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UMIVERSITY OF ILLINOIS BULLETIN

ISSUED WEJCXLT
' ,' XIV JUNE 18, 1917 No. 42

•= >red M second-claw matter Deo. 11. 1912. at the Post Offloe at Urban*. HI., under the Act of Aug. 24. 1912.]

PEECENTAGE OF EXTRACTION OF

BITUMINOUS COAL WITH SPECIAL
REFERENCE TO ILLINOIS CONDITIONS

0. M. YOUNG

ILLINOIS COAL MINING INVESTIGATIONS
COOPERATIVE AGREEMENT

(This Report was prepared under a Cooperative Agreement between the
Engineering Experiment Station of the University of Illi-
nois, the Illinois State Geological Survey, and
the U. S. Bureau of Mines)

BULLETIN No. 100
ENGINEERING EXPERIMENT STATION

PtTBLISHKO BT THE UNIVERSITY OF ILLINOIS, UflBANA

EUROPEAN AGENT
CHAPMAN <fc HAIA., LTD., LONDON

EXCHANGE

UNIVERSITY OF ILLINOIS
ENGINEERING EXPERIMENT STATION

BULLETIN No. 100 JUNE, 1917

PERCENTAGE OF EXTRACTION OF BITUMINOUS

COAL WITH SPECIAL REFERENCE TO

ILLINOIS CONDITIONS

C. M. YOUNG

ASSISTANT PROFESSOR OP MINING EESEARCH

ENGINEERING EXPERIMENT STATION

PUBLISHED BY THE UNIVERSITY OP ILLINOIS, URBANA

CONTENTS

PAGE

INTRODUCTION 7

1. Preliminary Statement 7

2. Acknowledgments 7

3. Summary g

4. Conclusions g

CHAPTER I. MINING METHODS AND CONDITIONS IN RELATION

TO EXTRACTION 11

5. Introduction 11

6. Subsidence ... . . . 18

7. Squeezes . ... ... . 20

CHAPTER II. EXTRACTION IN ILLINOIS 29

8. Plan for Division of Districts 29

9. Conditions Affecting Extraction 31

10. District I , . ... -;• ; . ....... 31

11. District II 32

12. District III . . . . . . , . . . . . . 33

13. District IV . . .'. . ... . .... 36

14. District V . . . . . . . 38

15. District VI . . . . '. ... . . . . . . 40

16. District VII . . . . . . . . ..... 53

17. District VIII . . . . . ; * • . ... 56

18. Conclusion . . ... ."* . . . . .. . . 59

CHAPTER III. METHODS AND RECOVERY IN THE UNITED

STATES . . . . . :-..... . . . 60

19. Early Methods in the United States ..... 60

20. Pennsylvania . . . . . . . . . * . '. 61

21. Connellsville District . . , . . . .... 75

22. Central Pennsylvania .... . .... . 83

23. Summary of Facts Relating to the Percentage of

Recovery in Pennsylvania . .... . '.- . 88

24. Maryland 90

25. West Virginia . . . . . - . . . . '. . 98

381240

• * ?*O**V**?5 * -,1 "

^ v V? . J^goorotaB (CONTINUED)

PACK

26. Ohio . . ............. 116

27. Kentucky . . . , , . . ...... 118

28. Tennessee . . . . . . . . . . . . . 121

29. Alabama . . . . ....... . . . 122

30. Indiana . . \ . . . . . . . . . ... 125

31. Michigan . ... . .... . ... '-. 126

32. Iowa . ..... ..... . . ... 126

33. Missouri .... . 1 ..... '. . . 127

34. Arkansas ... .... . . ..... 128

35. Kansas .......... ..... 130

36. Oklahoma . . . , ....... . . . . 132

37. Texas \ . .-.' •'."'. . .^. . .' . . , . . 133

38. North Dakota . . . . ...... . .... 133

39. Colorado . . . . . . . ..... . . 133

40. New Mexico . . . . ... . . ,. . . . 134

41. Utah ... . .. ... . . . . . . 134

42. Washington . . . . . . . . ... . . 141

APPENDIX. DEVELOPMENT OF MINING METHODS IN ENGLAND

AND ON THE CONTINENT ..... . . 142

43. Brief History of Coal Mining Practice in England . 142

44. Ventilation . . . . . '. . ..... . . 147

45. The Panel System . ... ..... . . 148

46. Square Work of South Staffordshire . . . . . 149

47. The Long-wall System ... /..-,. . . 150

48. Percentage of Recovery in England . .. ., . . 151

49. Percentage of Coal Lost . . . . , . ••„ . . 154

50. Mining Conditions on the Continent ... . . 156

51. Percentage of Extraction on the Continent . . . 156

BIBLIOGRAPHY . . . . . . . , . . . ... . 160

INDEX 166

LIST OF FIGURES

NO. PAGE

1. Map Showing Thicknesses of Coal and Values of Farm Lands, as Given

by the 1910 Census Reports . . . ; , .. ... . . . . . 19

2. Map of Districts of Cooperative Coal Mining Investigations . . . . 30
3. ^Pillar Drawing at Matherville, Illinois ... .' . . . . . . .^ . 35

4. uPillar Drawing in Franklin County, Illinois 45

5. Panel Long-wall . . . ../,.. „• . .....' .... 52

6. Plan of an Operation in Macoupin County, Illinois, Showing Extraction

in a Limited Area . .... . 55

7. Plan of Mine in Vermilion County . . . . '. . . . . . . . 57

8. Old Method of Room-and-Pillar in Pittsburgh, Pa., District .... 62

9. . Improved Method of Room-and-Pillar in Pittsburgh, Pa., District . . 63

10. Modern Method in Pittsburgh District . . 65

11. Pillar Drawing with Machines in Pittsburgh, Pa., District . . ... 67

12. Tapered Pillars . ... '-. , . . 68

13. Pillar Drawing, Curtain of Coal . -. ,. . . . . . . . . . 69

14. Proposed Plan for Pittsburgh-Buffalo Coal Company . /• . , . . 70

15. Extraction of Pillars under Draw Slate . . . . . ... . . 71

16. Detail of Pillar Work under Draw Slate . . . \ . . . . . . 71

17. Detail of Pillar Work in Absence of Draw Slate .... ..... • 73

18. Method of Reducing Pillar Work in Pittsburgh, Pa., District .... 74

19. Pillar Drawing in Connellsville, Pa., District . ....... . . 77

20. Concentration Method in Connellsville, Pa., District .' ,. ... . 79

21. Concentration Method in Connellsville, Pa., District — Order of Working 81

22. Concentration Method — Maximum, Medium, and Minimum Plans . . 82

23. "BigPillar" Method Used in Cambria County, Pa. . ... . . . 84

24. Block Long-wall with Face Conveyors . . . . . '. . . . . ' . . 87

25. Method of Working the Georges Creek Big Vein, 1850 91

26. Method of Working the Georges Creek Big Vein, 1870-1880 .... 93

27. Method of Working the Georges Creek Big Vein, 1890 94

28. Method of Working the Georges Creek Big Vein, 1900 . ... . . 95

29. Method of Working the Georges Creek Big Vein, 1904 96

30. Plan of Working— Fairmont, West Virginia, District . . . . . . 99

6 LIST OF FIGURES (CONTINUED)

NO. I PAGE

31. Pillar Drawing in Fairmont, West Virginia, District . ... . . 100

32. Wide Barrier Pillars and Room Stumps, Kanawha District, West Virginia 102

33. Plan of Working of Pocahontas Coal and Coke Company . ... .106

34. Single Room Method, Logan County, West Virginia . . . "*. . .112

35. Big Room Method, Logan County, West Virginia . . . . . . . 113

36. Block System of Retreating Long-wall, West Virginia x 115

37. Proposed Plan of Wind Rock Coal Company, Tennessee . . . . . 123

38. Panel Long-wall in Oklahoma . ... . . . . . . . , .131

39. Pillar Drawing in Utah ... . . , . . ... ... . . . 136

40. Pillar Drawing in Utah ... . 137

41. Pillar Drawing in Utah . 138

42. Pillar Drawing in Utah . . 139

43. Bell Pit . . .142

44. Bord-and-Pillar . . . ... . . . ... . . ... 143

45. Stoop-and-Room ....-.., . , . . . . 144

46. Old Square Work . . 150

LIST OF TABLES

NO. PAGE

1. Dimensions of Rooms and of Room Pillars and Percentages of Extraction 23

2. Principal Factors Governing Recovery of Coal in Different Districts . 24

3. Dimensions of Workings and Estimated Percentages of Extraction in

Illinois Mines 25, 26, 27

4. Values of Surface and of Coal Rights by Counties in Illinois ... 28

5. Districts into Which the State Has Been Divided for the Purpose of

Investigation . . . . . . . . ..... . . . . . 29

6. Percentage of Extraction in Kanawha District, West Virginia . . .103

7. Recovery of Coal in Mines of Pocahontas Coal and Coke Company . . 107

8. Statement of Thicknesses and Recoveries, All Mines, United States Coal

and Coke Company, 1902 to 1916, inclusive 108

9. Percentage of Recovery of Live Work and Robbing 109

10. Percentages of Coal Losses as Estimated by the Royal Commission of 1905 155

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL

WITH SPECIAL REFERENCE TO ILLINOIS

CONDITIONS

INTRODUCTION

1. Preliminary Statement. — The purpose of the discussion pre-
sented in this bulletin is to record the results now being obtained
in recovering coal in the mines in Illinois and in other bituminous
coal mining districts of the United States. A brief discussion is also
presented with reference to recovery in the principal European coun-
tries. Where the methods employed are now producing an unusually
good percentage of extraction, the conditions under which the min-
ing is carried on are described in considerable detail with the belief
that they may suggest changes in practice which will be helpful to
those who are now endeavoring to recover a greater percentage of
the coal in the ground.

Most of the data presented were obtained from those operating
the mines, and represent, therefore, calculations or estimates based
upon thorough familiarity with conditions. Some of the methods
by which high extraction is attained in other districts are described
with the hope that the coal producers of Illinois may find herein
suggestions which will prove helpful in their efforts to attain higher
recovery.

It has been impossible to include in a single publication all the
material available concerning the physical conditions encountered
and the methods adopted in the various coal fields, but there will
be found in the bibliography a list of books and articles in which
these subjects are covered in greater detail. It is the present pur-
pose to begin at an early date a more extended investigation of the
plans and dimensions of mine workings in Illinois with reference
to the cost of production and the percentage of extraction.

2. Acknowledgments. — The writer wishes to acknowledge his
indebtedness to PROFESSOR H. H. STOEK, head of the Department
of Mining Engineering, University of Illinois, and to MR. F. W.
DEWOLF, Director of the Illinois State Geological Survey, and also
to MR. G. S. RICE, Chief Mining Engineer, United States Bureau of
Mines, under whose direction the work of the Illinois Coal Mining

8 ILLINOIS ENGINEERING EXPERIMENT STATION

Investigations is being carried on. Professor Stock has been espe-
cially helpful in the collection of material for the present bulletin.
Many operators and engineers throughout the country have contrib-
uted statements concerning the districts with which they are familiar.
The state mine inspectors have assisted in the work by suggesting
mines at which particularly good records of extraction have been
made and also mines at which new methods are being tried with a
view of increasing the percentage.

3. Summary. — The facts and information presented in this bul-
letin include:

(1) A general statement of the importance of the • problem
of increasing the percentage of extraction of the coal in the ground
in order to utilize the coal resources to a greater extent than at
present, and, if possible, to decrease the cost of producing coal ;
also an account of previous efforts made to compile data upon this
subject.

(2) A statement with reference to the conditions which have
influenced the development of American coal mining methods and
which must be considered in changing these methods in order to
obtain more nearly complete recovery.

(3) A record of the recovery of coal in Illinois in the past,
and a discussion of the efforts now being made to increase the
percentage of extraction.

(4) An account of methods adopted in other states and in
certain European countries by which higher percentages of extrac-
tion are being obtained.

(5) A brief history of the development of English mining
practice, upon which American practice is founded.

(6) A short bibliography with reference to the subject of
coal mining methods.

4. Conclusions. — A summary of conclusions suggested by a study
of the data and information contained herein is presented as follows :

(1) In general in America probably one ton of coal has been
left in the mine for every ton brought to the surface.

(2) An effort is being made in many sections of the United
States and in a number of Illinois mines to decrease this loss
of coal.

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL 9

(3) The low percentage of Recovery in the United States is
largely due to economic conditions and to efforts to produce
cheap coal.

(4) Where economic conditions have been favorable, per-
centages of recovery have been obtained in the United States
quite as high as in any of the foreign countries in which usually
the economic conditions have not been such as to make the pro-
duction of cheap coal the determining element in the choice of
a method.

(5) The low price at which much of the coal land in the
United States has been bought has not offered an inducement to
save the coal.

(6) The best results in recovery are now being obtained in
districts where the value of coal land is high.

(7) As a general rule better extraction is being obtained in
West Virginia and Pennsylvania than in the Middle West.

(8) In view of the results being obtained in some other dis-
tricts, under conditions no more favorable than those in Illinois,
the percentage of extraction in Illinois should be increased.

(9) The best results are being obtained by the larger and
stronger companies which can afford to plan for the future.

(10) The low value of the smaller sizes of coal in the past
has been a drawback to pillar drawing, because very often pillar
coal has contained more of the small sizes than room coal. With
the increasing use of small sizes in mechanical stokers, the price
will undoubtedly advance to nearly the same level as that of the
larger sizes; thus this drawback to greater recovery will grad-
ually disappear.

(11) One of the reasons why newer methods have not been
generally tried is to be found in the prejudice, too common in
coal mining practice, against innovations, and in the fact that
mining methods have been based largely upon previous practice
in other countries or in other states.

(12) Many of the attempts to draw pillars have been unsys-
tematic. Upon such unsystematic work are based many of the opin-
ions concerning the technical and commercial practicability of
pillar drawing and the prejudices against it.

(13) Subsidence of the surface must be regarded as a neces-
sary accompaniment of mining. Instead of trying to prevent

10 ILLINOIS ENGINEERING EXPERIMENT STATION

subsidence, the pillars should be removed systematically so that
the surface subsidence will occur uniformly and not in isolated
spots. Although there may be a temporary disturbance of the
surface, after a short time its condition will be as good or nearly
as good as before the mining.

(14) In Illinois, at the present time, more than fifty per
cent of the coal is frequently left in the ground in an effort
to prevent squeezes and subsidence; even then it is not at all
certain that the desired result is accomplished.

(15) The best results may be obtained by driving room entries
to their full length, then by beginning the rooms at the inby end
of the entry, in order that pillar drawing may begin as soon as
the inby room is finished.

(16) To be effective, pillar drawing must begin as promptly
as possible after the rooms are worked out.

(17) Where pillars are left to be drawn subsequently, the
coal is usually lost, because the pillars are crushed through squeezes,
or because it is not found economical or convenient to take the
coal out and at the same time to keep up the output of the mine
with the compartively small amount of coal left. In other words,
unless pillar drawing follows very closely after the first working,
very little pillar coal is obtainable.

(18) In many districts poor top has prevented taking out
the full thickness of the coal, and one of the great losses is that
due to coal left in the roof. This loss has been overcome in some
cases very successfully, and should be carefully studied.

(19) The reported percentages of extraction are usually too
high because, in estimating, often only the section mined is con-
sidered and no account is taken of top or bottom coal left unmined.
Also frequently only limited areas of the mine are considered
instead of the mine as a whole.

(20) At different mines in the same region where physical
conditions are practically the same, the mining methods vary
widely with regard to length of rooms, number of rooms in a
panel, thickness of barrier pillars, etc. This variation in practice
suggests the advisability of a detailed study to determine, if possi-
ble, a standard method for a given set of conditions.

PERCENTAGE OP EXTRACTION OP BITUMINOUS COAL 11

£i

CHAPTER I

MINING METHODS AND CONDITIONS IN RELATION TO EXTRACTION

5. Introduction. — The subject of the percentage of coal extracted
from the mines in the United States has received very meager atten-
tion, except in the case of individual mines or companies. The only
comprehensive official study of an extended coal mining area has been
in the anthracite district of Pennsylvania, where the high value of
the coal and the knowledge that the supply is limited early stimulated
an interest in the subject. This interest led to the appointment of
the Coal Waste Commission which reported in 1893.*

In 1905 H. H. Stoekf published a table of coal pillar data which
contained percentages of extraction gathered largely by correspond-
ence. See Table 1, page 23.

In 1914 A. W. Hesse $ collected as much information as possible
on this subject, which is summarized in Table 2, page 24.

In previous bulletins of the Cooperative Coal Mining Investi-
gations tables of pillar data and percentages of extraction were given.
These are summarized in Table 3, pages 25, 26, 27.

Doubtless many of the figures in these tables and others on the
percentage of recovery are open to question, but they represented
the best and most nearly complete information available when they
were published. There are several reasons for questioning the accu-
racy of the figures on extraction. Chief among them is the fact that
estimates are usually based upon areas which are too small or
upon insufficient data. A single panel or a single lease is some-
times used as a unit upon which to base estimates, and often the
areas thus selected are favorably located. While the estimates may
represent results obtained with the given method of mining, they
by no means represent the average results for the mine as a whole.
The panel selected for measurement is usually one in which there
has been no squeeze, while all about it there may be squeezed areas
in which large amounts of coal have been lost. Many estimates are

* Report of • Commission Appointed to Investigate the Waste of Coal Mining with the
View to the Utilizing of the Waste, 1893.

t Mines and Minerals, Vol. 26, p. 107, 1905, and International Library of Technology,
Vol. 150, par. 40, p. 60.

t" Maximum Coal Recovery," W. Va. Mi n. Inst., June 3, 1914; Coll. Eng., Vol. 35,
p. 13; and Coal Age, Vol. 5, p. 1051.

12 ILLINOIS ENGINEERING EXPERIMENT STATION

based upon possible future recovery from pillars, which may or may
not be obtained.

Estimates covering extraction frequently do not take account of
top and bottom coal left in the mine, and the values reported often
refer only to the section of the coal actually mined. In mining
a coal bed ten feet thick, for instance, two feet of top coal may be
left unmined. The maximum percentage of extraction from mining
eight feet, in this case, would be eighty per cent of the total coal in
the bed. If, then, fifty per cent of the eight feet mined is obtained,
only forty per cent of the total coal in the bed is recovered.

The only accurate method of estimation is to divide the actual
amount of coal mined, as determined by the tonnage for which the
miner is paid, by the amount of coal in the ground as determined by
multiplying a given area by the average thickness shown in a large
number of sections of the bed.

Even where great care is exercised, results are often subject
to errors. The causes for these have been outlined by Smyth*
as follows: Inaccuracies in railroad weights of possibly five to ten
per cent, inaccuracies in estimation of coal used at the mines fre-
quently amounting to ten per cent, inaccuracies in estimating the
mean thickness of the bed amounting, even in very uniform beds,
probably to five per cent, difficulties of obtaining final figures until
a mine is worked out.

The present condition of the coal mining industry in this country
is a natural result of the course and character of its development.
In general, only those beds and even parts of beds have been worked,
the exploitation of which would result in the largest immediate
profits. Those methods of mining which were cheapest and which
promised the largest profit on the coal produced have been followed,
often without regard to the possible injury of the mine or the result-
ing loss of coal. There has been, moreover, no restriction of market,
and in many cases districts have been opened when there has been
very little demand for coal in the surrounding territory, but when
conditions of operation and transportation have been such as to
make it possible for coal from these districts to enter markets already
supplied. The result has been cheap coal, produced by wasteful
methods.

Another result has been over-development of the industry. The
opening in nearly all districts of too many mines has resulted in the

* Smyth, John G., Personal Communication.

