in the same operation in a by-product oven the energy expended is 
2,408,000 B.t.u., the equivalent of 172 pounds of coal, or 8.6 per cent 
of the heating value of the coal. 

As pointed out above it is apparent that it is possible to produce 
lower sulphur coke from a given coal in the by-product than in the 
beehive oven. Coals running as high as 35 per cent volatile matter 
have been used in a by-product oven although it is customary to mix 
high volatile coals with lower volatile types and thus produce a suit- 
able mixture. Kreisinger gives the following figures as representa- 

FIG. 1 06. Semet-Solvay coke pusher and cross-section of a regenerative 
oven. (By courtesy of the Semet-Solvay Co.) 

tive of the composition of the coal from a number of mines used in 
making by-product coke: Moisture, 2.77 per cent; Volatile matter, 
34.17; Fixed carbon, 56.94; Ash, 8.99; and Sulphur, 1.37. The an- 
alysis of the coke runs: Moisture, 0.79 per cent; Volatile matter, 
2.80; Fixed carbon, 79.29; and Ash, 17.14. In general, coals used 
run from 26 to 35 per cent volatile matter. The sulphur must not 
exceed i per cent in first-grade coke, and the ash in the coal must be 
less than 8 per cent if used for manufacture of first-grade coke. For 
second-grade coke sulphur has been placed at 1.20 per cent as a maxi- 
mum and ash in the coal at 10 per cent. 

In 1893 the production of beehive coke in the United States was 
9,464,730 short tons and of by-product coke 12,850 tons. In 1919 
the production of beehive coke was 19,650,000 short tons and of 
by-product 25,171,000 tons, 1 showing that the supremacy of the 

1 Mineral Industry, p. 116, 1919. 

3 22 


beehive is rapidly waning. The by-products recovered for the year 
1919 amounted to 668,200,000 pounds ammonium sulphate or its 
equivalent; 251,000,000 gallons of tar; 84,800,000 gallons of crude 
light oil and 367,700,000,000 cubic feet of gas. 

The cost of installing a large by-product plant has been one of the 
obstacles in the way of a more rapid introduction of the ovens although 
they are becoming very numerous, many of them being established 

FIG. 107. Semet-Solvay plant constructed for the Chattanooga Coke and 
Gas Co. (By courtesy of the Semet-Solvay Co.) 

in connection with the large metallurgical plants where the gas and 
tar are utilized for fuel. They are also built near cities where the gas 
can be utilized. The cost of some of the large plants runs from 
several hundred thousand to several million dollars. 

The main principle of the by-product oven is the heating of a 
chamber full of coal, which is connected with a system of condensers 
and stills. It is distinctly a distillation process. There are several 
types of ovens, such as the Semet-Solvay, Koppers, Otto-Hoffman, 
Otto-Hilgenstock, Coppee, Roberts, Willputte and Klonne. Of these 
the Semet-Solvay and Koppers are the most common in America 


with the Otto type next. The Koppers has vertical and the Semet- 
Solvay horizontal flues (Figs. 106 and 108). The modern ovens are 
of the regenerative type, that is, they use the waste heat, and live 
gas from the ovens to heat the regenerators which in turn heat the 
air drawn through them on its way to aid combustion in the flues, 
where the gas from the ovens is used to maintain heat. The direc- 
tion of the current of gas or air is reversed about every half hour 
and in that way the regenerators are kept hot. 

The ovens are arranged in batteries and each oven is a steel cham- 
ber surrounded by flues and lined with silica brick. The batteries 
vary in size, but 60 ovens make a battery in the large plants and the 
largest plants have 640 or more ovens. An oven of a large type is 
about 30 to 36 feet long by 10 feet high while the smaller types are 
only about 6 feet high. The coke is pushed out of the oven by a 
pusher and taken in cars to a quenching bath. As a rule about 8 
tons of crushed coal are fed into an oven with a charging machine 
and it is fired for from seventeen to twenty-four hours, depending 
upon requirements. A large plant will handle between 700 and 800 
tons of coal per hour. 

Derivatives from by-product ovens. The process of separating 
the various by-products from one another is very complicated and a 
vast number of derivatives are obtainable. (See chart, Fig. 5.) 
The volatile constituents are drawn off the ovens and through con- 
densers and scrubbers by means of powerful exhausters. The tar 
is practically all eliminated from the other constituents by the re- 
duction of temperature. The remaining tar is finally eliminated by 
the impinging method employed in tar extractors of the impact type 
in which the tar and other constituents are drawn against a combina- 
tion of perforated and plain plates, the tar adhering while the more 
fluid constituents pass on. The ammonia is removed by scrubbers 
in which water absorbs the gas, and the oils are distilled (Fig. 108). 

The common products of the ovens are coke, gas, tar and ammonia 
liquor. The coke is used for metallurgical, foundry and heating pur- 
poses, and the fines from the coke, known as coke breeze are burned 
under boilers in power plants or other steam plants. The gas may 
be scrubbed and used for illuminating purposes, or it may be used for 
heating. In some cases it has been used in internal combustion en- 
gines. The tar is used to a large extent as fuel, in road making, 




M * 
8 T 




in waterproofing, in paints and for other purposes. By heating it 
between 170 C. and 360 C. a number of derivatives may be ob- 
tained which include heavy and light oils, creosote, pitch and other 
constituents. The most important of the oils are benzol and toluol, 
the former of which on distillation gives a number of light oils such as 
gasoline and naphtha. The coal-tar dyes and numerous other val- 
uable constituents are derived by further distillation. The ammonia 
liquor is used chiefly for the extraction of sulphate of ammonia by 
treatment with sulphuric acid. The sulphate has extensive appli- 
cation in the chemical industries and in the manufacture of fertilizers. 

The total value of the by-products from coke produced in the 
United States in 1916 was placed at $61,931,595 of which nearly 25 
million dollars were obtained from the benzol and toluol. The value 
of the coke for the same year was $75,373,070. 

The following figures show the amount of coal used for coking in 
the United States, the average yield of coke per cent from the coal, 
and the value of the coke, for the years 1915, 1916 and 1917: 

Coal for ovens 

Average percentage yield 

Value at ovens 

Beehive ovens 




$ 56,945,543 






By-product ovens 















Of the states of the Union, Pennsylvania far surpasses all others in 
production, her output being about 60 per cent of that for the country. 

Manufacture of coke for domestic fuel. Some coke is now used 
for domestic and steaming purposes, but 80 to 90 per cent of all coke 
produced is used in the metallurgical industry. There has been a 
strong desire in recent years among men interested in fuels to find a 
fuel for domestic purposes with properties somewhere between those 
of coal and coke. 

A process has recently been tried out at Syracuse, New York, by 
Donald Markle, for one of the Pennsylvania anthracite companies, 
with the object of briquet ting and coking anthracite fines. Culm is 


washed, the coal crushed, cemented with 14 to 25 per cent of pitch 
to form briquets and then burned in an oven. The product is known 
as anthrocoal and it is claimed that the experiments tried have pro- 
duced a very satisfactory domestic fuel which on test was 20 per 
cent more efficient in a kitchen range than chestnut coal. 

The development of the process for carbonization of coal at low 
temperatures has led to the production of carbocoal, a fuel contain- 
ing a little more of the volatile combustible constituents of the coal, 
than that contained in ordinary coke, the ratio being about 3 to i. 
It, therefore, approaches anthracite as a fuel in burning longer, in 
being cleaner, in producing less smoke and in standing storage better 
than bituminous or other coals which lie below anthracite in fixed 
carbon. It has been shown by experiment in Canada 1 that lignite 
may be satisfactorily carbonized and the coked material, which is too 
powdery to be used in that condition, briquetted. From a ton of 
2000 pounds of this lignite 3150 cubic feet of gas, 10.2 pounds of am- 
monium sulphate, 5.3 imperial gallons of tar, and 910 pounds of car- 
bonized residue were obtained. The coal used contains 31.8 per 
cent moisture. The carbonized products had an available heating 
value 75 per cent above that of the original coal. 

Bituminous coal has been treated very satisfactorily by carbon- 
izing it at low temperature and briquetting the coke formed. From 
coals running over 32 per cent volatile matter where carbonized at 
850 to 950 P'. the following constituents have been obtained: 2 

By-products per ton of coal 

Dry tar 34 gallons 

Gas 8457 cubic feet 

Ammonium sulphate 21 pounds 

Light oil from gas 1.87 gallons 

Other tar oils . . 19.3 gallons 

Pitch, per cent of tar 43 

The average analysis of the briquets made from the residue is as 


Volatile matter 3.8 per cent 

Fixed carbon 85 . i " 

Ash n. i " 

1 Stansfield, Edgar, Carbonization of Canadian lignite. Jour. Ind. and Eng. Chem., 
Vol. 13, p. 17, 1921. 

2 Curtis, H. A., The commercial realization of the low-temperature carbonization of 
coal. Jour. Ind. and Eng. Chem., Vol. 13, p. 23, 1921. 


The production of such fuels has been put on a commercial basis 
within the last couple of years. A description of a plant at Clinch- 
field, Virginia, capable of treating 500 tons a day has been published 
by Eshereck. 1 In this plant there are 24 primary, low-temperature, 
and 10 high- temperature retorts. The primary retorts are arranged 
in four batteries and the crushed coal is fed into them from overhead 
bins. The semi-carbocoal is taken from these retorts, which are con- 
tinually in operation and carried to storage bins in the briquetting 
plant. It is then ground, mixed with pitch, fluxed and briquetted 
on heavy roll presses. The briquets are carried on a long conveyor 
and then by a steel charging car to the secondary retorts. The 
finished briquets are dumped from the secondary retorts, which are 
inclined, and later quenched. 

The by-products are carried through the same general process of 
condensing, scrubbing and distilling as in the other by-product 
processes described above. The process outlined is known as the 
Smith Process. It is found that the yield of carbocoal runs from 65 to 
72 per cent of the coal used, depending upon the character of the coal, 
and on account of the low temperatures at which the primary retorts 
are heated there is a much greater yield of tar oils than in ordinary 
by-product operations. In some cases it is over seven times as great. 
There is practically no production of pitch, but the other constituents 
are similar in quantity to those derived from a by-product coke oven. 

It seems very probable that this method of producing fuel will 
have a rapid development and that in the future practically all of 
our fuels will be treated in some such manner. It is also probable 
that some of the liquid by-products obtained from this process will 
be used in our homes as domestic fuel. 

1 Eshereck, George, Jr., Prospect that soon no coal will be used without preliminary 
devolatilization. Coal Age, Vol. 18, p. 327, 1920. 




From a geological standpoint coal is distributed through the vari- 
ous formations from the Upper Devonian to the Pleistocene although 
the latter contains only low-grade coal and the former a very limited 
quantity. In the later Pleistocene and the Recent rocks large beds 
of peat not yet changed to coal are found in many countries. 

The earliest coal deposits known are in the Upper Devonian in 
northern Russia and on Buren Island, Norway, and they are coincid- 
ent with the first great development of land plants on the earth. 
Between the Devonian and Pleistocene there is not a geological system 
without at least some coal somewhere on the globe. Certain systems, 
however, carry the bulk of the valuable coal. Taking the earth as 
a whole the Carboniferous is the most important for high-grade coal 
while the Tertiary contains most of the lignite. The Mississippian, 
or Lower Carboniferous, as it is known outside of the United States, 
carries valuable coal in Virginia, Scotland, Spitzbergen, Russia, 
Corea and Manchuria. The Permian is very important in the South- 
ern Hemisphere, particularly in Australia, India and Africa, and this 
system also carries some coal in Europe, the United States and eastern 
Asia. The Triassic is a prominent coal-bearing system outside of 
America as it contains the coal of Tasmania, some in Queensland and 
New South Wales, Australia, considerable in Hungary, Austria, 
Japan, China and South Africa and a small field in North Carolina and 
Virginia, in the eastern United States. The Jurassic is not important 
in America outside of Alaska and small areas in the Yukon but it 
is of great importance in China and Corea, and it is also coal-bearing 
in New Zealand and Austria. The Upper Cretaceous is one of the 
great coal-bearing periods in the earth's history especially in western 
North America and Central Europe, while the Lower Cretaceous, or 
Comanchean of some of the United States geologists, except in its 



earlier formations, is probably the most barren of coal of all the 
systems from the Lower Carboniferous onward. It carries good 
coal in western Canada and in limited areas in the western states, a 
little in South Australia, and low grade bituminous coal in Spain. 
The abundance of coal in the Upper Cretaceous and Tertiary, follow- 
ing its scarcity in the Lower Cretaceous repeats the conditions exist- 
ing in the Lower and Upper Carboniferous. The Lower Carbon- 
iferous and the Lower Cretaceous were periods of extension of the sea 
over the continents, except in the earlier stages of the Lower Creta- 
ceous when many lakes and swamps existed, while it gradually with- 
drew during the following periods leaving great flat areas covered 
with swamps, as in the case of our coastal plains of the present day. 
Extension of the sea and marine deposition or, on the other hand, very 
high lands with rapid erosion do not go together with coal formation, 
but the gradual restriction of the sea and the formation of coal work 
together harmoniously. 

The period of coal formation begun in the Upper Cretaceous con- 
tinued into the Tertiary and most of the lignite of the world was 
formed in that period. Every continent contains some coal of this 
age and America and Europe have very large supplies. There is 
some good anthracite and bituminous coal of Tertiary age but most 
of the coal outside of the mountain regions is of the lignite type be- 
cause it has not been changed to a higher form by heat or pressure 
or by these two agencies combined. 

As to the occurrence of coal in rocks older than the Upper Devon- 
ian, the question is often asked why coal should not exist in these 
older formations. The only explanation is that the land plants had 
not reached a stage in their evolution which made them sufficiently 
abundant and widely distributed to form extensive deposits of coal. 
Deposits of vegetal matter were made in earlier formations, even 
back in the pre-Cambrian, as shown by beds of black shales and 
deposits of graphite, but these were of quite limited extent and ap- 
parently made from aquatic plants. It is also true that from the close 
of the pre-Cambrian until the Carboniferous not only the American 
continent but some of the others as well were largely covered with the 
sea and marine deposits were the main types being formed. It re- 
quires proper topographic conditions as well as an abundance of land 
plants to produce coal. 








Great Britain 















Pleistocene or 

3 leistocene 






3 liocene 



















Cretaceous (Upper) 

Cretaceous (Upper) 





(i) Laramie 

(i) Upper Chalk 


Ober Kreide 

(2) Montana 

(2) Lower Chalk 

(3) Colorado 

(3) Marls 

(4) Dakota 

(4) Upper Green- 


(5) Gault 

Comanchean or 

Cretaceous ( Lower } f Eocretacique 



Lower Cretaceous 

(i) Lower Green- 

(i) Gault 




(2) Wealden 

(2) Weald 







(i) Upper 

(i) Oolite 

(i) Neojurassique 

(i) Malm 

(2) Middle 

(2) Lias 

(2) Mesojurassique 

(2) Dogger 

(3) Lower 

(3) Eojurassique 

(2) Lias 


(Newark series) 





(i) Rhaetic 

(i) Rhaetic 

(2) Keuper 

(2) Keuper 

(3) Bunter 

(3) Muschel- 



(4) Bunter 





Great Britain 




Permian (Dunkard) 

Permian or Dyas 





(a) Thuringien 

(a) Zechstein 

(a) Igneous series 

Upper Barren 

(b) Saxonien 

(b) Rothlie- 

(b) Upper or 




(c) Atunien 

Coal Measures 

/ \ y% 





^6^ .L/empsey 

(d) Middle Coal 

(l) Pennsylvanian 

(i) Upper Carbon- 



or Upper Car- 


() Upper Ma- 


rine Series 

(a) Monongahela 

(/) Lower or 

or Upper Pro- 

(a) Stephanien or 

(a) Ottweiler 

Greta Coal 





(b) Westphalien or 

(b) Saarbrucken 

(g) Lower Ma- 

(b) Conemaugh 


rine Series 


or Lower Bar- 

(a) Coal Measures 


ren Measures 


(c) Allegheny or 


- Lower Produc- 

tive Measures 

(d) Pottsville or 

(b) Millstone Grit 

(c) Namurien 

Millstone Grit 

(2) Mississippian 

(2) Lower Carbon- 




or Sub-Car- 

iferous; Culm, 

Kulm or Koh- 


or Limestone 


(a) Mauch Chunk 


(b) Pocono 












Lower Silurian 

(i) Goth-Landien 



(2) Ordovicien 







Proterozoic or 

Pre-Cambrien or 

Eozoisch or 







Archaeozoic or 







The following table shows the geological distribution of the different 
types of coal on the various continents and their relative abundance. 
More detailed tables are given for the individual continents where the 
coal resources of those continents are described. 





























Jurassic and Triassic 



B 1 







A B 


B c 












Lower Carboniferous . 






A, Anthracite; S, Semibituminous; B, Bituminous; B, Subbituminous; L, 
Lignite, including brown coal; C, Cannel. Capital letters are used to indicate 
large and important deposits and lower case for small or unimportant deposits 
of the same variety 

Geographically, coal is almost universally distributed as there are 
very few countries which do not have some coal. Even Antarctica 
has a considerable supply. There are a few countries, including 
Egypt, Thibet and Bolivia, which do not report any workable de- 
posits. Norway has little or none outside of Spitzbergen and her 
other northern islands. Switzerland has had very small supplies 
and they are said to be nearly exhausted. Many other countries 
have very little coal in proportion to their political importance. 
Such are, for example, Italy, Roumania, Sweden, Brazil and the Argen- 
tine Republic. Japan is poorly supplied in proportion to her popula- 
tion and she will no doubt expect to control large areas on the main- 
land of Asia to take care of her industrial development, because history 



has shown that the accessibility of large coal supplies is an essential 
factor in the great industrial development of any country. A glance 
at the table showing the coal resources of the various continents will 
show that Africa and South America are not well supplied with coal, 
although no doubt further geological work on these continents will 
reveal much larger resources than are here indicated. North Amer- 
ica is lavishly supplied, and Europe, Australia and eastern Asia have 
plenty. The distribution of the coal deposits will have a very im- 
portant bearing on the future economic history and commercial 
relations of these continents and especially on those of certain 
countries. This is well illustrated by the international problems 
arising from the distribution of coal during the war and immediately 
following it. 

The following table will show the coal resources of the world by 
continents, in so far as geological data exist regarding them. This 
is the best and most complete estimate which has so far been com- 

(In million metric tons; i metric ton = i .1023 short tons) 

Class A 

Classes B and C 

Class D 

Anthracite and 
some dry coals 

Bituminous coals 

brown coals and 


Oceania . . 


1 33 4.8l 

36 27O 

I7O 4.IO 





I O<4. 

e>7 83Q 




2 811 906 

5TQC C28 




36 682 

784. IQO 


4.Q6 84.6 

3QO2 Q4.4. 

^yy/>/ u o 


( l ) From the Coal Resources of the World. Twelfth International Geologi- 
cal Congress, Morang & Company. For detailed discussion of classes of coal 
see Classification of Coals, Chapter V.. The above estimates include all seams i 
foot and over in thickness and less than 4000 feet deep; and 2 feet and over in 
thickness and between 4000 and 6000 feet below the surface. 

The outstanding features indicated in this table are the tremendous 
amount of coal in America and anthracite in Asia. The latter is 
mostly in China. It seems probable, however, that much coal has 


been classed as anthracite in China which will turn out to be semi- 
bituminous or high-grade bituminous coal. Nevertheless, China far 
surpasses all other countries combined in her resources in this variety 
of coal. America has little anthracite in comparison with her re- 
sources in bituminous and brown coals. 

The following table from Mineral Industry shows the coal produc- 
tion of the various countries of the world from the year 1911 to 1916. 
During the war the production of some countries almost ceased and 
since the beginning of the war it has been impossible to secure accurate 
data concerning the production of many countries. As indicated by 
the table, the output of the United States has increased rapidly and 
her production has almost passed the 6oo,ooo,ooo-ton mark. She 
has also become the leading exporter of coal since the exports of 
Great Britain have decreased from over 75,000,000 tons before the 
war to less than 20,000,000 in 1919, while those of the United States 
have more than doubled and are now said to be over 30,000,000 tons 
per annum. Few of the great industrial countries can look forward 
to exporting high-grade coal in very large quantities for an indefinite 
period because of the rate of increase in domestic requirements and 
the exhaustion of the more accessible seams. 



FOR YEARS 1911-1916 

Country or State 1911 






United States 496,371,126 
Great Britain 304,518,927 
Germany 258,223,763 
Austria-Hungary . . 54,960,298 
France 43,242,778 




59, 987 

(a) .12,000 










(d) 53,396,400 
(a) 19,000,000 









(d) 52,679,712 









(c) 22,000,000 

(a) 19,900,000 
(o) 24,000,000 


I 016,654 





Russia 29,361,764 
Belgium 25 411,917 

Japan 19.436,536 

India 13.494. 573 

China 16,534,500 

Canada . . .11,323,388 

New South Wales . .9,374,596 
Transvaal (&) 7,112,254 

Spain 4,316,245 

New Zealand 2,315,390 
Holland 1,628,097 

Chile i 277 191 

Queensland 998,556 
Mexico (a) 1,400,000 

Bosnia and Herze- 
govina 848,510 

Turkey 799,168 

Italy 614,132 
Victoria 732,328 
Orange Free State (e) 482,690 
Dutch East 
Indies (a) 600,000 
Indo-China (a) 460 ooo 

Sweden 343 707 

Servia . 335 495 

Western Australia (a) 300,000 
Peru (o) 300 ooo 

Formosa 280,999 
Bulgaria 270,410 

Rhodesia 212,529 

Korea 138,508 

Tasmania (a) 70 ooo 

British Borneo (a) 100,000 
Spitzbergen . . 44 092 

Brazil 16 535 

Portugal (a) 10,000 

Venezuela (a) 10,000 
Switzerland 8,267 
Philippine Islands. . (a) 2,000 
Unspecified (0)1,016,947 

Totals. . 1,309,574,000 





( J ) From Mineral Industry, 1917. 

(o) Estimated, (b) Transvaal, includes Natal and Cape of Good Hope and figures are only for 
coal sold, (c) Approximate. (d) Hungarian production estimated at 10,000,000 short tons, (e) 
Represents only coal sold, probably 10 to 12 per cent less than production. 



America is here considered as two units North and South. 
America undoubtedly has the greatest coal deposits of the world, 
but it is a striking fact that so far as our knowledge of the resources 
of the two continents extends the southern contains only about 
six-tenths of one per cent as much coal as the northern continent. 
A better knowledge of the geology of South America will no doubt 
extend her known resources but the disparity between the future 
supplies of the two continents will profoundly affect their trade 

North America 

In a discussion of North America's coal deposits there are included 
those of Canada, Newfoundland, the West Indies, the United States, 
including Alaska, Cuba, Mexico and Central America. The following 
table shows the relative resources of these countries in so far as we 
have reasonably definite knowledge regarding them. Mexico has 
considerable good coal but her resources are not well known outside 
of a few areas explored by American or European companies. 

This table shows the great extent of the coal supplies of the United 
States in those types of coal which are used so much in the industries. 
Canada is also unusually well supplied with bituminous coal and with 
lower grades but she is deficient in anthracite and in related high- 
carbon coals. This deficiency will probably not be so keenly felt in the 
future, however, as it has been in the past, because with the develop- 
ment of the use of partially devolatilized fuels such as carbocoal a 
substitute for anthracite will be provided in many parts of the country. 
The coal deposits of Canada and the United States, especially of the 
latter, have been gone over fairly well, and the above estimate of the 
resources may be regarded as comparatively accurate. Considerable 




changes will be made, however, in these figures as more geological 
work is done, particularly in those for Canada since there are very 
large areas in Canada on which little field work has been completed. 

(In million metric tons; i metric ton = i .1023 short tons) 

Class A 

Classes B and C 

Class D 

Anthracite and 
some dry coals 


coals, brown coals 
and lignites 


Ne wf oundland . 



United States . . . 
Central America 











Z, O73, 4^1 

Table from The Coal Resources of The World, Morang & Co., 1913. A detailed 
statement regarding the different classes of coal may be found in Chapter V 
on Classification of Coals. The estimates include all seams i foot and over 
in thickness and 4000 feet or less in depth; and all seams 2 feet and over in thick- 
ness and between 4000 and 6000 feet in depth. 

The geological age of the coals in North America ranges from 
Mississippian, or Sub-Carboniferous, to Pleistocene, the main periods 
for their formation being the Upper Carboniferous, or Pennsylvanian, 
the Cretaceous, and the Tertiary. The table given below shows their 
geological distribution. 




United States 



Central America 




New Brunswick 







Yukon Territory 

N. W. Territory 





Atlantic Coast 

Interior Province 


Great Plains 

Rocky Mountain 

Pacific Coast 
























Tertiary undifferen- 










Upper Cretaceous 









Lower Cretaceous 

















Pennsyl vanian 















A. Anthracite; A. Semianthracite; S. Semibituminous; B. Bituminous; B. Subbituminous; L. 
Lignite and brown coal. Capital letters indicate important deposits and lower case relatively unim- 
portant to unworkable deposits of the same type. 


PLATE XI. The Coal-fields of Canada. (i 

D. B. Bowling Canadian Geological Survey.) 




The production, and the geological age, of the coals of Canada 
have been given in the preceding tables and the following table sums 
up the distribution and the characters of the coals in the various 
provinces as worked out by D. B. Dowling. 



Actual Reserve 
Calculation based on actual thick- 
ness and extent 

Probable Reserve 
(Approximate estimate) 

Area Sq. 

Class of 

Metric tons 
(i metric ton = 
1.1023 short tons) 

Area Sq. 

Class of 

Metric tons 

B 2 


B 2 


Nova Scotia . . . 


273 . 5 





New Brunswick. . 


B 2 




D 2 








D 2 



D 2 



D 2 













B 2 B! 


B 2 Bi 



A 2 


A 2 


A 2 B 2 


A 2 B 2 


British Columbia 

439 j 






D 2 


DiD 2 






A 2 Bs 







D 2 


Arctic Islands 


B 2 Bs 








* 20,000,000 tons deducted for the amount of coal already exhausted in Alberta. Table from Coal 
Resources of the World. For details of classes of coal see Classification of Coals, Chapter V. This table 
contains all seams of I foot or over to a depth of 4000 feet. 

1 For detailed accounts of the coal deposits of Canada see The Coal Resources of the 
World, Twelfth International Geological Congress, (Morang & Co.), An Economic In- 
vestigation of the Coals of Canada, by J. B. Porter and R. J. Durley, Department of 
Mines, Canada; The Coals of Canada, by D. B. Dowling, Memoir 59, Canadian Geol. 
Survey, 1915; and The Coal Fields of British Columbia, by D. B. Dowling, Memoir 69, 
Canadian Geol. Survey, 1915. 


In addition to the figures mentioned here there might be added 
17,499,000,000 metric tons of coal of Class B 2 which occurs in seams 
over 2 feet thick lying at a depth between 4000 and 6000 feet, in the 
provinces of Nova Scotia, Alberta and British Columbia. 

From the accompanying map (Plate XI) it will be observed that 
the coal deposits of the Dominion are almost all located in the ex- 
treme eastern and in the western parts of the country. Quebec and 
Ontario, the most populous and the most important of the prov- 
inces commercially have no good coal and they receive most of their 
supply from the United States. Quebec is without coal of any kind 
and Ontario has a few million tons of low-grade lignite in the inter- 
glacial deposits south of James Bay. Nova Scotia on the east and 
Alberta and British Columbia on the west have high-grade coal in 
large quantities while Saskatchewan and Alberta have very large 
resources in lignite and subbituminous coal. 

Nova Scotia. The coal of Nova Scotia is all of Pennsylvanian, 
or Upper Carboniferous, age except for thin and unmined seams in 
the Mississippian, or Lower Carboniferous. Thin seams occur in 
the Millstone grit but most of the coal lies above this formation. 
There are five important areas producing coal the Joggins and 
Springhill areas in the Cumberland field; the Pictou, Inverness 
and Cape Breton, or Sydney, fields. In the Joggins area there are 
two seams 3 to 5 feet in thickness, and the beds are inclined at angles 
of as much as 50. The coal is of fairly good quality but is high in 
ash. This area has been famous for its buried Carboniferous trees 
which are abundant in the sandstones of the Coal Measures. The 
Springhill area is considerably faulted and it seems to represent the 
central part of the basin in which the Joggins seams were laid down. 
There are a number of seams of which five can be mined and they 
make up a total of about 50 feet of coal, the thickest seam reaching 
13 feet. In the Pictou field there is a little coal in the Millstone grit 
and in the Permian, but all the workable coal occurs in the Coal 
Measures proper, in two large fault blocks. One fault has a down- 
throw of about 2600 feet. There are four seams in the Westville 
area of this field varying from 6 to 18 feet in thickness and separated 
from one another by from 90 to 260 feet of strata including some 
beds of oil shales. As a rule the beds dip gently. In the Stellar ton 
area of the Pictou field there are 9 seams, some of which are very 


thick. The Main seam varies from about 6 feet to 45 feet in thick- 
ness and the Deep seam from 20 to 33 feet. The other seams are 
rather thin. There is one bed of oil shale with a coal seam, in this area. 
It is 5 feet in thickness and it was formerly mined for the extraction 
of oil. 

FIG. 109. Allen Shaft, near Stellarton,Pictou coal field, Nova Scotia. 
(Photo by H. Ries.) 

The Inverness field is largely under the sea. The measures dip 
seaward at from 12 to over 75-and the seams mined run about 6 to 
7 feet in thickness. 

In the Sydney field, which occupies the northern part of Cape 
Breton County the Coal Measures dip gently seaward, being disturbed 
by only small folds. They have been mined on the slope under the 
sea for more than a mile from the shore. The number of seams in 
this field varies from i to 12 with an aggregate thickness of coal 



from i foot to 46 feet. It is expected that the workings will in time 
extend nearly 3 miles from the shore. 

New Brunswick. In New Brunswick the upper members of the 
Pennsylvanian are lacking. The Millstone grit is widely distributed 
over the province and it contains a few thin seams of which one is 
worked where it runs around 18 inches and over in thickness. The 
seams are shallow, the coal is high in ash and sulphur but lends it- 
self readily to hand picking. A little anthracite is reported from Le- 
preau in St. Johns County. 

FIG. no. Coal seam (retouched) in sea cliff on coast of Nova 
Scotia. (Photo by H. Ries.) 

Ontario. There is a small area of about 10 square miles along 
the lower part of the Moose River/ south of James Bay, which is 
underlain by lignite. This coal was formed in an interglacial period 
and it lies between two beds of boulder clay. It is suitable for future 
briquetting operations. There are no Carboniferous rocks in Ontario 
and Quebec. The formations are largely pre-Cambrian, except for 
some older Palaeozoics in the southern part of Ontario and around 
James Bay. 


Manitoba. In the Tertiary rocks capping a hill called Turtle 
Mountain and in adjacent hills along the International Boundary 
there are some seams- of lignite. The eastern part of Manitoba is 
covered with pre-Cambrian rocks and the western portion chiefly by 
marine Cretaceous. 