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL 13

idleness of many mines during a large part of each year with the
accompanying increase in the cost of production. In dull periods
coal has frequently been sold for less than the cost of production
in order that mines might be kept in operation and certain fixed
charges met. This subject was taken up by Bush and Moorshead in
1911 in a paper* before the American Mining Congress in which it was
said that the production in this country exceeded the consumption
first in 1891, and that the difference between consumption and capacity
for production had steadily increased. The strike of 1910 in Illinois,
Indiana, and the Southwest emphasized the over-capacity of the
mines of that region. Though the mines of Illinois were idle during
six months of the year, the production of 45,900,246 tons was only
ten per cent less than the production of the previous year. The
mines of Oklahoma, Arkansas, and Missouri were also idle during
six months of 1910 because of the strike, but the production showed
an average decrease of only twenty per cent. It was also said that
the possible capacity of West Virginia mii)es was seventy-five per
cent more than the total production, that the output in the Pittsburgh
and the No. 8 Ohio districts was reduced t ) thirty per cent of the
normal production during the three or four months of each year
when navigation on the lakes was closed, and that few properties
during the three preceding years — 1909, 1910, and 1911 — had been
operated more than 225 working days per year.

This over-production, with its small profit or even loss in the
operation of mines, results in a natural tendency to employ only
those methods which will insure cheap coal. It is natural, also, that
under these conditions there should exist an attitude of hesitancy
with regard to the adoption of new or different methods. Neither
the coal producer nor the public has as yet become aroused to the
full realization of the fact that the natural resources of the country
are not inexhaustible. The coal mining engineer of America accord-
ingly, has not had a,:< his problem the development of methods of
extraction which would result in the largest percentage of ultimate
recovery, but rather the development of methods which would result
in the lowest cost of production, hi many cases, however, as is
shown by the detailed descriptions given later, where economic con-
ditions have seemed to warrant it, methods have been developed by

*Bush, B. F., and Moorshead, A. J., "The Condition of the Bituminous Coal Industry,"
Proc. Amor. Min. Cong., p. 246, 1911.

14 ILLINOIS ENGINEERING EXPERIMENT STATION

American engineers and coal producers which have given a percent-
age of recovery equal to that secured in any European country.

The fact should be borne in mind, when comparisons are made
between mining methods in different countries, that, while it is true
that the percentage of extraction is less in this country than in most
of the European countries, the cost of coal to the consumer and the
profit to the producer are also less.

The subject of the comparative cost of production of coal and
of the comparative profits realized in Great Britain and in the
United States was taken up by Rice* substantially as follows: the
average value of coal in the United States on cars at the mine in
1913 is reported as $1.18 per short ton for bituminous coal and $2.13
per short ton for anthracite. In Wales, in 1913, the average value
per short ton at the mines for all kinds of coal was $2.55, and in
Great Britain as a whole, $2.21. In the German Empire the average
value for all kinds was $2.27, and for Westphalia it was $2.37 per
short ton. Net mining profits in Great Britain and in Germany are
between twenty-five and fifty cents per ton, while profits in the United
States for bituminous coal are probably not more than five cents
per ton.

It is a matter of course that more expensive methods of mining
cannot be adopted without increasing the cost of the coal, and under
the conditions which have prevailed in the coal industry for many
years there could be no material increase in the cost of coal to the
producer without a corresponding increase in the selling price. The
prevailing opinion, however, that the percentage of recovery cannot
be greatly increased without an increase in the cost of production is
questionable, and certainly this increase in cost would not be as
great as is generally believed. This is a matter which can be con-
clusively determined only by actual trial of new methods extending
over a sufficient period to insure the reliability of the results. The
fact that the adoption of methods which result in an increase in the
percentage of extraction has been possible in some districts with little
or no increase in cost at least furnishes a reason for thinking that
similar changes could be made in other districts with similar results.

Careful planning of operations over long periods and steady
working are necessary in order to obtain a high percentage of ex-

*Rice,G.S." Mining Costs and Selling Prices of Coal in the United States and Europe
with Special Reference to Export Trade," Second Pan-American Scientific Congress

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL 15

traction. At present these conditions are impossible in many districts
and can be attained only by centralized control of production and
selling price, which will provide against alternation of idle and rush
periods with the disorganization which accompanies them. Under
existing conditions it is feared by operators that the necessary co-
operation would be interpreted and attacked as a violation of anti-
trust laws. In some of the European countries syndicates working
in cooperation with the governments regulate the output of the
mines and the selling price of coal with results which are said to be
highly satisfactory and conducive to a high recovery.*

One of the chief commercial factors affecting the choice of a
method has been the cost of coal in the ground. This has generally
been very low, and the loss of coal, therefore, has not been consid-
ered a serious matter. Even at the present time the value of coal
rights in the southern Illinois field, where the No. 6 bed is worked,
is estimated at not more than $100 to $150 an acre, and it has been
only a very short time since such coal rights could be purchased
for less than $50 an acre. The thickness of this coal is somewhat
variable, being in some places fourteen feet or more, but, if we
assume that only about seven feet is worked, the output will amount
to about 12,000 tons per acre and the cost of coal in the ground will
be about one cent per ton. A great deal of the coal in the state,
however, has been bought at a very much lower figure. In some
cases also there is a second bed of coal which will be available later,
and when this is considered, the cost of coal in the ground will
be much less than one cent per ton.

This phase of the subject was discussed by Rice,t in 1909, as
follows :

'•'The influencing conditions causing the great losses that are at
present incurred are:

1. Cheapness of 'coal in place'; that is, in the seam.

2. Low market prices, resulting from extreme competition.

3. Character of the seam, roof, and floor as determining the
method of mining.

4. Surface subsidence due to mining.

5. Interlaced boundary ownerships.

*Scholz, Carl, "The Economics of the Coal Industry," Proc. Amer. Min. Cong., p. 241,

tRice, George S., "Mining-Wastes and Mining- Costs in Illinois," Trans. Amer. Inst.
Min. Eng., Vol. 40, p. 31, 1909.

16 ILLINOIS ENGINEERING EXPERIMENT STATION

6. Carelessness in mining operations.

The first two factors, taken together, are the controlling ones in
most mining operations in influencing the choice of a mining system.
The majority of Illinois operators are sufficiently progressive to find
ways and means to take out practically all the coal under a given
area if it could be made evident that it paid to do so. That many
do not do all that can be done in this direction is apparent ; but if,
without unusual investment, a profit of operation could be shown
in taking out all the coal over the profit made by present methods,
the industry could undoubtedly find men to accomplish the task.
In other words, from an engineering standpoint practically all the
coal under a given area can be taken out. It is a question of cost.
"Cheapness of Coal in Place. — This is chiefly due to the great
abundance of coal. Except in the barren northern one-fourth of
the State, lying north of the outcrop of the coal-basin, the develop-
ment of a tract depends primarily not on the possibility of finding
coal in that particular locality, but on the question whether it is
a suitable place, from a market standpoint, to open a mine, the
thickness of seam and the quality of the coal being considered.

' ' The price of coal rights varies from $10 per superficial acre in
the middle part of Illinois, away from the mining centers to $100 per
acre near developed mines. Or, in the case of leasing, from 2 cents
per ton run-of-mine hoisted, in the southern part of the State, to
5 cents in the northern part. The cost of the fee is relatively so much
cheaper per ton than leasing that the latter system is not much used.
The ownership of the coal by tjie operator is conducive to better min-
ing, but relative to other items that go to make up the total, the cost
of the ' coal in place ' is so low as to be almost negligible. In central
Illinois, in some cases, at a cost of only $10 per acre, two workable
seams, from 6 to 8 ft. thick, are obtained. Allowing only 50 per cent
yield of the two seams, 13,000 tons would be produced per acre, the
purchase cost thus being 1/13 of a cent per ton, or about 1/1000 of
the total cost of production in central Illinois. In the Wilmington
long-wall field the average cost of the coal rights is about $50 per acre.
The seam there, although it averages a trifle less than 3 ft. in thick-
ness, produces about 5,000 tons per acre. The cost is therefore about
1 cent per ton in place, which is 1/130 of the total cost of production.
Hence, it may be seen that there is little incentive, from the stand-
point of the purchase price of the coal, to save the latter in mining
operations. "

PERCENTAGE OP EXTRACTION OF BITUMINOUS COAL 17

The cost of coal rights has very greatly increased since Rice's
discussion, and there is every reason to believe that the value of
coal in the ground will be much greater in the future than it has been
in the past. During most of the productive period, however, the
coal in the ground over a considerable part of the State has been
worth not more than one-tenth of a cent per ton, and under these
circumstances the loss of coal has, naturally, not been considered a
serious matter. What has been important, and still is, is the extrac-
tion of coal at low cost, and the subject of high recovery is one of
increasing importance at the present time.

Every ton of coal left in the ground represents the loss of a
possible profit. Every ton of such coal represents a loss in increased
value. An acre of coal left in the ground at any time means the
extraction of another acre at some later time when the value of
coal in the ground will be greater. In other words, producers are
now extracting coal, worth possibly $150 an acre, which might be
left until it would reach even a greater value if it were not for
the fact that coal was wasted in the ground when it was worth only
fifty dollars an acre.

A low percentage of extraction increases the cost of production,
because, for a given output, the workings must cover a larger area.
This involves longer haulage roads, and, consequently, a greater in-
vestment in rails and trolley wire, greater maintenance expense, greater
consumption of power, lower output per unit of equipment, and lower
output per man. With long haulage roads there is greater chance
for derangements of the track or for falls of roof, which may cause
the stopping of haulage until the trouble is removed or may result
in wrecks if the trouble is not discovered in time. Another source
of danger lies in the greater haulage speed which must be employed
on long roads if the output is to be maintained.

The cost of ventilation is also higher, because these larger work-
ings require a larger quantity of air to maintain safe conditions, and
more power is required to circulate air through the longer passages.
There is, moreover, a greater loss of power because of the more
numerous stoppings, which are often inefficient.

Another difficulty accompanying the spreading of the workings
over a large area is that of providing the intensive supervision which
is highly desirable in coal mining, particularly where skilled work-
men have been replaced by comparatively unskilled laborers, and

18 ILLINOIS ENGINEERING EXPERIMENT STATION

the pick has been replaced by explosives and mining machines. Unless
the cost of operation is to be increased by the employment of a larger
number of foremen or face bosses, this intensive supervision can be
obtained only by concentration of the workings.

6. Subsidence. — One reason for the use of methods involving
low extraction is the desire to maintain the original surface of the
ground. Rice* discussed surface subsidence as follows:

" The influence of this factor upon the yield results from the high value
of Illinois lands for agricultural purposes. ... If the long-wall system were
applied to the thick seams, when applicable at all, it would cause a considerable
derangement of the surface, and when the latter is so nearly level as the prairie-
land of Central Illinois, it makes the question of subsidence a serious one. . . .
However, until the agricultural land in the United States becomes insufficient
to fill the needs of the population, which would be reflected in a continual in-
crease of price for farming land, the money -loss from temporarily destroying the
surface in places is relatively small, as compared with the selling price of the
coal mined from the seam. Taking the average value of the surface at $125 per
acre, if 80 per cent be rendered worthless the immediate money-loss would be
$100 per acre. A seam 6 ft. thick would contain per acre 11,000 tons of coal in
place, yielding, at 90 per cent, 9,900 tons. The damage done by practically de-
stroying the surface would be only 1 cent per ton. If the land-prices should rise
to an amount two or three times as great as the value stated, this loss would still
not prohibit mining."

As far as the long-wall district is concerned, very little if any
damage has resulted from subsidence, and little attention has been
given to the subject. The most noticeable effects are generally tem-
porary, and farm operations are not hindered.

The subject of the relation of surface values to subsidence in
Illinois has been considered by L. E. Young in Bulletin 17 of this
series, f Fig. 1 is a map reproduced from this bulletin, on which
the approximate values of farm lands are shown. Table 4, page 28,
shows the relation between coal values and surface values. The
land values indicated on the map and set forth in the table suggest
that it might be possible, at least in many cases, to mine coal at a
small profit even if the value of the surface were totally destroyed.
There is no need, however, for assuming the permanent destruction
of the surface or even its serious permanent injury. Generally any
damage resulting from subsidence could be largely or wholly re-

*Rice, Op. cit., p. 40.

Lewis E" "Surface Subsidence in Illinois," 111. Coal Min. Invest., Bulletin 17,

MAP OF

ILLINOIS

wTjrs i . \yr"

. MACorf. . '. \ h^ — ' T~V^

sifii OQ I- . A > • • J • V:--'.

Unknown coal I • '. 'I
Average value
of farm land $138.30
per acre

Seals of Mil..
10 O 10 30 UO 40 BC

^i^^irat^rv»-i/

J^iHgmLvjK

^^•.131^^^5.44

«^^««^^|M^

^M^m^

^H^Sw

\ *\,*'

1$3\.S*^^

22.23

fp-P El

FIG. 1. MAP SHOWING THICKNESSES or COAL AND VALUES OF FARM LANDS, AS
GIVEN BY THE 1910 CENSUS REPORTS

20 ILLINOIS ENGINEERING EXPERIMENT STATION

paired, especially if it were accepted that mining is certain to result
in subsidence and operations were so planned as to reduce the sur-
face damage and the cost of restoration to the lowest possible amount.

When the coal producer owns nothing but the coal rights, unrea-
sonable damages for surface subsidence are sometimes imposed. The
measure of the damages is not always merely the decreased produc-
tive value of the land, nor the cost of restoring it to its former con-
dition by artificial drainage; the formation of a small pond has
often been claimed to lower the market value of a farm to a consid-
erable extent, simply because it made the farm less sightly. Under
these circumstances, operators naturally desire to avoid disturbing
the surface for they know that an attempt will be made to recover
damages and that, even if they escape the payment of exorbitant
amounts, they will incur considerable expense in defending the
suits. An effort, accordingly, is often made to conduct the mining
operations in a manner which will not result in surface subsidence.
The result is that the loss in the ground represents an important
percentage of the coal, in many cases more than half that contained
in the area worked.

It is very important that the allowable damages for surface sub-
sidence be regulated by some law. This law should fix the damage
payable by the coal producer, in case he is legally responsible, upon
the basis of the actual damage done to the surface. Under such a
law the operators would .know the extent and character of their
responsibility and could, without fear of excessive or unreasonable
damages, proceed according to methods which would yield the highest
possible percentage of extraction justifiable under such conditions.

7. Squeezes.— Closely related to, but not identical with, the
subject of surface subsidence is that of squeezes. There may be
subsidence without a squeeze, but with the conditions in Illinois
a squeeze is usually followed by subsidence. The removal of a por-
tion of a deposit throws additional weight upon the pillars left and
if these pillars are not strong enough to support this additional
weight, they will crack and crush, causing a movement of the over-
lying material. This movement is called a " squeeze," or sometimes
a " creep." Large quantities of coal are often left in the mine in
the form of pillars in an effort to prevent a squeeze, which may not
only interfere with the operation of the mine and entail a loss of

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL 21

the coal in the squeezed area, but large areas of the mine may
become inaccessible for future economical working. A more nearly
complete extraction of the coal properly carried out should, however,
result in less damage from squeezes.

There are two ways in which a squeeze may be prevented or
stopped; first, by the use of a support strong enough to prevent any
movement of the overlying rock, and secondly, by a fracture of the
rock above the excavated portion so that the weight on the pillars
will not be sufficient to crush them.

The first method may be employed by either leaving natural
supports (coal pillars) of sufficient size and strength to hold the
roof without any movement, or by the use of artificial supports,
such as timber or iron columns, or sand or culm filling. The cost of
timber or iron would prohibit their use if a large percentage of
coal was to be extracted. Filling is not generally non-compressible,
but it occupies most of the space from which coal has been removed,
prevents any scaling off of pillars, and eliminates any possibility of
movement of pillars. The filling method, however, is hardly to be
considered feasible in Illinois because of the cost. In the Upper
Silesian coal field where this method is most extensively used, the
cost is from twelve to eighteen cents per ton.*

Another difficulty arises from the fact that the material would
have to be flushed into the mine with water, and then the water
would have to be pumped out. This water would probably have an
injurious effect on the clay bottom. The material, moreover, would
have to be brought from a distance unless the value of the land
should be so small as to permit the use of material from the neigh-
boring surface, and this condition would rarely prevail in Illinois.

In the leaving of coal pillars of sufficient strength to prevent roof
movement, the amount of coal which must be left varies with local
conditions. It is difficult, if not impossible, to determine this factor
in advance, and in attempting to approach as closely as possible
the limit of safety, it often occurs that too much coal is removed.
Even if the limit is not passed so far as immediate movement is
concerned, it may be passed with reference to ultimate movement
and the crushing of the pillars.

Apparently, so far as a large part of the State of Illinois is con-

* Gullachsen, Berent Conrad, "The Working of the Thick Coal Seams in Upper Silesia,"
Trans. Inst. Min. Engrs. Vol. 42, p. 209, 1911.

22 ILLINOIS ENGINEERING EXPERIMENT STATION

cerned, it is necessary to leave in the ground about one-half of the
area of the coal if movement of the overlying beds is to be pre-
vented.

The desirable dimensions of the rooms and the pillars vary widely
from wide pillars between wide rooms to narrow pillars between
narrow rooms. One company had squeezes when it drove 25-foot
rooms on 50-foot centers, but it has had no trouble with 30-foot
rooms with 60-foot centers. This is a question not simply of the
crushing strength of the coal nor of the ability of the bottom to
withstand pressure, but of the effect on the pillars of scaling at
the sides. In other words, the strength of the pillar is not deter-
mined merely by its original size but by its effective size after the
scaling action, which may follow the extraction of the room coal,
has occurred. This scaling action is increased by the shattering
effect of explosives.

The use of coal in the ground to prevent squeezes and sub-
sidence, which is what abandoning of pillar coal amounts to, ought
to be considered only as a last resort. It has been found that
squeezes can be prevented by the removal of so little coal on the
advance as to leave a solid support, and by the complete removal
on the retreat so that the roof is left entirely without support.
This process prevents the gradual settling which occurs when some
support is left and produces a sharp bending, or localization of
stress, sufficient to cause a rupture of the overlying rock and
prevent the transference of weight from the mined-out area to
the standing coal. This is the only certain method which has been
found for the prevention of squeezes unless an absurdly large quan-
tity of coal is abandoned. The means by which squeezes may be
prevented vary under different conditions, but the essential consider-
ation is that the roof of the mined-out area shall be left absolutely
without support either from coal or from timber, so that it must
fall.

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL

TABLE 1»

DIMENSIONS OF ROOMS AND OF ROOM PILLARS AND PERCENTAGE OF

EXTRACTION

LOCALITY AND COAL SEAM

Width of
Room
Feet

Width of
Room
Pillars
Feet

Per Cent
of Coal
Left in
First
Working

Total
Per Cent
of Coal
Recovered

Alabama :
Newcastle seam

10-20

Blue Creek

Blocton

Flat Top

Arkansas:
Sebastian County

18-30,

Colorado:
Trinidad series

usually 24
20-25

20-25

50-80

Illinois:
Springfield

15-20

Staunton (machine mines)

Indian Territory

18-30

10-12

Iowa

usually 24
21-30

9-15

Maryland:
Georges Creek

12-16

40-100

Pennsylvania :
Connellsville

Connellsville

Pittsburgh

21-24

12-18

85-95

Clearfield

21-24

40-50

80-95

West Virginia:
Fairmont
Clarksburg, Pittsburg seam

18-24
18

18-40
32

40-60
64

95
90

Mineral County, Pittsburg seam
Tucker County, Davis or Kittanning seam

12
18

48
22

80
35

95 (?)
90 (?)

Putnam County, Pittsburg seam
New River, Sewell-Nuttall seam

30
24

15
26

34
60

75-85
60-80

Thacker, (Thacker) Lower Kittanning seam
Logan, Lower Kittanning seam

18-21
21

42
20

67
57

Kanawha (No. 2 Gas), Lower Kittanning seam
Pocahontas, Double Entry, No. 3 Pocahontas seam .
Pocahontas, Panel System, No. 3 Pocahontas seam .
Raleigh, Sewell-Nuttall seam

28
18
18
25

12-20
42
42
25

40
68

80
952
90

1H. H. Stoek, Mines and Minerals, Vol. 26, p.
Technology, Vol. 150, par. 40, p. 60.

2Estimated.

107, 1905, and International Library of

The widths of rooms and room-pillars given in Table 1 show
that there were few cases in which plans were made for the extrac-
tion of more coal from pillars than from the advance workings.

ILLINOIS ENGINEERING EXPERIMENT STATION

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PERCENTAGE OP EXTRACTION OF BITUMINOUS COAL

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ILLINOIS ENGINEERING EXPERIMENT STATION

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ILLINOIS ENGINEERING EXPERIMENT STATION

TABLE 41
VALUES2 OF SURFACE AND OF COAL RIGHTS BY COUNTIES IN ILLINOIS

County

Value of Coal
per Acre

Number of
Coal Bed

Average Surface

Value, Census of

1910

Bond $25

Bureau 10-100

Christian 10-50

Franklin 35-100

Fulton 15-100

Gallatin 20-25

Grundy 10-25

Henry 135

Jackson 25-75

La Salle 10-100

Livingston - 10-50

Logan 20- 50

Macoupm : . . 15-50

Madison 10-40

Marion 20

Marshall 15

McLean 15

Menard 26-30

Montgomery 25- 50

Morgan 20- 30

Peona 20-50

Perry 25

Putnam 15

Randolph 25

St. Clair 10-100

Saline 50-150

Sangamon 20-100

Scott • 10-40

Shelby 10-25

Vermilion 100-150

w&r1::::::::::::::::::: II

Williamson 50-150

Woodford 15

2, 6

2,5

5,6

6,5

6,7

1,2

$ 45.43

114.53

123.63

38.48

88.18

48.60

75.52

112.03

31.27

142.92

161.76

156.49

69.74

70.53

39.45

123.92

171.85

122.04

73.49

124. 2H

107.67

30.62

104.69

36.11

81.57

39.88

138.30

83.21

88.72

138.85

129.80

104.08

30.61

154.27

Igi61 Young, Lewis E., "Surface Subsidence in Illinois," 111. Coal Min. Invest., Bulletin 17, p. 55,

2 These prices are not offered as an authoritative basis for valuation but indicate in a general
manner the prices at which coal has been sold or at which it is held in some of the important counties.

PERCENTAGE OP EXTRACTION OF BITUMINOUS COAL

CHAPTER II

EXTRACTION IN ILLINOIS

8. Plan for Division of State into Districts. — At the beginning
of the work of the Cooperative Coal Mining Investigations, the
State was divided into districts in order that those beds which are
similar in general conditions might be studied and considered to-
gether. This subdivision into districts is shown by Fig. 2, and
the districts are described in Table 5.

TABLE 5

DISTRICTS INTO WHICH THE STATE HAS BEEN DIVIDED FOR THE PURPOSES
OF INVESTIGATION

Investi-
gations,
District

Coal Seam

Method of Mining

Counties

Investi-
gations
Numbers
for Mines
Examined

Long-wall

Bureau, Grundy, La Salle, Marshall,
Putnam, Will, Woodford

1 to 11

Room-and-pillar

Jackson

12 to 16

III

1 and 2

Room-and-pillar

Brown, Calhoun, Cass, Fulton,
Greene, Hancock, Henry, Jersey,
Knox, McDonough, Mercer, Mor-
gan, Rock Island, Schuyler, Scott,
Warren

17 to 24

Room-and-pillar

Cass, DeWitt, Fulton, Knox, Logan,
Macon, Mason, McLean, Menard,
Peoria, Sangamon, Schuyler, Taze-
well, Woodford

25 to 42

Gallatin Saline

43 to 49

6 (east of Duquoin
anticline)

Room-and-pillar

Franklin, Jackson, Perry, William-
son

50 to 65

VII

6 (west of Duqouin
anticline)

Room-and-pillar

Bond, Christian, Clinton, Ma-
coupin, Madison, Marion, Mont-
gomery, Moultrie, Perry, Randolph,
Sangamon, Shelby, St. Clair, Wash-
ington . ...

66 to 90

VIII

6 and 7

Room-and-pillar

Edgar, Vermilion

91 to 97

(Danville)

In the present publication the conditions prevailing and the
methods followed in the various districts are described, and the
extent to which these affect the percentage of recovery is discussed.
Material and information has been gathered at various times, and

—

Seal*-.

ioorf,l.»

FIG. 2. MAP OF DISTRICTS OF COOPERATIVE COAL MINING INVESTIGATIONS

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL 31

some of it, especially that relating to physical conditions and usual
methods of operation, has been published in previous . bulletins of
this series. These facts are summarized in Bulletin 13.*

9. Conditions Affecting Extraction. — Since there is an immense
quantity of coal underlying the state and only a comparatively small
portion has been extracted, it is perhaps natural that little serious
attention has been given to the subject of high recovery. Those con-
trolling production have been concerned principally with other
phases of the subject, not because they have been indifferent to the
highest possible utilization of resources, but because they have believed
that the methods in use were giving the lowest possible cost of pro-
duction; and low cost of production has been regarded as a neces-
sity for the development of the Illinois fields in competition with
other coal fields.

Table 3, rearranged from Bulletin 13, gives the dimensions of
the workings and the estimates of recovery for the mines examined
by the Cooperative Coal Mining Investigations.

The values for the percentage of extraction given in the last
column of Table 3 are, in most cases, founded upon estimates fur-
nished by the operators. In many instances subsequent investi-
gation has shown that these values are not correct. There are only
a few mines in the state from which it has been possible to obtain
accurate data on recovery because of the lack of information on
which such data could be based. Generally, it has been found that
persons estimating the percentage of recovery have been inclined
to use values too high and have failed to take into account some of
the sources of loss. Later figures on extraction, the most trust-
worthy it has been possible to obtain, will be found in the descrip-
tions of the districts.

10. District I. — The No. 2 bed varies in thickness from two feet,
eight inches to four feet, the average thickness being about three
feet, two inches. On the east side of the LaSalle anticline the thick-
ness of cover ranges from 40 to 200 feet; on the west side the bed
lies at a depth of 350 to 550 feet. In the eastern, or Wilmington,
section the roof is a smooth gray shale, though sandstone is found
in some places. In the western or LaSalle field the roof is a gray

*Andros, S. O., "Coal Mining in Illinois," 111. Coal Min. Invest., Bui. 13, 1915.

32 ILLINOIS ENGINEERING EXPERIMENT STATION

shale. In the Wilmington field the floor is a dark gray fire clay
varying in thickness from a few inches to several feet. When this
clay is wet, it heaves badly under pressure. In the LaSalle field
the floor is fire clay, but a hard sandstone is sometimes found im-
mediately beneath the coal.*

Nearly all the coal produced in this district is mined by the
long-wall method, and this method, of course, gives the highest
possible percentage of recovery. G. S. Rice says that at one mine
in which a record was kept for six years the loss of coal from all
causes was five per cent.t

11. District II. — The No. 2 seam is found under shallow cover
ranging from 25 to 160 feet. In most places the floor is sandstone,
but shale or clay is occasionally found. In places a wet and fluid
sand is found about thirty feet below the surface, and it has a marked
effect upon surface subsidence, causing the formation of rather
deep pits instead of gentle sags. The bed is divided into two benches
by a shale parting, varying in thickness from one-eighth inch to
thirty-six feet. The bottom bench varies in thickness from S1/^
to 4 feet, and the top bench has an average thickness of two feet.
Where the parting between the benches is less than four inches thick,
the two benches of the seam are worked as one and the working
faces in rooms and entries are from six to seven feet high. Where
the parting is more than four inches thick, only the lower bench
is mined and the parting becomes the mine roof. When both benches
are worked and the bed is more than six feet thick, only the lower
six feet of coal are mined, eight to twelve inches of top coal being left ;
but if the coal is not more than six feet thick the full thickness of
the bed is mined, and the gray shale overlying the coal becomes
the roof.

With one exception, the mines examined are operated by the
unmodified room-and-pillar method. Operations are carried on with-
out close adherence to the projected sizes of rooms and pillars. The
result of this practice is a rather high percentage of extraction, as
pillars are gouged to a considerable extent, t At one mine in this

*Andros, S. O., "Coal Mining Practice in District I," HI. Coal Min. Invest Bui 5
p. JO, 1914.

fRice, George S., "Mining-Wastes and Mining-Costs in Illinois," Trans. Amer. Inst.
Mm. Engrs., Vol. 40, p. 31, 1909.

t Andros, S. O.. "Coal Mining Practice in District II," 111. Coal Min. Invest., Bui. 7,

PERCENTAGE OP EXTRACTION OF BITUMINOUS COAL 33

district which is operated on the panel system and in which a serious
attempt is made to remove pillars as far as possible, the percentage
of extraction is probably higher than at any other mine in southern
Illinois. At this mine the shaft is 115 feet deep. There are triple
main and cross entries, each ten feet wide, with 20-foot entry pillars.
Barrier pillars on main and cross entries are twenty feet wide. Rooms
are twenty feet wide with 10-foot pillars. All cross-cuts are eight
feet wide. Although there are no exact figures on the percentage
of recovery, it is evident from the dimensions of the workings that
about two-thirds of the coal is extracted in the first working. Since
by slabbing pillars, forty to fifty per cent of the pillar coal is also
obtained, the final recovery probably amounts to about eighty per
cent. The rooms are widened about thirty feet before the end is
reached, little or no pillar coal is left beyond this point, and as
much of the remainder of the pillars as possible is taken out by
slabbing.

The possibility of extracting a large amount of pillar coal depends
upon the character of the top which may be allowed to fall without
serious consequences, because the shale and sand overlying the coal
seal the opening so that the influx of water is not seriously increased
by a break. When the top falls, the necks of the rooms are boarded
up and the water is handled by a pump.

12. District ///.—The No. 1 and No. 2 beds are worked. The
cover overlying the coal is thin. The topography of the surface in
many places is rolling, with hills about 150 feet high near Mather-
ville. Bed No. 2 lies at depths of seven feet to one hundred feet
with an average cover of fifty-five feet. Bed No. 1 averages four
feet in thickness and is broken in places by small faults, slips, clay
veins, and rolls. A poorly developed parting divides the bed into
two benches, the upper of which is in most places about two feet
thick.

The immediate roof in the northwestern part of the district is
of hard black shale which is easy to support. In the southern part
a bituminous calcareous shale, two to five inches thick, lies in places
immediately over the coal. This shale, called clod, is hard when first
exposed to the air but after exposure softens and falls. Throughout
the district the cap rock is limestone. In limited areas where the
shale is missing, this limestone forms the immediate roof. Above

34 ILLINOIS ENGINEERING EXPERIMENT STATION

the cap rock occurs a dense, fine-grained, non-crystalline limestone
locally called " blue rock. "

Below bed No. 1 there occurs in places an irregular band of hard
bone, three to six inches thick. The floor proper is of light gray
micaceous fire clay which contains plant stems and roots. This clay
heaves badly when wet and sometimes swells enough to fill the entry.
In parts of some mines a carbonaceous shale lies between the fire clay
floor and the coal; sometimes this shale is supplanted by sandstone.
These casual deposits are called " false bottoms."

Bed No. 2 varies in thickness from 1 foot, 10 inches to 4
feet, and averages 2 feet, 6 inches. The bed has a slight dip to
the east. A band of mother coal and iron pyrites persists throughout
the bed. This occurs about fourteen inches from the roof. The
immediate roof is of smooth and regular calcareous shale, known
locally as soapstone. The floor is of soft gray fire clay which con-
tains nodular concretions of iron pyrites called sulphur balls. The
coal in this district lies near the surface, but at no point is the over-
burden stripped.

Except at two mines, the mining system is the simplest form of
double-entry room-and-pillar. Table 3 shows the dimensions of work-
ings in the mines examined. The coal is gained during the first
working with a waste of pillar coal amounting to about 45 per cent of
the bed. At the two exceptions 75 per cent of the pillar coal is recov-
ered on the retreat, a large percentage for Illinois room-and-pillar
mines.

A main entry and a parallel air-course, each six feet high and
eight feet wide, are driven from each side of the shaft toward the
boundaries. At right angles to these main entries, pairs of cross
entries are driven every 500 feet. On the cross entries, after leaving
a barrier pillar of 50 feet, rooms are turned on 45-foot centers. Room
necks are 7 feet long and 8 feet wide, and are widened to the
left at angles of about 45 degrees; thus they reach the full
room width of 26 feet at distance of 14 feet from the beginning of the
widening. After the first room on each entry has been holed through,
the room-pillar cross-cuts are closed by gob stoppings, and the line of
No. 1 rooms is kept open; thus two additional air-courses are provided.

After the entry has been driven to the limit and the rooms on
it have been worked out, the last pillar on the entry is drawn; then
the other room pillars are drawn until the pillar between rooms

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL,

3 and 4 is reached. The room pillars between the main entry and
room 4 are left to protect the main entry and air-course. The method
of drawing pillars is illustrated in Fig. 3. When the room is driven

(a) (b) (c) Cd)

FIG. 3. PILLAR DRAWING AT MATHERVILLE, ILLINOIS

up to its full length, a 12-foot cut is made across the end of the
pillar (a), a 5-foot slab about 8 feet long is shot from the
side of the pillar, a 4-foot slab is shot from the end (b), and the
end of the pillar is squared up by shooting off another 4-foot slab (c).
Beginning again at (d), the process is repeated.

The hard roof is easy to support and often stands while 25 to 200
feet of pillars are being drawn. When the weight of the roof
becomes too heavy, the roof breaks at the pillar ends. The cracking
of the props gives ample warning of the break, and work is discontin-
ued until the roof falls. The interval between the first heavy cracking
of props and the breaking of the roof is usually not more than twelve
hours.

A break line of about twenty-five degrees with the face of the
rooms is roughly maintained. When roof falls prevent access to
the squared-up pillar ends, a 12-foot cut is again made completely
through the pillar, as at the face of the room when drawing began,
and with this new pillar end the procedure continues; consequently,
very little pillar coal is lost. Carl Scholz, President of the Coal

36 ILLINOIS ENGINEERING EXPERIMENT STATION

VaUey Mining Company, states that at mine No. 3 at Matherville
the loss of pillar coal does not exceed four per cent.

At the No. 3 mine of the Coal Valley Mining Company, the
cost of producing coal is much less on pillars than on advance work
in rooms. Room coal costs on the average $1.25 per ton at the pit
mouth, and pillar coal costs $1.015. This difference in cost exists
because track, yardage, bottom digging, and driving through rolls
and slips are properly charged against room coal, while there are
no such charges against pillar coal. When pillars are drawn, there-
fore, the average cost per ton for the total production is materially
reduced. At this mine rooms are worked with one man at the face,
but two men are placed at each pillar and at the face of each entry.
Only one man has been injured in connection with the pillar drawing.

With the extraction of such a large percentage of the bed sur-
face subsidence is to be expected. The topography of the surface
is rolling, and subsidence is usually indicated by cracks in the hill-
sides. The largest single area affected was reported to be one acre
which subsided from 6 to 12 inches.*

13. District IV. — In District IV the No. 5 coal is mined. The
average thickness of this coal is 4 feet, 8 inches according to data
taken at 240 mines and given in the Thirty-first Annual Coal
Report of Illinois. The No. 5 bed outcrops in Peoria, Pulton, and
Knox Counties, but is found at greater depths toward the east. It
lies from 300 to 600 feet below the surface in Macon County, 400 feet
in McLean, and from 260 to 300 feet in Logan.

The roof is of black sheety shale varying in thickness from a
few inches to 35 feet and containing occasionally ' ' niggerheads "
of pyrite. In many mines there is, in places, a layer of pyrite
two or three inches thick between the coal and the shale. Where
this layer is present, the shale is protected from the air and stays
up ; where it is not present, the shale falls badly and sometimes caves
to a height of 35 feet. A limestone occurs above the shale in most
mines, though in a few places a fine grained micaceous sandstone is
found. In some cases the shale is absent, and the cap rock becomes
the roof.

A great many clay veins extend through the coal and the roof
shale; there are also small faults, slips, and rolls, and places where

*Andros, S. O., "Coal Mining Practice in District III," 111. Goal Min. Invest., Bui. »,
pp. 11 et seq., 1915; "Coal Mining in Illinois." HI. Coal Min. invest., Bui. 13, 1916.

PERCENTAGE OP EXTRACTION OF BITUMINOUS COAL 37

the coal has been eroded and the space has been filled with drift. It
is difficult, therefore, to calculate the total tonnage and to project
any plan of operation. In many places the coal adheres to the roof
and separates from it with difficulty. In one mine about an inch
of coal is left to protect the roof shale from the air. In most
mines the floor consists of a dark gray clay which heaves badly
when wet.

Operations are conducted on the unmodified room-and-pillar system
or on the so-called panel system. Dimensions of workings are given
in Table 3. There are also four mines in the district which are oper-
ated on the long- wall system. Mining methods have not been given very
careful attention, and the variations in the coal bed tend to minimize
the effect of such attention as has been given. The method of mining
generally practiced in the district involves the running of parallel
main entries from the shaft toward the boundaries, and the turning of
cross entries from the main entries at intervals of 350 to 400 feet.
Rooms are turned off these cross entries on 30-foot to 42-foot
centers, and are driven 20 to 30 feet wide. Room pillars average
9 feet in width and rooms 26 feet, but pillars are gouged as the
miner pleases. This haphazard method is productive of so many
squeezes that in some mines a modification of the system has
been employed in which stub or room entries are turned off the
cross entries. This method approaches the panel system and is called,
locally, " block-room-and-pillar. " Sometimes a sufficiently large cross
barrier pillar is left to confine a squeeze to the block in which it
originates, but generally the barrier pillar is gouged and squeezes
ride over it unchecked until they reach a horseback or some ungouged
pillar which is large enough to stop them. In several mines squeezes
originating in rooms have traveled to the main barrier pillar and
to the solid coal at the entry face. In one mine an entry was saved
from a threatened squeeze by very heavy timbering ahead of the
squeeze.

Eleven of the sixteen mines examined are at present operated
on this semi-panel system, but the relative dimensions of room and
room pillar have not been changed from previous operations. These
dimensions are not safe 'under the roof found in the district: Room
width is not uniform, but rooms are narrowed to avoid horsebacks
and widened again where the coal resumes its normal thickness.
There is a temptation to get all the coal possible on the advance,

38 ILLINOIS ENGINEERING EXPERIMENT 8TATION

because the numerous rolls make uncertain the total tonnage which
can be extracted from any area, and the rolls interfere seriously
with any projected plan since cutting through them is expensive.

Pillars are drawn in only a few mines, and in these drawing is
not done systematically but is confined to shooting slabs off the thick-
est parts of the pillars. Room pillars are tapered to cross-cuts in
nearly all mines. In one case an attempt was made to draw pillars,
and a track was laid along the rib, but objections were raised by
the miners to this position of the track, and the attempt was aban-
doned. Principally because of the insufficient pillar-width, the floor
of fire clay heaves badly even when dry.*

Nineteen mines were examined in this district, and the estimates of
the percentage of recovery furnished at seventeen ranged from 55
to 75 per cent, averaging 67.26 per cent. It is probable that
most of the estimates are too high for, although the gouging of
pillars tends toward high percentage of extraction, careless methods
always result in the loss of much larger quantities of coal than is
supposed. One company, which has given careful attention to the
forms and dimensions of its workings, is extracting about 70 per cent
of the coal. It is doubtful however, if the extraction throughout the
district as a whole amounts to 60 per cent.

14. District V. — Bed No. 5 in Saline and Gallatin Counties lies
at a depth of 25 to 450 feet, being nearest the surface along the
southern portion of the district. The bed varies in thickness from
4 to 8 feet, and averages 5% feet in Saline County and 4 feet in
Gallatin County.

The roof of the No. 5 coal in this district is of shale which is
sometimes laminated and interbedded locally with bone and stringers
of coal for a distance of 3 feet above the seam. The roof usually
contains many concretions of iron pyrites called ' ' niggerheads. ' '
It breaks quickly when wide spans are left supported, and it is
drawn when it shows a plainly marked parting not more than 4
inches above the coal; but such a parting rarely occurs and the coal
bed is so thin that the top coal cannot profitably be left in place.
There are numerous falls which can be avoided only by making entries
narrower than at present.

*Andros, S. O., "Coal Mining Practice in District IV," HI. Coal Min. Invest., Bui. 12,
pp. 15 and 19, 1915.

PERCENTAGE OF EXTRACTION OP BITUMINOUS COAL 39

The floor is of fire clay which in places contains much sand and
heaves badly when wet. The bed contains many hills and rolls
causing grades as high as 15 per cent in the entries of some mines.
The coal is not pinched out at these hills, but follows the contours
with undiminished thickness. In some mines about 9 inches of bottom
coal is left below a "blue band," but as this bottom coal is not of
good quality, increased facility in shooting compensates for the loss of
coal.