Saskatchewan. The coal of Saskatchewan occurs in the Ter- 
tiary and Upper Cretaceous formations. The Tertiary formations 
seem to correspond to the Fort Union lacustrine and land-formation 
stage of the Eocene in North Dakota, and they are found in the hilly 
country in the southern part of the province. The strata lie prac- 
tically flat except for a syncline under the Souris River Valley and the 
seams outcrop along ravines and on hillsides. A good deal of coal is 
mined in the Souris Valley region and in a number of other places, 
and wagon mines are common as many of the western farmers dig 
their own coal. The Tertiary coal is practically all lignite and the 
maximum thickness of the seams is about 20 feet. The Cretaceous 
coals occur in the Belly River formation of the Upper Cretaceous 
along the Saskatchewan River, in the western part of the province. 
The coal lies from 200 to 300 feet below the surface and there are at 
least two seams about 4 feet and 8 feet thick respectively. They 
are not uniform in thickness or regular in distribution. This coal 
also is lignite. A little lignite occurs in the Middle Cretaceous south 
of Lac la Rouge. 

Alberta. In the province of Alberta coal occurs in the Kootenay 
series of the Lower Cretaceous; in the Belly River series, correspond- 
ing to the St. Pierre of the Montana series of the Upper Cretaceous; 
and in the fresh-water deposits of the Edmonton formation, corre- 
sponding to the Fort Union beds of the Eocene. 

The Kootenay series, regarded as lacustrine and terrestial in origin, 
contains the best coals of Canada, they being bituminous to an- 
thracite. It lies deeply buried beneath the younger sediments ex- 
cept where it is brought to light in the folds along the foothills or in 
the great fault blocks of the Rocky Mountains. Its thickness varies 
from 200 to about 3000 feet. The coal-bearing area in Alberta ex- 
tends from tlre International Boundary northward beyond the Atha- 
basca River and while little development work or even prospecting 
has been done in much of this great area, several very important 
mining districts have developed. The most important of these is in 



the region of Crowsnest Pass on the Crowsnest branch of the Can- 
adian Pacific Railway. Mines occur at several places in the Blairmore- 
Frank region. A half dozen seams occur, ranging from 3 to 17 feet in 
thickness. It was at Frank that the famous landslide occurred which 
carried away a section of Turtle Mountain. It destroyed a number 
of houses in the town, killing ninety-three people, and it buried 
the railroad through the valley, (Fig. in). The track was so deeply 

M* . * . 

FIG. in. D6bris from the landslide at Frank, Alberta, partly covering 
the town. (Photo by E. S. Moore.) 

buried that a new line was constructed over the debris which con- 
sisted chiefly of great blocks of limestone. The lower portions of 
the mountain are composed largely of shales and coal seams, while 
the upper portion contains heavy beds of limestone. The mining 
operations, which had been carried well through the mountain, 
apparently disturbed the overlying strata and a large crack devel- 
oped which caused a tremendous mass of rock to break away, slide 
down the mountain and across the valley. 

In the Coleman area there are three seams as much as 8, 10 and 16 



feet in thickness, respectively, within a thickness of 300 feet of strata. 
In the Livingstone basin lying a short distance northward from the 
Blairmore-Frank region, there are in Cat Mountain as many as twenty- 
one seams with a total of about 125 feet of coal. On the west fork of 
the McLeod River southeast of Folding Mountains there are four seams 



FIG. 112. Map of the Crowsnest coal area. (After D. B. Bowling.) 

in the Folding Mountain anticline on the eastern limb and they vary 
from 2 feet to 28 feet in thickness. On the western limb a combina- 
tion of seams forms one mass as much as 50 feet thick. 

In the Cascade area there is a continuous coal field extending for 
about 90 miles from south of the Kananaskis River northward to near 


the Saskatchewan River. This is a great fault block with a fault 
running along the western edge of the coal field. In some portions 
there are between 15 and 20 seams of coal with a maximum aggregate 
thickness of nearly 100 feet. Remnants of a very extensive coal- 
bearing area are found along the Bow River and there are mines at 
Canmore. At Bankhead, not far from Banff, semi-anthracite and 
anthracite are mined, and mines were formerly worked at Anthracite. 
These beds have been highly squeezed. Other important areas in 
Alberta are the Bighorn, Brule Lake, Nikanassin, Muskeg River, 
Shunda Creek, Costigan, and Moose Mountain in the foothills near 
Calgary. In Folding Mountain the beds are highly folded so that 
they are practically vertical. 

FIG. 113. Structure section through the Blairmore-Frank region, Alberta, i, 
Devono-carboniferous; 2, Lower cretaceous or Jurassic (Fernie shales); 3, Coal 
measures; 4, Equivalent of flathead beds; 5, Volcanic ash and agglomerates; 6, 
Upper cretaceous and laramie; 3-6, Cretaceous. Scale 4 miles = i inch. (After 
D. B. Dowling, Canadian Geol. Survey.) 

The abundance and high quality of the coal in western Alberta and 
the adjoining portion of British Columbia make this region the most 
promising coal-mining region of Canada. There is a great deal of 
good coking coal. 

The Belly River formation underlies about 16,000 square miles in 
eastern Alberta. The best coal in this formation is being mined at 
Lethbridge. The coal improves as the mountains are approached. 
Around Medicine Hat two seams, each about 5 feet thick, are exposed 
along the Bow River. In the vicinity of Calgary the Belly River 
formation is 'struck at depths of from 2560 to 2875 feet and the coal 
varies from 4 to 7 feet in thickness. At Edmonton the depth is about 
1400 feet and the coal about 6 feet thick. In the Peace River Valley 
there is some coal in the Dunvegan series supposed to be equivalent 
to this formation. There is much coking coal in the Belly River for- 



The Edmonton (Eocene) series occurs in a large synclinal basin 
which runs nearly parallel to the Rocky Mountains and extends over 
about 4 degrees of latitude. The dips are steep on the western and low 
on the eastern limb of the basin and the basin flattens out to the north- 
westward. At Calgary there is a seam of lignite about 13 feet thick 

FIG. 114. Peaks behind Canmore, Alberta. About two-thirds of mountain face is 
Palaeozoic strata thrust over folded Mesozoic coal measures. (Photo by H. Ries.) 

under cover of 1800 feet of poorly consolidated sandstone and clay. 
On the North Saskatchewan, west of Edmonton, a 25-foo.t seam out- 
crops and on the Grand Trunk Pacific Railway line at the Pembina 
River crossing it splits into two seams each 10 feet thick. About 
500 feet below this seam several smaller seams occur over several 


thousand square miles and they are mined at Edmonton, Tofield 
and at other places between Edmonton and Calgary. The coal varies 
from lignite in the northwestern part of the basin to a subbituminous 
and coking coal in the foothills of the Rockies. 

British Columbia. 1 The coal deposits of this province are grouped 
by Dowling under the five following heads: Southern, Central and 
Northern British Columbia, Vancouver Island and Queen Charlotte 
Islands. In the Southern district is located the Crowsnest area which 
is a basin of about 230 square miles around which lower beds have been 
uplifted and then eroded on a large scale leaving the coal field as an 
elevated plateau. The coal occurs here, as elsewhere in the Rocky 
Mountains, in the Kootenay series of the Lower Cretaceous and 
most of the better seams occur in the lower 2000 feet. It is said, 
however, that these upper seams are very largely cannel or other high 
volatile coals. 

The following is a tabulation of the seams in this area: 

At Morrissey 23 seams with 216 feet of coal in 3676 feet of measures 
At Fernie 23 seams with 172 feet of coal in 2250 feet of measures 
At Sparwood 23 seams with 173 feet of coal in 2050 feet of lower measures 
At Sparwood 24 seams with 43 feet of coal in 2015 feet of upper measures 

At Corbin a seam 80 feet thick is worked. The coal is in places 
highly faulted and folded and it is worked from tunnels. The coal- 
bearing strata occupy a basin which is in a hill, and on top of the hill 
there is so little cover that the coal, which is here 125 feet thick, is 
stripped and mined by steam shovels. 

The Flathead River area lying about 12 miles north of the Inter- 
national boundary gives promise of being a very important field 
for its size. It is probably a faulted block with the strata dipping only 
about 20 and exposing four seams which are 16, 20, 30 and 50 feet 
thick, respectively. The Upper Elk River area north of the Crows- 
nest area will probably be an important field as there are as many as 
eighteen seams in one section and there is an aggregate of 182 feet of 
coal in 1200 feet of strata. One seam reaches 31 feet in thickness. 
The coal in this area as in the others mentioned above is high-grade 
bituminous coal and it is used largely for coking. 

At Princeton on the Similkameen River there is a small basin con- 

1 Coal Fields of British Columbia, Compiled by D. B. Dowling, Memoir 69. Geol 
Survey, Canadian Department of Mines, 1915. 


taining lignite of Oligocene age. There are as many as seventeen 
seams in one section and the thickness varies from i foot to 18 feet. 
South of Tulameen similar lignite of Oligocene age occurs with two 
or three seams from 1 2 to 20 feel thick. In the Nicola and Quilchena 
basins there are also Oligocene deposits. Several collieries have been 
opened near the mouth of Coldwater Creek in the Nicola basin and in 
that region four seams running from 5 to 12 feet in thickness are mined. 
The coal is used for locomotives as it is of better grade than the lig- 
nite in the other regions. The basin is considerably broken by 
faults and it has been overlain by basalt flows. 

In the Central British Columbia region a number of coal deposits 
occur but many of them have not been proven to be of special im- 
portance. In the valley of the Bear River bituminous coking coal 
was found along the Grand Trunk Pacific Railway in three seams 
running from 4 feet to 9 feet in thickness. It is of Tertiary age. On 
the southern tributaries of the Skeena River the Lower Cretaceous 
rocks carry a few seams of mineable bituminous coal. In the Telka 
River area some thick seams of coal, 19, 24 and 13 feet in thickness 
occur. The coals are reported to be of coking quality. 

Several areas of coal-bearing rocks occur in the Northern British 
Columbia district. In the Groundhog Mountain area on the head 
waters of the Skeena, semianthracite coal occurs in Lower Cretaceous 
rocks of the Skeena series, resting on Jurassic volcanics. The area 
is greatly broken by faults. In the Peace River district there is a 
projection of the coal formations described for Alberta. Tertiary 
lignites also occur on the Liard and Taku rivers but the deposits are 
little known. 

The coal seams of Vancouver Island are of Upper Cretaceous age, 
according to C. H. Clapp, and they occur in the Nanaimo series which 
is supposed to be largely estuarine in origin and is about 10,000 feet 
thick. The topographic conditions during its formation were not 
uniform and the beds in many cases lack persistency. The series has 
in places been greatly folded and faulted. The coal is of bituminous 
quality. There are six main basins as follows: Quatsino Sound at 
the northern end of the island; Suquash on the east coast; Comox, 
Nanaimo and Cowichan, all on the Strait of Georgia; and the Alberni 
in the central part of the island. The Suquash, Comox and Nanaimo 
basins contain seams which are being worked. In the Suquash 


basin the beds are little disturbed and regular. The coal is a low 
carbon, high moisture, bituminous coal. In the Comox basin the 
lower seams lie over an irregular bottom and are quite irregular in 
thickness and distribution. In some places the coal is broken and 
coked by igneous intrusions. It is bituminous and coking and has 
the highest fuel ratio of any of the Vancouver Island coals. In the 
Nanaimo field there are many faults and the seams vary very greatly 
in thickness and quality within short distances, but they are quite 
persistent in extent. A case is cited by Clapp where a seam varies, 
within 100 feet, from 2 feet of dirty slickensided coal to 30 feet of 
clean coal. There are three seams with an aggregate of 10 feet of coal 
which is a high-volatile, coking, bituminous variety. This basin 
has produced the larger part of the coal of British Columbia. 

The coals of the Queen Charlotte Islands are of two geological 
ages Cretaceous and Tertiary, supposedly Miocene. The Creta- 
ceous coals vary from high- volatile bituminous to semianthracite and 
the Tertiary are subbituminous coals and lignites, some of the latter 
of very woody types. Part of the Cretaceous coal is coking. The 
semianthracite is unusually high in water and much of it is high in ash. 
The main basin lies on the southern end of Graham Island where the 
shales have been highly folded between masses of crystalline rocks. 
In some places the coal is greatly crushed. The Tertiary coals are 
not of much importance. 

Yukon Territory. Coal has been mined at five points in the 
Yukon: Tantalus Mine, and Five Fingers Mine on the Yukon River; 
on Cliff Creek; on Coal Creek, a tributary of the Yukon; and on Coal 
Creek, a tributary of Rock Creek. According to the conclusions of D. 
D. Cairnes, the coals are Jura-Cretaceous and Tertiary in age. The 
Tertiary coals are upper Eocene and they are lignites with con- 
siderable resin. In places volcanic rocks are associated with 
the soft shales and clays and loosely cemented conglomerates and 

There are two coal horizons in the Jura-Cretaceous rocks, the upper 
being the Tantalus conglomerates, about 1000 feet thick, and the 
lower the Laberge series about 3800 feet in thickness. The coal 
seams occur near the top of the latter series which consists of arkoses, 
graywackes, sandstones, tuffs, shales and slates. The coal is bitumi- 
nous and in most places non-coking. The coal of the lower seam 



when washed produces commercial coke. Some semianthracite occurs 
in the Whitehorse area. 

Northwest Territories. There are several coal basins in this 
region. One of these in Tertiary rocks, occurs in the Mackenzie 
River valley and runs a short distance up the Bear River at Fort Nor- 
man. There is probably a lignite area running south up the valley 
of the Mackenzie from Fort Norman and an area around the north- 
west side of Great Bear Lake. Three seams have been reported with 
a maximum of about 16 feet of coal. 

FIG. 115. The Tantalus coal mine on the Yukon River. (Photo by E. S. Moore.) 

Along the Peel and Horton rivers in the vicinity of the Mackenzie 
delta there are Cretaceous rocks carrying thin seams of coal with a 
maximum thickness of 4 feet. Some of the seams have been on fire 
in the past, producing reddened outcrops which offer striking features 
to the traveler. So far as known all the coal in the Territories is 

The Arctic Islands. Very little accurate information regarding 
the coal deposits on the Arctic Islands has been obtained but it is 
known that coal occurs at two horizons, in the Tertiary and in the 
Lower Carboniferous. The Tertiary coals are lignites and the older 


coals are bituminous. It is estimated that some 6000 square miles 
on Banks Island and the Parry Islands is underlain with Lower 
Carboniferous coals. Only one seam has been found but it is said 
to reach a maximum of 50 feet in thickness. Small deposits of Ter- 
tiary coal are believed to exist on Ellsmere, Baffin and Bylot islands. 
On Ellsmere Island a seam of Tertiary coal 25 feet thick has been 
reported from Cape Murchison. Cannel coal and oil shale have been 
found on the Parry Islands. 


Owing to the prominence of the large and well developed coal 
deposits in Nova Scotia little attention has been paid to the Newfound- 
land deposits which are not so extensive nor so readily mined as those 
in Canada. There are, however, at least two areas of Carboniferous 
rocks which carry considerable coal in Newfoundland. One area 
is on St. George Bay and the other is about 100 miles northeast of it 
in the Humber River valley. In the former area there are, according 
to J. P. Howley, as many as nine seams varying in thickness from 
i foot to 9 feet. The beds are greatly disturbed and many of the 
seams are of small extent. 

In the Humber River valley the strata are for the most part older 
than the Pennsylvanian and they carry oil shales and material re- 
sembling the albertite of New Brunswick. There are, however, in 
parts of the district small areas of the Coal Measures which carry 
several workable seams running up to about 6 feet in thickness and 
some of the seams are greatly folded although in much of this field 
the strata are nearly flat. The Newfoundland coals are bituminous 
to semibituminous in character. 



The United States not only has the largest deposits of coal of any 
country in the world but she is also developing them at a more rapid 
rate than any other country. A preceding table (page 335) shows 
the relative production of the countries of the world and the following 
table indicates the rank of the various states of the Union in pro- 
duction and the value of the coal produced. Pennsylvania has long 
been the chief producer in the country. 

o * 

H S 1 





>. 1? 



,S <8 %& 3 "8 3 i 

$> f IH M CO 00 W -* C 


O M ^^ M O VO OO t^t^vo IO O> IO 10 t^- O 


vo fO "^ 04 c^ovo Civo Tj-f-oS^^roo fO 

(C C C* M" VO* O* M* ^f fO 00* t> M* O* N 


III P$| 

ofoc*t--oo*o"iio** > 

^- M M 10 Oi M 

II - * 

^^ S'g s^sa 


8 R 


00 Jo "M ** N 

f~ (~0 N ro 

t^ N Ol 

cfi ^ M T? ro ro 







Q S 

o s 








10 00 

I I 




10 c ro oo 


1 I 
I I 


co oo" 




S 3 

Total bitumi 
anthracite .. 





C8 ^ 




o Cali 
b) Inclu 

A Indicates anthracite coal Q coking coal 


containing workable 
coal beds 

Areas that may Areas probably containing 

contain umrkable Workable coal beds under 

coal beds such heauy cover as not 

to be qvailable at present 


containing workath 
coal beds 

PLATE XII. Map of the coal-fields of the United States (U. S. Geol. Survey. 



Areas that may Areas probably containing 

contain workable workable coal beds under 

coal beds such heavy cover as not 

to be available at present 

I I I I 

Areas Areas that may 

containing workaSEe contain workable 

lignite beds lignite beds 

nted by permission from Rles 1 Economic Geology, published by John Wiley & Sons, Inc.) 



The Geological Survey has adopted, according to M. R. Campbell, 
the following divisions in classifying the coal areas of the country, 
(Plate XII): (i) Coal province (2) Coal region (3) Coal field (4) 
Coal district. The following provinces have been recognized: (i) 
Eastern province; (2) Interior province; (3) Gulf province; (4) 
Northern Great Plains province; (5) Rocky Mountain province; 
and (6) Pacific Coast province. These provinces are subdivided into 
regions as follows: The Eastern province is divided into (a) The 
Anthracite region of Pennsylvania; (b) The Atlantic Coast region, 
including the Triassic fields of Virginia and North Carolina; (c) The 
Appalachian region extending from northern Pennsylvania into 
Alabama and embracing also parts of Ohio, Maryland, Virginia, West 
Virginia, Eastern Kentucky, Tennessee and Georgia. The Interior 
province is divided into (a) the Northern region, containing only the 
coal field of Michigan; (b) The Eastern region including the fields 
of Illinois, Indiana and Western Kentucky; (c) The Western region 
including the coal fields of Iowa, Missouri, Nebraska, Kansas, Ar- 
kansas and Oklahoma and (d) The Southwestern region, in Texas. 
The Gulf province includes (a) The Mississippian region, in the 
east and (b) The Texas region to the west. The former includes the 
states of Louisiana, Mississippi and Alabama and the latter Arkansas 
and Texas. 

The Northern Great Plains province includes (a) The Fort Union 
region with the lignite fields of North Dakota, South Dakota, eastern 
Montana and the subbituminous field of northeastern Wyoming; 
(b) The Black Hills region of Wyoming; (c) The Assinniboine region 
in Montana; (d) The Judith Basin region in Montana; (e) The 
Denver region in Colorado; and (/) the Raton Mountain region of 
Colorado and New Mexico. 

The Rocky Mountain province is not clearly separated from the 
Great Plains province. It includes (a) The Yellowstone region of 
Montana; (b) The Bighorn Basin region of Wyoming; (c) The Hams 
Fork region of western Wyoming; (d) The Green River region of 
southern Wyoming; (e) The Uinta region of Utah and Colorado; 
(/) The San Juan River region of Colorado and New Mexico; and 
(g) The southwestern Utah region. 
The Pacific Coast province is not divided into regions. It em- 


braces coal fields in Calfornia, Oregon and Washington. It is the 
smallest of the provinces. 

The following table, prepared by Campbell for the Twelfth Inter- 
national Geological Congress, presents the areas of the various prov- 
inces, the types of coal in each, and the character of the coal. The 
total production of each state to the end of 1917 has been added to 
show the extent of exhaustion of the resources. The estimate in- 
cludes all seams not less than 14 inches thick and not more than 
3000 feet below the surface. A detailed description of the classes of 
coal mentioned in this table is found in Chapter V under Classifi- 
cation of Coals. 

The total estimated tonnage of all kinds of coal for the United States 
above 3000 feet in depth is 3,225,394,300,000 metric tons or about 
one-tenth more in short tons. The amount produced up to the 
end of 1917 was 12,130,805,450 short tons. By adding approxi- 
mately 50 per cent of this amount for waste in mining and other 
operations the total coal exhausted is approximately 18,196,203,175 
short tons. This is almost negligible compared with the coal re- 
sources of the country, being slightly more than one-half of one per 
cent, but in many fields the output represents the best coal from the 
most accessible seams. 





bo II 

'C c 



gftggJJ-fc ..^oo I 


Coal below 
surface from 
3000 to 6000 

and Semi- 
al (Class A 

ous coal 
i Class 

ous coal (No. 
i Class D) 





IS !f 

O O O lO O O OOOOOl^ 1000 O 

ooo^oioor* looiO'OO'O ^0*0 


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g & 










m S" 


S 8 

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i t 
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N. F. Fla 
Mountain fi 
Red Lodge 


o end 


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oo* rt 

3 J 



o o 

T QJ .fa < 



and Semi 


8 o_ 
* " 

s coal 
No i 
ass B) 




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H 1O IO 

t^ 10 N 

8 88888 88 




i i II 

ioq oo^ 





O O 


di ro 



roo o<OPO^-o 10 rooo TtTtro 

M O> M t Tt-lO Mt^OO 



3 I- 2 


tate and Field 

^<o T)T! '^ G .S C ! I i'O'S 

1 22 li l 1 iiS-jl* 






As indicated in the table (page 338) the coal seams of the United 
States range from Lower Carboniferous (Mississippian) to Miocene 
in age. The eastern part of the country in a general way may be said 
to carry the Carboniferous, Permian and Triassic coals and the west- 
ern and Gulf regions the Cretaceous and Tertiary coals. In a gen- 
eral way it may be said also that the coals of the east are of higher 
grade than those of the west because all the lignite and most of the 
subbituminous coal lies in the western part of the country or around 
the Gulf of Mexico. The Carboniferous system is the great coal pro- 
ducer of the east because at the beginning of that period large areas 
in the eastern part of the continent had but recently emerged from 
beneath the sea. There were excellent conditions for the develop- 
ment of great swamps on the then existing low lands as there are 
along the coasts of Virginia and North Carolina today. The west- 
ern part of the continent was still largely under the sea at that time 
and there is almost no Carboniferous coal in that part of the country. 
The age of the coal does not necessarily determine its quality, but, 
other things being equal, the older the coal usually the higher 
the fixed carbon because it has been longer subjected to pressure. 
There is much excellent coal in the West where the younger forma- 
tions have been sufficiently squeezed to devolatilize it. 
The geological age of the coal according to provinces is as follows: 
(a) Eastern province. Semianthracite occurs in the Pocono of 
the Mississippian in Virginia, in two small basins southeast of the 
main field, in Frederick, Pulaski and Montgomery counties. The 
other coals of the Eastern province all occur in the Pennsylvanian, 
or Upper Carboniferous, except those in the Atlantic Coast region and 
a few seams in the Permian. The coals in the Pennsylvanian run 
through the Pottsville, Allegheny, Conemaugh and Monongahela 
series. In the southeastern portions of the Appalachian region the 
coals are to quite a large extent of Pottsville age. For example, 
those of the famous Pocahontas field of Virginia and West Virginia 
are of lower Pottsville, those of the New River field of lower and 
middle Pottsville and much of the coal of Alabama and Georgia is of 
Pottsville age. This formation carries some coal throughout the 
whole Appalachian region but outside of the districts mentioned it 
is, as a rule, not an important producer. The other formations, 


especially the Allegheny and Monongahela, carry important coals 
throughout the region with the exception that the latter formation is 
not important in the southern part of the field. The Permian car- 
ries coal in Pennsylvania, Ohio and Maryland. In the Atlantic 
Coast region of Virginia and North Carolina the coal is Triassic in 
age, this being the only coal of that age in the country. 

(b) Interior province. The coals are all Pennsylvanian, the most 
widespread formations being the Pottsville and the Allegheny. 

(c) Gulf province. The coal is of Upper Cretaceous and Eocene 

(d) Northern Great Plains province. The coals in this province 
range from the Kootenay of the Lower Cretaceous, around the Black 
Hills, to the Fort Union of the Eocene, in which the bulk of the 
lignite occurs. There is much difference of opinion among geologists 
as to whether most of the coal occurs in the Cretaceous or in the 
Tertiary as the dividing line between the two systems is in many places 
not distinct. In the Dakotas all the important coal seams, which are 
almost entirely lignite, are of Eocene age, but there is a little coal in 
the Lance formation of the Upper Cretaceous. In Montana the coal 
runs from Jurassic through Lower Cretaceous and Upper Cretaceous 
to Eocene, very little of it being Jurassic. The Wyoming coals are 
Lower and Upper Cretaceous and Eocene and those of Colorado are 
mostly in the Montana series of the Upper Cretaceous with important 
beds in the Laramie and a little in the Dakota series. Those of New 
Mexico are also of Upper Cretaceous, (Montana) age with the excep- 
tion of a very small area of lower Pennsylvanian. 

(e) The Rocky Mountain province carries coals from Lower Cret- 
aceous to Miocene in age. In addition to the states mentioned under 
the Northern Great Plains province, Arizona contains Upper Cret- 
aceous coals; those of Utah are mostly in the Montana and Colorado 
series of the Upper Cretaceous, and some lignite occurs in the Eocene. 
In Idaho the coal is of Upper Cretaceous and Eocene ages. 

(/) In the Pacific Coast province the coals are chiefly Eocene in 
age but small areas are Miocene. 


PLATE XIV. Structure section through the Mahi 



and Shenandoah basins. (By courtesy of J. Bevan.) 



Eastern Province 

Pennsylvania. 2 Pennsylvania contains the anthracite region in 
the east and the bituminous fields in the west and north-central parts 
of the state. These two areas were originally connected but they have 
been separated by erosion. The strata in the bituminous fields are 
as a rule but slightly folded and the faults, although numerous in 
some districts, are not of great throw, while in the anthracite region 
the strata are characteristically highly folded and there are extensive 
thrust faults which complicate the mining operations. There are 
some anthracite beds which lie practically flat for considerable dis- 
tances. Such are, for example, some of those in the Northern basin 
around Scranton and Wilkes-Barre. These have, nevertheless, been 
subjected to great pressure but the strata have resisted buckling and 
the pressure has been transmitted to the coal seam changing the coal 
to anthracite. 

Anthracite region: In the anthracite region the coal lies almost 
entirely in the synclines as it has been protected from erosion by the 
Pottsville conglomerate, or as it is often called, Millstone grit, and the 
Pocono sandstones. These formations are brought up in the anticlines 
between the basins and between these formations the red Mauch 
Chunk shale and sandstone makes a distinct horizon-marker and 
indicates the lower limit of all coal. Usually the Pottsville conglom- 
erate marks the base but a few seams have been found in it. Some 
of the synclines are probably of great depth; over 4000 feet, in the 
Southern field. Mining has not so far been carried beyond 2200 feet, 
with the deepest shaft only 1850 feet, but it must be in the future. 
The region is usually divided into the Northern, Eastern-middle, 
Southern and Western-middle fields and these fields contain the 
following districts. The Northern includes Carbondale, Scranton, 
Pittston, Wilkes-Barre, Plymouth, Kingston and Nanticoke, these 
making up the Wyoming trade region. The Eastern-middle field in- 

1 For special comprehensive reports see: 22nd Annual Report, U. S. Geol. Survey, 
Part III, 1902; The Coal Catalog, E. N. Zern, Editor, Keystone Consolidated Publishing 
Co., Pittsburgh, 1918; The Coal Fields of the United States, with map, by M. R. Campbell, 
U. S. Geol. Survey; Coal, by E. W. Parker, Mineral Resources of the United States, 1910. 

2 Second Geological Survey of Pennsylvania; County Reports and Geologic and 
Topographic Survey Commission reports. Also 22nd Annual Report, U. S. Geol. Survey, 
The Pennsylvania Anthracite Coal Field by H. H. Stoek. 


eludes the Green Mountain, Black Creek, Hazleton, Beaver Meadow, 
and Panther Creek districts, these making up the Lehigh trade region. 
The Southern field includes the East Schuylkill, West Schuylkill, 
Lorberry and Lykens Valley districts, while the Western-middle field 
embraces the local districts of East Mahanoy, West Mahanoy and 
Shamokin. The last two fields are comprised in the Schuylkill trade 

The structure of the region is illustrated by the accompanying sec- 
tions (Pis. XIII and XIV) and the names of the seams and their 
relations to one another are also indicated. The anticlines lie in a 
general direction of about N. 70 E. and as a rule the folds are steeper 
on the northwestern side of the anticline than on the opposite side 
since the thrusts producing them came from the southeast. The 
thickest seam is the Mammoth which reaches 50 to 60 feet of com- 
paratively clean coal and in some places is doubled by folding so that 
over 100 feet of coal occurs in a stripping. Since the cover over this 
and some of the other seams is so thin much coal is mined by stripping 
off the cover and digging the coal with steam shovels. The depth of 
the cover removed varies from almost nothing to 90 feet, although one 
stripping will reach almost 200 feet in depth under exceptional 
conditions. This is at Locust Mountain. 

The best-known seams in the various fields are as follows: In the 
Southern field there are the six Lykens Valley seams in the Potts- 
ville conglomerate, No. VI being the lowest, and three of these beds 
are found also in the Western-middle field. They vary from thin un- 
workable seams up to about n feet in the Western-middle field. 
There are no workable seams in the Pottsville in the other two fields. 

The lowest bed in the Coal Measures proper is the Buck Mountain 
bed of the Southern, the Western-middle and Eastern-middle fields. 
This bed is thickest in the Western-middle field and it probably 
corresponds to the lowest split of the lowest Red Ash bed in the 
Northern field. It runs between 3 and 19 feet in thickness. Be- 
tween the Buck Mountain and Mammoth seams in the Southern 
field there is the Skidmore bed; in the Western-middle field there 
are the Seven-foot and Skidmore beds and in the Eastern-middle 
field the Gamma bed, the Wharton bed and the Parlor bed. 

In the Northern field the lowest workable beds are the three Red 
Ash or Dunmore beds, also known as the Powder Mill and Clifford 


beds. Above the Dunmore beds lie the Ross or Clark seam, and the 
Twin beds, followed by the two splits of the seam known as the 
Mammoth in the other fields. In this field this seam is known as 
the Baltimore, Pittston, Fourteen-foot, Big Bed or Grassy Island bed. 
Above this big seam lie the Rock bed and the Diamond bed, each 
about 3 feet thick, followed by the Hillman or Olyphant No. I, running 
up to about 15 feet in thickness. Above this seam is the Kidney, 
Diamond or Olyphant No. II which probably corresponds to the 
Diamond beds of the southern fields. It is about 5 feet thick in this 
field. The Abbott and Snake Island beds lie above it. 

In the Eastern-middle field the Mammoth bed which is here 
around 58 feet thick is the highest bed of importance and it is stripped 
a great deal. In the Western-middle field there are the Holmes 
bed, the Primrose bed, the Orchard beds, the Diamond beds and 
the Tracy beds, lying above the Mammoth seam which is here 
about 60 feet thick. 