The room-and-pillar system of mining is used exclusively, a main
haulage entry and a parallel air-course being noted in every mine
examined except one, — in which triple main entries were driven,
two for intake air and one for return air and haulage. In the smaller
mines and in many of the larger ones, the dimensions of workings
are not suited to the roof conditions. The main entries vary in width
from 14 to 16 feet. A few shaft pillars have been gouged. The
room stumps, which are left when rooms are turned off the cross
entries, are generally small. The closing of entries by roof falls
may often be attributed to local squeezes which ride over the room
stumps. Table 3 gives dimensions of workings for each mine exam-
ined.

The custom of driving wide rooms and entries, of leaving narrow
pillars throughout the mine, and of obtaining all the coal possible on
the advance without attempting to draw pillars has resulted in a
high percentage of extraction for Illinois mines. The percentages
given in Table 3 were calculated from the most nearly exact data
obtainable at the time of their publication but are unquestionably
too high. This reported extraction, averaging 67.1 per cent for the
seven mines examined, was accomplished only with greatly increased
expense for cleaning up.* One of the large operators of this dis-
trict reports an average recovery at ten mines of 60.5 per cent over
a 5-year period with a maximum of 72 per cent and a minimum of
52 per cent where the cover varies from 60 to 414 feet. Pillar draw-
ing is not practiced, and it would be impossible to gain the percent-
ages of coal given in the table if the dimensions given were adhered
to, but pillars are gouged to such an extent that there should be a
higher percentage of extraction than is calculated from the dimen-
sions of rooms and pillars in the table.

*Andros, S. O., "Coal Mining Practice in District V," 111. Coal Min. Invest., Bui. 6,
pp. 9 and 12, 1914.

40 ILLINOIS ENGINEERING EXPERIMENT STATION

15. District VI. — This district has experienced a rapid develop,
ment, because the No. 6 coal commands a ready market ; consequently
mining on a large scale is possible. Bed No. 6 lies close to the surface
along the Duquoin anticline* but dips sharply to the east, reaching
a depth of 726 feet at Sesser. A general uplift has brought it to
the surface along an east-west line extending through Carterville to
Marion and along a southeast line from Marion to the boundary of
the district. East of the area affected by the Duquoin anticline,
the bed has a pronounced dip to the north. Along the outcrop line
there are a few slopes and strippings, but the steep dip of the bed
leaves only a small acreage with thin cover, and the remaining open-
ings are shafts. The seam itself is thick, ranging from 7y2 to 14
feet and averaging, as shown by 130 borings, 9 feet, 5 inches. A
clean persistent parting of mother coal lies 14 to 24 inches below the
top of the bed, and a second parting generally appears 5 to 8 inches
lower down. Above the upper parting the coal occurs in layers 3 to 6
inches thick, with partings of mother coal between them.

The immediate roof consists of a gray shale 15 to 110 feet
thick. This shale does not stand well when the coal is removed, and
the top coal is generally left as a roof, at least until the rooms are
finished. The bottom is generally of clay, four inches to eight feet
thick, below which is limestone. There is only one persistent band
of impurity in the bed. This, which is known as the blue band,
generally consists of bone or shaly coal and is found uniformly at
a height of 18 to 30 inches from the bottom. Its thickness varies
from i/2-inch to 2y2 inches, t

The large number of squeezes which have occurred in mines of
District VI would seem to indicate the presence of one or more thick
beds of strong rock among the overlying strata. A study of the
logs of numerous wells does not, however, show the presence of any
continuous strong bed which would be a serious obstacle to the intro-
duction of methods allowing a larger percentage of extraction. The
State Geological Survey makes the following statement concerning the
overlying limestone: "Over a large part of the area within 25 feet
of the coal is a limestone cap rock which in places rests upon the
coal, except for the draw slate that lies between. Where the lime-

*Andros, S. O., "Coal Mining Practice in District VI," 111. Coal Min. Invest., Bui. 8,
tShaw, E. W., and Savage, T. E., U. S. Geol. Bur., Folio No. 185.

PERCENTAGE OP EXTRACTION OF BITUMINOUS COAL 41

stone cap rock is not present within- 25 feet of the coal it may be
entirely absent, or lie at a considerably greater distance above the
coal, amounting in some places possibly to as much as 100 feet. ' ' *
The limestone cap rock is of variable thickness up to about 11
feet, the average thickness being 4 to 5 feet.f In some places sand-
stones are found at various distances above the coal, but none
of these seems to be close enough to the coal to affect the choice
of a mining method. In other words, it seems that there is no layer
of rock, sufficiently near the coal to require serious consideration,
which cannot be broken by careful attention to the proper methods.
An examination of bore hole records of the Connellsville district of
Pennsylvania, where the percentage of coal extracted is very high,
indicates that there is more difficulty in breaking the overlying lay-
ers of rock in that district than would be experienced in most cases
in District VI of Illinois. At a few mines an unusually wide room
pillar is left in the middle of a panel for the purpose of limiting
the area affected by a squeeze.

According to Table 3, all mines in the district, except strippings,
are worked by the room-and-pillar method or by the panel method.
Where the latter is employed, frequently no attention is paid to
panel pillars so that the advantage of this method in the stopping
of squeezes is largely lost. Practice is not uniform in regard to the
number of rooms, which may be as low as 14 or as high as
30, turned from a room entry. The description of mining prac-
tice in this district $ given in Bulletin 8 of the Cooperative Investi-
gations says, "The immediate roof overlying the coal falls in slabs
after short exposure to the air and top coal is usually left to protect
it, but the cap rock is a tough coherent shale which does not break
easily. The first mines opened in the district had widths of rooms
and pillars unsuitable for this tough cap rock. New mines as they
were opened adopted the dimensions of the older mines and a great
waste has resulted through the loss of pillar coal. It will never be
possible in this district to draw any considerable portion of the
pillars where rooms 20 to 29 feet wide are driven with narrow room

*0ady, Gilbert H., "Coal Resources of District VI," 111. Coal Min. Invest., Cooperative
Agreement, Bui. 15, p. 88, 1916.

tlbid, p. 82.

* Andros, 8. O., "Coal Mining Practice in District VI," HI. Coal Min. Invest., Bui. 8,
p. 12, 1914.

42 ILLINOIS ENGINEERING EXPERIMENT STATION

pillars. Fear of yardage charges has been an important factor in
maintaining the present improper dimensions. . . . With present
dimensions when rooms have been driven 200 to 300 feet there is a
large area of unsupported cap rock. If an attempt is made to draw
pillars under such conditions a squeeze is usually started which often
rides over room and entry pillars and sometimes affects a large acre-
age. In one mine 85 acres were squeezed ; in another, 80. ' '

Early operations were carried on without regard to the possible
production of squeezes. Pillars were gouged out or entirely removed
whenever the demand for coal seemed to excuse this procedure; a
natural consequence was the occurrence of squeezes. At one mine
there have been five squeezes of which two involved about 80 acres
each, one about 40, one about 20, and one possibly 10. The present
plan for the future operation of this mine contemplates leaving
barrier pillars 150 feet wide along the important entries, and removing
this pillar coal later. It is believed that this plan will confine
roof movement to 'the worked out areas and that the entry pillars
and barriers can be extracted later. This plan is much the same
as that shown by Fig. 32, page 102.

At another mine a large squeeze approached within 125 feet
of the air shaft and caused a depression on the surface which neces-
sitated the regrading of a considerable amount of track, including
the track scales. Practice at this mine represents one extreme, since
no attempt is made at room-pillar drawing beyond driving cross-cuts
about 30 feet wide at the ends of rooms, and as much coal as
possible is taken on the advance. An attempt will be made to take
out barrier and entry pillars on the retreat. Rooms are driven
25 feet wide on 45-foot centers, and cross-cuts are 25 feet wide.
The excavated area is about 50 per cent and the top coal, which is
only 18 inches thick, is left up.

The figures for recovery of coal given in Table 3 are unquestion-
ably too high although they were based on the best information avail-
able at the time. The average percentage of extraction in District VI
is not more than 50 per cent, and it is probably nearer 45 per
cent. The maps of mines may show an excavated area of 50
per cent or even more, but they do not take into account the un-
mined top coal. The thickness of coal taken out is generally about
7 feet and top coal ranging from a few inches to 4 or 5 feet
in thickness is left. Even if the top coal is ignored, the extraction

PERCENTAGE OP EXTRACTION OF BITUMINOUS COAL 43

is not so high as the estimates generally indicate because of losses
in squeezed areas and boundary barriers.

Special investigations on the subject of recovery made at several
mines in Franklin County gave results which are summarized as
follows :

At one mine, the recovery in worked out areas where pillars
are not drawn is about 65 per cent; where the pillars are
taken, it is about 75 per cent.

At another mine, close observations were made in connec-
tion with a study of subsidence. In a panel where the ex-
traction was considered good and possibly above the average
for the mine 40 per cent of the coal is left as pillars. Two
feet or 20 per cent of the thickness of the bed is also left
as top coal, and the loss from this cause would be 20 per
cent of the remaining 60 per cent or 12 per cent of the total.
The total loss is then at least 52 per cent. No attempt has
been made to extract room pillars, but some entry pillars
are taken, and top coal is taken over the area in which these
pillars are drawn.

At one of the mines where the thickness of the coal is greater
than the average, little pillar work has been done. The coal
varies from 9^ to nearly 16 feet in thickness,* and about
9 feet of it is taken out. Generally about one foot of coal is
left on the bottom to avoid the possibility of taking up a bed
of "black jack" which is not easily distinguishable from coal.
This black jack is probably a coal of very high ash content. The
leaving of bottom coal results in the elevation of the working
place in the bed so that the top coal left is only 3 feet or
even less in thickness. In a few places in this mine some pillar
coal has been taken out. Where this was done, break-throughs
about 24 feet wide were driven at the ends of the rooms.
Then work was commenced at the ends of the pillars, and coal
was taken out by pick work. This work seems to have been
successful, but it has not been followed systematically. The
largest number of pillars which have been taken together was
six, and no attempt was made to obtain a break in the roof.

* Cady, Q.
). 58, 1916.

H., "Coal Resources of District VI," HI. Coal Min. Invest., Bui. 15,

44 ILLINOIS ENGINEERING EXPERIMENT STATION

The leaving of coal on the bottom is a practice followed
at only a few other mines. In some cases where the blue band
is thick the mining is done above it, and a portion of the upper
part of the bed, ordinarily included in the top coal, is taken
down. At two mines where this method is followed in part,
the blue band and the coal below it are left in where the blue
band is thick and the top coal is taken to within about ten
inches of the roof, at which point there is a parting. Greater
care is required to prevent the breaking of the top coal where
this is done.

At one of the mines in the southern part of Franklin County
a little pillar coal is drawn, though pillar coal is not depended
upon for an important part of the output. Kooms are 25
feet wide with 20-foot pillars. Rooms are holed through
into those of adjoining panels. When the rooms have reached
their full lengths, cross-cuts 24 feet wide are driven across
the ends of the pillars. In addition to these cross-cuts the
pillars are probably slabbed to some extent. The coal is about
9 feet thick, and about iy2 feet of top coal is left up. No bot-
tom coal is left. The barrier pillars are about 100 feet thick.
Break-throughs are 21 feet wide. It seems hardly proper to
speak of this kind of work as the extraction of pillar coal, but
it represents a practice which is common in this district.

At one of the mines, pillars are drawn, beginning in the
middle of a panel, in six rooms at a time; then another group
of six pillars is attacked, one pillar being left untouched between
the groups. This is simply another method of attempting to get
as much coal as possible before being driven out by a fall of
the top, and is not an attempt to break the cap rock.

Systematic work in the recovery of pillar coal as done at
one of the mines is illustrated in Fig. 4. The mine is operated
on the block system commonly called the panel system, though
the panels are not kept sufficiently isolated to warrant the
use of the term. Cross entries are driven at intervals of 1,370
feet, and panel entries are driven through from cross entry
to cross entry. On each pair of panel entries twenty-eight
rooms are turned to each side on 40-foot centers. A barrier
pillar 125 feet wide is left along the cross entry. After the
room entry is driven the rooms are necked, but only the first

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL

fourteen rooms on each side of -the room entry are worked,
and these are finished before the rooms at the other end of
the panel are driven. Break-throughs are normally 11 feet
wide; those at the ends of the rooms are 24 feet wide. Pillar
drawing is commenced when the rooms at one end of the
panel are finished, and the coal is taken out through the

PICK WORK

FIG. 4. PILLAR DRAWING IN FRANKLIN COUNTY, ILLINOIS

first cross entry, that is, the one next to room No. 1. The coal
from the remaining portion of the panel is taken out through
the next cross entry, that is, the one next to room No. 28. The
advantage of this method lies in the fact that the extraction
of the coal from the second half of the panel is not interfered
with, as far as haulage and ventilation are concerned, by move-
ments caused by pillar drawing in the first half. The pillar
coal is attacked first by the driving of 24-foot cross-cuts at the
ends of the rooms; then other cuts are made in the pillar

46 ILLINOIS ENGINEERING EXPERIMENT STATION

with the breast machine in such manner as to leave stumps be-
tween the cuts and the break-throughs. These stumps are
removed as far as possible by pick work, but the miners are
not always able to finish as much work with the machines as
is desired since this work is frequently interrupted by move-
ments of the roof. As much of the coal as is possible is then
taken out with picks. While the work at this mine is as sys-
tematic as that at any mine in southern Illinois, the company
has no exact record of the amount of pillar coal extracted,
but it is known that the pick-mined coal amounts to approxi-
mately 10 per cent of the output. When the pillars are not
drawn, the recovery is estimated by the operators to be about
65 per cent; when they are taken, the estimates run about 75
per cent.

Through the courtesy of the Franklin County Coal Operators'
Association (Illinois), data have been made available regarding the
extraction of coal in that county as presented in the following para-
graphs :

The coal mined is the No. 6 bed of the State Geological
Survey classification. Measurement of 113 sections taken in
twelve of the largest mines in the county gave an average thick-
ness of 9.2 feet of coal, the average minimum thickness for
the same twelve mines being 8 feet, and the average maximum
thickness 10.64 feet. The blue band, which is characteristic of
the No. 6 coal bed, varied from 14 to 2 inches in thickness, and
its average distance from the floor was 21.5 inches. Owing to
the difficulty of keeping up the shaly material above the coal
bed, the top coal is almost universally left as roof protection,
and, up to the present time, very little of this top coal has been
recovered, although some operators are expecting to recover it
at a later date in connection with pillar drawing. In one of
the twelve mines from which the data were obtained, top coal
was not left in the rooms. This, however, is exceptional prac-
tice, the average thickness of the top coal left in the twelve
mines being V/2 feet. The average thickness of coal mined was
7.46 feet, and the average tonnage per acre to January 1, 1916
was 6,627 tons. This is equivalent to 40.7 per cent extraction,
if it is assumed that all the 9.2-foot bed is available for ship-

PERCENTAGE OP EXTRACTION OF BITUMINOUS COAL 47

;ment, or to 41.6 per cent if it is assumed that the blue band
and refuse discarded in the loading, or 0.2 foot, is deducted
from the thickness of the bed. A very careful estimate for
each of the twelve mines noted, made by dividing the total
amount of coal in the area mined up to January 1, 1916 into
the actual shipments since the mine began operating, gave per-
centages of extraction varying from 37.7 to 49.5, or an average
of 41.4 per cent.*

For six of the twelve mines, data were available for the average
percentage of extraction in the portion of the bed actually mined;
that is, the total thickness less the top coal left up to protect the
roof. This average is 48.65. These mines are all comparatively new
mines, and in only a few cases has any portion of the workings
reached the boundary so as to permit drawing the pillars in return
workings. At many of the mines it is hoped to increase the per-
centages of extraction through subsequent pillar drawings, but the
amount of such increase is, of course, problematical. In many in-
stances squeezes have already occurred, but as a general thing only
the room pillars have been affected.

The twelve mines under discussion are representative of the
practice in Franklin County and to a great extent of that of southern
Illinois. In a number of these mines experiments are now being
conducted to determine in what respect present methods of working
may be modified to yield a larger percentage of extraction. Although
these mines are operating under practically the same physical con-
ditions and all on the panel system, the variation in the detailed
operations, such as the number of rooms per panel, or the width
of barrier pillars, indicate the necessity for a critical comparative
study of details to determine the best method for the given conditions.

Investigations in Williamson County supplied the following facts :

At one mine rooms are 21 feet wide on 40-foot centers.
From 2 to 2~y2 feet of top coal is generally left up on the ad-
vance. In one part of the mine the coal is 11 feet thick and
only iy2 feet of it is taken out. It is estimated that 40 to
50 per cent of the pillar coal is won. The top coal, which is the

* The Peabody Coal Company reports that the percentages of extraction at its four mines
in this district are 67, 63, 55, and 55.

48 ILLINOIS ENGINEERING EXPERIMENT STATION

best part of the bed, is taken out when the pillars are drawn.
There are no definite records on recovery, but it is probable
that 55 or 60 per cent is gained. If iy2 of the 11 feet are
removed, and 40 per cent of the pillars and all the top coal
over the area in which the pillars are drawn are removed, the
extraction is about 60 per cent.

In another mine a rather high percentage of extraction
is attained because of favorable conditions which permit the
leaving of small pillars. The coal is 9 feet thick and the depth
only 100 feet. Rooms are 24 feet wide on 35-foot centers. In
some cases top coal, about 20 inches thick, is left if the
machine runners think the top is insecure. Probably from
65 to 70 per cent of the coal is taken out. No pillar work
could be done with rooms and pillars of these dimensions, but
on one side of the mine 15-foot pillars are now being left with
the intention of taking them out on the retreat.

At some mines in the western part of Williamson County
considerable trouble has been experienced, because large quan-
tities of water enter when the top is broken. The cover here
is only about 100 feet thick and there are only 3 to 4 feet
of solid rock. The rooms of one mine are 20 feet wide and
are driven on 40-foot centers, although they are sometimes
crowded. Some rooms were driven on 32-foot centers, but
the pillars were not sufficient to prevent squeezes. En-
tries are 12 feet wide and entry pillars 20 and 25 feet wide.
The coal is 5 to 11 feet thick with an average thickness of
8 feet. Top coal averages 20 inches in thickness. Above the
bed is a shale; above this is a so-called soapstone, ranging from
2 to 8 feet in thickness and averaging about 4 feet; and above
this is a black shale. In some places a draw slate from 1 to
2 feet thick occurs above the coal, and above this is limestone
1 to 3% feet thick. Where is no draw slate, there is no lime-
stone. An unconsolidated sand is found in some places above
the coal. The pillars are sometimes slabbed a little to compen-
sate for the coal left in entry and barrier pillars. When this
slabbing is done, the extraction amounts to about 50 per
cent. In some cases extra cross-cuts are taken, and the extrac-
tion is thereby increased to about 75 per cent. On the
whole, the extraction is estimated to be about 60 per

PERCENTAGE OP EXTRACTION OF BITUMINOUS COAL 49

, — an estimate which is probably reliable since the work
is more carefully done here than at many other mines of the
district. Where more than 60 per cent of the coal is taken
out in this mine, the roof breaks and water enters in large
quantities. Although the amount of water is influenced by
precipitation, the flow is continuous. In one case where the
rock had been broken and a large quantity of water had entered
the mine, it was thought that the strata was drained to some
extent and that it would be possible 'to allow the top to break
at a slightly higher elevation. It was found, however, that
the new break allowed a large amount of water to enter the
mine, and it has been impossible for the company to do any
pillar work. It is planned, as some of the workings reach the
boundaries, to draw pillar coal. In these cases pumps will
already have been installed, and it will be possible to conduct
the water to these. The water, moreover, will be entering in
abandoned places and not between the workers and the shafts.
Some of the workings are now not far from the boundaries,
and the plan can be put into operation in the near future.

At another mine the coal is 9 feet thick, the top is of white
shale, and the bottom of fire clay. The top coal is about 2 feet
thick. The mine is operated on the panel system. No pillars
are drawn until the rooms on an entry have been finished;
then a cross-cut three machine-cuts wide, or about 20 feet,
is driven at the ends of the pillars in about half the rooms on
the inside end of the stub. Following this, another cross-cut
is made farther back in the pillar leaving a stump about 10
feet wide. The distance between the first and second cuts varies
according to conditions, or according to the judgment or incli-
nation of the machine men. If it is made farther back, some
of the pillar coal is lost. This operation is repeated until
the first break-through in each pillar is reached, the remainder
of the pillar being left standing until all the rooms on the stub
are finished; then the room stump and the entry pillars are
drawn. No effort is made to obtain a break in the roof, and
the leaving of stumps of pillars is likely, by partially sustain-
ing the roof, to bring on a squeeze. At present the driving of
rooms without necks is being tried, the purpose being to avoid
payment for narrow work; and it is believed there will not

50 ILLINOIS ENGINEERING EXPERIMENT STATION

be sufficient difference between the support left under that
system and that left under the present system to endanger the
entries. These rooms without necks are turned six machine-
cuts wide and are widened to seven cuts beyond the first cross-
cut.

At another mine the average thickness of the coal is 9 feet,
4 inches. The top coal is about 2 feet thick and is left up
until the pillars have been partly drawn back, being taken down
just before the track is removed. There is generally a good
parting between the main bed and the top coal, which is said
to be poorer than the main bed. Above the bed is shale of un-
known thickness, which has never broken high enough to expose
any other rock above it. This shale slacks when exposed to the
air. It does not form a very good top and most of the entries
are timbered. The bottom is generally of clay, but in some
places limestone appears next to the coal. Rooms are 20 feet
wide on 30- to 35-foot centers and are 185 to 190 feet long.
Stub entries are turned on 400-foot centers, and 16 to 18 rooms
are turned from a stub. The room pillars are gouged to a con-
siderable extent. It is planned that all the rooms in a panel
shall be driven to their full length before pillar drawing is
commenced, but this plan is not always followed, and squeez-
ing sometimes commences before all the pillars can be attacked.
This, of course, is promoted by the gouging of room pillars.
When the rooms are finished, cross-cuts 20 feet wide are driven
at the face with breast machines. The rest of the pillar
work is generally done with picks though machines are used
when possible. Movement of the roof, however, generally in-
terferes with machine work after the first cross-cut. The pick
work generally consists of slabbing along the sides of pillars,
but machines are sometimes used. Squeezes have always been
confined to the panels, and no entries have been lost until the
entry pillars have been drawn. A careful computation, based
upon a comparison between the actual area worked and the
number of tons hoisted, shows that the extraction at this mine
has been 48.89 per cent. This is one of the most thoroughly
worked mines in the No. 6 bed, and the estimation of percent-
age of extraction is undoubtedly as close as any that has been
made. The results found furnish one of the reasons for the

PERCENTAGE OP EXTRACTION OF BITUMINOUS COAL 51

statement that extraction in most mines of the district is less
than the operators of the mines believe it to be.

At a Perry County mine the general system is the same as in
Williamson County. Koom entries are driven through from cross
entry to cross entry. A somewhat closer adherence to the panel
system is to be noted, however, in that 25-foot pillars are left
at the ends of rooms. Rooms are 24 feet wide on 60-foot centers,
and they are driven 250 feet long. Break-throughs are staggered.
When the room is completed, an 18-foot cross-cut is driven
through the pillar at the end. Top coal, about 3 feet thick (the
best of the bed in quality* as it is at the mine last mentioned), is left
up until pillar drawing commences. Pillar drawing is commenced in
the middle of the panel. After the completion of the cross-cut at the
end of the first pillar attacked, the top coal is loosened by a light shot
near each rib. Work on the pillars is then prosecuted by making a
cut through the pillar, if the condition of the top will permit, wide
enough to leave an 8-foot stump at the end of the pillar and another
of the same dimension next to the nearest break-through. These two
8-foot stumps and whatever is left by the machines are taken out by
hand work. Two men are used on solid work and two on the machine.
This method has been found successful and a considerable amount of
pillar coal has been recovered, but pillar drawing is not a necessary
part of the system and is not always carried out. Where the pillar
coal and the top coal are taken, the recovery is said to be from 75 to
80 per cent of the coal in the area actually worked.

Several plans are now being tried or considered for the more nearly
complete extraction of the coal in this district. One of these, which
has so far been given only an incomplete test, is a panel long-wall
method. Double entries, which would have been -the room entries of
a panel under the ordinary methods of operation, were driven 340 feet
long. At the end, two rooms were driven on each side separated by
25-foot pillars. The rooms at the extreme end of the block on each
side were 9 feet wide and the ones further back were 18 feet wide;
each was 200 feet long. They were connected at the ends so that
ventilation was obtained, the course of the air current being as shown

*For a discussion of the differences between the top coal and the remainder of the bed
see "Chemical Study of Illinois Coals," by S. W. Parr, 111. Coal Min. Invest., Bui. 3,

52 ILLINOIS ENGINEERING EXPERIMENT STATION

in Fig. 5. Then the outby ribs of the 18-foot rooms were worked as
long-wall faces by continuous-cutting chain machines making a 6-foot
cut. The top behind the working face was propped. It was the in-
tention to support the immediate roof until the face had advanced
some distance and then to make an attempt to break the overlying rock
by the withdrawal of the props. This plan was found to be impossible,

FIG. 5. PANEL LONG-WALL

however, as the top fell when the face had advanced only about 40
feet. Other conditions made it necessary to discontinue the experiment
temporarily. In operating by this method, sprags were placed in the
cutting behind the machine to prevent the premature fall of the coal.
No trouble was experienced in getting the coal down ; it was produced
very rapidly and was easily handled. At present it is not known
whether the top can be broken along the desired line, but it will be seen
that this line is only 400 feet long and that it is interrupted in the

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL 53

center by the entry pillar. Even if it *fe not possible to break the top
and to work the coal back continuously on two longwall faces, it seems
that the attack can be repeated farther back in the block and that coal
can be produced as cheaply as by the ordinary method; also that a
much higher percentage of extraction can be attained. If it should be
necessary to follow the method by repeated attacks on the block, there
would be some resemblance to the ' ' single room ' ' method successfully
worked in West Virginia.

Various other plans for higher extraction have been suggested and
some have been partly applied, but the great demand for coal, which
has been stimulated by the European War, has caused coal producers
to concentrate all their attention upon the immediate production of a
large tonnage. Anything in the nature of experimental work will be
postponed until the return of more nearly normal conditions, but there
is reason to believe that successful efforts will be made to increase the
percentage of extraction and that the present large loss will be greatly
decreased.

16. District VII— The coal worked in District VII is the No. 6
bed on the west side of the Duquoin anticline. The thickness varies
from 2y2 feet to 14 feet and averages about 7 feet. There is a well
defined parting plane in the coal about 18 inches from the roof.
Where the roof is of black shale and where the coal is 7 feet or
more in thickness, the upper bench or "top coal" is left. The roof
is a non-calcareous black shale, a calcareous gray shale called locally
"white top" or "soapstone," an unconsolidated dark gray or black
shale called "clod" and made up of fragments of varying size and
hardness extremely difficult to support, or a hard gray limestone called
1 1 rock top. ' ' A poorly defined cleat or cleavage in the coal may be seen
in some places. The floor throughout the district is of fire clay
which generally heaves when wet.

The thickness of the coal is almost ideal for easy working and for
large production; some of the mines have obtained daily capacities
which rank among the highest in the world. The older mines have
been worked without much regard to system, but the newer ones are
more carefully planned. The planning, however, is directed toward
large daily production rather than toward a high percentage of extrac-
tion.

Varying roof conditions often make different entry and room

54 ILLINOIS ENGINEERING EXPERIMENT STATION

widths necessary in different sections of a mine. In many mines the
entries and rooms under rock top are too wide and the pillars too
narrow, — a condition responsible for squeezes which sometimes have
endangered even the shaft. Squeezes have occurred in thirteen of the
twenty-five mines examined in this district ; they have generally begun
in sections in which the roof was of limestone. In mines in which the
rooms are not frequently surveyed there is no definite knowledge of
room-pillar width except at cross-cuts. Table 3 gives dimensions of
workings at each of the mines examined.

In ten of the mines examined where the immediate roof was of
thick black shale, top coal was left to prevent variations of temperature
and humidity from affecting the shale of the roof proper, which spalls
badly when exposed to the air. Where no top coal is left, this black
shale usually falls with the coal or is drawn. Where there is less than
four inches of shale between the coal and the limestone, the shale is
drawn. In some mines where the latter is more than four inches thick
it is propped ; in others it is drawn, unless it is more than two feet in
thickness.* The Peabody Coal Company reports extractions at its
mines in this district of 65, 62, 60 and 50 per cent. At the twenty-five
mines examined, the average estimated percentage of recovery fur-
nished by the operators was 55.5 per cent. So far as is known, no
efforts have been made to extract a higher percentage of coal. The
reason for this attitude is to be found partly in the condition of the
surface, which in many places is so nearly level that any noticeable
subsidence disturbs the drainage and effects the value of the surface
for agricultural purposes.

At present the abandonment of a large percentage of the coal is a
result of the difficulties experienced in attempting to secure satis-
factory agreements with the owners of the surface. In some cases the
owners of coal rights are not the owners of the surface and are not free
from responsibility for surface damage. Since the operators have
found that the estimates of damage caused by subsidence are likely to
be very high, it has become the custom to operate the mines under
methods which will avoid subsidence. Unfortunately it has not been
possible to estimate the exact amount of coal which must be left in the
ground, and squeezes and subsidences have sometimes occurred when it
was thought that sufficient coal had been left.

S' °" ' °°al Mining Practice in District VII." 111. Coal. Min. Invest., Bui. 4,

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL 55

Even where low value of the land.vor good drainage reduces the
cost of possible injury to the surface by subsidence, no effort is made to
secure a higher extraction. The occurrence of squeezes is feared, and
experience shows that the only way to prevent them without radically
changing the system of mining is to leave large amounts of coal in the
form of pillars. One company which was formerly getting 50 to 60

FIG. 6. PLAN OF AN OPERATION IN MACOUPIN COUNTY, ILLINOIS, SHOWING
EXTRACTION IN A LIMITED AREA

per cent of the coal with frequent squeezes and subsidence has changed
the dimensions of rooms and pillars so that now only 40 to 50 per cent
is obtained. Thus far, with the new dimensions, squeezes have not
occurred. No effort has been made to extract pillars systematically
with the purpose of breaking the cap rock and thus preventing a
squeeze by relieving the stress on the pillars, but there is nothing to
indicate that this plan could not be carried out.

The plan of a portion of one of the mines is shown as Fig. 6. This

56 ILLINOIS ENGINEERING EXPERIMENT STATION

may be taken as a fairly typical projection of large mines in this dis-
trict. In many of the mines, including parts of the one illustrated,
the workings are on a panel system, but probably not enough attention
is paid to the matter of leaving pillars sufficiently wide to prevent the
spread of squeezes beyond the boundaries of the panels. This illustra-
tion is presented, because the mine was surveyed with unusual care in
connection with an investigation of subsidence which is being carried
on by the Cooperative Coal Mining Investigations. The rooms and
pillars are about 30 feet wide; this dimension was adopted with
the belief that the top would be held up by pillars of this width left
between 30-foot rooms. It had been found that the roof would fall if
25-foot pillars were left between 25-foot rooms. In the restricted area
measured, the extraction amounts to 59.2 per cent of the area worked ;
that is, 40.8 per cent of the area has been left as pillars.

17. District VIII.— In District VIII, seams 6 and 7 are mined.
In both seams there are numerous rolls of roof and floor called
" faults, " or " horsebacks. " In many cases the roll completely dis-
places the coal.

Seam 6 averages 6 feet in thickness. Near Danville the immediate
roof is of grayish black shale about 6 feet thick. This shale, lying
between the coal and a cap rock of dark gray nodular limestone, makes
a roof which is easy to support. In the vicinity of Westville and
Georgetown, the immediate roof is generally of gray shale which
shows no distinct bedding, has little cohesion, falls in conchoidal
masses, and is extremely difficult to support. Stringers of coal, fur-
thermore, extend from the seam proper into the roof material and
render the task of supporting the roof more difficult. Occasionally
there are 3 to 4 inches of black shale between the coal and the
gray shale which forms the cap rock. Wherever this black shale is
broken, air and moisture disintegrate the gray shale cap rock, and the
roof becomes unsupportable. In all parts of the Danville district the
floor is of soft fire clay.

Seam 7 varies in thickness from 2y2 to 5% feet, the average being
5 feet. The coal has two benches separated by a clay band one inch
thick, which persists throughout the bed from 6 to 8 inches above
the floor. This bed also has numerous rolls.

While the stripping operations, which are important in this dis-
trict, are conducted in the No. 7 bed, the largest underground oper-

PERCENTAGE OF EXTRACTION OP BITUMINOUS COAL 57

ations are in the No. 6 bed. The mines are operated on the room-and-
pillar method, or a modification of it, but the numerous rolls in the
roof prevent close adherence to the system. The frequent occurrence

FIG. 7. PLAN OF MINE IN VERMILION COUNTY

of rolls has a marked effect upon the manner of driving rooms. In a
roll area it is difficult to support the roof, and the expense of driving
through the hard rock of the roll is great; consequently, when a roll
is encountered in driving rooms it is customary to change thi direction

58 ILLINOIS ENGINEERING EXPERIMENT STATION

of the room and to drive it parallel with the roll until the coal resumes
its normal condition, as shown in Fig. 7, which is a map of a mine
typical of the district. Often it is necessary to abandon a room before
it has been driven to its proper length. Since the rolls are of frequent
occurrence, the amount of coal that may be gained in any section of
the mine is problematical ; consequently, the operator, on reaching that
portion of the coal where the seam regains its normal thickness, will
attempt to get as much of the coal as possible during the first working.
Little attempt is made to preserve a constant room-pillar width, and
the practice of gouging pillars is common in the smaller mines.* No
systematic pillar drawing is attempted, because with present practice
there is little pillar coal left to draw when the rooms are driven to their
full length. The roof is so treacherous, especially in the vicinity of
the rolls, that it is not safe to leave wide spans of roof unsupported by
pillars.

The width of room pillars at the mines examined varied from 4 to
16 feet, and room widths varied from 21 to 43 feet. Table 3 gives
dimensions of workings at each mine examined. Very narrow room
pillars were found in mine No. 91, where the following dimensions
were recorded ; room centers, 47 feet ; room widths, 43 feet ; room pillar
width, 4 feet.

Although pillar gouging in the district has resulted in a high per-
centage of extraction from the bed in the first working, it has caused a
subsequent loss of coal through squeezes due to narrow pillars. The
average extraction for the six mines examined, as reported by the oper-
ators, is 70 per cent. Table 3 gives also the percentage of the bed ex-
tracted at each mine. These percentages were calculated from meas-
urements made in the mines and were checked by records of produc-
tion per acre obtained from the books of each operating company and
by planimeter measurements of mine maps. The Peabody Coal
Company reports an extraction of 66 per cent at its mine in this dis-
trict.

At one of the mines, almost all the pillar coal was extracted after
all the advance work had been done, and the roof was supported
largely by the rolls which occurred at intervals of 60 to 100 feet. At
another mine pillars are being extracted, and it is estimated, that the
total recovery will amount to about 85 per cent.

*Andros, S. O., "Coal Mining Practice in District VIII," 111. Coal Min. Invest., Bui. 2,
p. 16, 1914.

PERCENTAGE OP EXTRACTION OP BITUMINOUS COAL 59

18. Conclusion. — It will be seen that nearly all the work in Illinois
described as pillar drawing is unsystematic. It is merely incidental
to the mining of room coal, and preparation for it is rarely made in
laying out the mines. There are no apparent reasons, so far as physical
conditions are concerned, except in a few instances, why plans could
not be made for leaving pillars large enough to support the top during
the advance work and for recovering the pillars on the retreat.
Squeezes could thus be avoided, and the percentage of extraction
could be increased materially. The commercial conditions which seem
to make such a course difficult could probably be overcome, except in
those cases in which subsidence of the surface subjects the operators
to claims for damages in excess of amounts which would seem to be
reasonable compensation for the injury done. The law covering pay-
ments for damages due to subsidence ought to be made so clear that
there could be no doubt concerning the amount to be paid, and
this amount should be limited to a fair compensation for the injury
actually done.

At present there is promise of a considerable improvement with
regard to the percentage of coal extracted from Illinois mines. The
subject is receiving more and more attention on the part of coal pro-
ducers and careful planning of the work with a view to high extraction
as well as to low cost will follow as the natural result of greater in-
terest on the part of the operators.

60 ILLINOIS ENGINEERING EXPERIMENT STATION

CHAPTER III

METHODS AND RECOVERY IN THE UNITED STATES

19. Early Methods in the United States. — This chapter presents
a discussion of early methods of mining coal in the United States, in-
formation regarding the percentage of coal recovered in different dis-
tricts, and descriptions of the most advanced methods employed for
obtaining high extraction, especially those which are applicable to con-
ditions in Illinois. In collecting this material all available sources of
information have been utilized. The descriptions of methods have been
taken largely from the technical literature of coal mining, but in in-
stances in which the correctness of the description seemed in doubt, or
in which statements concerning the percentage of extraction seemed
to need verification, the subjects have been reviewed by persons famil-
iar with the local conditions.

In response to the large number of inquiries sent out, many persons
have furnished the desired information in as nearly complete form as
possible, but in many cases there has been available no authentic in-
formation on the subject of recovery. The estimates are necessarily
more or less approximate because the conditions are such that it is
practically impossible to obtain correct values, or the subject has not
been considered of sufficient importance by the operators to warrant
the expenditure of the time and money necessary for obtaining the
values. It is believed that the values for percentage of extraction
given in the following pages represent the most reliable information
obtainable on the subject, but they are not presented as being abso-
lutely correct.

At the time mining was begun here, this country was a colonial
possession of Great Britain ; the methods of mining to which immigrants
were accustomed were those of Great Britain, and the application of
these methods to mining problems in America was a matter of course.
The development of the early English methods is discussed in the
appendix. The coal miners of this country, furthermore, have been
for the most part men who received their training in the work in
England, Scotland, or Wales, or children of such men, and not until

PERCENTAGE OF EXTRACTION OP BITUMINOUS COAL 61

a comparatively recent date did these miners loss their dominance in
the American coal fields. The conditions under which coal was found
in this country were also not very different from those in Great Britain.
It was natural, therefore, that bituminous coal mining practice in this
country should correspond to that of Great Britain at the time the
industry began here.

Mining in this country was begun in the Richmond (Virginia)
basin about the middle of the eighteenth century. There seems to be
no clear record of the methods followed, but it is known that a pillar
system was employed, and that, as the coal was reached in some places
at a depth of several hundred feet, a considerable amount of the coal
was left in the ground. It is said that the pillars were to be extracted
on the retreat, but no definite record is found to indicate that this was
done.

Western Pennsylvania was the next district to take up coal mining
on an important scale. Maryland and West Virginia followed, basing
their early methods for the most part on what had been done in Penn-
sylvania.

20. Pennsylvania. — The early history of coal mining in the west-
ern Pennsylvania district is typical of that in other sections of the
country, having a similar hilly topography. When coal mining was
commenced, an abundant supply of coal was found outcropping on
the hills in the neighborhood of Pittsburgh, and these seams were
attacked by numerous small mines on the outcrop. As the workings
were extended under cover, the single entry system was followed, and
as it was impossible to obtain good ventilation with this system, the
rooms were driven to only a short distance, and the entry itself was
not long. Later the double entry method was employed, in which two
parallel entries were used, respectively, for intake and return air.
Since the distance to which rooms could be driven was limited, it was
impossible to work any large territory by this method; hence, as the
size of the mines increased, the cross entry system was introduced.
The underground developments were the same whether the coal was
reached by drifts, by slopes, or by shafts.

Among the many experiments tried in the Pittsburgh bed was that
involving the use of double rooms with double necks, or of double
rooms with single necks, but the amount of timber required for posts
made these methods too expensive and by 1906 they were in use in a

ILLINOIS ENGINEERING EXPERIMENT STATION

very few mines. The long-wall system also was tried and abandoned.*
No record has been found of the time at which the drawing of
pillars was commenced, and it is probable that this method was fol-
lowed more or less from the beginning in such mines as were system-
atically developed.