In the Southern field the Mammoth seam has a number of splits 
making up a total of about 1 20 feet of coal and partings. The seams 
lying above the Mammoth bed are practically the same as those 
just mentioned for the Western-middle field with the addition of the 
Clinton beds. About twenty different beds have been worked in 
this field. 

It has been estimated that over 80 per cent of the coal in the Wy- 
oming basin and approximately 75 per cent of that in the other 
fields is marketable. The Pennsylvanian rocks are very thick in 
the Southern field, the Pottsville conglomerate varying from noo to 
1475 feet in thickness and the other formations making up 2500 feet 
more. In the Western-middle field about 1200 feet of measures 
remains, and in the Northern field a maximum of 2200 feet is found 
in the deep basin between Nanticoke and Wilkes-Barre. The aver- 
age thickness for the Pottsville conglomerate and the Coal Measures 
respectively, in the various fields is placed at the following figures: 
Northern field 225 and 1800 feet; Western-middle 850 and 1000 
feet; Eastern-middle 300 and 700 feet, and Southern 1200 and 2500 

An interesting feature in the Northern field is the buried valley 
between Pittston and Nanticoke in which a large stream flowed 
before the glacier passed over the region. When the glacier pushed 

03 a 



< 3 






across the valley in the Pleistocene epoch the valley was filled up 
and since the glacier melted away the Susquehanna River has made a 
new channel for itself. It has also been suggested that this valley 
may have been caused by glacial erosion. Since this pre-glacial 
valley is filled with debris which holds much more water than the 
solid rock, it is naturally a menace in mining operations and it has 
been pretty carefully mapped out. 



Homewood Sandstone 

Upper Mercer Coal 

20- -ZJ^I^I Lower Mercer Coal 




> Conoqueneasing 

Sharon Coal 

Sharon Conglomerate 

FIG. 117. Section of the Pottsville 
in Mercer County, Pa. (After I. C. 
White, U. S. Geol. Survey.) 

Upper Free port Coal (E) 

Lower Freeport Coal ( D ) 

Freeport Sandstone 

Upper Kittanning Coal (C') 
Johnstown Cement 

Middle Kittanning Coal (C) 

Lower Kittanning Coal ( B) 

Ferriferous Limestone 
Clarion Coal (A') 


FIG. 118. Columnar section through 
the Allegheny formation on the Alle- 
gheny River, Armstrong County, Pa. 
(After D. White, U. S. Geol. Survey.) 

Pennsylvania produces almost all the anthracite mined con- 
siderably over 99 per cent in the country. Anthracite was dis- 
covered by the earliest settlers about 1762 and used by smiths and 
for local purposes for a number of years before active mining began. 
The records of shipments begin about 1805, but coal is said to have 
been shipped during the Revolutionary War. At first the people 
in the towns would have nothing to do with it as they were skep- 
tical regarding its value as a fuel. 

The Bernice field of Sullivan County is regarded by some as part of 

3 68 


ittle Pittsburgh Coal 

Connellsville Sandstone 

Morgantown Sandstone 

11 -.T-_rJ "Elk Lick Coal 

Crinoidal Coal 



the anthracite region and the coal is put 
on the market as anthracite although it 
is more strictly semianthracite. It marks 
the transition from the anthracite region 
to the bituminous fields farther west. 

Bituminous region: 1 The bituminous 
fields of the state cover 14,200 square 
miles and while the southeastern border 
of the area has suffered a good deal of 
compression where the intensive folding 
found farther east dies out, the beds for 
the most part have gentle dips and the 
coal occurs in a large number of roughly 
parallel synclinal basins. The Broad top 
field in Huntingdon and Bedford counties 
is a remnant of the Coal Measures folded 
down into the mountains in that lo- 
cality and it is more disturbed than most 
of the other bituminous fields. Owing 
to the greater amount of folding which 
the eastern portion of the bituminous 
area has suffered, much of the coal is 
semibituminous in character and the 
Clearfield district is noted for its " Smoke- 
less coal " of this variety. 

The coals occur chiefly in the Alle- 
gheny and Monongahela series of the 
Coal Measures, between 40 and 50 per 
cent of the coal mined coming from the 
former series. The Pottsville (Fig. 117) 
contains the Sharon and Mercer coals 
mined in restricted areas. The Allegheny 
(Fig. 1 1 8) is about 300 feet thick on the 
average and contains the Brookville, or 

1 White, D., and Campbell, M. R., The bitumi- 
nous coal fields of Pennsylvania. 22nd Annual Rept. 
U. S. Geol. Survey, Pt. Ill, 1902. Also White, 
U. S. Geol. Survey, Bull. 65. 

Bakerstown Coal 

,Masontown Coal 


FIG. 119 Columnar section 
through the Conemaugh forma- 
tion on Dunbar Creek, Fayette 
County, Pa. (After I. C. 
White, U. S. Geol. Survey.) 


3 6 9 

Waynesburg Coal 



Uniontown Coal 


Sewickley Coal 

A coal, the Clarion or A 1 , the Lower Kit tanning or B, the Middle 
Kittanning or C, the Upper Kittanning or C 1 , the Lower Freeport 
or D and the Upper Freeport or E. The Brookville coal is 
worked in many places in the eastern counties of the bituminous 
fields and the Clarion coal is of workable thickness in numerous lo- 
calities. The Lower Kittanning is usually Feet 
less than 4 feet thick but it is uniform in 
distribution and character. It is also known 
as the Miller seam. It is a valuable coal 
in at least eleven counties. The Upper 
Kittanning is characterized by a large 
amount of cannel coal in Beaver and Clear- 
field counties. The Middle Kittanning is 
not relatively important as it is thin and 
in many places dirty. The Upper and 
Lower seams are well known for coking, 
domestic, gas-producing and other pur- 
poses. The lower Freeport or Moshannon 
seam is a well-known seam, especially in 
Clearfield, Jefferson, Indiana, Cambria and 
Center counties. This coal is adapted to 
almost all varieties of uses. The Upper 
Freeport extends over a large area but it 
varies greatly in thickness and quality. 

The Conemaugh series (Fig. 119) carries 
several seams such as the Berlin, Bakers- 
town and Coleman but they are compara- 
tively unimportant. 

The Monongahela series (Fig. 120) con- 
tains the famous Pittsburgh seam and the 
Redstone, Sewickley and Waynesburg seams. The former seam 
occurs in the southwestern portion of the state in Greene, 
Washington, Westmoreland, Fayette, Allegheny, Somerset and In- 
diana counties. It runs from 4 to 9 feet in thickness and averages 
about 7 feet over an area of between 2000 and 2500 square miles. 
The coal of this seam is excellent for a great variety of uses. It has 
been the famous coking coal of the Connellsville district, and West- 
moreland County furnishes one of the best of gas coals from this seam. 

..Redstone Coal 

Pittsburgh Coal 

FIG. 1 20. Columnar section 
of the Monongahela forma- 
tion in Fayette County, Pa. 
(After Stevenson, U. S. Geol. 



The Redstone seam is about 3 J feet thick. It is mined in a number 
of places in the southwestern counties, but on the whole it is not very 

important. The Waynesburg seam is 
mined in Westmoreland, Washington and 
Greene counties. It is about 3 feet thick 
on the average but locally it runs 6 feet, 
and in places it is a block coal. The coal 
is frequently bony. 

The Dunkard series of the Permian 
system carries the Washington seam which 
is worked to some extent in Washington 
and Greene Counties. It may reach 10 
feet in thickness but, like the Waynesburg 
seam, it carries much rock. 

Rhode Island. 1 The coal in this state 
is interesting chiefly because of the fact 
that it has been so squeezed and broken that 
some of it has been turned into graphite, 
and therefore does not burn. The propor- 
tion of fixed carbon is so high compared 
with the volatile matter that combustion 
will not take place in some of the coal. The 
coal is also very high in ash, much of it 
running 30 per cent or more. It has been 
mined intermittently. 

Ohio. 2 Many of the seams mined in 
southwestern Pennsylvania continue into 
Ohio. They are all bituminous. In the 
Pottsville formation (Fig. 122) there are in 
ascending order, Sharon, or No. i, the 
block coal; Quakertown or No. 2; and 

ru, ^"olumnar section Lower Mercer or No. 3. Of these the 
through the Dunkard forma- Sharon, which is about 3 feet thick, is the 

tion in Greene County, Pa. on }y one o f mu ch importance although the 
(After Stevenson, U.S. Geol. m j ned ^ certa ; n ^ The 


Sharon has been mined in limited areas, as 

1 Ashley, G. H., Rhode Island Coal. U. S. Geol. Survey, Bull. 615, 1915. 

2 Bownocker, J. A., The coal fields of Ohio, with map. U. S. Geol. Survey, Prof. 
Paper loo-B, 1917. Also, Bull. 9, Fourth series, Ohio Geol. Survey, 1908. 

OHIO 371 

around Massillon and Jackson. This coal is largely exhausted. 
It is characterized by coatings of calcium carbonate on the joints, 
known as " white cap." The sulphur is very low and the coal has 
been used raw in the blast furnaces in making pig iron. The 
Quakertown bed, also known as the Wellston or Jackson Hill bed, 
supplies good coal for domestic and steam purposes, and in Jackson 
County where it is mined most it runs about 4 feet in thickness. 
The Lower Mercer, or No. 3 and the Upper Mercer or No. 30, are 
unimportant. They are characterized by lying und^ thin lime- 
stones which go by the same name. The Upper Mercer is also 
known as the Bedford cannel and in Coshocton County it reaches a 
thickness of about 9 feet of which 5 feet is cannel. 

The Allegheny series contains the most widely extended and best 
beds of the state. The seams in ascending order are the Brookville 
or No. 4, the Clarion or No. 40, the Lower Kittanning or No. 5, the 
Middle Kittanning or No. 6, the Lower Freeport or No. 6a and the 
Upper Freeport or No. 7. The Brookville seam runs from 2 to 4 feet 
in thickness and it is not extensively mined as it is impure and thin 
over large areas. The Clarion bed lies under the Vanport, or Ferrif- 
erous limestone, which is a good horizon-marker. It is of compara- 
tively little value. The Lower Kittanning is not of great impor- 
tance but it is mined and a very important bed of clay lies beneath it. 
The Middle Kittanning is regarded as one of the most important in 
Ohio. It usually runs around 3 to 4 feet in thickness; it is high in 
sulphur in many places but is widely extended. In the Hocking 
Valley field what is known as the Jumbo " fault " causes much diffi- 
culty in mining. It is not a fault but an old " cut-out " where a 
stream has washed away the vegetal matter and deposited sand and 
mud in its place. The Lower Freeport is of little commercial im- 
portance except around Steubenville, while the Upper Freeport is a 
very important seam. The coal breaks down readily and is not 
suitable for transportation but it is a good steaming fuel. Its maxi- 
mum thickness is about 7 feet. Lying between the Upper Freeport 
and the Pittsburgh bed is the Conemaugh series, about 350 to 500 
feet thick. It contains the Mahoning, Mason and Anderson seams, 
the latter being equivalent to the Bakerstown of Pennsylvania, but 
they are thin and little worked. 

The Monongahela, or Upper Productive Measures, contains three 


seams of importance: The Pittsburgh or No. 8 at the base; the Red- 
stone or Pomeroy, or No. 8a; and Meigs or No. 9. The Pittsburgh 
is not as extensive or of as good quality as the Middle Kit tanning. It 
occurs in the three fields, Belmont County, Federal Creek and Swan 
Creek. The coal is used mostly for steam and domestic purposes. 
It runs about 6 feet in thickness with several clay partings in many 
places, and thin limestones occur in the shales of the roof. In some 
areas, as in Jefferson County, the coal is mined with steam shovels. 
The Pomeroy was for years regarded as the Pittsburgh bed of Penn- 
sylvania but it is now known to be the equivalent of the Redstone. 
It runs from 2 to 5 feet in thickness and is high in ash. The Meigs 
Creek is an important bed but in many places it is irregular. It is 
the equivalent of the Sewickley seam of Pennsylvania. The coal is 
used mostly for steam and domestic purposes. It is like many of 
the Ohio coals in being high in sulphur, and bands of pyrite frequently 
occur. In the Dunkard group of the Permian there are several thin 
seams but they are not of importance. 

Maryland. 1 The coals of Maryland occur in the following five 
basins: Georges Creek, Upper Potomac, Castleman, Upper Youghio- 
gheny and Lower Youghiogheny, all confined to Allegheny and 
Garrett counties. The Georges Creek basin is the most prominent 
producer with most of the remaining coal coming from the Potomac 
basin. The coals are mostly semibituminous. The following seams 
are recognized: Brookville, Clarion, Lower Kittanning, Upper Kittan- 
ning, Lower Freeport and Upper Freeport, in the Allegheny series. 
Those of the Pottsville are unimportant. In the Conemaugh the 
Bakerstown seam occurs and is of some importance. The Mononga- 
hela carries the Pittsburgh seam and the Upper Sewickley, also known 
as the Gas coal. The Pittsburgh seam or " Big Vein " has been the 
main source of the coal of the state but the other seams are being devel- 
oped more and more in recent years. This seam runs about 8 feet 
in thickness although in the southern part of the field it reaches 14 
feet. The coal is massive and breaks down in large blocks. It fur- 
nishes a famous bunkering and steaming coal and can be coked, but 
it is not used to any extent for the latter purpose. 

West Virginia. 2 Many of the coal seams of Pennsylvania, Ohio 

1 Clark, W. B., Maryland Geol. Survey, Vol. V, 1905. 

* White, West Virginia Geol. Survey, Vol. II, 1903 and Bull. 2, 1911. 


Coal No. 7 a 
Fire clay 

Sandstone andjshale |5si5 

Coal No. 7 
Fire clay 

Gray shale 

Buff limestone 
Black band iron ore 
Fire clay 
Coal No, 6 b 

Shale and limestone 

Coal No. 6 i 
Fire clay 

E2~==J 0-50 


Gray or black shale |=f=^E-=| 5-50 

Coal No. 6 
Fire clay 

Gray or black shale |EE:^=| 

Coal No. 5 
Fire clay 

Shale and sandstone fe~t 


Fire clay 
Coal No. 4 

Shale and sandstone 

Coal No. 3 b 
Shale and sandstone 
Coal No. 3 a 
Limestone with iron oi 

Fire clay 5-15 

Shale and sandstone 

Coal No. 2 
Fire clay 



Gray shale 

Coal No. 1 
Fire clay 






Stripe vein 
Brush Creek 


f Upper Freeport 
I Cambridge 
] Big Vein 
I Waterloo 


Lower Freeport 

Upper Ktttanniiig 

(Hocking Valley 
Middle Kittanning 

Lower Kittanning 
New Castle 

Gray ferriferous; 
Putnam Hill. 
Upper Clarion 

f Homewood 
\ Piedmont 

( Bruce 

\ Upper Mercer 
( Lower Mercer 
\ Flint Ridge canne 

Upper Massillon 

f Wellston 
1 Quaker.tow.n 

Lower Massillon 



Jackson Shaft 



Coal No. 13 

Stwidstoiu* andLsh.a.1 


Black shale 
Coal No. 8 
Fire clay 



Shale and sandstone pE^^'S 110 


Crinoidal limestone 


Coal NO. 7 b 

Fire clay 

Shale and. sandstone 


Coal No. 7 a. 

Fire clay 



Meig Creek 

Redstone in 



f Grof. 
< Stripe vein 
Brush Creek* 

FIG. 122. Columnar section of the Carboniferous formations in Ohio. 
Hazeltine, U. S. Geol. Survey). 



and Maryland extend into West Virginia, the main one being the 
Pittsburgh bed. This state is the second most important producer 
in the Union and her production is increasing rapidly. The main 
fields of West Virginia are the Fairmont or Clarksburg, the Piedmont 
or Elk Garden in the northern part of the state, and the New River, 
Kanawha and Pocahontas fields in the southern part. The Piedmont 
field is a narrow field lying in the Potomac basin to the east of the 
others and it carries semibituminous or " smokeless " coal in the 
following well-known veins: Pittsburgh, or " Big Vein," Thomas, 
or Upper Freeport, and Davis, probably Upper Kittanning. The 
Pittsburgh seam reaches a thickness of n feet. 

Much of the coal from West Virginia, especially in the southern part 
of the state, occurs in the Pottsville formation and this formation 
seems to increase in relative importance in the states to the south- 
west. The seams in the Pottsville in ascending order are the famous 
Pocahontas seams, Nos. 3, 4 and 6 of the Pocahontas field. Poca- 
hontas No. 3, known as the Thick seam and lying at the base of the 
Pottsville, reaches 12 feet in thickness though usually running around 
6 feet. Pocahontas No. 4 also runs about 6 feet in thickness and 
No. 6 is not mined to any great extent. It runs up to 5 feet in thick- 
ness. The coal of this field is semibituminous, low in ash and sulphur 
and therefore suitable for mixing with high volatile coals in by-product 
ovens. It is a wonderful steam coal. In the New River field the 
lower and middle Pottsville, known as the New River group, carry 
the Fire Creek, Beckley, Welch, Sewell and laeger seams. Of these 
the Sewell, varying from 2 to 5 feet, the Beckley about 4 feet and the 
Fire Creek, 3 to 7 feet, are the most important and most largely mined 
seams. The coal is semibituminous and coking. In the Kanawha 
field the group of rocks named after the field is of Upper Pottsville 
age. The seams are the Eagle, Powellton, Gas, Alma, Cedar Grove, 
Chelton, Winifrede, Coalburg and Stockton. Of these the Eagle, 
Gas, Cedar Grove, Coalburg and Stockton are important. Some of 
these beds reach 1 2 feet in thickness. The Cedar Grove and Stockton 
carry cannel and the Coalburg and Stockton are known as the splint 
coals. The coal of the Kanawha field is bituminous to semibitumi- 
nous. It is coking, some of it is excellent gas-producing coal, and in 
general it is of high grade. 

In the Allegheny series the Lower Kittanning, Lower Freeport and 


Upper Freeport seams are found. The first seam is important in 
three of the fields and reaches 7 feet in thickness. The Upper Free- 
port is important in the northern part of the state, in places reaching 
9 feet. These coals are good steaming and by-product coking coals, 
used chiefly for mixing with other types. In the Conemaugh the 
Bakerstown seam is worked to some extent in the Potomac basin. 

In the Monongahela the Pittsburgh, the Redstone, Sewickley and 
Waynesburg seams all occur in the northern fields only, the Pitts- 
burgh in the Fairmont, Panhandle and Piedmont fields. The Pitts- 
burgh seam averages 8 feet 6 inches, of which 7 feet are mined. It 
is a lump coal, high in sulphur in places, but much used in beehive 
coking where sulphur is low. It is a high grade bituminous steam- 
ing and domestic fuel. The Sewickley is an important seam reach- 
ing 10 feet in thickness. It is a good coal, containing much min- 
eral charcoal. The Waynesburg is mined but little. 

Virginia. 1 Virginia is said to have produced the first bituminous 
coal in the United States, coal having been discovered in 1700, min- 
ing begun in 1787 and shipments make in 1789. This coal occurs in 
the Atlantic Coastal region in rocks of Triassic age and in a syn- 
clinal basin much cut by faults and so intruded by igneous rocks that 
in places- the coal has been changed to natural coke. The coal is 
bituminous to semianthracite and some of it is of high grade. Some 
seams are very thick, but mining conditions are bad and mining 
has only been carried on intermittently. This field extends into 
North Carolina. 

The other fields of Virginia are the Pocahontas or Flat Top field, a 
continuation of the field of the same name in West Virginia, and the 
Big Stone Gap field which extends into Kentucky. In Frederick 
County there is a small isolated field, and another in Pulaski and 
Montgomery counties. In these fields the coal is of Mississippian age, 
and in the Pocono formation. This is geologically the oldest coal in 
the country. The coal is semianthracite to anthracite and of good 
quality. It is mined when thick enough to work, and some seams 
reach 4 feet or more in thickness. 

1 U. S. Geol. Survey, igth Annual Kept., Pt. II, p. 393, 1898, Geology of the Rich- 
mo,nd Basin, Virginia, by N. S. Shaler and J. B. Woodworth; also Bull, in, 1893, Geology 
of the Big Stone Gap Coal Field of Virginia and Kentucky by M. R. Campbell; Mineral 
Resources of Virginia by Watson, Bulls. 9 and 12. 



FIG. 123. Outcrop of the "Big" seam at Pocahontas, Va. with crossbedded 
sandstone above it. (Photo by H. Ries.) 

FIG. 1 24. Breaker for semibituminous coal at the Merrimac Mine, Mef rimac, Va. 

(Photo by H. Ries.) 


The seams mined in the other fields are, in ascending order, the 
Darby, Jawbone, Kennedy, Imboden, Lower Banner, Upper Banner 
and Pocahontas No. 3. The Pocahontas No. 3 is a continuation of 
this seam from West Virginia and here it is of the same quality and 
averages about 9 feet thick. The other seams occur chiefly along 
the extreme western part of the state. The Upper Banner and the 
Imboden are very important and the latter is a specially good coking 
coal. The other seams are all mined to a greater or less extent and 
some of them run as high as 10 feet in thickness. They are Potts- 
ville in age and of bituminous character. 

Kentucky. 1 The coal fields of Kentucky occur along the south- 
east and the northwest borders of the state, the southeastern portion 
being included in the Eastern province and the northwestern in the 
Interior province. The coal-bearing rocks of the southeastern part 
of the state are Pottsville and Allegheny. The Pottsville is about 
500 feet thick and carries a large number of coal beds. There are 
about a dozen workable beds, the main ones being the Flag, Fire 
Clay, Hazard, Keokee, Leonard, High Splint, Dean, Harlan, Miller's 
Creek and Elkhorn. These seams range in thickness up to about 9 
feet. The Keokee is equivalent to the Darby seam of Virginia. 
The High Splint as the name indicates, carries splint coal, an im- 
portant gas coal. The coals are bituminous. Some seams are good 
coking and particularly good gas coals. There is a good deal of can- 
nel coal in this field forming seams, or bands and lenses in the bitumi- 
nous seams. 

In the northwestern section of the state the main seams are known 
as Nos. 9, ii and 12, of which No. 9 is equivalent to No. 5 of Illinois. 
No. 9 is the most important producer. It averages about 5 feet in 
thickness and lies within 300 feet of the surface. In places this seam 
is badly faulted. No. 11, lying higher up, is more irregular but 
thicker in places than No. 9, being about 6 feet thick. No. 12 is 
worked in some areas. The coals are bituminous and higher in 
volatile matter than those to the east. They are also high in sulphur 
and ash. 

1 Annual Kept., Inspector of Mines of Kentucky, 1902. Also Ky. Geol. Survey, 
series 2, Pt. XI, Vol. IV, by Moore; and Bull. 18, 1912 by Fobs. For analyses see Ky. 
Geol. Survey, New series, Chemical Reports. 


Tennessee. 1 The Tennessee coal beds occur in the following 
basins: Wartburg, Walden, Sewanee and Cumberland. In the 
last-named it is said the Coal Measures are over 3000 feet thick and 
that they contain almost 100 feet of coal. The Wartburg basin has 
three or four beds which are now worked, one of which, the Brice- 
ville, is about 4 feet thick. In the eastern part of the Walden basin 
the beds are sharply upturned, but for the most part the coals of 
Tennessee lie quite flat. The best known seams in the state are the 
Sewanee, Jellico and Coal Creek. The coals are all bituminous and 
most of them are suitable for steam, domestic purposes and gas manu- 
facture. The Coal Creek coal is used in coking. 

Georgia. 2 Only 167 square miles are underlain with coal in this 
state and the coal is all of Pottsville age. The Walden basin of 
Tennessee crosses through Georgia into the Warrior and Blount 
Mountain basins of Alabama. The Lookout basin extends into 
Walker County, Georgia. In this basin the coal is of high quality, 
being semibituminous to semianthracite and low in sulphur. Part 
of it is coked. The rest of the coal in the state is bituminous. 


FIG. 125. Structure section in the northern part of the Cahaba Coal Field, Ala. 
(By Charles Butts, U. S. Geol. Survey.) 

Alabama. 3 The Coal Measures in crossing from Georgia widen 
out in Alabama and form four important basins, the Coosa, Ca- 
haba, Warrior and Plateau basins. The Coosa basin is a deep syn- 

1 Hayes, C. W., The Southern Appalachian Coal Field. U. S. Geol. Survey, 22nd 
Annual Rept. Pt. Ill, p. 227, 1902. Also Resources of Tennessee I, No. 5, by Ashley. 

2 McCallie, Georgia Geol. Survey, 1904. 

3 Butts, C., The northern part of the Cahaba Coal Field, Ala. U. S. Geol. Survey, 
Bull. 316, p. 76, 1907. Also reports by McCalley on the Warrior Field, 1900 and by 
Gibson on the Coosa Field, Ala. Geol. Survey, 1895. 



cline of unexplored depth about 60 miles long by 6 wide. It con- 
tains a large number of seams. Two seams are worked, the Eureka 
and the Coal City. This basin is considerably faulted and folded. 

The Cahaba basin covers about 350 square miles and is very deep, 
the coal beds probably extending more than 3000 feet below the sur- 
face, (Fig. 125). The thickness of the Coal Measures is usually 
considered about 5500 feet. There are about ten seams mined and 
the coal is bituminous and coking. 

The Warrior is the most important of the basins. The best known 
seams are the Pratt and the Mary Lee as they furnish most of the 
coal mined in the Birmingham district, and this coal furnishes the 
coke after washing. The Pratt seam in places reaches 16 feet in 
thickness. Besides these two seams 16 other beds are worked in 
this basin. The Plateau field is small and undeveloped but it con- 
tains many good beds. The coals in Alabama are all of Pottsville 

age and bituminous in character. 


T/tc Interior Province 

Michigan. 1 The coal basin of Michigan contains a compara- 
tively flat-lying, slightly faulted series which includes the Potts- 
ville and Allegheny formations of the Pennsylvanian and which is 

FIG. 126. Structure section in Bay County, Mich., from the Amelith Mine to the 
Central and Michigan mines. It shows glacial drift overlying the eroded surface of 
the Coal Measures. (After Lane, U. S. Geol. Survey.) 

overlain by glacial drift. There are seven coal-bearing horizons of 
significance and these are known as the Lower Coal, Lower Rider, 
Saginaw, Middle Rider, Lower Verne, Upper Verne and Upper Rider. 
The seams are very irregular in thickness and character and they 
change rapidly from place to place (Fig. 126). The coal is of bitu- 

1 Lane, A. C., The Northern Interior Coal Field. U. S. Geol. Survey, 22nd Annual 
Report. Pt. Ill, p. 313, 1902. Also Geol. Survey, Michigan, Vol. VIII, Pt. 2. 



Rallsford Shale 

Shaly Limestone 

^\ Conglomerate 


Sandy Shale 

Fie. 127. Columnar sections of the Coal Measures in Illinois. 
(Illinois Geol. Survey.) 


minous rank, is non-coking and dry and is used for steam, producer 
gas, domestic, and related purposes. 

Illinois. 1 Illinois has the largest area of Carboniferous coals of 
any of the states as nearly three-fourths of the state is underlain by 
Coal Measures. The basin is comparatively flat with from 1500 
to 2000 feet of measures near the center. The seams are faulted in 
many places by small faults and near the Kentucky border the beds 
are caught in overturned folds and considerably faulted. The fields 
are covered with glacial drift so that prospecting is often carried on 
with difficulty, shafts being necessary to reach the coal. The shafts 
in the state run from 25 feet to 1000 feet in depth but the majority 
are probably less than 300 feet. The beds as a rule are extensive 
and persistent. The coals are both coking and dry but the coals 
which will coke are high in sulphur, the average running around 3 
per cent for many of the mines, and they are therefore unsuitable for 
commercial coke. They are used mostly for domestic, steam and 
locomotive purposes. Much of the coal is washed and sized. The 
longwall method of mining is used to a considerable extent in this 

In geological age the coals are Allegheny and Pottsville. The 
most important seams are Nos. 2, 5, 6, and 7. No. i seam and a 
few others occur in the Pottsville and are worked in the southern 
part of the state, No. i probably corresponding to the Mercer 
horizon farther east. No. 2 occurs in the Carbondale formation, 
which is regarded as equivalent to the Allegheny, and is a very per- 
sistent bed averaging around 4 feet in thickness. It is regarded by 
some as equivalent to the Clarion coal of Ohio and Pennsylvania. 
In places it contains many sulphur balls. These concretions are 
also common in No. 5 and in the roof shale above that seam. No. 5 
runs about 4 to 5 feet in thickness and is an important seam. No. 6, 
or the "Belleville" seam, is probably the most persistent in the 
state, and in the western part is mined to a depth of about 800 feet. 
It runs from 5 to 6 feet in thickness over large areas and in places it 
reaches 9 feet. No. 7 is mined around Danville and is from 5 to 
7 feet in thickness. It contains much sulphur which can be read- 

1 Ashley, G. H., The Eastern Interior Coal Field, U. S. Geol. Survey, 22nd Annual 
Report, Pt. Ill, p. 271; Bulls, i to 15, 111. Coal Mining Investigations, at University 
of Illinois, also Bulls. 4, 8 and 16, Illinois Geol. Survey. 


ily separated by picking and washing. Another higher seam, No. 8, 
is mined in some localities. 

Indiana. 1 The coal beds of Indiana occur along the western 
border of the state and the coal is all of bituminous rank. It occurs 
in the Pottsville and Allegheny formations as in Illinois. Work- 
able coal is found at eight horizons at least and six of these are 
producing. The main seams are known as the Lower and Upper 
Block, the Minshall, and seams Nos. 2, 3, 4, 5, 6, and 7. No. 8 is 
thin. The lower coals, including the Block and Minshall seams, 
are of Pottsville age and are characterized by being non-coking, 
pure and dry coals which break into rectangular blocks. The seams 
usually run about 3 feet in thickness as an average. The other 
seams are classed as bituminous coals of Allegheny age and they 
run from 3 to 10 feet in thickness with 5 feet a very common figure 
and the beds very persistent. The shafts run from 50 to 450 feet 
in depth for most of the field. 

Iowa. 2 The coal fields lie in the southern and central part of the 
state and cover about 12,500 square miles. The beds are of lower 
Pennsylvanian age, as in Illinois and Indiana, and they occur in the 
Pottsville and Allegheny formations. These are represented by 


FIG. 128." Ideal cross-section of the formations in Mahaska County, Iowa, illus- 
trating the character of the Coal Measures in Iowa. (After H. Hinds, Iowa Geol. 

two series of rocks, the lower, or Des Moines, and the upper, or 
Missouri group. The Missouri group contains much limestone and 
little coal, the Nodaway bed being the only one mined, and it fur- 
nishes less than i per cent of the coal mined in the state. It is 16 to 
20 inches thick and fairly persistent. The Des Moines group, al- 
though consisting chiefly of shale and sandstone, has a thin lime- 
stone bed near the middle. It carries a well-known seam, the Mystic 
or Centreville bed, which is persistent and extends over into Mis- 

1 Ashley, G. H., Stratigraphy and coal beds of Indiana Coal Field. U. S. Geol. Survey, 
Bull. 381, p. 9, 1908; also Indiana Dept. of Geol. and Nat. Res., 33d Annual Rept. 1909. 

2 Hinds, Henry, The coal deposits of Iowa. Iowa Geol. Survey, Vol. XIX, 1908. 


souri. The lower part of the Des Moines group carries a number of 
beds and while they locally run up to 10 feet or more the average 
is about 5 feet in thickness. The seams are characterized by their 
lack of persistency and their sudden changes in quality. They lie 
nearly flat and while faults are numerous they are not large. The 
coal is dry, non-coking, comparatively high in sulphur and used al- 
most entirely for domestic and railroad purposes. The coal field 
is covered with glacial drift so that there are few outcrops and pros- 
pecting is difficult. For this reason little is known about many of 
the seams. Much of the coal lies 400 to 500 feet below the surface. 

Missouri. 1 The same geological series occur in Missouri as in 
Iowa, the Pennsylvanian rocks being divided into the upper, or Mis- 
souri group and a lower, or Des Moines group. The upper is quite 
largely a limestone series and carries little coal. Most of the seams 
occur in the Des Moines group. Those near the base are very ir- 
regular and lack persistency while the seams associated with the 
thin limestone beds higher up in the group are very persistent and 
comparatively regular. The main fields are the Bevier where the 
Bevier seam is 3 to 6 feet thick; the Lexington with a seam 14 inches 
to 2 feet thick which is mined by the longwall method; the South- 
western field; the Novinger field with a seam 3^ feet thick and prob- 
ably equivalent to the Bevier seam; the Marceline where a 29-inch 
seam is mined; and the Mendota where the coal lies at about the same 
horizon as that in the Lexington and the bed is supposed to be equiva- 
lent to the Centreville seam of Iowa. It is not mined to any great 
extent. There are a number of " pockets " of coal lying in isolated 
areas east of the main field. Some of these are very thick but limited 
in extent, Parker mentioning one where the coal is 80 feet thick 
and consists of ordinary bituminous coal and cannel. 

The seams of Missouri mostly lie nearly flat and the faults, while 
numerous, are small. There are many horsebacks, concretions and 
other obstructions in mining. Owing to the shallowness of the seams 
in parts of the state, approximately 20 per cent of the annual output 
is produced by the use of steam shovels. The coals are not high grade 
as they are high in sulphur, moisture and ash. They are used as 
domestic and steaming fuels. 

1 Hinds, H., Missouri Bur. Mines and Geol., Vol. XI, 2nd series, 1912. 


Kansas. 1 About 20,000 square 
miles are underlain by Pennsyl- 
vanian rocks in this state and it 
is estimated that nearly three- 
fourths of the area will prove pro- 
ductive. The field lies in the 
eastern portion of the state and 
the most important and best- 
known localities are in Cherokee 
and Crawford counties which fur- 
nish over 90 per cent of the coal. 
The geological series are much 
like those of Iowa only less dis- 
tinctly marked, with limestone 
more abundant in the lower series 
and the coal distributed more 
widely through the various forma- 
tions. The thickness of the meas- 
ures is about 3000 feet and on 
the whole the beds lie nearly flat, 
(Fig. 129). The Cherokee seam is 
the main bed and it varies from 3 
to 10 feet in thickness with an 
average of about 40 inches. This 
coal is washed and it may then 
be coked but most of it is used for 
locomotive and domestic fuel. 
Much coal is mined by stripping 
methods where it lies near the 
surface. The weathered coal from 
the pits is non-coking because of 
oxidation. It is used raw in some 
of the zinc furnaces. 

In the Leavenworth district a 

1 Howarth and Crane, Kansas Geol. 
Survey, Vol. Ill, 1898. Also the Western 
Interior Coal Field by H. F. Bain, U. S. 
Geol. Survey, 22nd Annual Report, p. 339, 



thin seam is mined at a depth of 700 to 1150 feet. This is the only 
deep mining, according to Parker, which is carried on in the Western 
Interior field. Another area occurs in the Osage County district where 
a seam is mined at a horizon about 2000 feet above the Cherokee 

A small lignite field also occurs in Kansas with coal of Cretaceous 
age which is mined for local consumption. 

Oklahoma. 1 The rocks carrying coal in . NMIESOF 
Oklahoma apparently represent most of the COAL BEOS 
Pennsylvanian formations. There are two main 
fields, the Cherokee and the Choctaw, the latter 
much the more important. The coals vary from 
ordinary bituminous to semibituminous. Some 
of the coals are coking and a number of ovens Paris 
are operated, but most of the coke is too high in 
sulphur for iron furnaces. There are about ten Charleston, 
workable seams of which the following are the 
best known: Hartshorne, Dawson, Henryetta, 
McAlester, Cavanal and Witteville, upper and 
lower. The Henryetta is the most important 
seam in the Cherokee field and averages about 
3 feet in thickness. The Hartshorne seams H" 
run from 2 to 7 feet in thickness and the 
McAlester coals about 4 feet. The strata are 
much folded and faulted in parts of the fields, 
and many of the mines carry considerable gas. 

u PP er 


Fort Smith 


EG. 130 . Generalized 
columnar section of the 
coal-bearing rocks of Ar- 
kansas. (After Collier, 
U. S. Geol. Survey.) 

Gulf Province 

Arkansas. 2 The coal beds are well exposed 
in this field and they have suffered consider- 
able folding, faulting and erosion. They are 
of Pennsylvanian age, Pottsville to Allegheny, 
and the coals vary, even in the same seam, 
from bituminous to semibituminous and semianthracite, the fuel 
ratio increasing from about 5 on the western side of the field to 

1 Taff, J. A., The Southwestern Coal Field. U. S. Geol. Survey, 22nd Annual Rept., 
Pt. Ill, p. 367, 1902. 

2 Collier, A. J., The Arkansas Coal Field. U. S. Geol. Survey, Bull. 316, p. 137, 1906. 


nearly 8 on the east. There are three seams, of which the Harts- 
horne, corresponding to the seam of the same name in Oklahoma, is 
the most important. This seam is about 8 feet thick and it 
supplies nearly all the coal of the state. Other seams which are 
mined a little are the Charleston, lying about 700 feet above the 
Hartshorne and the Paris about 1000 feet above the latter seam. 
There is some lignite lying in the lowlands southeast of Little Rock. 
It is mined to a small extent but is practically undeveloped. It is 
of Tertiary age and listed under the Gulf province. 

Texas. 1 There are three fields in Texas with coals of three differ- 
ent ages and grades. One of the fields in the north-central part of 
the state belongs to the southwestern field of the Interior province. 
The coal is Pennsylvanian in age and mostly of bituminous rank al- 
though there are portions of it which might be more properly classed 
as subbituminous. The Pennsylvanian is here divided into the fol- 
lowing divisions in ascending order: Millsap, Strawn, Canon, Cisco 
and Albany. The structure is simple, the basin dipping gently north- 
westward and westward. There are three workable seams, two of 
which are worked. They are thin, in few places more than 2 feet. 
No. i seam is in the Millsap and the Cisco formation carries two 
workable beds, one known as No. 7 which is the highest bed worked. 
The coals are high in sulphur and ash and are therefore used mostly 
for railroad and other steaming purposes. 

The Eagle Pass field is a small one on the Rio Grande and it ex- 
tends over into Mexico. The strata are considered to be of Upper 
Cretaceous age and the coal is subbituminous in rank. The beds run 
from 5 to 6 feet in thickness and dip steeply in parts of this field. 

The large lignite field extends across the state from the Sabine 
River to the Rio Grande. The rocks are of Eocene age and the coal 
varies from woody lignite to subbituminous grade. The latter oc- 
curs in the Laredo field along the Rio Grande where the rocks have 
been compressed by the uplift of the Sierra Madre Oriental, a little 
to the southwest, in Mexico. Campbell has pointed out that in the 
southern part of the state the lignite consists chiefly of trees and 
other coarse fragments of plants while in the northern part there is a 
much greater proportion of spores, seeds and other related vegetal 

1 Dumble, E. J., Texas Geol. Survey, 1892. Phillips, W. B., and Worrell, S. H., 
The fuels used in Texas. Bull. University of Texas No. 307, 1913. (Numerous analyses.) 


matter in the coal. The lignite occurs in the three upper divisions of 
the Eocene at comparatively shallow depths and the beds vary from 
a few inches to about 25 feet in thickness. Those being mined usually 
run between 4 and 8 feet, except in Webb County where the coal 
is subbituminous and the seams mined are less than 3 feet thick. The 
lignite field belongs in the Gulf province. The known field is much less 
than the probable field as the seams are largely unprospected. The 
lignite is largely used for domestic purposes, for steam, and in gas 

The Northern Great Plains and Rocky Mountain Provinces 
These two provinces are considered together here since many 
states are included in both of them. 

Arizona. Arizona is not yet a producer and has not been well 
prospected, but it contains several fields and a large reserve of coal 
of subbituminous quality. It is of Cretaceous age. The main area 
is the Black Mesa field, a flat, open, synclinal basin with coal in thin 
benches. The other field of which something is known is the Deer 
Creek field in the copper-bearing region of the state. This forms a 
simple synclinal basin with the rocks greatly broken and the coal of 
little value in the southwestern part. Two beds of workable thick- 
ness running from 24 to 30 inches are reported by Campbell. 

New Mexico. 1 This state contains coal varying in rank from 
subbituminous to anthracite, the latter occurring where the coal has 
been locally metamorphosed by igneous intrusions as in the Cerillos 
field. There are five fields: (a) The Raton field of Coif ax County, 
which is an extension of the Trinidad field of Colorado and will be 
discussed under that state; (b) The San Juan River region, in- 
cluding the Gallup and Monero producing districts, and extending 
into Colorado; (c) A little-known area in Valencia, Bernalillo and 
Sandoval counties; (d) The Los Cerillos field in Santa Fe County; 
and (e) The Whiteoaks field in Lincoln County. Outside of the 
Raton field the coal is practically all subbituminous and all the 
coals of the state are regarded as of Upper Cretaceous age, chiefly 
Montana, except in a very limited area near Pecos, carrying lower 
Pennsylvanian coal. 2 Near Monero the coal is bituminous. Some 

1 Storrs, L. S., The Rocky Mountain Coal Field. U. S. Geol. Survey, 22nd Annual 
Rept. Pt. Ill, p. 449. Also U. S. Geol. Survey, Bulls. 285, 316, 381, 471 and 531. 

2 Gardner, J. H., U. S. Geol. Survey, Bull. 381, p. 449, 1908. 

3 88 


of the fields, as for example the Carthage field, are complexly faulted 
and igneous intrusions are common. 

Colorado. 1 This state is the largest coal producer west of the 
Mississippi. The fields of the state are as a rule divided into the 
Eastern, the Park and the Western groups. The Eastern group con- 
tains the following fields: Trinidad, Canon City and South Platte. 
The Park contains the South, Middle and North Park. The Western 
group is the largest and includes the Yampa field in the north, the 
Danforth Hills, White River and Grand Hogback to the north of 
Grand River, the Glenwood Springs basin, Crested Butte and Grand 
Mesa just south of the Grand River, Book Cliffs near Grand Junc- 
tion and the Durango field in the southwestern part of the state. 



3000 Feet 

FIG. 131. Section between Occidental and Oakdale mines, northwest of La Veta. Colo. 
(After G. B. Richardson, U. S. Geol. Survey.) 

The coals are subbituminous in the North Park field and Denver re- 
gion, partly bituminous and partly subbituminous in the Durango 
field, partly bituminous and partly anthracite in the Uinta Basin 
region, and partly subbituminous, partly bituminous, and partly 
anthracite in the Yampa field. The other fields all contain bitumi- 
nous coals of varying grades. The anthracite and other high-carbon 
coals occur in those areas where the coal has been highly compressed 
or heated by igneous rocks and thus devolatilized. The same seam 
may carry coal ranging from bituminous to anthracite, the latter 
near the igneous rocks. 

The age of the Colorado coals is mostly Upper Cretaceous, the 
bulk of the coal occurring in the Mesaverde formation of the Mon- 

1 U. S. Geol. Survey, 22nd Annual Rept., Pt. Ill, p. 427. Also Bulls. 297 (Yampa) 
316 (Danforth Hills, Book Cliffs and Durango) 317 (Book Cliffs) 381 (Denver Basin, 
South Park, Colorado Springs, Trinidad) Folio No. 9 (Crested Butte). 



tana series. Some is Laramie, a little Dakota and a small amount 
of Eocene age. 

The Trinidad field forms part of the Raton Mountain area which 
extends over into New Mexico. It is divided into the Trinidad 
district to the south and Walsenburg district to the northeast. The 
rocks are of Laramie age and the coal-bearing series varies in thick- 
ness from 1500 to 3000 feet. In this field there are as many as eight 

,_ - ,^' x ' v x '</;~\ v A "* r\. s ^ V s " / / \* *"" v -N X -" \ > ^ ^ ' s ./ i yS-N ^^/ x"^ / \ /^x ^ v ""-t ^ . N| _ f* . 


FIG. 132. Sills of igneous rock in "Laramie" formation and bed of natural coke, 
in Purgatory Valley, near Trinidad, Colo. (After G. B. Richardson, U. S. Geol. 

workable beds, varying from 2 to 14 feet in thickness in the lower coal- 
bearing group of beds, which is about 250 feet thick. These beds 
lie just above the Trinidad sandstone, and about 500 feet above the 
sandstone is the middle coal-bearing group carrying at least four 
seams, 2 to 4 feet thick. Lying about 1000 feet, on the average, 
above the Trinidad sandstone, is the upper coal-bearing group of 
shales carrying several seams, but these are unimportant so far as 


The coal from the Trinidad field is bituminous, that from the 
northern part being non-coking while that from the southern makes 
an excellent coke. An interesting occurrence in the Walsenburg dis- 
trict is the niggerhead coal described on page 235. The coal in some 
of the seams adjacent to igneous rocks forms peculiar spherical struc- 
tures known locally as " niggerheads " and consisting of quite high- 
grade coal. Such bodies have been found in a few cases in other 
fields where igneous rocks have intruded the coal seams. In some 
places considerable natural coke, or carbonite, has been formed by 
igneous rocks in the Trinidad field. The structure of this region 
varies from places where the beds are practically flat and undis- 
turbed to others where they are highly folded, faulted and intruded 
with igneous rocks. 

The Canon City field is a small one containing bituminous coal 
in the Laramie formation. The rocks vary from flat-lying to 
steeply dipping. 

The South Platte field includes the counties around Denver and 
contains subbituminous coal of Laramie age. The beds are com- 
paratively flat except where the strata are more closely folded near 
the mountains along the western border. The beds are fairly thick 
in parts of the field and there are four of them in most places. The 
coal is not of high grade and it is used chiefly for domestic and steam 

The North Park field is reported to carry very thick coals of bitu- 
minous rank, some seams as high as 30 feet in thickness, but little 
mining is done. No mining is now carried on in the South Park 
field although some mines were operated during the last century. 

The Yampa field occupies a large synclinal basin with several 
minor anticlines and synclines running nearly parallel across it. The 
strata are in a few places greatly disturbed by faults, but as a rule 
the faults are of little importance. Most of the basin is not badly 
folded. The coal-bearing series is the Mesaverde of the Montana 
series of Upper Cretaceous. This series is about 3500 feet thick 
and it is overlain by approximately 2000 feet of Lewis and Laramie 
strata, the Laramie carrying thin beds of coal. The thickness of 
the seams varies up to about 12 feet. In the Anthracite Range, 
especially around Pilot Knob, there is some anthracite and natu- 
ral coke produced by action of the igneous rocks which sometimes affect 

UTAH 391 

the coal for a distance of 50 feet or more. The coals in this field 
vary from subbituminous to anthracite. 

In the Danforth Hills and Grand Hogback fields, which represent 
part of the Uinta basin region, there is one coal-bearing horizon, 
the Mesaverde, and this is a distinct ledge-making formation be- 
cause of the sandstone which it contains. The structure of this 
region is simple as there are broad basins with minor folds, and 
faults are not numerous. There are as many as seven seams varying 
in thickness from 4 to 48 feet, making an aggregate thickness of 
coal of about 108 feet. Some of these seams are separated by over 
1000 feet of intervening strata. The mines through this region are 
subject to much trouble with explosive gas and spontaneous com- 
bustion of the coal. 

In the Crested Butte district of the Uinta Basin region consider- 
able anthracite has been formed by igneous activity and both bitu- 
minous coal and anthracite occur in this field. 

The Durango field, lying in the southern part of the state, extends 
over into New Mexico in the San Juan River region and of the 73,900 
square miles in this field only 1900 lie in Colorado. The coals in 
this field vary from subbituminous to bituminous. Their geological 
age is Upper Cretaceous, Dakota, Montana and Laramie. The 
Mesaverde formation of the Montana carries the best coals, the 
seams averaging around 5 or 6 feet in thickness. The Dakota coals 
are not of much inportance, and while the seams in the Laramie are 
very thick one reported to be as much as 80 feet the coal is 
of an inferior quality to that from the Mesaverde formation. The 
coal from several localities in the latter formation makes good coke. 
The structure of the basin is comparatively simple except around 
Gallup and in the southern end of the basin where the rocks have 
been highly disturbed. 

Utah. 1 The Uinta Basin region contains the largest area of coal 
lands in the state and it extends across the Colorado boundary from 
the Crested Butte district. The beds are deeply covered, going well 
below 3000 feet in the centre of this basin, and probably out of reach 
of mining operations. The coals are bituminous and coking. Prac- 
tically all the coal mined in the state comes from the vicinity of 

1 U. S. Geol. Survey, 22nd Annual Rept., Pt. Ill, p. 453. Also, Bulls. 316, 341, 415 
and 47 1. 








Sunnyside, Castlegate, Winterquarters and Clear 
Creek. There are about 20 seams in this dis- 
trict, with a maximum individual thickness of 
about 20 feet. The seams occur in the base of 
the Mesaverde (Montana) of the Upper Creta- 
ceous. In the Coalville field, which is a small 
one, two seams running about 7 to 14 feet in 
thickness are mined. The coal is in the Colorado 

The other field is the Colob Plateau field which 
carries a seam in the Colorado series from i to 
10 feet thick. The coal varies from bituminous 
to semianthracite and impure anthracite. Be- 
cause of the closely folded nature of some of 
the strata much of the coal is of poor quality. 
In Kane County cannel occurs, and a little an- 
thracite is found in Iron County. 

Wyoming. 1 Wyoming probably contains the 
second largest resources in coal of any state in 
the Union, North Dakota coming first. The 
coals of Wyoming are, however, of higher grade 
than those in North Dakota since the coal in the 
latter state is all lignite and that in the former 
is not below subbituminous, while a considerable 
amount of it is bituminous in rank. 

The following regions are recognized: Black 
Hills and Powder River regions of the Great 
Plains province; the Bighorn Basin, Wind River 
Basin, Green River Basin, Hams Fork region, 
and the Hanna field, all of the Rocky Mountain 
province. Of these areas the Powder River 
region is the largest. It lies between the Bighorn 
Mountains and Black Hills and runs from the 
Platte River to the Montana boundary. It 
represents the extension of the Fort Union 
region of North Dakota. About 11,000 square 

1 U. S. Geol. Survey, 22nd Annual Rept., Pt. Ill, p. 439. 
Also, Bulls. 225, 260, 285, 316, 341, 381, 47i and 531, and 
Prof. Paper 56. 


miles are underlain with coal beds more than 3 feet thick. The rocks of 
the field are of Fort Union (Eocene) age and they consist of a lower mem- 
ber of 2500 to 2800 feet of dull-drab, bluish and brown shales and sand- 
stone interbedded with many coal seams. The upper member is sub- 
divided into the Tongue River, Intermediate and Ulm coal-bearing 
groups. The sandy beds are in many places only slightly consoli- 
dated. In the Tongue group which is about 800 feet thick there are 
at least seven seams ranging from 5 to 32 feet in thickness. The 
Ulm group is 900 to 1150 feet thick and there is a distinct horizon- 
marker in the lower part of the group in the form of a shell bed which 
in some places is directly overlain by a coal seam and in other places 
separated from it by 30 to 40 feet of sand. There are two workable 
beds in this group, the Arvade, 5 to 10 feet thick, and the Felix, 
6 to 30 feet thick. The Ulm group contains the Lower Ulm or Healy 
bed, 10 to 1 5 feet thick. The coal is all lignite and is used for domestic 
purposes, steam, and producer gas. The structure of the basin is 
very simple and the beds lie almost horizontal. 

The main mining centers of the state are in Uinta and Sweet- 
water counties. These areas furnish medium-grade bituminous coal. 
Subbituminous coal is mined in Sweetwater, Carbon, Sheridan, Con- 
verse, and Bighorn counties. 

The coals of Wyoming vary in age from Lower Cretaceous, of the 
Kootenay series in the Black Hills region, through the Mesaverde 
formation in the Montana series of the Upper Cretaceous, to the 
Fort Union of the Eocene. The older coals are of much higher grade, 
as a rule. At Cambria a bituminous coal is mined from the Lower 
Cretaceous rocks. In the Bighorn, Wind River, Hams Fork, and 
Green River regions the coals are of Upper Cretaceous (Montana 
and Laramie) and Eocene age. They vary from lignite through 
subbituminous to bituminous and are non-coking. They are used 
for domestic purposes, steaming and producer gas. 

North and South Dakota. 1 North Dakota probably has the 
largest reserve of coal of any state in the Union. The coal of the 
Dakotas is, however, all lignite. It is estimated that nearly 35,000 
square miles in North Dakota and 11,000 in South Dakota are un- 
derlain with coal-bearing beds and that North Dakota contains 633,- 

1 U. S. Geol. Survey, 22nd Annual Kept., Pt. Ill, p. 456. Also, Bulls. 285, 341, 381, 
471, and 531. 



329,800,000 tons of lignite. The coal is almost entirely in the Fort 
Union beds of the Eocene. The beds run as high as 30 feet in thick- 
ness and many of them are continuous for many miles. The Lance 
formation contains a little coal, but in most places the seams are too 
thin to work. The latter formation does not appear in the northern 
part of North Dakota but is extensively distributed around the border 

FIG. 134. Lignite seam, Williston, N. Dak. (After F. Wilder, photo. Reprinted by 
permission from Ries' Economic Geology, published by John Wiley & Sons, Inc.) 

between the Dakotas. The lignite is mined only along the main 
lines of the railroad's and chiefly for domestic purposes, steaming 
and producer gas. 

Montana. 1 This state contains extensive coal lands. The Fort 
Union Basin of the Dakotas extends into this state and contains 
over half as much lignite as North Dakota in nearly the same 
area. The other areas in Montana are the Bull Mountain field, 
the Assinniboine region, the Judith Basin region, the Flathead River 
field, the Mountain fields, the Yellowstone region and the Red Lodge- 
Bridger field. The Bull Mountain field, which is being developed, 
contains rocks of Fort Union and Laramie age or slightly older. The 

1 U. S. Geol. Survey, 22nd Annual Rept., Pt. Ill, p. 460. Also, Bulls. 316, 341, 356 
(Great Falls Field) 381, 531, 647 (Bull Mountain), University of Montana, Bull. 4, by Rowe. 


structure of the synclinal basin is simple. The coal varies from 
lignite in the Tertiary rocks to subbituminous and low-grade bitu- 
minous in the older formations. There are 20 seams over 2 feet 
thick and the " Mammoth " seam runs from 8 to 15 feet. 

The field which is most largely worked is the Red Lodge-Bridger 
field where coal has been mined for a good many years. There are 
seven seams running from 3 to 12 feet in thickness. The coal is 
high-grade subbituminous, fairly high in moisture, and it soon breaks 
down or " slacks " when exposed to the air. 

The Great Falls field in Cascade County, forming part of the 
Judith Basin region, produces considerable coal at Sand Coulee, 
Stockett and Belt. The coal is bituminous and dirty and it occurs 
in the Kootenay series of the Lower Cretaceous. The seams in some 
places reach nearly 15 feet in thickness. The North Fork Flathead 
River field is considered to contain unimportant bituminous and sub- 
bituminous coals of Jurassic age as well as the Cretaceous coals. The 
Assinniboine region is represented by the Milk River Field. The 
strata belong chiefly to the Montana group and are buried under 
glacial drift. All the coal in this field occurs in the Judith River 
formation of the Montana series except a little lignite in the Fort 
Union. The coal beds are, as a rule, lenticular and they run up to 
9 feet in thickness. Faults and folds are common in this region. 
The coal is of fairly good subbituminous grade. In many areas in 
this state, as in the other western states, the coal beds have been 
burned, leaving slag and reddened rock. This is partly due to the 
ease with which the coal ignites. 

The Pacific Coast Province 1 

California. 2 The coal fields of California are very limited and 
there is no prospect of her ever becoming a great coal-mining state. 
The fields are also widely scattered, the main ones being as follows: 
lone Mine in Amador County, Mount Diablo of Contra Costa Coun- 
ty, Coral Hollow of Alamada County, Priest Valley and Trafton of 
San Benito County, and Stone Canyon of Monterey County. The 

1 Smith, G. O., The coal fields of the Pacific Coast. U. S. Geol. Survey, 22nd Annual 
Kept., Pt. Ill, p. 473, 1902. 

2 Campbell, M. R., Coal of Stone Canyon, Monterey County. U. S. Geol. Survey, 
Bull. 316, p. 435, 1907- 


coal in Stone Canyon is of bituminous rank with a composition 
approaching cannel. A bed 10 to 14 feet thick has been exploited. 

The coals in the southern part of the state are bituminous and non- 
coking; those in the northern part are lignite, and those lying be- 
tween these fields are subbituminous. Practically the only coal pro- 
duced in the state, in some years at least, is lignite, which comes 
chiefly from the lone Mine, Amador County. The coal is of Eocene 
and Miocene age. The coal industry of all the western states where 
fuel oil is found in abundance is vitally affected by that commodity 
and will continue to be so affected as long as oil is abundant. 

Oregon. 1 Oregon has very little coal and comparatively little 
mining has been done. In the Coos Bay field, in the southern part of 
the state, mining has been carried on and coal is shipped from the 
Beaver Hill and Newport mines. The coal is subbituminous in 
grade. The coal in this field is difficult to mine and much of it lies 
below sea level. In the Eden Ridge field, also of Coos County, 
the coal is bituminous and coking as the strata have suffered more 
squeezing than in other parts of the county. The coal is shaly and 
dirty. A number of other small fields in the state contain thin or 
impure coal seams, but there is no development in these fields. The 
Oregon coals are used for domestic and steaming purposes. 

Washington. 2 There are five coal fields, confined to the western 
and central parts of this state. They are the North Puget Sound in 
Skagit and Whatcom counties, South Puget Sound in Pierce and King 
counties, Puget Sound basin lying just east of Seattle, the Roslyn 
field in Kittitas County on the east flank of the Cascade Mountains, 
and the Southwestern field in Lewis and Cowlitz counties. 

Washington is the only state in the Pacific province containing 
coking coals. These coals are in the North and South Puget Sound 
fields. The coals of this state range from subbituminous rank to 
anthracite. Coal has been mined in Washington since about 1860, 
the first mined being lignite, but spontaneous combustion closed oper- 
ations. The bituminous coals are used chiefly on the ocean-going 
ships and the subbituminous for domestic purposes. 

1 Diller, J. S., Coos Bay Coal Field. U. S. Geol. Survey, igth Annual Rept., p. 309, 

2 Washington Geol. Survey, Vol. II and Bull. 3. Also U. S. Geol. Survey, Bulls. 531 
and 541. 


The coals in King County lie under a heavy mantle of glacial 
drift. They are of Eocene age, like the other coals of the state, 
but owing to the compression which they have suffered in mountain 
building they have been changed from lignite to subbituminous and 
bituminous rank. In this county the beds have been highly folded 
and broken so that in parts of the field mining is difficult. The 
ash in the coal is high. Pierce County carries the best coals in Wash- 
ington so far as known, as coals are bituminous, semibituminous 
and even anthracite where the rocks have been highly squeezed, 
broken and intruded by igneous rocks. The bituminous coals will 

In the Roslyn field the beds lie regularly, and it is easy to mine 
the Roslyn seam, running between 2 and 3 feet thick. There is 
also another seam known as the " Big " seam which is full of part- 
ings and very dirty. It reaches nearly 20 feet in thickness. The 
coal is bituminous. 

The Puget Sound field is characterized by the tremendous number 
of coal seams which the formations contain. In one place there 
are about 125 seams, the majority of which are unworkable. This 
indicates a great number of changes, probably rapid ones, in the 
climatic or topographic conditions, or both, during the formation 
of these beds. 

Alaska 1 

The coal fields of Alaska are but partially known, as so little ge- 
ological work has been done on this tremendous area. More or 
less work has been done on certain regions and fields, and a rough 
estimate of the character of the coals and their resources may be 
given. The accompanying map and the following table show the 
geographical and geological distribution of the coals, so far as known. 

The following fields or areas are recognized: Bering River, Matan- 
uska, Cook Inlet, Alaska Peninsula, Nenana, Northern Alaska and 
many other less-known fields and areas. 

1 Brooks, Alfred H., and Martin, George C., Coal resources of the world. Inter- 
national Geological Congress, Vol. II, 1913. U. S. Geol. Survey, 22nd Annual Rept., 
Pt. Ill, p. 515, 1902; and Bulls. 284 and 314. 





Character of coal 

Principal distribution 




Yukon basin and 

other parts of Al- 




Yakutat Bay and 

other localities. 


Miocene or Eocene 

Anthracitic and bi- 

tuminous. Chiefly 

Bering River. 


lignitic, also some 
bituminous and sub- 

Throughout Alaska, 
notably on Cook In- 


let, in Matanuska 

Valley and Yukon 



Upper Cretaceous 

Subbituminous and 

Alaska peninsula, Yu- 


kon and Colville 



Lignitic, subbitumi- 

Near Cape Lisburne 

nous and bituminous 

and in Matanuska 





Yukon River. 



Twenty miles south 

of Cape Lisburne. 

' Table by A. H. Brooks and G. C. Martin, Coal Resources of the World. 

The Bering River is an important field lying 25 miles northeast 
of Controller Bay. The coal beds run from 3 to 25 feet in thickness, 
in the Kustaka formation which is about 2000 feet thick and of 
Miocene age. The field is greatly folded and faulted and in many 
places, especially in the eastern and western ends of the field, the 
coal beds are so badly crushed as to ruin the coal. The coals vary 
from anthracite, averaging about 81 per cent, to semibituminous 
with 72 per cent fixed carbon. Some of the bituminous coal will 

Another important field is the Matanuska, lying along the valley 
of the Matanuska River, about 25 miles from Knik-Arm. The 
measures are deeply covered with gravel in parts of the field. The 
rocks are of Eocene age and in the eastern part of the field highly 
folded and faulted. It is probable that the field will cover about 100 
square miles. The seams range from 3 to 32 feet in thickness. In 
the west end of the field the coal is lignite and in passing eastward 
it changes to bituminous coal and anthracite. Some of the coal is 
high in ash but the average content is favorable. 

In the Cook Inlet field lignite occurs in the Kenai formation of 



the Eocene. There are fifteen or more seams running from 3 to 7 
feet in thickness. On the Alaska Peninsula lignite occurs in the 
Kenai formation, but better coal is found in the Chignik formation of 
the Upper Cretaceous around Chignik Bay and Herendeen Bay. In 
this formation the coal is subbituminous and bituminous of fair 
quality, but little is known of the extent of the seams. 






FIG. 135. Alaska, showing distribution of coal deposits. (After A. H. Brooks. 
Reproduced from "Coal Resources of the World." Published by the 1 2th Interna- 
tional Geological Congress, Toronto, Canada.) 