Toward the end of the last century, the double entry system had
been further developed by the turning of room or butt entries from
the cross or face entries. In some mines a few of the entries were
driven to the boundary, and then all the rooms were opened at once,
but some of the center rooms would sometimes reach their limits before

FIG. 8. OLD METHOD OF ROOM-AND-PILLAB IN PITTSBURGH, PA., DISTRICT

those whose pillars should have been drawn first. In other cases only
the inby half of the rooms on each entry was turned first, while in still
others one entry was completely exhausted before any side work was
done on its parallel entry. In most cases, a room-and-pillar method
was used with double entries, each about 9 feet wide. Main entries
were separated by a pillar 51 feet wide with cut-throughs for
ventilation. The main entries were driven on the butt of the coal, and
face entries were turned from them about 1,000 feet apart. From
these face entries, secondary butt entries or room entries were driven

*Dixon, Charlton, "A New Method of Coal Mining," Mines and Minerals, Vol. 27,
p. 32, 1006.

PERCENTAGE OF EXTRACTION OP BITUMINOUS COAL

about 400 feet apart. Eooms about 20 feet wide and 200 feet long
were turned on the face of the coal. Tne room necks were 21 feet long
and 9 feet wide. Room pillars were 15 or 20 feet wide, according to
the cover above the coal. The rooms were turned from the butt entries
as fast as these were driven, room pillars being drawn as mining pro-

FIG. 9. IMPROVED METHOD OF ROOM-AND-PILLAR IN PITTSBURGH, PA., DISTRICT

gressed.* The objectionable features of this method are : — poor ven-
tilation, dangerous gob, entries filled with fallen dirt requiring expense
for cleaning up, maximum extent of track for the minimum quantity
of coal, thus greatly increasing the cost of animal haulage, loss of
thousands of tons of coal, compulsory driving of narrow work in room
turning, and squeezes, which damage the coal and greatly increase
the hazard of mining.

The difficulty of ventilation becomes most serious when the rooms
from one entry are holed through into those approaching from a neigh-
boring entry (see Fig. 8). Often this will occur two-thirds of the dis-
tance up each of these entries; thus all the pillars below the short
circuit are deprived of proper ventilation at a point where it is con-
stantly needed. After the pillars are drawn and the roof falls, there
is no appreciable movement of air through the gob, and it often fills
with explosive gas.

*Auchmuty, H. L., in Coal and Metal Miners' Pocket Book, 9th ed., p. 295.

64 ILLINOIS ENGINEERING EXPERIMENT STATION

A method described by Dixon, in the article previously referred
to, was soon adopted with various modifications, although it is possible
that it was already in use in one or more places at that time. Accord-
ing to this method the territory was laid off into blocks (see Fig. 9)
1,570 feet long, allowing for a barrier pillar 200 feet wide along the
main entries and for another 200 feet along the next pair of face en-
tries. A pair of room entries separated by a 54-foot pillar was driven
through the center of this block, and thirty rooms were turned from
each entry. Rooms were 240 feet long, about 26 feet wide, and were
driven on 39-foot centers, thus leaving 13-foot pillars. Room turning
was begun at the inby ends of the room entries, a reversal of the com-
mon practice of the time. The drawing of pillars was commenced as
soon as the rooms were finished, and the line of break was kept at the
proper angle by carefully timing the extraction of pillars. In this
method the ventilation was considerably better than in the earlier
method ; but the air current, after passing through the district of pillar
work on one room entry, went through the advancing rooms turned
from the other. This difficulty was avoided in later methods by ex-
hausting one room entry before room work was done on the other. The
roof in the entries was easily maintained because the entries, with the
exception of those on which rooms were being worked, were in solid
coal. At the finishing of a block the minimum of track was in use for
the minimum of coal passing over it. Track was not left in place
awaiting the withdrawal of entry pillars ; therefore it was not exposed
to the corrosive action of mine water. Since the room pillars were
attacked immediately, there was little danger of deterioration of coal
or of trouble from falls. Most of the props could be recovered as they
had not been subjected to any great pressure. Under the old system
50 per cent of the wood rails in rooms were lost while awaiting the
attack on the ribs, and about 75 per cent of the posts were lost.

Referring to the conditions and the methods employed in mining,
P. W. Cunningham* said in 1910:— "The operator in the Pittsburgh
coal field, with the price of coal where it is to-day, must get the largest
percentage of lump with the least amount of fine coal, and this by
machine mining, in order that he may compete with coal operators in
other fields/' The rooms, therefore, are made as wide as possible to
obtain the greatest percentage of lump coal, and the pillars are left

* Cunningham, P. W., "The Best Methods of Removing Coal Pillars," Proc. Coal Min.
Inst. Amer., p. 275, 1910; p. 35, 1911.

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL

as narrow as possible, because the greatest percentage of crushed coal
comes from them. This fact explains why the use of narrow rooms
and wide pillars, common in the Connellsville district, does not appeal
to operators in the Pittsburgh district. It also explains the loss of
much pillar coal, because a period of dull market results in the stop-
ping of pillar work and only large coal from the rooms is marketed. A
large number of rooms, accordingly, may be driven up to their limits

FIG. 10. MODERN METHOD IN PITTSBURGH DISTRICT

without the extraction of room pillars, and the recovery of these pillars
is unprofitable after the rooms have stood for a number of years.

Fig. 10 illustrates the series of operations incident to one method
of extraction of stump and chain pillars. In this method, rooms are
turned and worked out progressively along one of a pair of room en-
tries, probably the last, the pillars being drawn back as soon as the
rooms are finished. There is thus a diagonal line of rooms advancing
and another diagonal line, practically at right angles to this, retreat-
ing. On the other room entry of the pair, the driving of rooms is
commenced at the inby end and proceeds outward. In some instances
the entry pillars have been drawn on the retreat as illustrated in Fig.
10, and in others they have been left until all the rooms and room

66 ILLINOIS ENGINEERING EXPERIMENT STATION

pillars have been finished. In the latter case it has sometimes been
possible to obtain the coal from these entry pillars, but frequently all
or part of it has been lost. The method illustrated in Fig. 10 was in
use in the Pittsburgh district proper, that is in the high coal along the
Monongahela River. Cunningham says that the extraction by this
method would average about 80 per cent. Some companies, however,
claim an extraction of 90 per cent. Some differences in percentages of
extraction may be accounted for by the different methods followed in
estimating: the whole bed from the limestone to the top of the seam
may be taken into consideration, or the thickness of the slate partings
may be subtracted.

One of the principal reasons for taking the rooms turned from one
of a pair of butt entries on the advance and those turned from the
parallel butt on the retreat was that this procedure made it possible
to have the air current always blowing from the room work to the
pillar work. This constantly moving current of air prevented gases
set free by the pillar work from being carried to men working in
advancing places. The miners in the pillar workings used locked
safety lamps, while those in the room workings used open lamps.

Until about 1910, mining machines Were used in the Pittsburgh dis-
trict only in room and entry work, while pillar coal was undercut with
picks. A method designed to permit the mining of pillars by machines
is illustrated by Fig. 11. Cunningham gave the following facts con-
cerning this method: — 24-foot rooms are turned on 39-foot centers.
After the room is worked out with a machine, a cut about 25 feet
wide is made across the end of the pillar; then another cut of the
same width is made far enough back on the pillar to leave a stump
5 to 8 feet wide, and the stump is removed by pick work after the
machine work is finished. The stumps serve to protect the machine
runners and the machine by supporting the top. It was said that at
one mine where this system was used 70 per cent of the pillar coal was
extracted with machines, and 30 per cent was pick mined. Good falls
were obtained, and no ribs were lost. The recovery of timber was not
so good as in the Connellsville region or in mines where there is no
refuse gobbed along the roadways.*

An old and common method of working is illustrated by Fig.

*For another description of the method in use about 1910 see Schellenberg, P. 0., "Sys-
tematic Exploitation in the Pittsburgh Coal Seam," Trans. Amer. Inst. Min. Engrs., Vol. 41,
p. 225, 1910.

PERCENTAGE OF EXTRACTION OP BITUMINOUS COAL

12. Track is laid in the middle of the room, and the room pillars are
made as narrow as possible after the room has advanced 100 feet, or to
the first cut-through. Commonly no attempt is made to recover the
pillar coal beyond this point, though it is often recovered nearer the

FIG. 11. PILLAR DRAWING WITH MACHINES IN PITTSBURGH, PA., DISTRICT

entries by working the pillar along the side of the fall. One of the
chief operators in the Pittsburgh district claimed a recovery of 90 per
cent of marketable coal by this method, but it seems that such a recov-
ery could be made only over an area of a few acres and that the recov-
ery over the entire area of the mine would be much lower. Schellen-
berg expressed the opinion that the recovery would not be more than
60 per cent if an area of 10 acres were considered.

ILLINOIS ENGINEERING EXPERIMENT STATION

In the discussion of Cunningham's article, G. S. Baton said that
entry pillars were not often recovered in the Pittsburgh district except
under remarkably favorable conditions. In his opinion not more than
40 per cent of the entry pillars were recovered where there was much

5 6

FIG. 12. TAPERED PILLARS

overburden. It is probable that a larger percentage than this is being
recovered now in the more carefully operated mines. Another practice
in pillar drawing which had been used in the Pittsburgh district and
in other districts is illustrated by Fig. 13. A curtain of coal is left to
keep out the gob when drawing room pillars, and the loss of coal
amounts to about as much as it does where the pillars are narrowed
and not drawn.*

It has been seen that in most of the methods employed in the Pitts-
burgh district, the pillar coal is taken out by pick work, and it has been
within only a very recent period that even the room coal has been
undercut by machines. Machine mining of pillars is cheaper than
pick work and operators have recently introduced this more advanced
method wherever it seemed possible. The immediate reason for this
action has been the increased cost of production, largely due to high
wages and expenses caused by changes in the laws affecting mining,
without a corresponding advance in selling price. Since the demand

* Cunningham, F. W., Op. Cit., p. 275, 1910.

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL 69

is still greater for the lump coal than for the smaller sizes, it has been
necessary to increase the size of the pillars to prevent the objectionable
crushing of the pillar coal. Another reason for increasing the width
of the pillars is to be found in the practical difficulty of using machines
on very narrow pillars. The thickness of room pillars varies, but the
most common distances between the centers are 33, 36, 39, and 42 feet.
With 33-foot room-centers, the room pillars are lost entirely ; with 36-
foot room-centers, about 55 per cent of the pillars are recovered ; and

FIG. 13. PILLAR DRAWING, CURTAIN OF COAL

with 39- to 42-foot centers, from 60 to 70 per cent of the pillars are
recovered.* Many miners at the present time have not the skill to do
the best pillar work, even if the cost were not too high, and for this
reason, if a higher percentage of pillar coal is to be won, cutting with
machines, which can be operated successfully only on wider pillars,
must be employed.

A method adopted for future working at the Marianna and the
Hazel mines of the Pittsburgh-Buffalo Company in Pennsylvania and

* Edwards, J. C., and Gibb, H. M., "An Ideal Method of Mining," Mines and Minerals,
Vol. 33, p. 665; and Edwards, J. C., "Machine Mining in Room Pillars," Mines and Min-
erals, Vol. 34, p. 591.

ILLINOIS ENGINEERING EXPERIMENT STATION

the Annabelle mine of the Four States Coal Company in West Virginia
is illustrated by Fig. 14.* The plan as outlined is intended for coal
under a cover of 300 to 500 feet. There are two sets of triple main

DDD
DnnDDDDDDDnDDDDDDDDDD

FIG. 14. PROPOSED PLAN FOE PITTSBURGH-BUFFALO COAL COMPANY

entries separated by an unbroken pillar 50 feet thick. The operation
really includes two distinct mines except that the coal goes over the
same tipple. The loaded and empty haulage roads on each side are
driven 10 feet wide, and the airway is driven 16 feet wide. These
widths are necessary in order to avoid the expense of a fourth 10-foot
entry.

The panel system planned is known as the "half advancing and
half retreating" system. The panels are divided into blocks 500 feet
wide by entries driven ' ' end on " in pairs, and from these butt entries

*Ibid.

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL

the rooms are turned on the face of the coal. The butt entries on the
side toward which the development of the panel is progressing, that
is on the inby side, are termed ' ' advance headings ' ' ; the exterior or
outby entries are ' ' retreat headings. ' ' A chain breast machine is used

FIG. 15. EXTRACTION OP PILLARS UNDER DRAW SLATE

TIG. 16. DETAIL OF PILLAR WORK UNDER DRAW SLATE

in rooms and entries and a short-wall machine on pillars. Both ma-
chines continue in use until the last room on the retreat entry is com-
pleted ; then the short- wall machine is left to finish the pillars, and the
breast machine is transferred to another pair of butt entries under
development. By the time room 14 is turned, room 2 has been finished,
and work can be begun on the pillar between rooms 1 and 2. Kooms
on the advance entry are 255 feet long and those on the retreat entry
246 feet long from the entry centers ; this difference in length is made,
because the chain pillar and entry stumps are brought back with the

72 ILLINOIS ENGINEERING EXPERIMENT STATION

room pillars on the retreat entries. The method has been worked out
for two general conditions ; first, where a draw slate is encounted, and
secondly, where there is no draw slate.

The method to be used where draw slate is encountered is illustrated
by Fig. 15. In this illustration room 1 is shown as finished. In rooms
2 to 9, inclusive, the pillars are being drawn. Room 10 has reached its
limit, and the cross-cut at the face is being driven through the pillar
to room 9. Rooms 11 to 18, inclusive, are being driven. Fig. 16 shows
in detail the method of recovering the pillars by the short-wall ma-
chine where draw slate is encountered. From the point A, the track
is laid in 14-foot sections, and steel ties are used; consequently, the
track is easily assembled or detached. Curved rails are used in the
same way so as to give easy access to the cross-cuts. After the cross-
cut B is finished, the curves and two 14-foot sections of the track are
detached, and an 18-foot cut is made in the pillar at C by working on
the butt of the coal and leaving a stump D, 10 by 39 feet. The draw
slate from the first cut is gobbed in the room proper. The remainder
of the draw slate from this cross-cut is gobbed in the outby part of the
cross-cut, and the track is laid in the inby part. A cut is next made
through the stump D, into the gob above, and small blocks or stumps
E and F are left on each side of the cut to be taken out with the pick.
After the block E has been removed, all the tracks in the cross-cut,
except the two curve rails, are removed ; when the block F has been re-
moved, the curve rails and the two 14-foot sections of straight track
are taken up, and the operation of driving through the pillar is re-
peated as the illustration shows. In this way the room pillar is ex-
tracted back to the point A.

The method of operation in the second case, where the draw slate
is not encountered, is the same as in the first case, except for the
manner of attacking the pillars which is illustrated in detail by Fig.
17. After the room has been completed and the cross-cut B driven,
the two curve rails and seven sections of track are detached ; thus the
track is left in position to be assembled quickly for easy access to the
cross-cut H, which is next driven. The 39- by 94-foot pillar is then
split from H to B, and a 9- by 94-foot pillar is left on each side ; then
an 18-foot cross-cut D is driven through the 9- by 94-foot pillar on the
rib nearest the gob, and a stump is left to be removed by the pick.
The other 9- by 94-foot block is removed in the same way, and the oper-
ation is continued until the whole pillar has been removed. The entry

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL

stumps and chain pillars of the butt headings are won in the same
manner as the room pillars.

Both of these methods are in use at several mines and are meeting ,
with success. In both methods 90 per cent of the coal won is cut by
machines. This percentage can be increased considerably, since it has
been demonstrated that under favorable conditions part of the pick
blocks can be recovered by the machine. One-third of the coal is mined
from the rooms and two-thirds from room pillars. When draw slate
is encountered, the 39- by 10-foot stump pillar will always afford ample

FIG. 17. DETAIL OP PILLAR WORK IN ABSENCE OF DRAW SLATE

protection to the miners; and where no draw slate is found, the two
9- by 94-foot stump pillars together with the timbering will give ade-
quate protection.

Among the plans tried in the Pittsburgh district with the object of
reducing the cost of mining by substituting more machine work for
pick work is one (Fig. 18) which promised to be successful, but failed,
because the miners demanded room-turning prices for the short
rooms.* This added cost would have defeated any other advantage of
the system. The method, however, seems to be based upon principles
which may find application under other circumstances. The method
was adopted, because a provision of the mining scale of the Pittsburgh
district prohibited the drawing of ribs by machines unless short-wall
machines were used. The plan was to continue the employment of
the breast machines already in use and thus to increase the percentage

*Affelder, W. L., "Rib Drawing by Machinery," Coal Min. Inst. Amer., p. 232, 1912;
and Personal Communication.

ILLINOIS ENGINEERING EXPERIMENT STATION

of room coal. It seemed profitable to increase the percentage of room
coal since the cost for machine-cut run-of-mine coal was 45.28 cents
per ton, including a differential of 2/3 of a cent on account of rolls,
while the price for pick mining was 64.64 cents per ton; the average
price for cutting, loading, and pick work was 51.92 cents. This average
was based on the assumption that the working was regular with rooms
25 feet wide on 40-foot centers. Machine work was done with the
common breast machines. The mining system was the ordinary method

20 40 so 80

SCALE

FIG. 18. METHOD OP REDUCING PILLAR WORK IN PITTSBURGH, PA., DISTRICT

of machine mining with 25-foot rooms on 40-foot centers with cross-
cuts three runs wide and room necks 21 feet long. Rooms were 250
feet long, but as the neck was 21 feet long, the length of the actual
room was 229 feet. All estimations of the percentage of extraction
were based on a block 229 feet long and 120 feet wide. In this old
system of mining, 65.7 per cent of the coal was produced as machine
coal and 34.3 per cent as pillar coal drawn with the pick. The mine
was operated on a run-of-mine basis. The new system was started
with 36-foot rooms on 117-foot centers ; but it was expected that if the
system should prove successful, these dimensions would be changed

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL 75

to 40-foot rooms on 120-foot centers. The illustration shows the form
and dimension of rooms. Two 25-foot rooms were driven from the cross-
cut with 10-foot pillars on each side. These pillars were somewhat
weak, but the rooms were not long, and the pillars were drawn quickly.
It was admitted that the system would reduce tonnage for a time if
the mines developed were not sufficiently advanced, but it was claimed
that when the main rooms had been driven to within 50 feet of their
intended length, the production from them would be much greater
than from the ribs of three rooms of the older system. As soon as the
pillars were drawn, the recovery of the so-called ' c rooster ' ' coal would
rapidly increase the output. In the Pittsburgh bed, the rooster coal
lies above the draw slate and a laminated coal 12 inches to 2 feet
thick. Although in most mines this coal is not taken out, in the Pan-
handle district it seems to be better fuel than the bottom coal and is
being mined in several places. The cover in the section in which this
method was employed was from 75 to 125 feet thick. The small pillars
were extracted by pick work, and the rooster coal also was obtained
at pick prices.

21. Connellsville District. — The methods of production in the
Connellsville field have become more intensive than those in the other
districts of western Pennsylvania. The excellent quality of the Con-
nellsville coke and the fact that the coal from which it is produced is
found in only a limited area have made the coal so valuable that it
has been found advisable to pay particular attention to high percent-
age of extraction. In this district, there has been, moreover, no
objection to the crushed coal from pillars as the product goes to the
coke ovens where fine coal is desirable. The same fact influenced the
relative sizes of rooms and pillars. While in the gas coal district it
was thought desirable to take as great a quantity as possible from
rooms, in the Connellsville district the practice of getting a large part
of the coal from the pillars has developed in order that the percentage
of extraction may be as high as possible. It is of interest to trace the
more recent developments in mining practice here, because the extrac-
tion in the better planned mines of this district is unusually high.

Conditions and methods in this district are discussed by F. C.
Keighley* as follows:

*Keighley, F. C., "Mining Coal with Friable Roof and Soft Floor," W. Va. Coal Min.
Inst., Dec. 10, 1914; Coal Age, Vol. 7, p. 1008.