In Northern Alaska there are three coal-bearing formations: one 
is Carboniferous, supposedly Mississippian, containing high-grade 
bituminous coals with low ash content; another is Jurassic with a 
large number of beds of subbituminous coal running as high as 1 2 
feet in thickness; and the third is Tertiary, carrying lignite. The 
older beds are considerably folded and faulted but those in the Ter- 
tiary are quite flat. 

In the Nenana field there are a number of beds running from 3 
to 30 feet in thickness. They occur in the Eocene, and the coal 
is mostly lignite. 



The table given below is a summary of the estimates of Brooks 
and Martin for the coal fields of Alaska, in so far as information is 



Area in 
square miles 

Estimated amount of coal in metric tons 
(i metric ton = 1.1023 short tons) 


coal fields 

<u % 








Pacific Coast.. 
Interior Region 
Arctic Slope... 




















* This estimate is based on seams 3 feet or more in thickness and lying less than 3000 feet deep for high- 
grade coal (anthracite to semibituminous), and less than 2000 feet deep for lower grades (bituminous to lignite). 


The coals of Mexico are but little developed. Only one state 
produces any quantity and submits regular reports of production. 
There are several regions, according to R. T. Hill 1 , which contain coal, 
and the coals are of three geological ages: Tertiary, Upper Creta- 
ceous and Triassic. The Tertiary lignites represent a continuation 
of the deposits of that age in the United States, but so far as known 
they are of no importance in Mexico. The Triassic coals occur in 
two districts, the Mixteca district in the south where there are a 
large number of seams of workable thickness but too high in ash 
to be valuable, and the Santa Clara field where the coal is semi- 
anthracite and anthracite because it has suffered much from com- 
pression and igneous intrusions. Natural coke and graphite in suffi- 
cient quantity to be mined have resulted from these disturbances. 
The seams run 4, 8 and 10 feet in thickness. 

The producing fields are all Montana (Upper Cretaceous), in age 
and they occur in Coahuila. They are known as the Eagle Pass, 
Sabinas and Barroteran fields. There is a small production from 

1 Hill, Robert T., The coal fields of Mexico. Coal Resources of the World, Vol. II, 
P- 553- 


the Eagle Pass field, which is situated in the vicinity of Eagle Pass, 
Texas and Porfirio Diaz in Mexico. This field is a continuation of 
the field of the same name in Texas. In the Sabinas field there 
are two beds 4 to 6 feet thick, of good, coking, bituminous coal. 
A clay seam between the beds causes some difficulty in working. 
The Barroteran field is a continuation of the Sabinas field along 
the north side of the Santa Rosa Mountains. In this field the 
seam is 8 feet thick with 14 inches of clay and shale and it is regular 
and persistent. The coal is bituminous and coking. A number of 
American companies are working mines in Mexico in the Sabinas 
and Barroteran fields and a considerable number of coke ovens are 
in operation. 


The only countries in Central America reporting any coal re- 
sources are Honduras and Panama. The former country reports 
5,000,000 metric tons, all lignite except about 1,000,000 tons of 
bituminous coal in the district of El Paraiso. The beds run from i 
foot 6 inches to 4 feet in thickness, but they have never been mined. 
Panama has a little lignite in the province of Bocas del Toro on the 
coast and in the interior. That on the coast is largely submarine 
and under porous strata while that in the interior is too high in sul- 
phur to be valuable. It is interesting to note that the sulphur is 
said to increase as the volcano Chiriqui is approached. 


Cuba has no coal and the only resources reported for the West 
Indies are found in Trinidad. The coal has not been exploited, 
but there are two districts in which it is known to occur. These 
are near Manzanilla and Sangre Grande on the east coast. In the 
former area the coal is lignite, the seams thin, not exceeding 4 feet, 
and the deposit is poor in quality. In the Cunapo district, near 
Sangre Grande prospects are a little better. There are two seams 
of subbituminous coal, one of which is 5 feet thick and can be traced 
fcr a considerable distance, but they lie on an irregular bottom and 
are probably not of much importance. 

1 Coal Resources of the World. 


South America 

South America is apparently deficient in good coal deposits, and 
very little definite information has been collected on her coal re- 
sources as the best available data place her actual reserve at 2,089,- 
000,000 metric tons and her probable reserve at 32,010,000,000 tons. 
The geological ages of the coals are Permo-Carboniferous, Creta- 
ceous and Tertiary, (Plate XV). The following countries are reported 
to carry at least some coal: Colombia, Venezuela, Ecuador, Peru, 
Bolivia, Argentina, Brazil and Chile. The coals vary from anthra- 
cite to lignite in character. 

Colombia. 1 Coal is found in several departments of the country, 
but worked in few. Mines are operated in the vicinity of Bogota in 
the Departments of Cundinamarca and in Boyaca and to a lesser ex- 
tent in the Department of Antioquia. The coal is bituminous and 
most of it is used locally for railroads, and for domestic and metal- 
lurgical purposes. According to Gamba the largest fields are in 
the districts of Cauca and Valle where there are three seams of medi- 
um-grade bituminous coal, with an aggregate thickness of 6 feet 
6 inches and estimated resources of 20,000,000,000 metric tons in 
seams over i foot thick and less than 3000 feet deep. Little or no 
mining has yet been done in these departments. The Departments 
of Cundinamarca and Boyaca have the same number of seams with 
the same aggregate thickness of coal and resources of 6,000,000,000 
metric tons. The same number of seams with the same aggregate 
thickness contain 1,000,000,000 metric tons in Antioquia. No es- 
timate of the resources of the Department of Narino is available, 
but they are believed to be very large as there is supposed to be a 
large unstudied field in the vicinity of the Putumayo River. These 
figures make a total estimate of twenty-seven billion tons in the 
best-known fields. Miller and Singewald 2 quote Ospma as saying 
that in the western coal area there are as many as six seams, one 
as much as Q| feet thick. Most of the coal is a hard compact lignite 
except where it has been subject to considerable metamorphism. Ap- 
parently this coal is a subbituminous coal, as the term is used in the 
United States. 

1 Gamba, F. P., Coal resources of Colombia. Coal Resources of the World, 1913. 

2 Miller, B. L., and Singewald, J. T. Jr., Mineral deposits of South America, p. 357, 




Valparaiso f^ ;Mendoza 

Santiao / Buenos Ai 

Cuiriuina ni / San Rafael 



200 400 

800 Statute Miles to 1 Inch 

Capitals -.' Other Cities 

Mesozoic Coals 
Paleozoic Coals 


from 60 


PLATE XV. Coal fields of South America. (Reproduced from "Coal Resources of 
the World," published by the i2th International Geological Congress, Toronto, 



F. Lynwood Garrison 1 mentions some peculiar coal from Ca- 
cagual on the Taraza River. There are several seams varying from 
a few inches to 5 feet. The coal is compact and glassy and it re- 
sembles cannel. It possesses a distinctly laminated structure and 
it can be lighted with a match. It burns with a glow like punk and 
not with a long flame as cannel does. This coal has the pe- 
culiarity of being overlain by rich gold-bearing gravels. Analyses 
show its composition to be as follows: Moisture, 13.6 to 15.36; 
Volatile matter, 38.10 to 47.41; Fixed carbon, 44.40 to 32.67; Ash, 
3.80 to 4.56 and Sulphur, 0.54 per cent. Garrison also quotes anal- 
yses by Percy which show coals from Colombia with oxygen and 
nitrogen combined varying from 12.06 to 22.12 per cent. 

The better coals of Colombia are of Upper Cretaceous age. There 
is considerable lignite of Tertiary age, but little is known regard- 
ing it. 

Venezuela. According to Miller and Singewald 2 coal is widely 
distributed in Venezuela north of the Apure and Orinoco rivers and 
the Llanos. The age is doubtful, probably Cretaceous and Tertiary. 
All the coals are lignites or subbituminous except for one area of 
semianthracite. There are numerous seams, the thickest reported 
running up to about 10 feet. Some of the areas in the Balcelonia 
district have been highly folded. 

Ecuador, Peru, Bolivia. Ecuador does not report any operating 
coal mines but this country has a little coal of good quality, varying 
from lignite to anthracite. The places so far mentioned are at 
Cojitambo, Mangan and Biblian in the province of Cafiar. Anthra- 
cite occurs at San Antonio de Pomasqui, north of Quito. It is of 
Tertiary age. 

Peru has rather extensive coal-bearing areas running through the 
Andes Mountains. The quality of the coal varies from low-grade 
bituminous to anthracite. Her resources have been placed at ap- 
proximately two billion tons, of which seven hundred million are 
anthracite and semianthracite. The age of the coal is Cretaceous 
or Tertiary. According to Borlkjof 3 , anthracite containing from 84 
to 87 per cent fixed carbon, occurs in Cajabamba province, and in 

1 Garrison, F. Lynwood, Mining and Scientific Press. Vol. 98, p. 219, 1909. 

2 Op. cit., p. 542. 

3 Borlkjof, J. Camilo B, The coal deposits of Peru. Eng. and Min. Jour., Vol. 88, 
p. 983, 1919. 


Chota, about 140 miles from the Pacific, there are four anthracite 
beds from 13 to 65 feet thick. There is estimated to be 700,000,000 
tons of coal in this area. There is a large amount of coal in the Depart- 
ment of Lima and in the Province of Chamcay, at Checras. In the 
provinces of Parquin and Quiruragra there is a bed which reaches a 
thickness of 13 feet and the resources are estimated at 720,000,000 
tons. This is the largest and most important field in Peru. It is situ- 
ated near the Cerro de Pasco copper camp and coal is being mined by 
this company. A number of coal mines are worked in Peru, some 
of them being highly gaseous. It seems probable that Peru will be 
found to contain much larger reserves than those mentioned above 
and that she will be quite an important producer of high-grade coal 
in the future. 

Practically nothing is known regarding the coal deposits in Bolivia 
beyond the fact that they seem to be of small importance and to 
be Permo-Carboniferous in age. A few outcrops of impure seams 
occur on Lake Titicaca but little work has been done on them. The 
inhabitants of that country, most of which lies at an elevation of 
over 8000 feet above sea level, suffer a great deal from cold owing 
to the great altitude and the scarcity of fuel. 

Brazil. A number of coal mines have been operated from time 
to time in Brazil, but so far very little coal sufficiently free from 
slate and low enough in sulphur and ash to make a good industry 
has been found. The extensive report of I. C. White 1 shows that 
only by laborious picking, washing and briquetting can a satisfactory 
fuel be obtained. The most favorable localities are in the south 
near the Uruguay border. The coal occurs in the Rio Bonita beds 
of the lower Permian which are correlated with the lower Karroo 
of South Africa. 

Argentine Republic. No coal deposits of importance have been 
found in this great country. Thin seams are found in a number 
of places, as the Permo-Carboniferous rocks outcrop along the eastern 
border of the Andes and a seam has in recent years been exploited 
at Salagasta in the province of Mendoza. It is reported that a 
seam 10 to 12 feet thick was struck at a depth of about 2000 feet. 
The coal is fairly low-grade bituminous. In Mendoza there are 

1 Final Report of I. C. White,Chief of the Brazilian Coal Commission, Rio Janiero, 1908. 


some beds of Albert! te which somewhat resembles coal but is a solid 
derived from petroleum. 

Chile. 1 There are two provinces in Chile which contain coal 
fields of importance and in which coal is being worked. These 
are Arauco and Concepcion. In the former the places where mines 
are worked are Maquehua, Arauco, Pilpilco Cuyinco, and Lebu 
and in the latter Penco, Lirquen, Coronel and Lota. The seams 
worked vary in thickness from 0.70 meter to 1.85 meters. At Coro- 
nel eight seams are mined and at Arauco six seams. In the Penco 
district the coal is mined to a considerable extent beneath the sea. 
The strata are little folded as a rule but normal faults are fairly 
numerous. The age of most of the Chilian coal is Tertiary, probably 
Oligocene or Miocene, and it is of bituminous rank; much of it being 
of inferior quality. The coal resources of Chile are estimated at 
2,082,000,000 metric tons. 

1 Michado, Miguel R., Le Charbon du Chili et sa Distribution Geographique. Coal 
Resources of the World, Vol. II, p. 581. 



A A Ah ^S y t' v p Be /[ r J ^ ^\ , 

S^wl &{t*>, ( X 

Sary.* ^tr^tJ "X-v 

PLATE XVI. The Coal fields of western Europe. (Reproduced from "Coa 


:es of the World." Published by the i2th International Geological Congress, 




Europe 1 

Europe was the mother of the coal-mining industry, which still 
flourishes on that continent, although in some respects America 
has surpassed her in the development of mining operations. Al- 
though her resources are small compared with those of America, 
Europe is well supplied with high-grade coal and she is more careful 
to utilize a greater proportion of it than we have been in America. 

The table given below shows the actual and estimated resources 
of coal in the various countries of the continent and the accompany- 
ing maps picture the area and distribution of the coal fields (Plates 
XVI and XVII.) 

This table indicates that the German Empire controls by far the 
largest coal resources of the countries of Europe. Great Britain 
comes second, Russia in Europe third, Austria fourth and France 
fifth. Italy has almost no coal in comparison with her population. 
Russia has a large estimated tonnage of anthracite almost twice 
that of the United States and second only to China. The figures 
given for Roumania do not properly indicate her probable reserves. 
The annual production of European countries is given on page 335. 

Great Britain. 2 Great Britain has long been one of the leading 
coal-producing states of the world and she is surpassed in production 

1 For comprehensive descriptions of the coal deposits of Europe see Atlas general des 
Houilleres (Text and Atlas) by E. Gruner et G. Bousquet, Comite Central des Houil- 
ISres de France, Paris, 1911. Also Coal Resources of the World, International Geological 
Congress. Vol. I. 

2 For comprehensive reports see the Coal Resources of Great Britain by A. Strahan, 
Coal Resources of the World. Also various Memoirs of the Geological Survey of England 
and Wales on individual fields. Analyses of British Coals and Coke and the Character- 
istics of the Chief Coal Seams worked in the British Isles, by Greenwell and Elsden. 
Colliery Guardian, London, 1907. Reports of the Royal Commission on Coal Supplies, 



(i metric ton = 1.1023 short tons) 

Actual Reserve 

Probable Reserve 


Class of Coal 

Class of Coal 







cite in- 
some dry 

nous coals 

coals and 

Great Britain and Ireland: 


B 79,869 
B 31,402 
B 18,876 
B 8 


B 46,030 
B 195 
B 1,685 
B in 


Scotland . 






B 2,016 
C 2,016 
B 358 
C 386 





B 296 
C 296 
B 567 
C 431 





Other fields 

North of Ardennes Massif. . 

Armorican Massif 





B 2,600 
C 670 
B 3 

B 2 

B 233 
C 114 






B 6,260 
C 420 
B 13 
C 630 
B 24 
B 1,079 
C 632 



Central Massif 


Lignite areas 











C 30 

B 7,oco 
B 1,000 
B 3-ooc 







Denmark (Faroes) 










Actual Reserve 

Probable Reserve 

Class of Coal 

Class of Coal 








cite in- 
some dry 

nous coals 

coals and 

Saar district 

B 718 
B 10,325 
B 225 
B 10,458 
B 247 




B 2,226 
B 155,662 



L Silesia 

U Silesia 


Left of the Rhine 

Other districts 
North German States 


B 4 
B 2,970 

B 2 

B 106 
B 57 





B 109 
B 38,012 

B 43 
B 8 
B 2,525 

B 18,014 

B 253 




Bosnia and Herzegovina 


Dombrova (Poland) . 

Donetz . . 

S. W. Russia 

W. Urals 


B 57 






Total for Europe 








* From the Coal Resources of the World. Estimate based on seams more than I foot thick and less 
than 4000 feet deep and on seams more than 2 feet thick and between 4000 and 6000 feet in depth. For 
detailed description of the classes of coal, see Classification of Coals, Chapter V. 



England and Wales 



























Russia m Europe 









Eocene . . 



Tertiary undifferen- 









Upper Cretaceous 








Lower Cretaceous 





Triassic (Rhaetic) 






Upper Carboniferous 
(Pennsylvanian) . . . 


































Upper Devonian 



A, Anthracite and semianthracite; S, Semibituminous; B, Bituminous; B, Subbituminous; L, 
Lignite. Capital letters indicate important deposits and lower case relatively unimportant deposits of 
the same type. 


only by the United States. She has given us many of our mining 
methods and many of the principles involved in our mining apparatus 
as well as a wonderfully efficient and hardy class of mining men. 
Her coal supplies have been one of the very important factors in the 
attainment of her high position in the industrial and commercial 
world, and she has exported coal lavishly to those countries less 
favored by nature in coal deposits than she. The tables given 
above show that she is exhausting her supplies at a much greater 
rate in proportion to her resources than any of the other great com- 
mercial countries with the exception of France. The conclusion of 
the Royal Commission on Coal Supplies in iSyi 1 was that there 
was enough coal in sight to continue the existing rate of production 
for 1273 years, but that, considering the probable rate of increase 
in production, there was sufficient coal to last between 325 and 433 
years. The latter figure would be much too high if the rate of in- 
crease should continue a few years longer. 

Several very thorough reports have been prepared on the coal 
resources of the islands and the available supplies are very well 
known. The fields are usually divided into two groups, known as 
(a) the Visible and Proved fields; and (b) The Concealed and as 
yet unworked fields. The first group includes those fields where 
the Coal Measures are not deeply buried by later formations, and 
the second group those fields where they are deeply covered but where 
they are known to exist in synclinal basins. In computing the re- 
sources it was assumed that a thickness of i foot of coal represents 
960,000 tons per square mile, or 1500 statute tons per acre. The 
various fields with the number and thicknesses of the seams, the 
character of the coal and the resources of each field are set forth 
in the following table compiled by Strahan. 

1 Reports of the Royal Commission on Coal Supplies, 1871 and 1905. 


O O 

g O 

o o 

I 58 

cC | to 

I M 







S 8 



o S 

s ?8S S a 




PQ PQ pq PQ pq PQPQ 

pq < pq'pq pq w pq pq pq pq pq pq pq pq pq pq pqpq 

pq <j <j pq pq pq pq pc ipq pq pq pq pq pq pq pq pq pqpq 



1 4 4| 

ia^ * BS 

5555 .8.8.2 5 5 i 33 



In addition to the totals given above there are calculated to be 
6,207,847,000 metric tons of actual reserve in seams running over 2 
feet in thickness and lying at depths between 4000 and 6000 feet. 

(Including seams of i foot or over to a depth of 4000 feet.) 


Coal Seams 

Actual Reserve 
(Calculations based on actual 
thickness and extent) 




JClass of Coal 

Metric tons 
(Metric ton = 
1.1023 short tons) 

Clackmannan and Perth 




20 to 50 feet 
100 to 140 ' ' 

Unknown pos- 
sible reserve 


128 i 



B 2 ,B 3 
B 2 ,B 3 
B lt B 2 , B 3 


B. B 3 
A lt A 2 , BI, B 2 , B 3 
B 2 
A lf A 2 , BI, B 2 , B 3 
B 2 
A., BI, B 2 
B 2 





Under the Firth of Forth 

Edinburgh, Haddington and 





Argyllshire (Marvern) . . . . 



1 For description of classes of coal see under Classification of Coals, Chapter V. 

In addition to the actual tonnage reserve for Scotland mentioned 
in the above table there are probable reserves of 1,685,000,000 metric 
tons in seams over 2 feet thick lying between 4000 and 6000 feet in 
depth in the Firth of Forth, and in the Fife and Kinross districts. 

The coals of Great Britain are all of the higher ranks, bituminous, 
semibituminous and anthracite. In England and Wales they all 
occur in the Coal Measures proper, or the Pennsylvanian as the 
term is used in the United States. In Scotland the Lower Carbon- 
iferous (Mississippian) carries good coal and there are thin workable 
seams in the Calciferous sandstone. The latter is a formation in 
the lower part of the Lower Carboniferous and should not be con- 
fused with part of the Devonian of America. 


In England and Wales the Millstone grit is well developed and in 
some places it is very thick, reaching about 5500 feet in thickness 
in Lancashire. As in America it consists of quartz conglomerate 
and micaceous, arkosic sandstone. It carries small seams of coal. 
In Scotland^it is in most places comparatively thin and it is a sand- 
stone known as " Moor rock. " This rock also carries thin coal 

The Coal Measures reach a maximum thickness of between 10,- 
ooo and 12,000 feet in Wales and in the midst of the series there 
is a sandstone and conglomerate known as the Pennant grit. It 
is in many places almost barren of coal but in others there are a 
number of good seams. In a few localities it carries pebbles of coal 
showing that vegetal matter had already formed coal which could 
be eroded when this formation was laid down. In many of the coal 
fields, fire clay or " seat earth " is found beneath the coal seams, 
leading early writers to consider that this was always an accom- 
paniment of coal seams. Iron ore, in form of the carbonate, often 
known as "black band, " occurs in a number of the fields. This 
ore owes its origin to the presence of abundant carbon dioxide de- 
rived from decaying vegetation in the waters when the iron was 
laid down. 

Cannel coal is abundant in some fields, and some of it carries 
numerous fish remains showing that the spores which formed the 
coal were laid down in ponds of open water where fish could live. 
A peculiar coal known as Torbanite, which is a boghead, has long 
been mined at Torbane Hill, Scotland. It is similar to an oil shale 
in the products derived from distillation but it is nevertheless a 
type of coal. Its status was once fixed by law in an important suit. 

Some fields are greatly faulted as, for example, the Cumberland 
field, and others are extensively intruded by basalt and other igneous 
rocks, especially some of the Scottish fields and the Coalbrook- 
dale and Dudley fields of England. Mining has been carried on 
in England to a great depth, in some places exceeding 3000 feet. 

South Wales. 1 -- This famous coal-field occurs in parts of Mon- 
mouth, Glamorgan, Brecknock and Carmarthen counties. It oc- 
cupies a syncline with steeply dipping strata on the southern limb. 

1 Strahan, A., and Pollard, W., Coals of South Wales with special reference to the 
origin and distribution of anthracite. Memoir Geol. Survey, England and Wales, 1915. 


The Coal Measures, which reach a thickness of nearly 12,000 feet, 
may be divided into three divisions: a lower consisting mainly of 
shales and containing the bulk of the coal seams; a middle series 
known as the Pennant series consistly chiefly of sandstone and coal- 
bearing only in the western part of the field; and an upper series 
consisting mainly of shales carrying coal seams. The anthracite 
occurs near the northwestern and western part of the field and the 
same seams occur as bituminous coal in the southern and eastern 
portions of the field with the well-known semibituminous, smoke- 
less steam coals lying between the two extremes, (Fig. 33). In 
one part of the field the anthracite reaches an undetermined depth. 
There is one condition which remains almost constant throughout 
the field and that is the higher fixed carbon of the coal in the deeper 
seams. In any section there is in almost every case a nearly uni- 
form increase in the fuel ratio with depth. This has not, however, 
been responsible for the origin of the anthracite. Strahan and Pol- 
lard concluded that they could find no satisfactory explanation for 
the occurrence of the anthracite in one part of the field, semibitu- 
minous in another part and bituminous in another, as there are no 
igneous intrusions, there is no particular difference in the character 
of the vegetation forming the coal in different parts of the field, 
and the depth of burial or the length of time since burial will not 
account for the changes. They also doubt that pressure could cause 
the difference, but the writer believes that this is the only satisfactory 
explanation. The relative proportions of the various varieties of 
coal have been placed as bituminous 30.42 per cent; semibituminous, 
or steam coal, 47.31 per cent; anthracite 22.27 P er cent. 

In Glamorganshire the number of seams varies from twelve at the 
eastern end with an aggregate of 42 feet of coal to about forty in 
the western part with 120 feet of coal. In Pembrokeshire the Pennant 
series is found throughout the field. The number of seams in the 
eastern part runs from eight with 21 feet of coal to eighteen with an 
aggregate of 33 feet in the western part. The strata are highly dis- 
turbed and the coal is all anthracite. 

It is believed that there is a large deposit of coal under Swansea 
and Carmarthen bays. A large fault with a throw of approximately 
3000 feet runs under Swansea Bay and cuts the coal field so as to 
duplicate the measures. 


Ireland. 1 There are several coal fields in Ireland, the largest 
being the Leinster field covering 95 square miles in Kilkenney, Carlow 
and Queen counties. The coals occur in the Coal Measures and the 
seams which are worked are quite thin, varying from i foot 8 inches, 
to 4 feet. The Ballycastle field, 4! square miles in area, in County 
Antrim, contains seams 4 to 6 feet thick in the Lower Carboniferous. 
Numerous intrusions of dolerite cut this field. The Tyrone field 
carries a number of seams in the Coal Measures running up to 9 
feet in thickness and the Gortnaskea seam is 6 feet thick with 22 
inches of cannel. Other fields are the Lough, Allen and the Tipper- 
ary, besides other very small and scattered areas. In very few 
places in Ireland have the Coal Measures been covered by later 
rocks, and tremendous areas of these rocks have been eroded from 
the island. 

France. 2 France is deficient in coal for her future need as a 
great manufacturing country, and during the Great War she was 
cut off almost entirely from her best coal fields, which lie in the 
northeast. The coal areas have been divided into five regions by 
M. Defline as follows: (i) North of Ardennes Massif; (2) Eastern 
area; (3) In Armorican Massif; (4) In Central Massif; (5) In Alps, 
Maures, Pyrenees and Corsica. 

The most important area is that of Valenciennes where the quality 
of the coal varies from anthracite to high volatile bituminous. The 
beds occur in the Westphalian series of the Coal Measures. There 
are a large number of seams, in the north basin as many as 69, but 
none are very thick, 2 meters being near the maximum. Parts of 
the Coal Measures have been faulted beneath the Silurian and Dev- 
onian formations and in the Pas-de-Calais basin the strata are ex- 
tensively faulted and folded, (Fig. 73). A considerable amount 
of coal lies more than 4000 feet from the surface. The Boulonnais 
basin which is a continuation of that of Valenciennes is concealed 
by Cretaceous and Jurassic strata and the coal has been reached by 
borings. This basin is very small. 

1 Cole, B. A. J., and Lyburn, E. St. John, The coal resources of Ireland. Coal Re- 
sources of the World, Vol. II, p. 629. 

2 Defline, M., Les ressources de la France en combustibles mineraux.' Coal Resources 
of the World, Vol. II, p. 649. Reports on individual coal fields in the publications of the 
Department of Public Works, Paris under the head of Etudes des Gttes Mineraux de la 


The basins in the east include Pont-a-Moussqn and Ronchamp. 
The former is a prolongation of the Saarbruck basin and the Coal 
Measures are completely concealed beneath Triassic and Permian 
rocks at a depth between 2000 and 3000 feet. The measures belong 
to the Stephanian and Wesphalian series and, judging from borings, 
there are from one to seven seams with a maximum aggregate of 
about 20 feet of coal, although the coal-bearing strata have not 
been penetrated. Ronchamp field is in the small basin overlain 
by Permian strata. The Coal Measures belong to the Stephanian. 
There are 3 to 6 meters of bituminous coal in three seams. 

FIG. 136. Coal mine near St. Etienne, France. (Photo by E. S. Moore.) 

The basins in the Armorican Massif include the Cotentin, Maine, 
Basse-Loire and Vendee. In the first field the coals are Stephan- 
ian and are of little importance since they are thin and of poor 
quality. The Maine field, in Brittany, contains coals of Dinantian 
or Lower Carboniferous age. The coal is an impure anthracite and 
occurs in very irregular seams, one reaching 60 meters in thickness 
at one point. The Basse-Loire field is also of Dinantian age and the 
rocks are highly folded and faulted. The coal is of poor quality. 
The Vendee field is of Westphalian age and the coal beds overlie 
gneiss and schist. 

In the Central Massif there are a great number of small areas 


of which the St. Etienne basin, near the town of that name, is the 
most important. The Coal Measures rest on granite and gneiss 
and belong to the Stephanian series. The coal contains from 
7 to 35 per cent volatile matter. There is one seam known 
as the Grande Couche which reaches a thickness of 15 meters in 
this field and 20 meters in the Commentry basin. The number 
of seams runs as high as thirty-five in the St. Etiehne basin. 

The other fields in this region are all small, and the rocks are of 
Stephanian age. The Commentry basin is one of the most inter- 
esting. It is 9 by 3 kilometers in diameter, and is characterized by 
the large size of the boulders in the conglomerates in the Coal Meas- 
ures. Some writers have suggested that these may be of glacial 
origin and others that they may be due to torrential streams carry- 
ing the material into a lake. It was in this basin that Fayol found 
the trees with tops headed downwards, which he regarded as evi- 
dence of drift origin. Some of the conglomerate in the Coal Meas- 
ures carries pebbles of coal apparently derived from previously ex- 
isting coal seams. 

In the Alps seams of highly folded and for the most part inferior 
anthracite outcrop at various points from Briancon to the Little 
St. Bernard and run over into Italy and Switzerland. The seams 
are irregular in extent and thickness and reach a maximum thick- 
ness of about 10 meters. 

Lignite occurs in an important basin known as the Fuveau basin, 
also in less important areas in the Vosges Mountains and in the 
Rhone basin. The Fuveau deposits are of Upper Cretaceous age 
and the seams run up to 2 meters in thickness. The lignite in the 
Vosges Mountains is Triassic and Jurassic in age and that in the 
Rhone basin is Upper Cretaceous and Tertiary. 

Spain and Portugal. 1 -- The most important coal-bearing provinces 
of Spain are Asturias and Leon in the northwest and Teruel in the 
east. In age the coals are Upper Carboniferous, Cretaceous and 
Tertiary, and they vary from anthracite to lignite. In Asturias 
there are as many as eighty seams with 112 feet of coal, but as a rule 
the seams are not numerous and none of them are very thick. The 
older coals are anthracite to bituminous and the Cretaceous and 
Tertiary coals lignite or subbituminous. 

1 Coal Resources of the World. 

ITALY 419 

Portugal has little coal. Near S. Pedro de Cova there is a folded 
area of Coal Measures carrying anthracite, and near Tigueira the 
upper Jurassic strata contain bituminous coal of medium quality. 

Switzerland. 1 This is an old mining state in which coal has 
been mined for over two and a half centuries. The reserves for the 
future are not over 80,000 metric tons. The coal is Carboniferous, 
Jurassic, Eocene and Pleistocene in age and on account of the ex- 
cessive folding and compression which the rocks have suffered most 
of it has been changed to anthracite and some of it even to graphite. 

FIG. 137. Highly faulted and squeezed coal seam in the mountains of 

There is a little lignite of Eocene and Pleistocene age. The reserves 
of Switzerland in metric tons are placed at 4000 tons actual and 
50,000 tons probable reserve in anthracite, and 500 tons actual and 
25,000 tons probable reserve in brown coal, or a total of 79, 500 metric 
tons. Much of this coal is difficult to mine owing to disturbances 
which the rocks have suffered. 

Italy. 2 Italy has but little coal and all but about i per cent 
of the coal produced is lignite or subbituminous in rank. Anthracite 
of Carboniferous age occurs in many places in highly folded rocks 
but most of it is of little economic importance. Most of the lignite 
and subbituminous coal mined comes from Tuscany and Umbria 
but these coals are widely distributed throughout the country. Beds 
up to 30 meters in thickness are reported as occurring in Tuscany. 
The age of the coal is Carboniferous, Triassic, Eocene, Miocene and 

1 Coal Resources of the World. 

2 Coal Resources of the World. 



Belgium. 1 This country is comparatively well 
supplied with high-grade coal. The seams all 
occur in the Coal Measures which are divided 
into the Upper or Stephanian and the Lower or 
Namurian series, the former carrying the bulk 
of the coal in the Flenu and Charleroi forma- 
tions. There are three fields in Belgium: (a) 
Dinant field in the southern part of the country 
and including numerous isolated small basins 
within a large syncline; (b) Namur field in the 
central part of the Haine-Sambre-Meuse trough; 
and (c) Campine field in the north. The Dinant 
fieldas unimportant. The Campine field contains 
the largest estimated reserves, they being placed 
at 8,000,000,000 metric tons. This field has not 
yet been worked as the coal lies deep and our 
knowledge is confined chiefly to borings. The 
Namur field is estimated to contain 3,000,000,000 
metric tons reserve, and while there are numerous 
seams they seldom exceed 2 meters in thickness. 
The structure of the basin is complex, (Fig. 138). 
In 1910 the average thickness of the seams worked 
was 0.65 meters. The coal is chiefly bituminous 
with some cannel. Part of this basin is very deep 
and the deepest coal mines in the world, about 
3900 feet, are found here. About one half of the 
coals of Belgium are coking. 

Netherlands. The Coal Measures in the 
Netherlands, which only outcrop in the south 
and east, are of the same age as those of Belgium 
and those of Westphalia between which they form 
a connecting link. The strata occur as great 
fault blocks. There are five possible fields of 

1 Renier, Armand, Les ressources houill&res de la Belgique. 
Coal Resources of the World. Vol. Ill, p. 801. Also, Stanier, 
X., Des rapports entre la composition des charbons et leurs con- 
ditions de gisement. Annales Mines Belgique, V. 1900; and 
Denoel, L., carte et tableau synoptique des sondages du bassin 
houiller de la Campine. Annales Mines Belgique, IX, 1904. 


which two are comparatively well known: (i) South Limburg with a 
maximum aggregate of 38 meters of coal of anthracite and bituminous 
rank; (2) South Peel of which little is definitely known but which 
is likely to be a comparatively large field. The other fields are 
known only by a few test borings. The coals are anthracite, 
semibituminous and bituminous with a good deal of gas coal. 

Denmark. Denmark has no coal production although before 
1880 lignite was mined on Bornholm Island from Jura-Trias forma- 
tions. There are nearly fifty seams but all are thin. On the Faroes 
Islands and in Iceland coal of Tertiary age, which has been changed 
locally from lignite to anthracite by basaltic flows and intrusions, 
is mined for local use. 

Germany. 1 Germany contains the largest supplies of coal of 
any of the European countries so far as known. The coals are of 
Carboniferous, Permian, Cretaceous, Tertiary and Pleistocene ages. 
The Tertiary and Pleistocene coal is lignite, or Braunkohle, and 
the Carboniferous is bituminous coal, or Steinkohle. There are six 
districts containing Carboniferous strata, as follows: (i) Saar; (2) 
Westphalia and Rhine province; (3) Lower Silesia; (4) Upper Silesia; 
(5) Saxony; and (6) Left of the Rhine. Saxony contains some Permian 
beds. There are considerable areas of Cretaceous coals which are 
but little known and there are four districts containing lignite. The 
latter are: (i) Prussia and the North German States; (2) Saxony with 
Oligocene and Miocene beds; (3) Bavaria; and (4) Hesse, the latter 
two containing coals in undifferentiated Tertiary formations. 

The Saar district includes parts of Alsace-Lorraine, Prussia and 
the Palatinate in which a large area of the Coal Measures (Ott- 
weiler and Saarbruck formations) together with Permian and Meso- 
zoic formations have been folded into a large anticline. Erosion has 
removed the upper beds so that the Coal Measures are well exposed 
except in the southwest portion where they are deeply buried and 
much water in porous strata causes trouble in mining. The total 
thickness of coal worked amounts to over 40 meters and the forma- 
tions are divided in vertical section according to the types of coals 
which they contain, as follows: The fat coal, the lower flaming coal 
group, the upper flaming coal group, and the dry coal group. The 

1 Die Kohlenvorrate des Deutschen Reiches. Coal Resources of the World. Vol. 
Ill, p. 821. 


rocks have been extensively faulted and intruded by igneous rocks, 
(Fig. 139). There are many deep mines in this district. 

There is a connection between the coal-bearing formations along 
the Rhine, in Westphalia, Holland, Belgium and France. The coals 
occur in the Upper and Lower Carboniferous. In Westphalia and on 
the right side of the Rhine the beds are gently folded and but little 
faulted. On the left side of the river they are extensively faulted. 


Neunkirchen Lebach 

Lean CoalB Group Upper Lower Fat Coals Group 

5 10 15Kio. 

FIG. 139. Section through the Saar basin. 

The Coal Measures are buried to a depth of 700 meters in some 
places by Triassic, Cretaceous and Tertiary formations, and thick 
deposits of quicksand in the latter formations have made special 
mining methods necessary. On the left side of the Rhine the coal 
may reach a maximum aggregate of 32 meters, while on the right 
side the maximum thickness is about 30 meters with a maximum 
of thirty-three seams. 

The main feature in the Lower Silesian districts is the depth of 
the basin, which exceeds 2000 meters in the center, and the Coal 
Measures are deeply covered by Cretaceous and other rocks. The 
basin is extensively faulted and crushed and igneous intrusions are 
abundant, with the result that considerable coal has been coked 
by natural processes. The mines are very gaseous. The coal is 
chiefly Upper Carboniferous but to some extent Lower Carbonifer- 
ous in age. The coal is described as being platy (probably splint 
coal), fibrous and dull, and some of it is cannel coal. 

Upper Silesia is a very important field, the second in Germany in 
importance. It is noted for the number and thickness of its seams. 
They are not so deeply buried as those of the Lower Silesian dis- 


trict, not being over 150 meters below the surface, but the Carbon- 
iferous strata are very thick. They reach 7000 meters in the south- 
western part of the district. The coals are Upper Carboniferous 
in age and the strata may be divided into a lower marine group 
(Randgruppe) and an upper brackish group (Muldengruppe) . It 
is near the base of the latter that the thick coal seams occur. In 
the western part of the district there are said to be 477 seams con- 
taining an aggregate of 272 meters of coal, 124 of these seams being 
workable and carrying 172 meters of coal. In the eastern part are 
105 seams of which 30 are workable, and they contain 62 meters of 
coal. The Upper Silesian field extends into what were formerly 
parts of Russia and Austria. It is highly folded but little faulted. 

Coal mining has been carried on in Saxony since the tenth century 
and the better seams are practically exhausted in the Lower Car- 
boniferous strata. The coal is now procured on a small scale from 
the Upper Carboniferous and Permian formations. 

Lignite occurs extensively in Prussia and the North German States, 
especially in the Saxony-Thuringia district. The beds range from 
Eocene to Miocene in age. These lignites have been extensively 
employed for briquetting and for the production of by-products, such 
as gas, oils and paraffin. 

Brown coals running from Miocene to Pleistocene in age occur in 
parts of Bavaria, and a small deposit of Oligocene age in this prov- 
ince is believed to be of undoubted drift origin. 

Austria. 1 There are three main coal-bearing areas in Austria. 
These are in the Alps, at the foot of the Alps, and in northern Austria. 
In the Alps there are coals of Carboniferous, Triassic, Jurassic, 
Upper Cretaceous and Miocene age. The Miocene coals are lig- 
nites, the seams reaching a maximum of 12 meters in thickness. 
The others are bituminous and occur for the most part in thin seams 
although mined in many places. Along the foot of the Alps impor- 
tant reserves of lignite occur in the Miocene rocks. 

In parts of what was formerly northern Austria extensive depos- 
its of lignite of Oligocene and Miocene age and also considerable 
beds of Upper Carboniferous coal are found in the middle Bohemian 

1 Petrascheck, W., Die Kohlenvorrate Osterreichs. Coal Resources of the World, 
Vol. Ill, p. 1013. 


fields. Thick and numerous coal seams occur near the Prussian 
boundary but they are covered deeply in most areas by later rocks. 

Hungary. 1 Hungary, so far as known, is deficient in coal depos- 
its. She has lignite, subbituminous and bituminous coal. The lig- 
nite and subbituminous coals occur in the Jurassic, Cretaceous, Ter- 
tiary and Quaternary formations and the bituminous coals in the 
Carboniferous and Jurassic. The brown coals or lignites are the 
only really important coals commercially. A considerable amount 
of the lignite formerly belonging to Hungary is in Croatia and Slav- 

Bosnia and Herzegovina. 2 The deposits of these states, like those 
of many other countries in southern Europe, have not been fully 
developed. Coals occur in Carboniferous, Permian, Triassic, Creta- 
ceous and Tertiary formations, but the principal resources of these 
provinces are in the lignites of Tertiary age in the Zenica-Sarajevo, 
the Ugljevik-Priboj and the Baujaluka areas in the vicinity of Sa- 
rajevo, in Bosnia. In the Tuzla basin northeast of Sarajevo there 
are important Pliocene lignites with seams reaching 10 to 20 meters 
in thickness. 

Serbia. 3 Like the last-named states, Serbia has coal ranging 
from Carboniferous to Tertiary in age. The upper part of the Coal 
Measures lies on crystalline rocks and carries a few seams of mine- 
able coal which in many places is impure and requires picking and 
washing. The Upper Cretaceous carries good seams of coal and 
also rests on crystalline rocks. The Jurassic coals are dirty but 
otherwise of fair quality. The Cretaceous and Tertiary coals are 
lignites. The mineral deposits of Serbia are as yet poorly devel- 

Roumania. 4 The most important coal deposits of Roumania are 
the Pliocene lignites and subbituminous coals of the Comanesti 
basin. A little anthracite is mined in the Carboniferous of the Carpa- 

1 De Papp, Charles, Les Ressources Houilleres de la Hongrie. Coal Resources of the 
World, Vol. Ill, p. 961. 

2 Katzer, F., Die Kohlenvorrate Bosniens und der Hercegovina. Coal Resources 
of the World, Vol. Ill, p. 1075. 

3 Milojkovitch, F. A., Die Kohlenvorkommen Serbiens. Coal Resources of the World, 
Vol. Ill, p. 1093. 

4 Marzec, L., and Tanaseseu, I., Les Reserves de Charbon de la Rumanie. Coal 
Resources of the World, Vol. Ill, p. 1107. 


thians. There is also some Mesozoic coal. The anthracite coal is 
of little importance. Roumania has apparently not developed her 
coals to any great extent and very little seems to be actually known 
regarding her real reserves. 

Montenegro. This state carries some good bituminous coal of 
Carboniferous age, one seam on the Albanian frontier reaching over 
6 feet in thickness. Little attempt has been made to develop min- 
ing operations. 

Greece. Coal is mined in Greece only at Coumi, but lignite 
deposits of Tertiary age are widely distributed. The actual reserve 
is placed at 10,000,000 metric tons and the probable reserve at three 
times this figure. With the redistribution of lands in Europe, Greece 
will receive from Turkey in Europe the principal coal field of that 
country, lying near Keshan. This coal is of bituminous rank and 
some of it resembles a hard cannel. There is also considerable Ter- 
tiary lignite on the Marmora coast and at Telvino and Triano. 

Bulgaria. 1 Bulgaria has extensive seams of coal although they 
have not been developed and little attempt has been made to estimate 
her reserves. The coals are of three varieties, anthracite, bituminous 
coal and lignite. The anthracite lies in the Isker valley and while it 
is comparatively dirty and the seams are thin the volatile constitu- 
ents are less than 4 per cent. It is Carboniferous in age. Bitumi- 
nous coal of Cretaceous age-is found in much-folded rocks in the Balkan 
basin. This coal is used in making briquets and in coking. It is 
very gassy. The seams are comparatively thin. 

The Tertiary lignites and subbituminous coals are widely dis- 
tributed and there are six main fields. In some places seams range 
up to 12 feet in thickness. 

Turkey. 2 Turkey has retained practically no coal lands in Eur- 
ope. In Asia Minor there are a number of important fields of Car- 
boniferous and Tertiary age. Along the Aegean and the Sea of 
Marmora there are good Miocene and Pliocene lignites which are 
mined locally. On the Asiatic coast of the Black Sea there 
are bituminous coals in the Lower Carboniferous, or Culm, 
and in the Westphalian and Stephanian series of the Coal Meas- 
ures. The seams are numerous although not thick, and mining has 

1 Bontchew, G., Coal Resources of the World, Vol. I. 

2 Dominian, Leon, Coal Resources of the World, Vol. I. 


been carried on at a number of places. Some areas have been greatly 
faulted. There is considerable coal, some of it anthracite, in the 
eastern part of Asia Minor, in the provinces of Bitlis and Erzoom. 
In the latter province lignite is mined. Lignite is also mined in 
Syria, near Beirut. Coal has been mined to a small extent in Meso- 

Poland. The Dombrova basin contains many thick seams, es- 
pecially those in the Reden group of rocks where one seam reaches 
12 meters in thickness. The rocks are Carboniferous in age, (Penn- 
sylvanian) and the system is thick. Much faulting has occurred. 
The upper seams contain much ash and in many places the coal 
is mined in open pits as the measures lie near the surface in parts 
of the basin. The coal of Paleozoic age is bituminous, but the 
northern part of the basin contains extensive lignite deposits which 
are also mined. Other smaller basins which are not well known 
occur in this country,. as well as in a small corner of the Upper Silesian 
field which lies mostly in Germany. 

Russia. 1 As indicated in the table showing the resources of Eur- 
ope our information regarding the coal fields of Russia is rather in- 
definite since very little knowledge has been gained concerning the 
actual reserves. There are apparently very large resources in an- 
thracite. The best-known basin is the Donetz which has furnished 
most of the coal mined. This is the most important Russian area 
and there are about 135 workable seams in the Lower and Upper 
Carboniferous strata in this field. This basin is so folded and faulted 
as to make mining conditions difficult in many areas. The fuel is 
bituminous coal and anthracite, the latter forming about 13 per cent 
of the output (Plate XVII.) 

The Lower Carboniferous rocks form a great arc where they out- 
crop and approach the surface in the Moscow district. The main 
seams occur in the central part of the basin and they are known 
chiefly from borings because they are deeply buried by Carboniferous 
limestones. The coal is chiefly bituminous but some boghead, or 
cannel coal occurs. 

Considerable bituminous coal mining is carried on along the west 
slope of the Ural Mountains in folded Lower Carboniferous rocks. 

1 Tschernyschew, Th., and others, The coal fields of Russia. Coal Resources of the 
World, Vol. Ill, p. 1149. 


^Paleozoic ] jMesozoic Fi^ Tertiary 
^ ^3 

SO Longitude 35 

East 40 

50 100 200 300 400 

L- i- 

from 45 Greenwich 50 

PLATE XVH. The coal fields of European Russia. 



Similar conditions exist in Siberia along the east slope where in ad- 
dition to bituminous coal there is a great deal of lignite mined in the 
Mesozoic and Tertiary formations and some anthracite is dug from 
closely folded basins in Carboniferous rocks. 

The Caucasus district contains coal of Jurassic and Miocene age, 
the former bituminous coking coal and the latter lignite. The Tur- 
kestan coals are of little importance so far as known but they are 
in age Carboniferous, Rhaetic and Jurassic. The coals vary from 
coking bituminous to anthracite. 

Among the other districts, those of Sudjensk and Kuznetzk give 
promise of being important as there is over 100 feet of coal in about 
seventeen seams. The coal varies from high- volatile gas coal to semi- 
anthracite and is Carboniferous in age. Numerous undeveloped 
areas of Permian coal-bearing rocks are known to occur along the 
Yenisei River but they have not been extensively prospected. The 
coals are bituminous in character. 

Considerable amounts of coal of Jurassic and Tertiary ages, vary- 
ing from bituminous coking coal to lignite, occur in the Irkutsk 
and other basins. The Russian Sakhalien carries coals of Upper 
Cretaceous to Pleistocene age and of bituminous to lignite in char- 
acter. Finland is without commercial coal deposits although small 
quantities of anthracite have been found. Tertiary lignites are 
widely distributed over European and Asiatic Russia. 

Sweden, Norway and Spitzbergen. 1 Sweden has only a small 
coal field, in the province of Skane, in the south. The fuel is high- 
volatile bituminous to subbituminous coal and it occurs in Jura- 
Trias formations (Rhaetic-Liassic) associated with fire clays. The 
seams vary from 6 inches to 3 feet in thickness. The coal is mined 
at a number of places and the estimated reserves amount to about 
115,000,000 tons. Sweden's production of coal supplies less than 
8 per cent of her requirements and the remainder of her supply is 

Norway has no coal except a little on some of the northern islands. 
On Ando Island a seam of high-ash cannel coal, i meter thick occurs 
in Jurassic rocks. It has not been mined. Buren Island contains 
coal of Devonian age not yet worked. This is probably the oldest 
known coal in the world. 

1 Coal Resources of the World. 

^y> v i / 

. I O / *^ *\ ^ ' 

Hfll .Ct V 


Tertiary Coals 
Mesozoic Coals 
Paleozoic Coals 

Longitude 80 East 


from 90 Greenwich 

Coal fields of Asia. 


ASIA 429 

Spitzbergen has been known for many years to contain consider- 
able deposits of good coal, and mining operations have been carried 
on for a number of years by several small companies and by one large 
American concern. The island is almost covered with snow and ice 
most of the year, but sufficient information has been collected to 
fix the age of the coal deposits as Carboniferous, Jurassic and Ter- 
tiary. The only valuable Carboniferous coal so far located is at 
the head of Ice Fiord, where a seam 7 meters in thickness occurs. 
The Jurassic coals so far as known are unimportant. The Tertiary 
coal occurs near the base of the Miocene and is a good quality of 
subbituminous to bituminous coal. It is mined on Advent Bay 
by an American company. All shipping must be done during about 
three summer months owing to the unfavorable weather conditions. 
The ground is said to be frozen to a maximum depth of about 400 
meters but the Tertiary rocks in this area are thick and the mining 
operations are carried on without great hardship in spite of about 
four months of continual darkness. On account of the scarcity of 
coal for domestic and industrial purposes in that part of the world 
the Spitzbergen output finds a ready market. 


Asia is well supplied with coal although little is yet known re- 
garding very large areas of that continent. The following table 
indicates the resources of the continent by countries and provinces 
in the various kinds of coal, and the accompanying map of the con- 
tinent shows the distribution of the coals, (Plate XVIII.) 

This table brings out two important points. One is the enormous 
resources of China in anthracite, although it seems probable that 
considerable coal classed as anthracite may be nearer semianthracite 
and semibituminous coal than true anthracite. In any case China 
leads the world by a tremendous margin in -this commodity. The 
other point is the lack of definite knowledge regarding the continent's 
coal deposits. A few of the other countries, especially Siberia, un- 
doubtedly have large reserves which are little known. 


Actual Reserve 
(i metric ton = 1.1023 short tons) 

Probable Reserve 


Class of Coal 

Class of Coal 








and semi- 

nous coals 

coals and 






B 4 


C 9 





B 6201 


B 5,490 

C 292 

C 658 

Shantung. . 


B 2842 


B 2,241 



B 123 


B 414,217 




B 5,129 



B 2,700 

Kiangsu. . . 



B 187 


B 117 

Chekiang. . 


B 6 

Chekiang. . 



B 325 

B 3,070 

Fukien .... 





B 255 

Kuangsi . . . 
Hunan. . . . 


B 42,000 

Szechuan. . 


B 60,000 


Kueichou . . 

B 30,000 

Yunnan. . . 

B 30,000 









coals . 



B 5 

Tertiary. . . 

C 5 

Karaf uto . 

C 17 

C i,345 


C 336 

C 2,106 




C i 



C 14 


Kyushu . . 

C 542 

C 2,374 

Taiwan. . . 

C 385 


C 896 






Estimated by Kinosuke Inouye. 




Actual Reserve 
(i metric ton = 1.1023 short tons) 

Probable Reserve 


Class of Coal 

Class of Coal 


and semi- 

B and C 

nous coals 


coals and 


B and C 


Manchuria. . 
Siberia. . 

B 31 
C 378 

B 48 

B 24. 
C 30 

C 119 





B 223 
C 508 
B 66,034 

B 53,037 

C 210 

B 22,657 
B 246 

C 28 





Indo-China . 
Bikai and 



Tertiary . . . 




B 1,858 



Total in 








1 From Coal Resources of the World, Vol. I. Estimate based on all seams less than 4000 feet deep and 
more than 14 inches thick, together with all seams between 4000 and 6000 feet deep and more than 2 feet 
thick, of workable coal. For description of classes see Classification of Coals, Chapter V. 

China. 1 The coal deposits of China are widespread. A very 
large area occurs in northern China covering most of the southern 
part of the province of Shansi, and another large field is found in the 
south covering parts of Hunan, Kueichou, Yunnan and Szechuan 
provinces. The age of the coals is Permo-Carboniferous, Rhaetic 
(Triassic), Jurassic and Tertiary, and the coals vary from lignite to 
anthracite. Some of the lignite is considered as Pliocene in age. 
The anthracite and other low- volatile coals occur in areas which are 

1 Drake, N. F., and Kinosuke Inouye, The coal resources of China. Coal Resources 
of the World, Vol. I, pp. 129-214. 


more folded or compressed than the others, and considerable areas 
have been so crushed as to be almost unmineable. It is stated that 
in the Sieu River district in Hunan province, where much anthracite 
is mined, the seams of anthracite average 15 feet in thickness, and 
one seam, apparently of anthracite, is 50 feet thick. There is a 
large amount of good coking coal in the country. 

Korea. 1 Coal has been mined in Korea for many years but on a 
small scale and in a primitive way. The coals are of Paleozoic (appar- 
ently Carboniferous), Jurassic and Tertiary age. The Carbonifer- 
ous coals so far discovered are of little importance but little is known 
about the possibilities of the rocks of this age. The Jurassic coals are 
most important. The Tertiary coals are lignites. Most of the coal 
mined is semianthracite. It is powdery, and is sent to Japan where 
it is made into briquets. Japan takes nearly all the production 
and most of the coal used in Korea is imported. 

Manchuria. 2 Manchuria has large resources in coal and there 
are a large number of small mines operated in a primitive way. Large 
operations are, however, being carried on in the important Fu-Shun 
field. The age of the coal is Carboniferous, Jurassic and Tertiary. 
The coals range from low grade bituminous to semianthracite. Most 
of the coal mined is from the Tertiary and it varies from subbitu- 
minous to bituminous. In this field one of the seams has a remark- 
able thickness and mining has been carried on for many centuries. 
It is stated that coal was mined here for a porcelain factory 600 or 
700 years ago and that it was also used for copper smelting possibly 
as far back as 3000 years ago. Mining was prohibited by the govern- 
ment in the eighteenth century. The main seam in the Chien- 
chin-chai section varies in thickness from 130 to 200 feet with nearly 
a hundred thin partings aggregating about 20 feet. The quality 
of the seam varies considerably where folded, shrinking to 75 feet; 
and the partings increase to an aggregate of 70 feet in 130 feet of 
coal. The coal is subbituminous to bituminous and is low in sulphur 
and ash. 

Japan. 3 Mining of coal has been carried on in a primitive way 
in Japan for centuries, but about 1868 real, active mining began 

1 Kinosuke Inouye, Op. cit., p. 215. 

2 Kinosuke Inouye, Op. cit., p. 239. 

3 Kinosuke Inouye, Op. cit., p. 279. 

INDIA 433 

under foreign engineers. The center of the coal-mining industry is 
in northern KyQshu and large mining plants are also in operation in 
Hokkaido. Chikuho, which is considered the richest and most im- 
portant area, is well developed, and the Miike field is developing 
rapidly. Japan exports a good deal of coal and imports little al- 
though the imports from China are growing. 

The coals of Japan are Triassic (Rhaetic), Jurassic, and Tertiary 
in age. The Rhaetic and Tertiary are of most importance, the 
latter being the best of all. Most of the Mesozoic fields are small 
and scattered and they have suffered much from folding and igneous 
intrusions. In the Tertiary the best coals occur in the Miocene. 
There is some lignite in the Pliocene. Some semianthracite coal 
occurs in the Mesozoic formations and natural coke occurs near ig- 
neous intrusions. Most of the coal mined is bituminous, much of 
it high-volatile. There is considerable coking coal. 

The Ishikan coal fields are remarkable for the number of seams 
and their thickness. In the lower series of the Tertiary there are 
said to be as many as 150 seams, lens-shaped, and ranging from a 
few inches to 60 feet in thickness. The coal is bituminous. 

India. 1 Very little definite information is obtainable regarding 
the extent of the coal deposits of India. They occur in the Gond- 
wana system, of Permo-Carboniferous age, and in the Tertiary, 
both in the Eocene and Miocene. There are unimportant and little- 
known areas in the Jurassic and Cretaceous. The older coals 
occur only in the Damuda series of the Lower Gondwana system. 
The Damuda series overlies the Talchir series, which is of glacial 
origin. The conditions in India strongly resemble those of South 
Africa and Australia where the coal deposits of the Permo-Carbon- 
iferous group are indirectly associated with glacial deposits and there 
are the same types of plants in the Glossopteris flora. 

The main Gondwana fields occur in the following provinces: Ben- 
gal, Bihar and Orissa, Central India, Central Provinces and the 
Nizam's Dominions, the most important being those of Bengal, 
Bihar and Orissa. Active operations are carried on in the Ran- 
iganj, Giridih and Jherria fields. The coal is of bituminous quality, 

1 Hayden, H. H., The coal resources of India. Coal Resources of the World, Vol. I, 
p. 353. See also Memoirs Geol. Survey of India, Vol. XLI, by R. R. Simpson. 


a good deal of it being of inferior grade. The seams have been in 
many places intruded, broken and altered by igneous rocks. 

In the Umaria field of Central India mining is regularly carried 
on. In the Central Provinces there are three basins, Sarguja and 
Chattisgarh on the northeast, the Satpura and Chindwara basin 
on the northwest and the Godavari basin extending for nearly 300 
miles down the Godavari and its tributaries. The possibility of the 
rocks of the Sarguja basin connecting with the Satpura basin and 
these again with those of the Godavari beneath the Deccan trap 
has been suggested. This would give tremendous reserves not yet 
exploited or computed. The Mesozoic and Tertiary coals occur in 
Assam, and there is a group of collieries near Margherita opera- 
ting on seams aggregating 80 feet of coal. The coal is friable and 
high in sulphur. In Baluchistan a colliery is operated at Khost, but 
the seams of this district are thin and limited. Burma so far as 
known has little good coal. 

With regard to the countries adjacent to India, it is reported that 
Afghanistan apparently has large coal deposits, but little is known 
regarding them. Thibet has no coal so far as known. 

Persia. 1 Coal is widely distributed over Persia and is mined 
by primitive methods for local use, in a great number of places. Very 
little is known regarding the extent or quality of most of the seams. 


The coal in this island is lignite and low-grade bituminous coal, and 
it is almost all of Tertiary age. The better coal is Eocene but there is 
some in the Oligocene, Miocene and Pleistocene formations. A num- 
ber of mines are worked and the labor is chiefly Chinese, Malay 
and Javanese. At Brooketon in the State of Sarawak, there are 
five seams with thicknesses of 28, 26, 29, 5 and 2 feet respectively. 
The first two of these seams are worked. The beds are tilted up 
to 80 degrees. The coal is very low in ash, one analysis showing only 
1.58 per cent, and sulphur is low. Spontaneous combustion occurs 

1 Rabino, H. L., The coal resources of Persia. Coal Resources of the World, Vol. 

I, P- 365- 

2 Evans, J. W., The coal resources of British Territory in North Borneo. Coal Re- 
sources of the World, Vol. I, p. 89. Also see Coal Mining in Borneo by James Roden. 
Trans. Inst. Min. Eng., Vol. 28, p. 240, 1904-05. 


under favorable conditions and there is a large amount of water in 
the mines. This field apparently extends under the sea to the north 
end of the Island of Labaun. Some of the coal contains a large 
amount of resin which the natives use for lighting purposes. The 
Silimpopon coal field on the river by that name is near the coast 
and shipments can readily be made. There is little gas in the mines 
and open lights are used. 


A large amount of coal is distributed through these islands. It 
is all Tertiary in age, Eocene and Pliocene. The coal is of lignitic 
and subbituminous rank. The production of the island of Sumatra 
amounts to about half a million tons a year and this comes chiefly 
from the Soegar area of the Ombilin field in which some seams reach 
a thickness of over 30 feet. The other field on the Sepoetih River 
is not of much importance. Java contains some coal but the seams 
are thin. Borneo has a much larger supply with more and thicker 
seams than the other islands. The probable resources of all the 
islands are probably about one billion tons. 


The important deposits of the Philippines are all Tertiary, chiefly 
Miocene in age, and these coals are mostly lignitic and subbituminous, 
with a little coal of bituminous rank. The total known area under- 
lain with coal seams amounts to about 53 square miles of which 
less than 7 square miles are of workable quality. There is a much 
larger unprospected area which will no doubt prove to contain val- 
uable seams. The fields occur on the islands of Baton, Cebu, Min- 
danao, Masbate, Mindoro and Luzon. On Luzon Island the coal 
is around Sugud Bay, and on the Island of Mindanao it is on Si- 
buguey Bay in the southwest corner of the island. Of these fields 
those on Baton and Cebu islands are regarded as most important. 
On the former island there are estimated to be about 26,000,000 
tons of subbituminous coal in two to eight seams, 3 to 12 feet thick. 
The western part of the field is highly faulted and folded. 

On the island of Cebu the coals lie from 8 to 15 miles from the sea. 

1 Douglas, E. A., Coal Resources of the World, Vol. I, p. 95. 
* Dalburg, F. A., Coal Resources of the World. Vol. I, p. 107. 


The coal is subbituminous and it occurs in a series of faulted and 
folded Oligocene and Miocene strata over 2000 feet thick. Some 
of the seams reach a thickness of 15 feet. The coal on Mindanao 
and Polillo islands is classed as bituminous by Dalburg. That on 
Mindoro Island near Bulalacao is lignite and the seams, six in num- 
ber, run up to 12 feet in thickness. On Sugud Bay, Island of Luzon, 
the seams of subbituminous coal vary from 10 to 27 feet in thickness. 
The beds are considerably folded in parts of the field. 

The Philippine coals are used chiefly by inhabitants of the islands 
for domestic purposes and on ships, and in recent years several mines 
have been operated on a fairly large scale. In most cases these 
are controlled by American mining men. Scarcely any of the coal 
cokes well. The total resources of the islands are placed at: bitu- 
minous coal, 4,959,200; subbituminous coal, 31,285,200; and lig- 
nite (black) 30,092,000 metric tons. Apparently the black lignite 
mentioned in the reports would be largely classed as subbituminous 
coal in this country according to our present custom. 


Longitude 20" West 

PLATE XIX. The coal fields of Africa. (From "Coal Resources of the World," 
published by the i2th International Geological Congress, Toronto, Canada.) 





Africa 1 

The Dark Continent is so large and there is so much of it which 
has not been thoroughly explored that anything like an attempt to 
accurately describe its coal deposits is impossible at this time. The 
accompanying map (Plate XIX) shows the distribution of the coals 
so far as known and the following table gives the estimates of the re- 
sources as compiled by the International Geological Congress in the 
year 1913. 