76 ILLINOIS ENGINEERING EXPERIMENT STATION

"The coking coal known variously as the No. 8, Pittsburgh, or
Connellsville seam has in places an extremely bad roof. This difficulty
is strongly marked in the Connellsville basin, but can be found in
other troughs. . . . The thickness of the coal and its softness
might lead one to anticipate that it could be mined cheaply, but the
friable roof creates a difficulty which its other qualities cannot over-
balance. . . .

. . . "I have projected workings at depths ranging from 200
to 700 feet, using a dozen or more different schemes, and have never
found any marked difficulty in protecting the main headings and
air-courses of any mine. But I have experienced some trouble occa-
sionally in protecting the branch, or butt, headings, and I have
always had more or less trouble with the rib coal in the rooms.

"It is true that in many cases the roof will fall in headings and air-
courses in spite of all that can be done, but such falls are gradual
and are removed as part of the regular mine operations. On the
other hand, when falls occur in the rooms they often come suddenly
and cover a large area, and the break extends so far above the coal
that they often reduce and may entirely cut off the production from
a certain section of the mine, not only for a day, but perhaps for
weeks at a time.

"It is clear, then, that any improved method of mining must pro-
vide for the protection of the rooms rather than for the care of the
headings. . . .

"Panels have been projected 1,000 feet wide and 2,000 to 4,000
feet long. . . . Such a panel is subdivided into a number of
smaller panels that are themselves served by two parallel entries driven
at right angles or at some other angle to the flat or face heading
depending on the pitch of the coal. These are known as butt headings.
These sub-panels are generally 1,000 feet long and 300 to 600 feet
wide. . . *

"Various widths have been chosen for rooms with 8 to 30 feet
as limits, but the general belief is that rooms and headings should be
driven 10 feet wide in the Connellsville region. There seems to be
no opportunity to improve on this width. The best work has been
obtained with large room ribs — 50, 70 and 90 feet thick; but the
success has not been as great as might be expected, though, with room
ribs of the two larger dimensions, and with any ordinary care in
mining, a general creep or squeeze cannot occur.

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL

"This is not true when room, ribs are made of smaller dimensions,
such as 30, 40 or even 50 feet. In the initial stage of rib drawing with
such light ribs great success is secured, but when trouble occurs it
is usually in the form of a general squeeze or creep that almost
paralyzes the output. It has often seemed for a time that the small
ribs in the rooms resulted in cheaper mining; but when a squeeze
or creep took place the small rib did not permit of the driving of a
new road with safety and profit, and consequently the coal remain-
ing in the rib could not be taken out.

"With 70-, 80-, or 90-foot ribs there is always sufficient coal left
to permit driving a new road with safety through the pillar no matter

i «; • t « — £A

M-0* — -4- — /$-0*— -4v-

- /ff-0'— -t- /g-

FIG. 19. PILLAR DRAWING IN CONNELLSVILLE, PA., DISTRICT

how badly the roof may have fallen or the coal be shattered on the
edges of the pillars.

"Nearly all experienced miners concede that with narrow ribs
only 50 per cent of the coal is recovered. The best results claimed
is 65 per cent, while 90 and 95 per cent has often been recovered with
the larger-rib system. The problem is whether the heavy cost of timber
and the still greater cost of labor will counterbalance the loss of from
35 to 50 per cent of coal. I am disposed to believe that the larger
rib, making a larger yield possible, will assure a handsome margin. "

Fig. 19 illustrates a modern method of pillar drawing.* In this
method a cut is made across the pillar, and an 8-foot stump is left;
then this stump is taken in a retreating direction in from two to
four sections, according to the width of the pillar. In the example
given the rooms are 12 feet wide and are on 84-foot centers. After

* Cunningham, F. WM "The Best Method of Removing Coal Pillars," Coal Min. Inst.
Amer., p. 275, 1910; p. 35, 1911.

78 ILLINOIS ENGINEERING EXPERIMENT STATION

the removal of the coal in each section, the props are drawn and
the roof is allowed to fall, the break being controlled by a row
of props across the end of the cut. After the last section of the
stump has been taken out, the last of the track drawn, and the
roof dropped across the room on the line of the end of the
remaining pillar, another cut is made across the pillar and the
process continues. While the falls represented in the sketches appear
to be large, a better break is obtained with these than with short
falls. This method has proved to be safer for the miners and to give
a greater recovery of posts and coal than the methods which pre-
ceded it.

A highly developed and systematized room-and-pillar method is
the so-called concentration method used in some of the mines of
the H. C. Frick Coke Company,* and developed largely by Patrick
Mullen, one of the company's inspectors. This method was designed
to satisfy certain requirements, among which were safety of operation,
completeness of extraction, reduction of cost through the greater use
of machines, and an increase of daily output per man. A patent cov-
ering this method has been applied for.

It is well understood that liability to accidents is decreased by
close supervision. Under the older system in the Connellsville region,
it was possible for the face boss to visit each working place only
once in two or three days. In order to increase the amount of super-
vision without increasing the number of officials, the plan of getting
the working faces closer together was tried ; this plan, however, neces-
sitated a decrease in the number of working places and in the number
of workmen, and it was realized that only by increasing the production
of each miner could the output of the mine be kept up.

The only possible way of increasing the output per man was by
replacing pick work with machine work. This substitution was made
in room work; but it was found that, on account of narrow headings
and narrow rooms with large room centers, machines in the narrow
work alone would not accomplish the desired results, since the bulk
of the coal comes from the pillars. The problem of the use of ma-
chines for pillar extraction, which was an entirely new one in the Con-
nellsville district, has been worked out very successfully (see Fig. 20).

* Mullen, Patrick, "New Mining Methods as Practiced by the H. O. Frick Coke Com-
pany," Proc. Bngrs. Soc. W. Pa., Vol. 32, p. 714, 1916; Coal Age, Vol. 10, p. 700, 1916;
Howarth, W. H., "Mining by Concentration Method," Coal Min. Inst. Amer., Dec. 22, 1916;
Coal Age, Vol. 9, p. 125, 1916.

PERCENTAGE OP EXTRACTION OF BITUMINOUS COAL

The mine is blocked by driving at A double butt entries, 10 feet wide
on 50-foot centers and 1,200 feet long, across the panel with break-
throughs every 100 feet; the pairs of butt entries being driven 350
feet apart, the panel is divided into blocks about 350 by 1,200 feet.
These blocks are then subdivided into blocks about 90 by 100 feet,
by 12-foot face rooms at B 350 feet long on 112-foot centers, driven

FIG. 20. CONCENTRATION METHOD IN CONNELLSVILLE, PA., DISTRICT

at right angles to the butt entries and connected by 10-foot break-
throughs on 100-foot centers. A pillar of this size is considered ample
to support any thickness of cover under any conditions of floor or
cover to be found in the Connellsville region. In this manner a
whole panel can be prepared for the intensive part of the work in
which butt rooms are driven from the face rooms 10 feet wide on
25-foot centers.

As the main face room advances, the necks of the butt rooms to
be driven are excavated to a depth of three machine cuts. After
a main face room has been advanced 50 feet, there are available

80 ILLINOIS ENGINEERING EXPERIMENT STATION

for the machine to cut two places which allow a production of forty
tons ; and when the room has advanced to a point where the first cross-
cut is turned off, there are three places to cut in each main face room
yielding sixty tons. This main room may continue to the end of
the section or to the end of the coal field, butts or producing entries
being turned off at projected distances. It is necessary that the oper-
ation be carefully planned and that the proper order of the work
be closely adhered to. Pig. 21 shows the general schedule of oper-
ations with the position of the line of roof fracture at different dates.
It is claimed that the general plan can be easily modified to suit all
conditions such as depth of cover, presence or absence of draw slate,
and nature of coal, bottom, and roof.

The projection takes three forms known as (a) maximum, (b)
medium, and (c) minimum, according to the rate at which coal is
produced (see Fig. 22.) The maximum plan is applicable where
the thickness of cover does not exceed 125 feet, where the coal is
hard, and where the general physical conditions of roof and bottom
are good. The medium plan is applicable where the cover does not
exceed 250 feet with the same physical conditions of the coal, bottom,
and roof as for the maximum plan. The minimum plan may be
applied to coal underlying any thickness of cover ; the coal may be hard
or soft, and the physical conditions of roof and bottom may be
good or bad, provided, of course, that mining machines in any form
can be used.

With the minimum plan, the butt rooms are driven in succession
so that each room is 50 feet beyond the one succeeding. Two butt
rooms advancing furnish 40 tons and one butt rib retreating furnishes
40 tons, or a total of 80 tons on the retreat ; the main face room ad-
vancing yields 60 tons, or a total of 140 tons from one main face
room. These quantities apply, of course, to coal of the thickness of
that mined in the Connellsville basin — about 7 feet.

The medium plan will yield the same tonnage from the advancing
main rooms, but the retreating work is so arranged that the face
of each butt room is 30 feet behind that of the preceding room.
This arrangement allows three butt rooms to be advanced at a time
with a production of 60 tons, while two butt ribs are being extracted
with a production of 80 tons ; thus 140 tons are taken from the butt
rooms and ribs and 60 tons from the advancing main rooms, a total of
200 tons for each main room.

PERCENTAGE OP EXTRACTION OP BITUMINOUS COAL

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ILLINOIS ENGINEERING EXPERIMENT STATION

In the maximum plan the working of the butt rooms is so timed
that the face of one room is 15 feet behind the face of the pre-
ceding one; four butt rooms are advanced and four butt ribs are

(A)

FIG. 22. CONCENTRATION METHOD — MAXIMUM, MEDIUM, AND MINIMUM PLANS

simultaneously withdrawn. The four advancing butt rooms will pro-
duce 80 tons and the four retreating butt ribs will produce 160 tons.
With the 60 tons produced from the advanced main" room, there is
thus produced 300 tons for each main room.

The work is thoroughly systematized and proceeds with great regu-
larity. After the miner has cleaned up his place and the day's run

PERCENTAGE OP EXTRACTION OP BITUMINOUS COAL 83

is completed, the machine crew enters and cuts the place to a depth of
approximately 7 feet. Following the machine crew, the timber
men reset any posts which the machine men have removed, post up
any cross bars which have been notched in the coal over the machine
cut, and put the place in good condition according to a prescribed
system of timbering. The timber men are followed by the driller
who bores the holes with an electrically driven drill. The driller is
followed by the shot firer who charges and tamps the hole, and after
an examination of the conditions, fires the charge. After the coal has
been shot down, empty cars are placed by the gathering locomotives
so that when the loader arrives at his working place in the morning
he finds it in safe condition, the coal ready to load, and the empties
in place. Miners loading under these conditions regularly obtain
18 to 20 tons per shift. The average of the loaders for short-wall
mining machines in all mines of the company for the month of
August, 1916, was approximately nineteen tons per shift. At mines
where there is a full equipment of mining machines, the machine
coal runs from 80 to 90 per cent of the total output. The recovery
under the concentration system is from 90 to 92 per cent, while under
the ordinary methods it is 80 to 85 per cent.* In the values given,
the top or bottom coal left in place is not considered. The aver-
age thickness of top coal left is about 6 inches and the values for ex-
traction, based on the entire thickness of the seam would be some-
what lower than the values given. Coal is left for two reasons. In
the entries, from 6 to 8 inches of top coal is left as a protection. In
the room work, such top or bottom coal is left in place as is neces-
sary to keep the sulphur content of the coke made from the coal down
to the required amount. It is found that the highest sulphur content
of the bed occurs at the top or at the bottom and, by frequent analyses,
it is determined how much of this top and bottom coal may be left.

22. Central Pennsylvania. — A method known locally as the "Big
Pillar System" has been developed to meet conditions incident to the
soft bottom in the Lower Kittanning, "B," or Miller, bed in the south-
ern and eastern parts of Cambria County, and in the adjoining terri-
tory, f

The physical conditions for which this system was developed
include a hard roof, very difficult to break, and a soft fire clay bot-

*Dawson, T. W., Personal Communication.

tSUliman, W. A., "Big Pillar System of Mining," Proc. Co»l Min. Inst. Amer., p. 76,

ILLINOIS ENGINEERING EXPERIMENT STATION

torn. A sand rock from 10 to 40 feet thick occurs above the coal;
but between this sand rock and the coal there is usually from 1 to
6 feet of slate or sandy shale, which is more or less affected by the
air and which breaks away from the sand rock, especially in the road-
ways. The falling of this top tends to relieve the pressure, but not
enough to prevent squeezing. The worst squeezes are encountered
where the sandstone is only 10 feet thick.

LtmuuittS!

FIG. 23. "Bio PILLAR" METHOD USED IN CAMBRIA COUNTY, PA.

Under these conditions, the ordinary system of turning rooms with
40-, 50-, or 60-foot centers does not work satisfactorily. When the room
pillars are drawn back to the stump, under the ordinary system the
pressure is so great that a stump, even 30 or 40 feet square,
*will not protect the entry. Instead of breaks occurring in the roof
along the line of the stumps the bottom breaks and heaves, and
squeezes occur. Since the coal is soft and has a columnar fracture,
the stump is badly crushed, and no amount of timbering is sufficient
to prevent the closing of the entry. Thousands of feet of entry and
much coal have been lost as the result of squeezes in a bed of this
kind. The bed is only about 3^ feet thick so that it is necessary to
take up the bottom, and the provision of space for storing bottom is
one of the considerations involved in planning this system. The
average dip is about eight per cent.

In the "Big Pillar" method (Fig. 23), haulage entries are driven
on the strike and rooms are turned up the pitch. Entries are 10
or 12 feet wide. Rooms are turned on 100-foot centers from the
entries, and, at a distance of from 100 to 125 feet from the entry,
rooms called "crooked" rooms are turned at right angles, that is,

PERCENTAGE OF EXTRACTION OF BIT0MINOXJS COAL 85

parallel with the entry. There is thus left along the side of the
entry a series of blocks 75 by 75 feet or 75. by 100 feet, according to
the length of the rooms driven from the entry. As soon as a crooked
room has intersected the straight room toward which it is being
driven, an intermediate room is turned up the pitch from the crooked
room; thus the rooms above the crooked rooms have 50-foot centers.
The straight rooms are driven to such distances that the roof will
break at the edge of the big pillar or by settling will relieve the
strain. Sometimes they are only 250 feet long, and sometimes, under
heavy cover, as much as 400 feet.

When the straight rooms are started, they are widened on the
outby side so that the cross, or crooked, room can be turned off the
straight rib, a matter of importance because of the necessity of storing
bottom which is taken up in the roadway. Beyond the crooked rooms,
the straight rooms are widened on the inby side; thus the men who
drive a room are able to start the drawing of the pillar as soon as the
room is finished. The room pillars are drawn back to the crooked
rooms, and the irregular little blocks caused by the necks of these
rooms are removed as completely as possible. The big block is then
left standing to serve as a barrier to protect the entry, and if the
space mined out is sufficiently broad, the roof will usually break.
Even if the roof does not break, the strain seems to be relieved before
reaching the entry. The upper edge of the big pillar may be badly
crushed, and the roadway of the room may be heaved almost down
to the entry, but the entry itself will be practically unaffected.

When the entry is finished and the stumps are being drawn, the
system presents a special advantage in that a better output can be
obtained than with the smaller stumps. Where stumps are small, the
output is limited to the work of two gangs, but with the big pillars
eight or ten places may be worked at all times on the retreat. The
big pillars are split by a room driven up from the entry at the same
time that a skip is taken along the rib of the old room. These two
working places are cut through to the old falls about the same time,
and the intervening portions of the pillars are brought back. This
method leads to large recovery of coal, although there are no state-
ments available concerning the exact percentage. There is some loss
in the extraction of the pillars, and the coal at the edge of the big
pillars is badly crushed. The method is not used in other beds in
the same district, because the conditions are better.

86 ILLINOIS ENGINEERING EXPERIMENT STATION

In the Somerset County district, there has been developed a panel
system which permits a high degree of concentration of work and a
large percentage of extraction. The coal is low, and the miner is
obliged to push his cars to the face of the room and to drop them down
to the entry. The seam often dips from two to five per cent, and butt
entries are driven off the main haulage slope on a grade of one per cent
in favor of the load. From these, entries are driven to the rise at
convenient distances, from which rooms are turned on the strike of
the bed. Not only does the method result in a high percentage of
extraction and facilitate the handling of the cars by hand in the
rooms, but it also concentrates the work of mining. Two men work-
ing together will produce from ten to twelve tons of pick-mined coal
per day, but when the men work singly it has been found that a good
miner can load from seven to eight tons per day.* Under this system,
the total extraction is reported to be about 93 per cent. About
50 per cent of the coal comes from rooms and entries, and the
remainder from pillars. t This method is similar to that illustrated
in Fig. 32, page 102, which shows a plan of operation of the Carbon
Coal Company in West Virginia.

Because of the recognized objections to the room-and-pillar system,
much attention has been given to the possibility of employing the
long-wall system in the Pittsburgh bed and in other beds of western
Pennsylvania. So far as can be learned, there is only one mine at
which a long-wall system is being used in these districts, although
there is an approach to it in some so-called " panel long-wall" or
"block long- wall" methods. In these methods, dependence, however,
is not placed on the weight to break down the coal; in fact, weight
at the face is prevented so far as possible by causing the roof to break
near the face.

It is worth while to review some of the experiments in the intro-
duction of long-wall methods, because it is only by these methods
that complete extraction is attained, although there is a close approach
to it in the best applications of some forms of pillar working.

One of the attempts} was started about 1899 in the Lower Kittan-
ning, " B," or Miller, bed where the coal was from 3 feet, 6 inches

*l£ajer, John, "Mining by Concentration Methods," Coal Age, Vol. 9, p. 345, 1916.

fCoxe, Edward H., Personal Communication.

$ Claghorn, Clarence R., "A Modified Long-wall System," Mines and Minerals, Vol. 22,

& 16; Thomas, J. I., "Mechanical Conveyors as Applied to Long-wall Mining," Proc. Coal
n. Inst. Amer., p. 55, 1907; Delano, Warren, Personal Communication.

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL

to 3 feet, 10 inches in thickness, and- had an average dip of eight
per cent. The roof was of blue slate and the floor of hard fire clay.
Most of the coal lay under a fairly level surface about 174 feet thick,
near the top of which was a moderately hard sandstone. The plan
adopted involved blocking out the mine with entries and taking out
the coal in each entry on the retreat. The faces were 250 to 300 feet

FIG. 24. BLOCK LONG-WALL WITH FACE CONVEYORS

long. One machine-cut produced from 125 to 150 tons of coal. Break-
rows were made of stout, round, hardwood posts, 6 to 8 inches in diam-
eter. These were capped with a 2-inch lid of soft wood set on a little
slack to facilitate drawing. It was found that the track along the
face took up too much space, and a conveyor, which was put in made it
possible to set the props closer to the face. At first there were two
faces, one slightly in advance of the other, each served by a conveyor
which delivered coal to cars let down the block entry. Later, as
shown by Fig. 24, a conveyor, by which the coal was lowered to the
cars on the level, was installed in the block. Because of the unfavor-
able trade conditions in 1907, operations could not be carried on

88 ILLINOIS ENGINEERING EXPERIMENT STATION

with the regularity essential to the success of the system as then used.
The attempt, accordingly, was temporarily abandoned, but a revival
of the plan is being seriously considered.

Another attempt at long-wall mining was made with very similar
mechanical arrangements in the Cement seam near Johnstown. In
this instance two faces were cut, but a shortage of power compelled
the abandonment of the experiment before the second face had been
completed. Until that time the mining had been economical and the
recovery was almost perfect.*

At present the Maryland Coal Company of Pennsylvania is using
eight long- wall conveyors at St. Michael. The coal is about forty-two
inches thick. No description of the operation is available, but it is
evidently considered successful, as the number of conveyors is being
increased. Two other companies in Pennsylvania and one in Mary-
land have recently decided to employ the same method.!