Actual Reserve 
(In millions of metric tons) 
''i metric ton = 1.1023 short tons) 

Probable Reserve 
(In millions of metric tons) 

Class of Coal 

Class of Coal 


Class A 

and some 
dry coals. 

B and C 


Class D 
nous coals. 
Brown coals 
and lignites 




Belgian Congo 
Southern Nigeria . . . 


B 306 
C 37 




B 90 

B 119 

C 31 

B 28,800 
C 7,200 
B 4,600 

B 2,880 
C 960 





South Africa: 


Orange Free State.. 
Cape, Basuto and 

1, 660 






1, 660 




For detailed description of classes see Classification of Coals, Chapter V. The reserves are 
figured on all seams which are i foot or over in thickness and less than 4000 feet deep; and on all 
seams of 2 feet and over which lie between 4000 and 6000 feet jn depth. 

1 For detailed descriptions of deposits in Africa see Coal Resources of the World, 
Vol. II, pp. 375-428. Also Colonial Reports of the Museum of the Imperial Institute, 
London; Reports of the Department of Mines, Union of South Africa. 




The geological ages of the coals of Africa are indicated in the table 
given below: 









r -3 











a 1 












o 8, 

l a 





1 b 




Upper Cretaceous 


Triassic including Rhaetic . 

R s 











A, Anthracite; S, Semibituminous; B, Bituminous; B, Subbituminous; L, Lignite; C, Cannel. 
Capital letter indicates important deposits, lower case unimportant or unworkable deposits. 

The main coal fields of Africa are in the southern portions of the 
continent. Egypt has traces of lignite and bituminous coal but 
nothing workable. The Anglo-Egyptian Sudan is also lacking in 
workable coal although traces of lignite have been found. Abys- 
sinia is little better off, but according to Dum and Grabham the 
natives mine coal near Addis Abbaba, the capital of Abyssinia. The 
East Africa Protectorate has no workable seams and Madagascar 
has a very limited amount so far as is at present known. In the 
lanapera area of the island there are several seams reaching a maxi- 
mum thickness of 8 feet 4 inches, and according to Bonnefond the 
coal is like cannel in character. 

Southern Nigeria. In southern Nigeria good subbituminous coal 
and lignite have been discovered. The former is probably of Creta- 
ceous and the latter of Tertiary age. According to J. W. Evans, 
the best-known lignite areas occur in the vicinity of Onitsha and 
Asaba on the other side of the Niger River. In the latter locality 
six seams of lignite ranging from 8 to 20 feet in thickness have been 
examined, and this coal was found to make good briquets when 
tested in Europe and compared with the German lignites. The 


seams of subbituminous coal reach nearly 6 feet in thickness and 
they outcrop in the escarpment about 45 miles east of the Niger 

Nyassaland has very little coal which is sufficiently clean to be 

Rhodesia. The Wankie coal field is the only one in Rhodesia 
where coal is being mined. This field lies about 60 miles south- 
east of Victoria Falls on the railroad line to Bulawayo. The coal 
lies in the basin of the Zambesi River and like the other fields of 
South Africa it occurs in the Karroo series which apparently in- 
cludes rocks ranging in age from Carboniferous to lower Jurassic, 
with no well-marked lines of division between them. The main 
coal-bearing formation is in the Lower Matobola which corresponds 
to the Ecca series of Cape Colony and the High Veld coal measures 
of the Transvaal. It lies just above the Dwyka conglomerate which 
is of glacial origin and usually regarded as of Permian age. Some 
geologists have considered at least some of the coal beds as of the 
same age as the Rhaetic of Europe. The seams are comparatively 
shallow in depth and vary from i foot to 12 feet in thickness. 

The other fields of Rhodesia are the Mafungabusi lying just north- 
east of the Wankie field, the Lufua and Losita about 50 miles to the 
northwest of the latter field, and the Luano some 75 miles east of 
Broken Hill, on the railroad line. A small field near Tuli lies about 
150 miles southeast of Bulawayo, and another on the Sabi River, 
near Sabi, 225 miles southeast-by-east from Bulawayo. These two 
fields are not on a railroad. It is supposed that a concealed field 
lies beneath the Victoria Falls basalts. The largest number of seams 
explored is in the Luano field where four have been found reaching 
an aggregate thickness of almost 18 feet. The thickest single seam 
is in the Wankie field and it runs up to 12 feet. The ash in the 
Rhodesian coals is high like that in the coals of South Africa, most 
of them running over 13 per cent. 

Belgian Congo. In the Belgian Congo there are two coal fields 
according to Renier, known as the Lukugo and Lualabo. The coals 
in the former field are regarded as of Permo-Carboniferous age and 
there are three flat-lying seams running over 10 feet in thickness. 
The coal is much lower in ash than much of that in South Africa. 
It averages around 10 per cent. In the Lualabo field the coal is 


probably of Triassic age and there are several seams several feet in 
thickness. It is of inferior quality, however, as much of it is high in 
sulphur and very high in ash. 

Union of South Africa. The coal deposits of the Union of South 
Africa occur in the Karroo series which apparently includes rocks of 
Carboniferous, Permian and Triassic ages as they are known else- 
where. The seams usually lie within 200 feet above the Dwyka 
formation, the basal conglomerate of the Karroo series. Much of 
the coal is undoubtedly of Permian age and the same peculiar plant 
associations, usually known as the Glossopteris or Gangamopteris 
flora, which are found in the coal measures of India and Australia, 
are found here associated with the glacial deposits. The coal is 
practically all of the bituminous variety. A little lignite occurs in 
Cretaceous and Tertiary rocks but it is unimportant. One feature 
of most of the coal is the high ash content which runs from 6 to 30 
per cent and averages between 10 and 15 per cent. 

Transvaal: In the Transvaal the coal seams lie quite flat and 
occupy the high lands. They are usually of shallow depth, those 
worked being less than 400 feet deep. Many of the deposits occupy 
rather limited and isolated basins owing to the topographic con- 
ditions existing when they originated. They are also associated 
with coarse sediments, and some writers have considered that practi- 
cally all of the South African coals are of drift origin, but in certain 
places stumps and roots are found in place beneath the seams indi- 
cating their in situ origin. In the Transvaal the main field is the 
Witbank or Middleburg and in it there are five known seams, giving 
an aggregate thickness of about 56 feet of coal. The average thick- 
ness of the seams worked runs around 10 feet, the maximum reaching 
about 20 feet. 

Cape of Good Hope and Natal: In these provinces as in the 
Transvaal, the coal occurs in the Karroo series, but near the top. 
The Dwyka lies at the base of the Karroo in this region as elsewhere 
in South Africa and includes a thick glacial till. The coal occurs in 
the Molteno beds which are younger than the beds containing the 
coal in the Transvaal and they are apparently of Rhaetic (Triassic) 
age. The mines are worked by adits and the workings are confined 
largely to the portions of the seams near the outcrops, because many 
of the seams have been so broken up by intrusions of igneous rock 


that their extent is uncertain. Much of the coal has been devolati- 
lized and anthracitized by the heat of these intrusions. A consider- 
able amount of the coal is semianthracite and it is high in ash, usually 
above 20 per cent. It is low in sulphur but a large amount of clinker 
is produced and it is said that this clinker is taken care of on the 
locomotives by specially designed fireboxes. There are some beds 
of lignite of Tertiary age but they are not of much importance. 

In Natal, the coal, which is similar to that in the Cape of Good 
Hope Province, has been extensively intruded by igneous rocks and 
to quite an extent converted into semianthracite. Many of the 
mines are sufficiently gaseous to require the use of safety lamps. 

The coal industry in Africa is very young and much will be added 
in the coming years to our knowledge of the geology and the coal 
resources of the continent. From the general character of the ge- 
ological conditions on the continent, however, it seems improbable 
that Africa will ever be, comparatively speaking, a great coal-produc- 
ing continent. 

Oceania 1 

Oceania includes, for the purposes of this discussion, the continent 
of Australia and the islands of New Zealand and Tasmania. 

Australia's reserves of high-grade coal are considerable, although 
they are smaller than those of Great Britain and very small compared 
with those of the United States or Canada, two countries to which 
Australia is almost equal in size. The table given below shows the 
estimated reserves for New Zealand and the various states of Aus- 
tralia. The latter country holds the record for the thickest coal 
seams in the world. There are two seams of brown coal in Victoria, 
which are 266 and 227 feet, respectively, in thickness. 

1 For comprehensive reports see The Coal Resources of the World, Vol. I. Also 
Coal-fields and Collieries of Australia by F. Danvers Power (Critchley Parker). Hand- 
book for Australia, British Assn. Adv. Sci. 1914. Reports of the various state Geolog- 
ical Surveys and Departments of Mines. 





100500 200 400 600 800 

Tertiary Coals 











North Cape 







Blen-y?"' 61 " 11 ** 011 




U0 from Greenwich 150 




(In millions of metric tons, i metric ton = 1.1023 short tons.) 

Actual Reserve 

Probable Reserve 

Class of Coal 

Class of Coal 



B and C 





and some 


coals and 

dry coals 



New South 


B 118.4.30 


B 40 

B 12 


Queensland. . . 


B 1766 



B ii,on 


C 165 

C 7Si 

West Australia 




B 65 

C i 








New Zealand . . . 

B 26 


B 99 


C 363 

C 423 









1 These figures are based on seams I foot and over to a depth of 4000 feet; and 2 feet and over between 
4000 and 6000 feet in depth. Coal Resources of the World, Vol. I. For description of classes of coal, see 
Classification of Coals, Chapter V. 

Geological age of coals: The geological ages of the coals in Oceania 
vary from Carboniferous to Tertiary, the most important fields being 
Permo-Carboniferous (Permian). The latter are closely related to 
the coal deposits of India and South Africa and to some of those of 
South America. These deposits are characterized by the same pe- 
culiar plant associations, as Gangamopteris, Glossopteris and Rhacop- 
teris are among the outstanding fossil plants of the Australian coal 
measures. Lepidodendron, so abundant in the Coal Measures 
throughout the rest of the world is present in the Devonian and 
Carboniferous rocks in Australia but absent in the Permo-Carbon- 
iferous, as the violent changes in climate wiped out this and related 
genera and ushered in the Glossopteris flora. The same interesting 
glacial conditions prevailed in Australia in the Permo-Carboniferous 


W>T jBSiig 

oiog- UJ9JTS8M. _ 


as in India and South Africa and the 
same difficulty is experienced in trying 
to separate the Carboniferous from the 

The other geological systems carrying 
important coal seams are the Triassic 
in Tasmania, the Jura-Trias in Queens- 
land, the Upper Cretaceous in Queens- 
land and New Zealand, the Miocene 
in Victoria and the Tertiary in New 
Zealand. The rank of the coal varies 
from bituminous and anthracite in the 
Permo- Carboniferous to bituminous and 
lignite in the Mesozoic and lignite in the 
Tertiary formations. 

New South Wales. 1 The coals of 
this state are of high grade and are 
bituminous in rank. They are valuable 
as gas, domestic and steaming coals. 
Much of the coal is of good coking 
quality. There are four important 
fields, the Maitland, Newcastle, Illa- 
warra or Southern, and the Lithgow or 
Western field. The coal in all these 
fields is of Permo-Carboniferous age and 
the strata are divided as follows, in 
descending order: 

in feet. 

(1) Upper or Newcastle Coal Measures 

with twelve seams of coal varying 
from 3 to 25 feet in thickness with 
aggregate of 35 to 40 feet work- 
able coal. Glossopteris predom- 
inates over Gangamopteris. . . 1400-1500 

(2) Dempsey series. Fresh water de- 

posits without coal 2200 

(3) Middle, or Tomago, or East Mait- 

land Coal Measures with six 

1 Pittman, E. F., The mineral resources of New 
South Wales, 1913. 



in feet. 

seams of coal 3 to 7 feet in thickness and aggregating 18 feet of 

workable coal 500-1800 

(4) Upper Marine series with glacial erratics in shales 6400 

(5) Lower or Greta Coal Measures with approximately 20 feet of work- 

able coal in two seams, the Upper seam 14 to 32 feet thick and the 

Lower seam 3 to 1 1 feet thick. 100- 300 

(6) Lower Marine series, containing much igneous rock and beds of glacial 

till at base. The rocks of the Carboniferous system are marine 
and fresh- water sediments with an abundance of igneous rock, and 
in parts of Australia are 20,000 feet thick. They are not coal-bear- 

The Newcastle field has been the most important producer in 
the state but many of its collieries are already exhausted. In some 
places the mines extend beneath the sea. Some seams have been 
intruded with granite which has produced natural coke and nigger- 
head coal. In the Illawarra and Lithgow fields the coal occurs in 
the Newcastle series. This series is continuous from Newcastle to 
Illawarra and again from Sydney westward to Lithgow. At Sydney 
Harbor the upper seam is worked at a depth of 2882 feet. 

New South Wales contains a large amount of oil shale known in 
Australia as kerosene shale and resembling the Torbanite of Scot- 
land. The seams occur as lenses, sometimes reaching about a mile 
in extent, and from a few inches to about 4 feet in thickness. They 
are of Permo- Carboniferous age and the organic matter in them 
comes from the spores of plants. 

Queensland. This is the second most important state in Aus- 
tralia in coal reserves. The coal is almost all bituminous except a 
few million tons of semianthracite in the Dawson River field. There 
is some lignite, but this is of comparatively little importance. The 
coals are mostly of Permo-Carboniferous age, although the bulk of 
the coal so far worked is Jura-Trias in age. The Burrum field is 
considered to be of Cretaceous age, probably Lower Cretaceous. 
The Blair Athol field carries a seam of good clean coal 66 feet thick 
at a depth of only 120 feet below the surface. This coal is Permo- 
Carboniferous in age. 

Victoria. The coal resources of Victoria have not been very 
fully determined. There is some bituminous coal of Jurassic age 
but the main reserves are in the Miocene brown coal and the thick- 


est seams known occur in this state. At Morwell a bore hole passes 
through 780 feet of brown coal in a depth of 1010 feet of strata and 
there are three very thick seams running 266, 227 and 166 feet, re- 

FIG. 141. Thick series of Coal Measures on coast of New South Wales, at Shep- 
herd's Hill. (Photo by E. S. Moore.) 

spectively. This coal averages 35.08 per cent water; 29.24 per 
cent volatile matter; 33.28 per cent fixed carbon; and 2.40 per cent 
ash. It can no doubt be used for briquetting and in gas producers. 



Tasmania. Permo- Carboniferous coal in thin seams and high 
in sulphur has been mined a little for domestic purposes in the Mer- 
sey and Preolenna coal fields. Most of the coal mined comes from 
the Triassic formations which have suffered much faulting and which 
have also been much disturbed by intrusions of igneous rock. The 
coal is high in ash and it is not used much except for domestic pur- 
poses and on some of the railroads. Two collieries are at work 
near St Mary's and they together produce about 60,000 tons a year. 

Considerable oil shale, known as Tasmanite shale, is found on 
the island and it is said to yield 40 to 50 gallons of crude oil per ton. 


FIG. 142. Collieries at the state mine, Port Elizabeth, New Zealand. (Photo 

by E. S. Moore.) 

Western Australia. The only productive field in this state is 
the Collie field lying south of Perth. This field is a block of Permo- 
Carboniferous measures about 50 square miles in extent. It lies at 
quite a shallow depth and is little folded or faulted although surrounded 
by faults, one on the southwest having a throw of about 2000 feet. 
The coal is friable, non-coking, subbituminous to bituminous in rank 
and partly of the splint variety. It has a high moisture content. 
The low fuel ratio of the coals in the Collie field is due to the lack 
of pressure exerted on these beds even though they occur in for- 
mations as old as the Permo-Carboniferous. 


South Australia and Northern Territory. South Australia con- 
tains some Jurassic coal in the Leigh's Creek field, and a small 
amount has been mined. It is, however, of poor quality. A seam 
47 feet thick is said to have been penetrated at a depth of about 
1500 feet. In the Great Australian Artesian Water Basin lignite 
occurs in the Lower Cretaceous and in the southern part of the state 
lignite of Tertiary age occurs in a number of places, but there has 
been little exploitation. 

The Northern Territory, so far as known, has no important coal 

New Zealand. 1 New Zealand has inadequate fuel supplies for 
her future needs as at the present rate of increase in production her bi- 
tuminous coal will be exhausted in less than fifty years. Her main re- 
serve lies in the Tertiary brown coals. The seams are notably lenticu- 
lar in form and they occur as if deposited around the margins of basins. 
There is a little anthracite in the South Island, in the folded and 
faulted areas and where the seams have been intruded by igneous 
rocks, but the quantity is very small. The geological age of the 
coal runs from Jurassic through the Upper Cretaceous and the Ter- 
tiary. Possibly there is some lignite of Pleistocene age. The thick- 
nesses of some of the seams are as follows: 50 to 60 feet of brown 
coal in the Waikato district near Auckland; 53 feet of bituminous 
coal in the Buller-Mokihinui district; and 80 feet of lignite in Central 
Otago. As stated above, however, the seams are very irregular 
in thickness, and they are commonly lenticular in outline. 


T. W. E. David 2 , who spent considerable time in Antarctica on 
geological work with the Shackleton expedition, states that the coal- 
bearing rocks in this great continent may cover something less than 
12,000 square miles. Coal has been found at the head of Beard- 
more Glacier and at Mackay Glacier, 605 geographical miles Epart. 
The coal-bearing area is a long, narrow " horst " bounded by large 
faults. As many as six seams with 22 feet of coal have been seen. 
The enclosing rocks are believed to be of Permian age and the coals 
are therefore related to those of Australia. 

1 Marshall, P., Geology of New Zealand, Wellington, N. Z., 1912. 

2 Coal Resources of the World. 


Numbers refer to pages. Illustrations are indicated by an asterisk after page numbers. 

Africa: coal fields of, 438; coal resources, 

table of, 438; geological age of coals of, 

439; map of, 437. 
Ala-Kool, algae in, 176. 
Alaska: coal fields of, 397; coal resources 

of, 400; entry on Coal Lands of, 240; 

lignite from, 83;* map of, 399. 
Alaskan coals, stratigraphic position of 


Alberta, coal in, 343. 
Alethopteris serli, 205.* 
Algae, 186; ia bogheads, 175. 
Alkalies in coal, 37. 
Allegheny formation, section of, 367. 
Allen, A., 290. 

Allen Shaft, Pictou coal field, 341.* 
Alliance Breaker, 304.* 
Allochthonous, 124, 129. 
Ambrite, 102. 
American Society for Testing Materials, 


Andreaeales, 188. 

Andre's rule for shaft pillars, 276. 

Andrews, E. B., 128. 

Andros, S. O., 305; illustration by, 283. 

Angers, 81. 

Angiosperms, 184, 185, 206; first appear- 
ance of, 213. 

Annularia, 198, 193.* 

Antarctica, coal deposits in, 448. 

Anthracite, 81, 94, 93;* market sizes of, 
301; of Keboa., 81; specific gravity of, 
4; standards of preparation of, 302; 
anthracite mine model, 274;* anthra- 
cite mining in Pennsylvania, 277; an- 
thracite region of Pennsylvania, 363. 

Anthrax, n. 

Anthrocoal, 326. 

Anticline, 222. 

Anticlinorium, 223. 

Apparent specific gravity, 7. 

Araucarian pines, 211. 

Arber, E. A. N., 154, 156. 

Arctic islands, coal in, 351. 

Arctic tundra, 132. 

Argentine Republic, coal in, 405. 

Arizona, coal in, 387 

Aristotle's Meteorology, 2. 

Arkansas: coal in, 385; section of forma- 
tions of, 385. 

Ash determination, 50. 

Ashes: from coal, composition of, 52; 
fusibility of, 53, 121; from trees, compo- 
sition of, 38. 

Ashley, G. H., 89, 95, 147, 148, 255, 262, 
370, 378, 381, 382. 

Ashley's Use Classification, 118. 

Ashmead, D. C., 302; illustration by, 

Asia: coal fields of, 429; coal resources, 
table of, 430; map of, PI. XVIII. 

Asiminia triloba, 157. 

Asterophyllites, 198, 193.* 

Australia: coal resources of, 443; mining 
methods in, 288. 

Austria: coal fields of, 423; coal resources 
of, 409. 

Autochthonous, 124, 129. 

Autun, bituminous schists of, 175. 

Bacilli, 159.* 

Bacteria in coal, 158.* 

Bailey, E. G., 43. 

Bain, H. F., 263. 

Bald cypress, 211. 

Balfour, 174. 

Barnes, C. R., 186. 

Barrier pillars, 273; rule for size of, 275.. 




Barsch, O., 12. 

Bathvillite, 103. 

Battery, 279. 

Battery breast, 279.* 

Baumhauer, E. H. V., 70. 

Baxton megaspores, 14.* 

Bayley, F., 307. 

Beard, J. T., 290. 

Beaver, Pa., Quadrangle, structure sec- 
tion of, 366. 

Bedson, P. P., 21. 

Beehive coking, 318. 

Beehive ovens, 319.* 

Belgian Congo, coal in, 440. 

Belgium: coal fields of, 420; coal resources 
of, 408; structure section in, 420. 

Bell, 220. 

Bennettitales, 207. 

Bernice Field, 367. 

Beroldingen, Franz von, n, 126. 

Bertrand, C. E., 12, 174, 175, 176; illus- 
tration by, 175. 

Bethune, 81. 

Bevan, J. P., 168. 

"Big" seam at Pocahontas, 376.* 

Biochemical process, 158. 

Bird, E. H., 320. 

"Bird's eye" coal, 94. 

Bituminous coal, 87, 85;* photomicro- 
graph of, 12; preparation of, 305; spec- 
ific gravity of, 4. 

Bituminous schists of Autun, 175. 

Black Creek seam, photomicrograph of ' 
coal from, 16. 

Black damp, 291. 

Black lignite, 84, 86. 

Blairmore-Frank region, structure sec- 
tion of, 346. 

Blandy, J. F., 217. 

Blind shaft, 267. 

Block longwall system, 284.* 

""Blossom," 242. 

Blowers, gases from, 25. 

Blumenbach, 84. 

Bogheads, 87; origin of, 174; phosphor- 
ous in, 36. 

Bolivia, coal in, 404. 

Bomb calorimeter, 72; for sulphur, 59. 

Bontchew, G., 425. 

Borlkjof, J. C. B., 404. 

Borntrager, 20. 

Bosnia and Herzegovina; coal fields of, 
424; coal resources of, 409. 

Botryococcus braunii, 176. 

Boulets. 310. 

Boulton, W. S., 264. 

"Bound" molecules, 21. 

Bousquet, G., 407. 

Bownocker, J. A., 77, 370. 

"Brasses," 34. 

Brazil, coal in, 405. 

Breaker; cross-section of the Alliance, 
304; the Loree, 306.* 

Breaking coal at face, 284. 

Break-throughs, 270. 

Breasts, 267, 271, 278. 

British Columbia, coal in, 348. 

British North Borneo, coal in, 434. 

British thermal unit, (B.t.u.), 71. 

Brongniart A., 84, 194, 202. 

Brooks, A. H., 397; illustration by, 399. 

Brooks, G. S., 312. 

Brownsville, Pa., Quadrangle, structure 
section of, 366. 

Brunton's slope chart, 250. 

Brushing down, 269. 

Bryales, 188. 

Bryophytes, 186, 188. 

Buckland, W., 126. 

Buffon, L., 126. 

Buggy system, 278. 

Bulgaria: coal fields of, 425; coal re- 
sources of, 408. 

Bulman and Redmayne, 264. 

Butts, Charles, illustration by, 378. 

Bureau of Mines Method of determination 
of specific gravity, 5. 

Burgess, M. J., 26, 27, 28. 

"Buried forests," 138. 

Burrell, G. A.. 291, 293. 

Byerite, 91. 

By-product coking, 320. 

By-product derivatives, 323. 

By-product tests on various coals, 28. 

Byron, T. H., 320. 

Cahaba Coal Field, structure section of, 



Caking coal, 87. 

Calamarieae, 198. 

Calamites, 198, 195,* 194.* 

Calcareous concretions, 230. 

Calcium in coal, 37. 

Calcium oxalate, 20. 

California, coal in, 395. 

Calorie, 71. 

Calorific value: calculated, 79; deter- 
mination of, 71. 

Calorimeter: standardization of, 77; va- 
rious types of .bomb, 72; calorimeter 
washings, 75. 

" Camel-backs," 220. 

Campbell, J R., 306. 

Campbell, M. R., 42, 44, 84, 86, 169, 
363, 368, 375, 395. 

Campbell's classification, 106. 

Canada: coal resources of, 339; map of, 
PI. XI. 

"Candle "coal, 89. 

Canmore, Alberta, 347.* 

Cannel coal, 87, 89; origin of, 174; photo 
micrograph of, 90; specific gravity of, 
4, , 

Canneloid, n. 

Cape of Good Hope, coal in, 441. 

Carbocoal, 326. 

Carbon, determination of, 63. 

Carbon dioxide, 22, 291. 

Carbon-hydrogen ratio and depth, dia 
gram of, 167. 

Carbonite, 98.* 

Carbon monoxide, 22, 292; detector of, 
294; effect on animals of, 293. * 

Carnegie, Pa., Quadrangle, structure 
section of, 366. 

Carnot, Ad., 36, 55, 70, 80. 

Cellulose, 18. 

Cement burning coals, 313. 

Central America, coal fields of, 401. 

Central Coal Basin rule for shaft pillars, 

Ceratizamia mexicana, 37. 

Chain pillar, 273. 

Chamberlin, R. T., 20, 22. 

Chamberlin, T. C , 155. 

Chamber longwall, 284. 

Chambers, 267, 271. 

Chance, H. M., 25 

Charbon, 2. 

Chemical analysis, 40. 

Chemical properties of coal, 18. 

Cherry Coal, 87, 88. 

Chile, coal in, 406. 

China: coal fields of, 431; coal resources 

of, 430. 

Chlorine in coal, 37. 
Choke damp, 291. 
Christopher, J. E., 320. 
Church, A. H., 86. 
Chutes, 278. 
Cincinnati arch, 151. 
Clanney, 296. 
Clark, A. H., 27, 31. 
Clark, H. H., 296. 
Clark, W. B., 372. 
Clarke, F. W., 19, 20. 
Classification: difficulties in, 3; of coal 

lands, 260; of coals, 105; of plants, 184. 
Clay veins, 214, 216, 215.* 
Cleats, 8. 

Climatic conditions, 155. 
Coal: amount derived from peat, 148; 

color of, 8; defined, 2; estimate of 

quantity in seam of, 258; origin of word, 


Coal apples, 229. 
Coal balls, 229, 233. 
Coalification, second stage of, 160. 
Coal Measure plants, composition of, 161. 
Coal Miner's Pocketbook, 264. 
Coal provinces, 355. 
Coemans, E., 196. 
Cohen, J. B., 21. 
Coke, 88; for domestic fuel, 325; and 

coking, 315. 
Coke breeze, 323. 
Cokedale Mine natural coke, 99. 
Coking coal, 30, 87; coking coals, 316. 
Col., 2. 

Cole, B. A. J., 416. 
Coleman, A. P., 157. 
Collier, A. J., 385. 
Collier's classification, 106. 
Colloidal fuel, 314. 
Colombia, coal in, 402. 
Colorado, coal in, 388. 



Combustion furnace, 63. 

Commentry Basin, 36; drifted material 

in, 142; fish remains in coal of, 18; 

open cut of, 287.* 
Competent beds, 170, 223. 
Composition of wood, peat, and coals, 96. 
Concretions in coal, 229. 
" Condensed " gases, 26. 
Conemaugh formation, section of, 368. 
Coniferales, 211. 
Connellsville basin coke, 99. 
Connellsville coal tested, 28. 
Constance, Lake, peat on, 147. 
Contiguous seams, working of, 280.* 
Contorted partings, 224. 
Contours, structural and surface, 248.* 
Coppee oven, 320. 

Cordaitales, 208, 209;* in Devonian, 182. 
Cost of mining, average, per ton, 257. 
Coulter, J. M., 186. 
Cowles, H. C., 1 86. 
Crane, W. R., 384; illustration by, 83, 

100, 223. 

Critical level, 136. 
Cross and Bevan, 161. 
Cross-cuts, 270; cross-entries, 269. 
Crowsnest coal area, map of, 345. 
Cryptogamic plants, spores of, 9. 
Curtis^ H. A., 326. 
Cut-out, 214; 215;* on Des Moines River, 


Cut-throughs, 273. 
Cycadales, 207. 
Cycadeoidea marshiana, 208.* 
Cycadofilicales, 206. 
Cycadofilices, 203. 
Cycads, Age of, 184, 208. 

Dakotas, coal fields of, 393. 
Dalburg, F. A., 435. 
Dana, E. S., 2, 3, 89, 91. 
Daubr'e, A., 101, 166. 
David, T. W. E., 156, 448. 
Davis, C. A., 131. 
Davy, Sir William, 296. 
Dawson, J. W., 12, 174, 209. 
"Debris," n. 
Defline, M., 416. 
Degousee, M. J., 140. 

De la Becke, 166. 

De Lisle, 87. 

Delta deposits, coal in, 139. 

Denmark: coal fields, of 421; coal re- 
sources of, 408. 

Denoel, L., 420. 

DePapp, C., 424. 

Depth: maximum of coal mines in foreign 
countries, 253; maximum, of coal mines 
in the United States, 251; of burial, 
166; of seam, determination of, 247; 
table for determination of, 249. 

Derivatives of coal and their uses, 

Fig- 5. 

Descloizeaux, A., 97. 
Devonian period, first appearance of land 

plants in, 179. 
Diatoms, 86. 
Dike, 228,* 231.* 
Diller, J. S., 396. 
Dip, 221.* 
Dismal Swamp, 139,* 141,* 142;* Lake 

Drummond in, 137;* map of, 135; 

peat in, 137. 

Displacement in fault, 225. 
Distillation, products of, 25. 
Domestic anthracite, preparation of, 300. 
Dominian, L., 425. 
Dopplerite, 83. 
Dorrance, C., 310. 
Double battery breast, 279.* 
Double room, 272.* 
Douglas, E. A., 435. 
Dowling, D. B., 339, 348; classification 

by, 112; illustration by, 345, 346. 
Drake, N. F., 431. 
Drift, 266. 

Drifted vegetation, 139. 
Drills in prospecting, 243. 
Dron's rule for shaft pillars, 275. 
Dry coal, 92. 
Dulong's formula. 79. 
Dumble, E. T., 99, 386. 
Duncan, W. G., 291. 
Dunkard formation, section of, 370. 
Dunkley, W. A., 312. 
Durley, R. J, 7, 8, 339. 
Dutch East Indies, coal in, 435. 
Duxite, 103. 



Dyer, B., 68. 
Dysodile, 86. 

Eastern-Middle Anthracite field, section 
through, 362. 

Ecuador, coal in, 404. 

Electric cap lamp, 296. 

England: coal resources of, 408; resources 
of various coal fields in, 412. 

Entries, 263, 270. 

Equisetales, 190, 198. 

Equisetum, 198. 

Eschka method for sulphur, 56 

Eshereck, George, Jr., 327. 

Ethane in coal, 20. 

Europe: coal fields of, 407; coal resources, 
table of, 408; map of, PL XVI; min- 
ing methods in, 287; geological age of 
coals of, 410. 

Evans, J. W., 434. 

Exposure before burial, 162. 

Face, 271. 

Face on, 272. 

Falkenau, brown coal of, 20. 

Fat coal, 92. 

Fats, composition of, 20. 

Faults, 224, 225,* 226. 

Fayol, H., 32, 129, 141, 162. 

Federal Trade Commission Report, 257. 

Ferns, 180, 201, 

Fieldner, A. C., 44, 52, 70, 73 

Filicales; see Ferns. 

Finn, C. P., 21. 

Fire damp, 22, 294. 

First mining in Virginia, i. 

First production in the United States, i. 

Fish remains in coal, 18. 

Fisher, C. A., 251. 

Fixed carbon, determination of, 56 

Flow, igneous, 229. 

Flow sheet of Alliance Breaker, 303. 

Fontaine, W. M., 184, 193; and White, 

illustration by, 204. 
"Fool's gold," 34. 
Foot-acre, value of, 255. 
Formula for composition of coals, 149. 
Fossil flora of coal-forming periods, 178. 
Foster's rule for shaft pillars, 276. 

Foundry coke, standard for, 316. 

Fracture in coal, 8. 

France: coal fields of, 416; coal resources 

of, 408. 

Frank, Alberta, landslide, 344.* 
Franke, G., 309. 
Frazer, J. C. W, 31. 
Frazer, T., 306. 
Frazer's classification, 105. 
"Free" paraffins, 21. 
Fremy, E., 30. 
Fresh water swamps, 133. 
Fuel ratios of Pennsylvania coals, map 

of, 172 

Fundamental matter, n. 
Fungi, 1 86; in coal, 159. 
Fusain, 100, 307. 
Fusibility: of ash, 121; of various coal 

ashes, 53. 

Gagates, 2, 97. 

Gamba, F. P., 402. 

Gangamopteris, 180; 211.* 

Gangamopteris flora, 156. 

Gangways, 267, 278. 

Garcia, J. A., 290. 

Gardner, J. H., 387. 

Gas manufacture: bibliography, cited, 
25; coals for, 311. 

Gases: evolved from coal below tempera- 
ture of decomposition, 23; in coal, 22. 

Geikie, A., 147. 

Geographic distribution of coal, 328. 

Geological age of coals: of Africa, 439; 
of Europe, 410; of North America, 
table of, 338; of Oceania, 443; of the 
United States, 360. 

Geological distribution of coal, 328; by 
varieties, table of, 332. 

Geological formations, table of, 330 

Georgia, coal in, 378. 

Germany: coal fields of, 421; coal re- 
sources of, 409. 

Gibson, 378. 

Gingkoales, 210; ancestors of, 182. 

Glanzkohle, 94 

Glossopteris, 180, 211.* 

Glossopteris flora, 156, 157. 

Gob side, 272. 



Gore, N. Z., retinite from, 102. 

Gottlieb, table by, 161. 

Gouge, 225. 

Goutal, M., 79. 

Goutal's curve, 80. 

Grains, cones, spores, 181.* 

Grains from Coal Measures, 185.* 

Grande Couche, 36, 214. 

Grand'Eury, F. C., 128, 191, 203; illus 
tration by, 150, 181, 185, 209. 

Graphic method for thickness, 244. 

Great Britain; coal fields of, 407; coal re- 
sources of, 408. 

Greece: coal fields of, 425; coal resources 
of, 408. 

Gresley, W. S., 130. 

Grinding thin sections, 15. 

Grout's classification, 109. 

Gruner, E., 407; classification by, 115. 

Gr Liner, L., 128. 

Guignet, E. 30. 

Gulf Province, 385. 

Giimbel, C. W., von, 12, 128. 

Gymnosperms, 185, 206; ancient types of, 
203; dominant in Triassic, 182. 

Gypsum in coal, 35. 

Hade, 225. 
Hadley, H. F., 31. 
"Half on," 272. 
Hall, A. A., 21. 
Hall, R. D., 36. 
Hamilton, N. D., 309. 
Hapke, L., 32. 
Hard coal, 94. 
Hardness, 8. 

Harper, Francis, illustration by, 133, 134. 
Harrisburg, 111., coal tested, 28. 
Haulage, 288; electric, 290.* 
Hausmann, J. F. L., 84, 87. 
Hauy, 94. 

Hazeltine, illustration by, 373. 
Hazleton, Pa., district, 95; structure sec- 
tion of, 362. 
Hawes, G. W., 161. 
Hayden, H. H., 433. 
Hayes, C. W., 378. 
Headings, 267. 
Heat, effects of, 168. 

Heave, 225. 

Heavy solutions for determination of 
specific gravity, 7. 

Heinrich, O. J., 101. 

Hepaticae, 188. 

Hilaire, B. S., 2. 

Hill, R. T., 400. 

Hillman Coal and Coke Co., illustration 
by, 292, 319. 

Hinds, H., 382, 383. 

History of first uses of coal, i. 

Hochstetter, 102. 

Hoffman, E. J., 31. 

Hogarth's flask, determination of specific 
gravity by, 5.* 

Hoisting, 289. 

Holmes, J. A., 42. 

Horn Coal, 89. 

Horsebacks, 214, 216, 215;* on mine map, 

Horsetails, 190; silica in, 37. 

Houille, 86, 87. 

Howarth, 384. 

Ho well, S. P., 298. 

Howley, J. P., 352. 

Hughes' rule for shaft pillars, 276. 

Humboldtine, 20. 

Humic coals, 87. 

Humus acids, 20. 

Hungary: coal fields of, 424; coal re- 
sources of, 409. 

Hutchinson R. P., illustration by, 300, 

Hutton, W., 11, 174. 

Huxley, 174. 

Hydrogen, 295 ; determination of, 63. 

Hydrogen sulphide, 295. 

Hydrogenous coals, 90. 

Hydroxide of sodium for softening sec- 
tions, 13. 

Igneous intrusions, 228.* 

Illinois: coal in, 381; section of Coal 

Measures of, 380 
Illuminating gas, 312. 
Inby, 271. 

Incompetent beds, 170. 
India: coal fields of, 433; coal resources 

of, 431- 



Indian Lands, 240. 

Indiana, coal in, 382. 

Inert volatile matter, no. 

In situ theory, 124. 

Interior province, 379. 

International Geological Congress, classifi- 
cation by, 113. 

lonite, 104. 

Iowa: cross-section of formations of, 382; 
coal in, 382. 

Ireland: coal fields of, 416; coal resources 
of, 408; peat in, 133. 

Iron in coal, 37. 

Iso-anthracitic lines, 173, 174; of South 
Wales field, 165. 

Isoclinal fold, 222. 

Isovols, 174. 

Italy: coal fields of, 419; coal resources 
of, 408. 

Ivanov S. L., analysis by, 177. 

Japan: coal fields of, 432; coal resources 

of, 430. 
Jeffrey, E. C., 12, 13, 101, 130, 174, 176, 

233; illustration by, 90. 
Jet, 97. 
John, von, 20. 
Johnson, W. R., 105. 
Johnston, F. W., 103. 
Jones, D. T., 21. 
Joseph, 1 66. 
Jukes, J. B., 127; illustration by, 229. 

Kansas: coal deposits in, 384; structure 

section of Coal Measures of, 384. 
Karst, 84, 94. 
Katz, S. H., 23. 
Katzer, F., 424. 
Kauri gum, 102. 
Kaustobioliths, 130. 
Kelley, W. P, 38. 
Kentucky cannel, 90. 
Kentucky, coal in, 377. 
Kerosene shale, 175. 
"Kettle," 220. 
Kick, J. J., 196. 
Kidston, 203. 
Kilkenny coal, 89. 
Kinosuke, I., 431, 432. 

Kirwin, R., 89. 

Kjeldahl-Gunning method, 68. 

Klonne oven, 322. 

Koppers byproduct coke plant, 324.* 

Korea, coal in, 432. 

Krafft, 20. 

Kressman, F. W., 32, 308. 

Le Conte J., 127. 

Laccolith, 228. 

Land Office Regulations, 238. 

Land plants, rise of, 180. 

Lane, A. C., 379. 

La Veta, Colorado, structure section near, 


Law of Hill, 1 66. 
Laws governing prospecting, 238. 
Leaf cushions, 192. 
Leaf traces of Sigillaria, 194. 
Leasing laws, 240. 
Lenhart, L. R., 52. 

Lepidodendron, 157, 180, 191; 179,* 183.* 
Lesher, C. E., 51. 
Lesley, J. P., 128. 
Lesquereaux, illustration by, 191, 193, 195, 

197, 200, 202. 
Lignite, 84; ignition temperature of, 32; 

85;* seam of, 394;* specific gravity of, 


Lignocellulose, 18. 

Liguria, 2. 

Link, F., n, 126. 

Locating new seams, 242. 

Loew, O., 104. 

Logan, W. E., 126. 

Loire basin coals, 31. 

Lonchopteris bricei, 206.* 

"Long horn," 272. 

Longwall, development in anthracite re- 
gion, 285.* 

Longwall method, 281. 

Longwall mine, 282,* 283.* 

Lord, N. W., 73, 77, 87. 

Loree Breaker, 306.* 

Lump anthracite, 301. 

Luster, 9. 

Lyburn, E., 416. 

Lycia, jet from, 2. 

Lycopodium, 190. 


Lycopods, 180. 
Lyes, 271. 

MacCulloch, J., 126. 

McCalley, 378. 

McCallie, 378. 

McConnell, W., 23, 24. 

McCreeth, A. S., 106. 

Macklin, J. F., illustration by, 290. 

Madura arantiaca, 157. 

Macrosporangia, 207. 

Magnesium in coal, 37. 

Mallett, E. J., 91. 

Maly, 102. 

Manchuria: coal fields of, 432; coal re- 
sources of, 431. 

Mangrove swamp, N. Z., 144.* 

Mangrove swamps, 138. 

Manitoba, coal, in 343. 

Map of: Africa, 437; Alaska, 399; Asia, 
PI. XVIII; Canada, PI. XI; European 
Russia, 427; Oceania, PI. XX; South 
America, 403; United States, PI. XII; 
Western Europe, PI. XVI. 

Marcasite, 34. 

Mariotte flask, 65. 

Marsh gas, 294. 

Marshall, P., 448. 

Marshes, 132. 

Martin, G. C., 397. 

Maryland, deposits in, 372. 

Marzec, L., 424. 

Maumen?, J., 71. 

Mellite, 20. 

Merrimac Mine Breaker, 376.* 

Metagami River timber, 145.* 

Methane, 22, 294; absorbed by coal, 23. 

Methyl orange indicator, 75. 

Mexico, coal in, 400. 

Meyer, von, 24. 

Michado, M. R., 406. 

Michigan: coal in, 379; structure section 

in, 379- 

Micrococcus, 159. 
Microscope in study of coal, 9, n. 
Middletonite, 103. 
Mietzsch, H., 128, 138, 154. 
Miller, B. L., 402. 
Miller, C. F., 38. 

Mills, J. E., 310. 

Milojkovitch, F. A., 424. 

Mine fires, 298. 

Mine gases, 290; relation of, to volatile 

constituents, 25. 
Mine level, 270. 
Mine ventilation, 296. 
Mineral charcoal, 100. 
Mineral coal, 2. 

Mineral constituents of coal, 33. 
Mineral, defined by Dana, 3. 
Mineral Industry, cited, 321, 335. 
Mineral Lands, 3, 238. 
Mineral Resources United States Geological 

Survey, cited, i, 255, 299, 353. 
Minimum thickness of seams mined, 253. 
Mining Engineering rule for shaft pillars, 


Mining machine undercutting ream, 289.* 
Mining machines, 286. 
Mining methods in foreign countries, 287. 
Mining of coal, 264. 
Missouri, coal in, 383. 
Mitscherlich, A., 70. 
Moffat, E. S., 164. 
Mohr, F., 145. 
Moh's scale, 8, 95. 
Moissan, H., 32, 86. 
Moisture, determination of, 49. 
Moisture oven, 49. 
Monoclinal fold, 222. 
Monongahela formation, section of, 369. 
Montana, coal in, 394. 
Montenegro, 425. 
Moore, E. S., 217; illustration by, 144, 

145, 148, 152, 227, 231, 236, 265, 287, 

344, 351, 417, 446, 447. 
Morwell, Australia, 214. 
"Mother-of-coal," 100. 
Mourlot, A., 39. 
Mud-screen product, 301. 
Muer, H. F., 60 
"Mur," 153. 
Murchison, R. L, 127. 
Musci, 1 88. 

Naked seeds, 206. 
Naphthenes, 21. 
Natal, coal in, 447. 



National Parks, 240. 
Natural coke, 98.* 
Neck, 271. 

Netherlands: coal fields of, 420; coal re- 
sources of, 408. 
Neuropteris, 201,* 202.* 
Neuss, 84. 

New Brunswick, coal in, 342. 
New Mexico, coal in, 387. 
New South Wales, coal in, 444; section 

through main coal basin of, 444. 
New Zealand: coal fields of, 448; coal 

resources of, 443. 
Newberry, J. S., 128, 196. 
Newfoundland, coal in, 352. 
Niggerhead coal, 230, 235; analyses of, 

237, 236.* 

Nitchie, C. C.. 312. 
Nitric acid, effects of, on coal, 30. 
Nitrogen determination of, 68. 
Non-caking coal, 88. 
Non-coking coal, 88. 
Normal fault, 225. 
Norris, R. V., 307. 
North America: coal fields of, 336; coal 

resources of, 337; geological age of 

coals of, 338. 

North Dakota lignite, 85.* 
Northern Anthracite field, section through, 


Northern Great Plains Province, 387. 
Northern Territory, Australia, coal in, 


Northrup, H. B., analyses by, 102. 
Northwest Territories, coal in, 351. 
Nova Scotia, coal in, 340. 
Norway, coal in, 428. 

Oak, composition of, 162. 

Oberfell, G. G., 291. 

Occluded gases in coal, 22. 

Oceania: coal fields of, 438, 442; coal 
resources, table of, 443; geological ages 
of coals of, 443 ; map of, PI. XX. 

Odell, W. W., 312. 

Odontopteris, 200.* 

Ohio: coal in, 370; section of Carbonifer- 
ous formations of, 373. 

Oils, composition of, 20. 

Okefinokee Swamp, 133,* 134.* 

Oklahoma, coal in, 385. 

Oleinic acid, 177. 

Oliver, F. W., 203, 204. 

Ombre de Cologne, 86. 

Ontario, coal in, 342. 

Ophioglossales, 190. 

Oregon: coal in, 396. 

Organic acids, salts of, 20. 

Origin of coal, 123. 

Osbon, C. C., 136. 

Otto-Hilgenstock oven, 322. 

Otto-Hoffman oven, 322. 

Outby, 271. 

Overthrust fold, 222. 

Ovitz, F. K., 22, 25, 26, 27, 28, 33, 309. 

Oxalic acid, 20. 

Oxygen, determination of, 70. 

Oxypicric acid, 30. 

Pacific Coast Province, 395. 

Packs; gob, 282; road, 282. 

Pack-walls, 282. 

Panel system, 277.* 

"Paper coals" of Russia, 20. 

Paraffin series, 20. 

Parmelee, C. W., 313. 

Parr, S. W., 31, 32, 42, 43, 52, 60, 62, 70, 
79, 149, 308, 309; classification by, 109; 
peroxide bomb calorimeter of, 67. 

Parrot coal, 89. 

Partings, 214, 215.* 

Pas-de-Calais coal basin, complicated struc- 
ture in, 232.* 

Peacock coal, 96. 

Peat, 82; rate of accumulation of, 146. 

Peat-bogs, 131. 

Pebbles of coal in Coal Measures, 164. 

Pechkohle, 86. 

Pecopteris, 199.* 

Peek's Handbook, 264, 300. 

Pennsylvania, 81; bituminous region of, 
368; coal fields of, 363; structure sec- 
tion through southwestern part of, 366. 

Pennsylvania anthracite: distribution of 
in 1917, 299; specific gravity of, 96. 

Pennsylvania bituminous coal, distribu- 
tion of in 1917, 299. 

Permissible explosives, 298. 



Permo-Carboniferous section in New South 

Wales, 157, 444. 
Persia: coal fields of, 434; coal resources 

of, 431. 

Peru, coal'in, 404. 
Petrascheck, W., 423. 
Phanerogams, 206. 
Phenol as solvent for coal, 31. 
Philippine Islands, coal in, 435 
Phillips, W. B., 386. 
Phosphorous, 36; determination of, in 

coal ash, 53. 

Photometric method for sulphur, 60. 
Photomicrographs of coal, 16; from Roy- 

alston showing spores and woody tissue, 

10; showing pyrite, 35; showing resin, 

19; showing spores in cannel, 90. 
Phylloglossum, 190. 
Physical constitution, 9. 
Physical properties, 4. 
Pila bibractensis, 175.* 
Pillar drawing, 280 
Pillar-and-stall system, 276. 
Pillars, size of, 273. 
Pinaceae, 211. 
Pinches, 215. 
Pines, see Pinaceae. 
Pinnularia, 198. 
Pishel, M. A., 88. 
Pitch, 222. 
Pittman, E. F., 444. 
Pittsburgh seam, 369, 371, 372, 374, 375; 

photomicrograph of coal from, 16. 
Plan of four-entry mine, 268. 
Plankton algae, 177. 
Plant spores used in distinguishing seams, 


Pliny, 2. 

Pocahontas coal tested, 28. 

Pocahontas field, 375. 

Poland, coal in, 426. 

Pollard, W., 7, 48, 63, 65, 69, 107, 166, 173. 

Pope, G. S., 43- 

Port Elizabeth, N. Z., collieries of, 447.* 

Porter, coal of, 81. 

Porter, H. C., 22, 25, 26, 27, 28, 33, 309. 

Porter, J. B, 7, 8, 339. 

Protugal: coal fields of, 418; coal re- 
sources of, 408. 

"Pot", 220. 

Potonie, H., 12, 90, 130, 138. 
Pottsville formation, section of, 367 
Powdered fuel, 313. 
Powell, A. R., 62, 317. 
Power, F. Danvers, 288, 442. 
Preparation of coal, 299. 
Pressure, effect of, on coal, 170. 
Prestwich, J., 97. 
Price of coal at mine, 256. 
Producer gas, 311. 

Production of world in 1913, i; by coun- 
tries, 335; and states, 352. 
Prospecting for coal, 238. 
Proximate analysis, 48. 
Psilo tales, 190. 
Pteridophytes, 186, 188. 
Pycnometer, 4. 
Pyridine, 32. 
Pyrite, 34. 
Pyroretinite, 104. 

Queensland, coal in, 445. 

Rabino, H. L., 434. 

Ranks of coal, 82. 

Rath, G. von, analyses by, 99. 

Reinchia australis, 176. 

Renault B., 12, 148, 149, 174, 175, 196, 198, 

207; illustration by, 158, 159, 210. 
Renier, A., 420. 
Resinous substances, 102. 
Resins: composition of, 20; in coal, n. 
Resources of world by continents, 333. 
Retinite, 102. 
Rhacopteris, 180, 211.* 
Rhode Island: anthracite of, 95; coal in, 


Rhodesia, coal in, 440. 
Rib, 271. 

Rice, G. S., 287, 297. 
Richardson, G. B., illustration by, 388, 

Ries, H., 172; illustration by, 341, 342, 

347, 376, 394- 
Riffle sampler, 46. 
Rittman, W. F., 25. 
Roberts oven, 322. 
Robertson, I. W., 291, 293. 



Robinson, W. O., 38. 

Rock chutes, 280. 

Rock Springs coal field, structure section 
of, 392. 

Rocky Mountain Province, 387. 

Roden, J., 434. 

Rogers, H. D., 90, 92, 101, 127. 

Rolls, 214, 216, 215,* 234.* 

Ronchamp, 81 

Rooms, 267, 271; inclined, 271.* 

Room-and-pillar method, 264, 267. 

Royal Commission on Coal supplies, 253. 

Royalston, 111., photomicrograph of coal 
from, 10. 

Royalties on leases, 259. 

Roumania: coal fields of, 424; coal re- 
sources of, 409. 

Russia: coal fields of, 426; coal resources 
of, 409; in Europe, map of, 427. 

St. tienne: fault at, 227;* tree trunks 
near, 148,* 152.* 

Ste. Colombe sur 1'Hero, 97. 

Saar basin, section through, 422. 

Safety lamps, 295. 

Salisbury, R. D., 155. 

Sampling, 40; English method of, 48; 
equipment for, 42; in laboratory, 47; 
laboratory apparatus for, 46; standard 
method of, 44. 

San Raphael, 39. 

Sapropelic coals, 90. 

Sapropelic deposits, 130. 

Sargasso Sea, 145. 

Saskatchewan, coal in, 343. 

Schering's celloidin, 13. 

Schrotter, 104. 

Schulze, Franz, n. 

Schwarzkohle, 87. 

Scotland- coal fields of, 413; coal re- 
sources of, 408. 

Scott, D. H., 203, 204. 

Scouring rushes, 198. 

"Seatearth," 153. 

Seibert, F. M., 293. 

Selvage, 225. 

Selvig,W A, 52. 

Semet-Solvay coke pusher, 321.* 

Semet-Solvay plant, 322.* 

Semianthracite, 92. 

Semibituminous coal, 92. 

Sequoia, 211. 

Serbia: coal fields of, 424; coal resources 

of, 409. 

Seyler's classification, 107. 
Shaft, 266, 267. 
Shaft bottom, 292.* 
Shaft pillar, 273. 
Shaler, N. S, 135, 375; illustration by, 

i35, 137, 139, Ui, 142. 
Shamel Charles, 238. 
Shepherd's Hill, New South Wales, 446.* 
Sheppard, S. E., 314. 
Sheridan coal tested, 28. 
Shoofly, 271. 
"Short horn," 272. 
Shove fault, 226. 

Shultz and Lewis, illustration by, 392. 
Siberia, coal in, 431. 
Sidings, 271. 
Sigillaria, 180, 194, 187.* 
Sigillarian cones, 195. 
Sigillariostrobus goldenbergi, 189.* 
Silica in coal, 37. 
Sill, 228. 

Singewald, J. T., Jr., 402. 
Sinnatt, F. S., 307. 
Stele, 190. 

Slate pickers in breaker, 300 . * 
Slickenside, 225. 
Slip fault, 226. 
Slope, 266. 
Smith, G. O., 395. 
Smith process, 327. 
Smithing coals, 313. 
"Sole," 153. 

Solms-Laubach, 193, 198. 
Solubility of coal, 29; relation of, to 

coking, 30. 

Somermeier, E. E., 77. 
Somme Valley, peat in, 147. 
Sorus, 189. 

South Africa, Union of, coal in, 441. 
South America, coal fields of, 402; map 

of, 403 

South Australia, coal in. 448 
South Wales: coal in, 414; origin of coals 

of, 1 68. 



South Wales field, diagram of ash and 
carbon-hydrogen ratios of coal of, 173. 

Southern Nigeria, coal in, 439. 

Spain, coal fields of, 418; coal resources 
of, 408. 

Specific gravity: defined, 4; of anthracite 
4; of "ash-free" and "moisture-free" 
specimens, 7; of bituminous coal, 4; 
of cannel, 4; of lignite, 4; relation of, 
to quality of coal, 8. 

Specific gravity, determination of: by 
Bureau of Mines, 5; by heavy solutions, 
7; by Hogarth-flask, 5; by hydrometer 
method, 6; by pycnometer, 4. 

Spermatophytes, 185, 186, 206. 

Sperr, F. W., Jr., 320. 

Sphagnum 132, 188. 

Sphenophyllales, 196. 

Sphenophyllum, 190. 

Sphenopteris, 197.* 

Spitzbergen: coal fields of, 428; coal re- 
sources of, 409. 

Splint coal, 87, 88. 

Split, 215.* 

Split-volatile ratio, 112. 

Spontaneous combustion, 307; chemical 
causes of, 32. 

Spruces, 211. 

Square-chamber method, 287. 

Squeezes, 214, 215. 

Standardization of calorimeter, 77. 

Stansfield, E., 32, 326. 

Stanton, F. M., 5, 44, 73. 

Steam coals, 314. 

Steinkohle, 2 

Stemkoenig, L. A., 38. 

Stephenson, George, 296. 

Sterling, Paul, 300. 

Stern, H., 307. 

Stevenson, J. J., 124, 128, 129, 138; illus- 
tration by, 369, 370. 

Stigmaria, 130, 153, 193; S. ficoides, 196; 
S. ficoides, 191.* 

Stink damp, 295. 

Stock, H. H., 96, 363; illustration by 
278, 280, 362. 

Stohman's solution, 76. 

Stone coal, 94. 

Stone damp, 295. 

Stopes, M. C., 230. 

Storage, 306; deterioration of coal in, 309 

Storrs, L. S., 387. 

Stout, D. A., 237. 

Strahan, A., 7, 107, 166, 173, 407; illus- 
tration by, 224; and Pollard, diagram 
by, 165, 167. 

Streak, 8, 9. 

Streptococcus, 159. 

Strike, 221.* 

Stringer of coal, 221.* 

Stripping Mammoth seam, 265.* 

Stripping method, 264. 

Structural contours, 248. 

Structural features of coal seams, 214. 

Stumps in Coal Measures, 150.* 

Stur, D., 192. 

Subbituminous coal, 84, 86, 93.* 

Succinite, 103. 

Sullivan Machine Co., illustration by, 289. 

Sulphates in coal, 34. 

Sulphides in coal, 34. 

Sulphur, 33; determination of, by Eschka 
method, 56; in ash, 62; in coke, 33, 
316; inorganic, 34; organic, 35. 

Sulphur balls, 34, 230. 

Sulphur diamonds, 34. 

Sulphuretted hydrogen, 295. 

Sulphurous gases, 27. 

Sumatra Swamp, 138. 

Summit Hill, 95. 

Superbituminous coal, 92. 

Sussmilch, C. A., 156, 210. 

Sweden: coal fields of, 428; coal resources 
of, 409. 

Swells, 214, 215. 

Swift, illustration by, 282. 

Switzerland, coal in, 419. 

Syncline: at Hazleton, 236;* pitching, 


Synclinorium, 223. 

System of Mineralogy, Dana's 2. 

Taeniopteris Newberriana, 204.* 

Taff, J. A., 98, 385- 

Tantalus Mine on Yukon River, 351.* 

Tasmania, coal in, 447. 

Tasmanite shale, 447. 

Tauber's drying apparatus, 66. 



Taxaceae, 211. 

Taylor, C. A., 70. 

Temperature, effect on constituents, 

evolved, 26. 
Tennessee, coal in, 378. 
Terre d'ombre, 86 
Texas, coal in, 386. 
Thallophytes, 186, 188. 
Theophrastus, 2. 
Thick seams: bench working in, 288;* 

mining in, 284. 

Thickening of seams in anticlines, 223. 
Thickest seam in world, 214. 
Thickness of formation: determination 

of, 245; curve for graphic determination 

of, 246. 
Theissen, R., 9, n, 13, 14, 15, 20, 34,36, 

101, 130, 176; illustration by, 10, 12, 14, 

16, 19, 35- 
Thin seams: mined in foreign countries, 

255 ; mined in United States, table of, 254. 
Thin sections, preparation of, 12. 
Thomas, J. W., 23, 24. 
Thracius lapis, 2. 
Throw, 225. 
Thrust fault, 225. 
Tile burning coals, 313. 
Time since burial, 163. 
Topographic conditions in coal-forming 

periods, 150. 
Torbanite, 87, 91. 

Toronto, Canada, glacial deposits, 157. 
" Tortoises" 220. 
Transformation of vegetal matter to coal, 


Transportation theory, 125. 
Transvaal, coal in, 441. 
Tree trunks in Coal Measures at St. 

tienne, 148,* 152.* 
Trees, composition of, 161. 
Trescot, T. C., 68. 

Trinidad, Colorado, section near, 389. 
Trinkerite, 104. 

Tri-radiate lines in spores, 14.* 
Tschernyschew, Th, 426. 
Tunnel, 266. 

Turbidimeter, Jackson's candle, 60. 
Turkey, coal in, 425. 
Turn-out, 271. 

Ultimate analysis, 63. 

Unconformity, 227. 

Underclays, origin of, 153. 

Underground work, 264. 

Uniontown, Pa., Quadrangle, structure 
section of, 366. 

United States: coal in, 352; coal produc- 
tion of, 352, 353, 354; distribution of 
coal of, by kinds, 355; geological age 
of coal formations of, 360; map of, 
PI. XII; table of coal resources of, 357, 
358, 359- 

Upthrow side, of fault, 226. 

Uses of coal, 299. 

Utah: coal in, 391; coal of, tested, 28. 

Value of world's production in 1913, i. 
Valuation of coal lands, 238, 250. 
Vanadium in coal, 39. 
Vandalia, Ind., photomicrograph of coal 

from, 19. 

Varieties of coal, 82. 
Vascular cryptogams, 180, 182. 
Venezuela, coal in, 404. 
Venice, Gulf of, peat in, 140. 
Victoria, coal in, 445. 
Vignon, Leo, 30, 88. 

Virginia: coal in, 375; first mining in, i. 
Volatile constituents, escape of, from seam, 

Volatile matter: determination of, 54; 

furnace for determination of, 54.* 
Voltzia, 182. 

Walchia, 182, 213; W. frondosa, 210.* 

Wales, coal resources of, 408, 412. 

WaUerius, J. G., 84. 

Walsen Mine, natural coke of, 99. 

Washington, coal in, 396. 

Water gas, 312. 

Watson, D. M. S., 230. 

Waxes, composition of, 20. 

Wedemeyer, K., 68. 

Weight of coal in foot-acre, 258. 

Welsh anthracite, specific gravity of, 96. 

Welsh coals, tests on, 24. 

West Indies, coal fields of, 401. 

West Virginia, coal in, 372. 

Western Australia, coal in, 447. 



Wheeler, R. V., 21, 27, 28, 31, 32. 

Wheelerite, 104. 

Whewellite, 20. 

Whitaker, M, C., 25. 

White, D., ii, 12, 14, 20, 33, 88, 101, 102, 
130, 156, 166, 170, 176, 195, .196, 203, 
368; illustration by, 367. 

White, I. C., 193, 372, 405; illustration by, 
367, 368. 

White damp, 292. 

White's classification, in. 

Wieland, G. R., 207; illustration by, 208. 

Wilder F., illustration by, 394. 

Wilkes-Barre, Pa., structure section at, 362. 

Willputte oven, 322. 

Witham, H., n, 126. 

Wood: changed to coal, 164; composi- 
tion of, 19. 

Woodworth, J. B., 375. 

Worrell, S. H., 386. 

Wright, C. L., 311. 
Wyoming basin, Pa., 171. 
Wyoming, coal in, 392. 

Xyloid lignites, solubility of, 29. 
Xyloid material, 9. 
Xylon, n. 

Yancey, H. J., 306. 

Yorkshire jet, 97. 

Yukon Territory, coal in, 350. 

Zalessky, M. D., 176, 235. 

Zamia, 207. 

Zamites, 207. 

Zeiller, R., 190, 195, 202, 203, 204, 207; 

illustration by, 179, 183, 187, 189, 194, 

199, 201, 205, 206. 
Zern, E. N., 315, 363. 



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