23. Summary of Facts Relating to the Percentage of Recovery
in Pennsylvania. — The recovery in the Pittsburgh bed, not including
the coke district, is estimated to be about 80 per cent. This esti-
mate is made on the following basis : The actual tonnage mined is com-
pared with the computed tonnage of the district worked out; every-
thing between the fire clay and the drawslate is included, and no deduc-
tion is made for impurities in the bed or for the average thickness
of four inches left on the bottom. This computation is obtained from
one of the largest operating companies of the district and is based
upon actual measurements. It is the opinion of this company, assum-
ing that this method of calculation is used, that 85 per cent is
probably the best possible recovery in this district. Some other
companies claim an extraction of 90 to 95 per cent, but this is cal-
culated after deducting the coal left in the bottom, the bearing-in
bands, and any other impurities in the bed which are taken out and
not weighed. Such high recoveries, of course, imply careful planning
for the extraction of pillars and for the execution of this work with-
out delay. $

Another company the workings of which lie along the Monongahela
River south of Pittsburgh, estimates the recovery as 86.7 to 90.6
per cent.

* Moore, M. G., Personal Communication.

t Link-Belt Company, Personal Communication.

t Sckluederberg, G. W., Personal Communication.

PERCENTAGE OP EXTRACTION OF BITUMINOUS COAL 89

In the Connellsville district the best practice gives from 80 to 85
per cent with the methods ordinarily used there. With the new
1 1 concentration ' ' method of the H. C. Frick Coke Company a recovery
of from 90 to 92 per cent is obtained.*

In the Johnstown district it seems impossible to obtain estimates
of the percentage of extraction, because all the seams in that district
vary in thickness within short distances, and are somewhat cut up
by rolls. In some seams, for example, the Miller seam in the vicinity
of South Fork, the recovery is almost perfect. The conditions are
favorable, the roof being well adapted to extraction of pillar stumps in
retreating, t

One of the companies operating in Jefferson County claims an
extraction of 90 per cent. The operations are in the Lower Free-
port bed, and conditions are somewhat peculiar because of bad roof,
lack of uniformity of the seam, and faults. Each district requires indi-
vidual development before an estimate can be made of the proportion
of faults to the whole area, and it is impossible to make an accurate
estimate of recovery until a district has been completely worked out.
The value given represents the proportion of coal extracted from
the area mined in which coal existed, and does not apply to the area
of faults, t

One operator in Clearfield County estimates an extraction of 95
per cent, based upon the amount of coal mined up to December,

One of the companies operating in Somerset County estimates
that, where mines are operated in an area of less than 300 acres
and under a cover not exceeding 200 feet, the recovery should be, and
in a number of instances is, in excess of 90 per cent. In the case of
a property of 1,000 or more acres, where the coal extends underneath
a hill giving cover of 300 to 700 feet, the recovery is from 85 to 90
per cent. Low coal, faults, and adverse grades still further reduce
this percentage. §

The attainment of the higher percentages in Pennsylvania has been
reached only within very recent years, and is not yet by any means
universal. There are still in operation a large number of old mines,

* Dawson, T. W., Personal Communication.

t Moore, H. G., Personal Communication.

$ Van Horn, H. M., Personal Communication.

fl Personal Communication.

§ Delaney, E. A., Personal Communication.

90 ILLINOIS ENGINEERING EXPERIMENT STATION

mostly small, in which high percentages of extraction are not obtained.
The more recent operations are planned for, and give, probably as
high a yield- of coal as can be expected from the area worked.

24. Maryland. — In the Georges Creek region of Maryland, the
Big-vein coal has been mined for about one hundred years, and the
methods used there furnish an illustration of progress in coal mining
engineering which is especially interesting in view of the increasing
attention given to the percentage of recovery.

In a paper on maximum recovery of coal,* H. V. Hesse discussed
the wasteful early methods of mining in the Georges Creek region and
suggested economic methods, as follows :

"A region of uniform and unusually severe conditions in the bituminous fields
has been selected to illustrate the results obtained over a long period. The
Georges Creek region of Maryland, with remarkable deposit of semi-bituminous
1 Big-vein1 coal, has operated in this seam and shipped to the market for nigh
unto a hundred years. . . . More than one miner still lives who 'dug
coal' before the war with the South, and ... he tells of the detail method
of extracting the coal, on account of which thousands of tons lie buried to-day,
much beyond recovery. .

"The 'Big-vein* seam occupies the geologic horizon of the Pittsburgh bed,
but differs considerably in structure and quality from the coal of Pittsburgh,
Connellsville, and Fairmont. . . . The top coal averaging 2 feet thick is left
up for a roof. Where this comes down the strata immediately above promptly fol-
lows. Very little of this top coal is therefore recovered. Both roof and breast of
the seam contain slips known among the miners as 'horsebacks,' which frequently
fall out without any warning. The coal is soft and the 'butts' and 'faces'
entirely absent.

"The methods of extraction in vogue at different periods in the history of
this field have established the fact that it is impossible to maintain wide work-
ing places for any length of time. Headings are driven 8 feet wide and
rooms from 12 to 15 feet. In the earlier days there was practically no definite
system of extraction, headings and rooms being driven at random and no pillars
recovered. Fig. 25 shows such a method in use about 1850. This is reproduced
from an actual survey made under the most trying circumstances. ... It
is estimated that fully 55 per cent of the original coal, not counting the top
coal, remains and it is expected to recover at least one-half of this, or 27 per
cent of the original, by careful operation and the use of about double the amount
of timber necessary under a good system of mining. The maximum cover over

* Hesse, H. V., "Maximum Recovery of Coal," Proc. W. Va. Coal Min. Inst., p. 75,
1908; and Mines and Minerals, Vol. 29, p. 373.

92 ILLINOIS ENGINEERING EXPERIMENT STATION

this district is 300 feet and the few comparatively large pillars, which were
inadvertently left standing at irregular intervals, saved the balance from being
crushed. In other sections of the same mine where a similar method was fol-
lowed, but these large pillars not left in, the workings are entirely closed and
the remaining pillars, containing over 50 per cent of the original coal, probably
lost forever. Fortunately mining operations during this period were not con-
ducted on a large scale and, consequently, the territory thus affected is limited
to a very small portion of the company's holdings.

Fig. 26 "illustrates two methods followed during the years between 1870
and 1880. These workings are inaccessible to surveys at the present time owing
to the creeps and squeezes induced by the irregular method of robbing the
small pillars. ... In the first method . . . the rooms were 14 feet
wide and pillars 26 feet. These pillars were found to be totally inadequate and
extracting them impossible. Cross-cutting the pillars at frequent intervals was
then attempted . after completion of the rooms, but this was generally accom-
panied by creeps closing a whole district at a time. The maximum height of
the superincumbent strata in this territory is 200 feet.

' ' The second method shown on Fig. 26 was adopted later. ... By
this method headings were driven from the main entry on the rise of the seam
at intervals of 1,000 feet to the level above, and two pairs of cross-headings
turned to the right. The rooms were driven from these cross-headings at 50-foot
intervals and 14 feet wide, leaving a pillar of 36 feet. The length of the rooms
varied from 300 feet to 550 feet. These pillars were also of insufficient size,
robbing was conducted spasmodically and although more coal was recovered than
in the adjoining districts a great deal was lost. In addition to the small pillars,
the method of robbing them was calculated to promote squeezes. It appears
to have been the method to hold the strata with props until sufficient coal had
been removed to enable the weight to break the props. As a general rule, how-
ever, before this was attained the weight had induced a creep which is well known
to have no limits within a territory of small pillars.

Fig. 27 "represents a method in use in 1890. . . . Rooms were turned
as shown from all headings on 100-foot centers and pillars split by half rooms.
The length of rooms varied from 300 feet to 600 feet and they were 14 feet
wide, leaving pillars 42% feet wide. These pillars were not strong enough to
support the overlying strata of 500 feet and the usual creep resulted when
pillar drawing commenced. .

Fig. 28 "shows a method adopted in 1900. The maximum dip is 15 per
cent and the greatest thickness of superincumbent strata 425 feet. The slope,
together with parallel air-course and inanway, are sunk on the heaviest dip of the
coal and double entries turned off to right and left at intervals of 1,000 feet
on grades of 1*4 per cent to 2*4 per cent in favor of the loads. From these
haulways, crossjieadings are deflected at intervals of 240 feet at an angle of
about 25 degrees and driven on a grade of 4 per cent to 7 per cent. Booms
varying in length from 100 to 800 feet are turned on the rise of the coal from

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL 97

these cross-headings. The rooms are driven 15 feet wide on 65-foot centers,
leaving pillars 50 feet wide. Twenty-five rooms are driven in each of these
diagonal panels. Unusually large protecting pillars are left along the main
haulage roads. This system has been found to be especially adapted to rapid
gathering of cars thus ensuring a large tonnage. It has been found, however,
that a very large recovery from the pillars is impossible, owing to the many
sharp angles; which, in a thick seam of soft coal, are always difficult and ofttimes
impossible to extract. This sharp-angle method was even resorted to formerly
in cross-cutting the pillars preparatory to drawing them, but this has been changed
to a rectangular method, thereby increasing the actual percentage of pillar coal
recovered from 80 per cent to 83 per cent. The distance of rooms apart has also
been increased in the last few years to 100-foot centers giving pillars 85 feet
thick. It is expected that the extraction of these will show a further increase
in the percentage of yield from pillars. The present yield from headings, rooms,
and pillars under this system is about 90 per cent, considering the recovery from
headings and rooms as 100 per cent.

Fig. 29 "illustrates a method instituted in the latter part of 1904. The
main haulway is an extension of the slope from the opposite side of the basin.
Double entries are turned off from this entry, on 1%-per cent grade, 400 feet
apart, from which rooms are driven directly on the rise of the coal. Booms are
from 13 feet to 15 feet wide and . . . they are driven at 100-foot intervals,
leaving a pillar 85 feet wide. The length of a panel is about 2,500 feet, con-
taining 22 rooms. There are five such panels in this district and when completed
it is proposed to draw the pillars in a retreating fashion with the line of pillar
work on an angle of 45 degrees across the whole district. A similar method in
another district ... is yielding 88% per cent from the pillars with a
total recovery of 94 per cent from headings, rooms, and pillars . . . the
greatest height of the overlying strata is 250 feet."

George S. Brackett states* that in 1898 he made some careful
estimates of the percentage of recovery over a period of a year in the
Georges Creek region of Maryland. The data for the computations
were obtained from two mines which were worked under the follow-
ing general conditions:

The thickness of coal was 7 feet, 3 inches; the inclination
was 5 to 18 degrees; the system of mining was the room-and-
pillar retreating method. All the entries were driven to the
boundary before any rooms were opened, and a good line was
maintained on the drawing of pillars. No. 1 mine had mod-
erate grades, and a better roof than No. 2. No. 2 had grades

* Personal Communication.
4

98 ILLINOIS ENGINEERING EXPERIMENT STATION

as steep as 18 per cent, and the roof was decidedly heavy on

pillar workings.

The following results were obtained:

Per Cent of Pillars Ob-
Total Per Cent tained, Including
of Extraction Chain and Barrier

No. 1 Mine 97.6 97.0

No. 2 Mine 82.1 71.3

The average total recovery of the two mines was nearly 90
per cent.

25. West Virginia. — The modern methods used in the large
mines of West Virginia are among the most advanced found in this
country. In many parts of the state, coal mining is carried on by
large corporations which are financially able to conduct operations
with a view to ultimate economy. In most cases this ability has re-
sulted in the development of methods of operation which lead to very
high percentages of extraction.

In the Fairmont district in the northern part of the state, the
more recently opened mines are planned for large production and a
high percentage of extraction. According to the West Virginia
Geological Survey, the Pittsburgh bed, which is the one mined in this
district, contains more than 7 feet of clean coal* and the average
total thickness of the bed is about 8 feet. The newer mines are
projected on the panel system; the last rooms on each room entry
•are turned first, and the pillars are drawn immediately, a line of
break being maintained at an angle of about 45 degrees with
the entries. A plan of operation used in this district is illustrated by
Fig. 30. The method of attacking pillars is shown in Fig. 31. One
of the principal operators in the Fairmont district estimates the re-
covery, where mines are laid out systematically on the panel system,
to be from 85 to 90 per cent of the entire seam.f

A company operating to the south of Fairmont estimates that
85 per cent is a good recovery. In the workings of this company, the
rooms represent 27 per cent of the total area ; the pillars down to the
heading stump, 39 per cent ; and the chain and barrier pillars, 34 per
cent. The recovery in these three classes of working would be re-
spectively, 100, 90, and 70 per cent. This would give a total yield

* W. Va. Geol. Sur., Vol. II., p. 180, 1903.
fSmyth, J. G., Personal Communication.

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL

of 86 per cent. This company has no very accurate figures on re-
covery.*

In the mines in the Freeport coal bed in the Piedmont, or Elk
Garden, district, there is ordinarily a good shale roof, although there

No, S Butt Heading

UBIK UU U LJ LJ LJ LJ LJ L/l

iiflaflflflaoafluJjL

Rooms 20ftm'de and 60ft. C.foC
Headings 10 ft wide and 25ft C.toC.

Distance between Butt Headings 30$ rt> 350ft . _
Distance between Face Headings 1500 to 1600 ft.

No. I Butt Heading}}

t, .. ,. .. i, ,. f. »^ *. »* n '* n f^JjL-j

Main NoQth Airways-

FIG. 30. PLAN OF WORKING — FAIRMO NT, WEST VIRGINIA, DISTRICT

are places in which the shale is replaced by sandstone. In the mines
in the Kittanning bed there are from 3 to 14 feet of shale
above the coal, and above this are 40 feet of sandstone, although
there are places where the sandstone forms the roof for short dis-

^Brackett, George S., Personal Communication.

100

ILLINOIS ENGINEERING EXPERIMENT STATION

tances. The percentage of extraction in this region is about 90 per
cent; in most of the new mines, however, an extraction of 97 or

*End of barrier, or line of next
heading before coal was

*X * . . /-WJQ * J **.t

extracted

FIG. 31. PILLAR DRAWING IN FAIRMONT, WEST VIRGINIA, DISTRICT

98 per cent is being reached. This rate of recovery is higher than
it formerly was, because changes have been made in the order of
driving rooms and drawing pillars. The earlier custom was to
drive long entries, from which rooms were turned on the advance.
The room pillars could not be drawn until the entry was finished
because of the danger of squeezes, and as this process sometimes occu-
pied four or five years, falls occurred which made it impossible to
recover a high percentage of the pillars. Under the present system,
room entries are driven long enough for 20 rooms, and the inside
room is turned first. Work on room pillars is commenced as soon
as rooms 19 and 20 are finished, and room and entry pillars are
taken out rapidly. Nearly all the pillar work is done with picks,
and there is little machine work carried on in the district. The pil-
lars are attacked by cross-cuts, and a stump about four feet wide

PERCENTAGE OF EXTRACTION OF' BlTUTtfiNOtJS 'COAE ' '101

is left next to the end. This stump is removed as soon as the cut
through the pillar is finished.*

In the Central West Virginia district the operations are in the
Lower Kittanning bed which averages 6^ feet in thickness. t The
conditions are almost ideal for a high rate of recovery. The bottom
consists of hard shale. The immediate roof is of bone coal 3 to 10
inches thick, above which are shales of varying hardness, 10 feet to
15 feet thick. Above this layer occurs sandstone of an average thick-
ness of 10 feet, and above this, shale and overlying earth. Nowhere
is the overburden greater than 90 feet in thickness. The extremely
favorable nature of the roof is shown by the fact that a complete
break is easily obtained with as few as 3 or 4 rooms. In more recent
workings 20-foot rooms are turned on 50-foot centers. The rooms
are driven 300 feet long, and a 50-foot pillar is left between the
heads of the rooms and the adjoining air-course. This pillar is never
pierced except in case of extreme necessity. The 30-foot room pillars
are taken out by driving cross-cuts through them every 30 feet re-
treating. The entry pillars are taken out with the room pillars.
If the entry stumps and the barrier pillars at the ends of the rooms
are considered, it is estimated that 75 per cent of the coal obtained
is taken out as pillar coal and 25 per cent as room coal. The cost of
room and of pillar coal is about the same. Bischoff estimated that
the recovery is at least 90 per cent, and possibly 95 per cent, although
no accurate records have been kept. In view of the unusually favor-
able conditions, it seems probable that this estimate is correct as there
is no apparent reason for loss, except that represented by the small
amount of coal which the loaders fail to shovel up. This statement,
of course, refers to only the area of actual mining operations.

The Pittsburgh bed is being worked also in Braxton and Gilmer
Counties about 75 miles south of the workings just mentioned.
While the same method of working is followed, the physical condi-
tions are different, and the extraction is not more than 75 per cent.
The coal is 6 to 8 feet thick. The bottom is of fire clay 8 to 15 feet
thick, and the immediate roof is of fire clay 2 to 6 feet thick. Above
this occurs a sand rock thicker than that found in the neighborhood
of Elkins, with a heavier overburden. In this southern district the

* Personal Communication.

t Bischoff, J. W., Personal Communication.

•::,?*• t,-:t^

? ^.- „ "-0 I ?* *,,*

% •»«?,•* ^•"» B»c<»««» -» > -% *^^
^\ 1» • * 5 V » * " * * o l> » \ *

102 ' iLUNOife' ENGINEERING EXPERIMENT STATION

coast of pillar coal is about three cents greater per ton that the cost
of room coal.*

The Kanawha region is unlike the fields farther south in that

WSSA T777A T/ffi
VSSSA T7777\ Tffift

Y////\ I///A Vffl/A
Y////\ T//S/1 itf/A

FIG. 32. WIDE BARRIER PILLARS AND BOOM STUMPS, KANAWHA DISTRICT,

WEST VIRGINIA

there is a larger number of operating companies with a correspond-
ing lesser concentration of ownership. Because of the number of in-
dividual operations it is impossible to give any general or standard
method, but the room-and-pillar method is universally used. At
least one operator is leaving a large barrier pillar, Fig. 32, and a
large room stump for entry protection. The first break-through is
driven about 80 feet from the entry, and break-throughs are kept

Bischoff, J. W., Personal Communication.

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL

103

perfectly lined up. Kooms are driven in order, and room pillars are
drawn back to the first break-through as soon as the adjoining rooms are
completed. The recovery under this method is said to be about 90 per
cent and where the roof is extremely good as much as 95 to 97 per cent.*
In a paper on the removal of coal from the No. 2 Gas Seam in the
Kanawha district, J. J. Marshall reported a very high percentage of
recovery and gave the following facts concerning the seam:f The
coal bed is made up of two benches separated by a solid parting
the thickness of which varies from 10 inches to 40 feet. It has been
found that it is not economical to remove this slate when its thick-
ness is more than 24 inches. The aggregate thickness of the two
benches averages about 9 feet, the upper bench ranging from 4
feet, 6 inches to 5 feet, 6 inches of clean coal and the lower bench
from 3 feet, 6 inches to 4 feet of clean coal. Where it is impossible
to mine both benches together, only the upper bench has been taken.
The thickness of cover varies from a few feet to 100 feet. After
the ordinary method of driving rooms and of drawing pillars on the
advance, the mine described has been developed until it is now in
position for the butt entries to be worked on the retreating system.
On June 30, 1911, the percentage of recovery was said to be as shown
by Table 6, nearly all the coal being mined by pick work :

TABLE 6
PERCENTAGE OF EXTRACTION IN KANAWHA DISTRICT

Total Acres

Percentage of Recovery

High Coal, Both Benches

84 61

91 8

Upper Coal, Upper Bench Only

67.87

98.7

152.48

94.9

Computations of areas are made from the mine map, and the
method of computation does not insure the accuracy of the percent-
ages given. It seems that the values are too high. If there is a loss
of 4 feet or more in thickness across the working face, it is recorded,
but if the loss is less than this, it is too small to show on the map
which is drawn to the scale of 100 feet to the inch, and the recovery

* Cabell, C. A., Personal Communication.

t Marshall, J. J., " The Removal of Coal from the No. 2 Gas Seam in the Kanawha
District," Proc. W. Va. Coal Min. Inst., p. 303, 1911.

104 ILLINOIS ENGINEERING EXPERIMENT STATION

is regarded as practically complete. It was said to be seldom nec-
essary to record a loss, especially in the upper coal.

In the Cabin Creek portion of the Kanawha district little atten-
tion has been paid to the extraction of pillars until recently, and the
extraction has amounted to only about 50 per cent. For the past
3 or 4 years, however, the extraction has been about 85 per cent.
Since the proper sizes of pillars are now known and the men have
a better understanding of pillar work, it is expected that the per-
centage of extraction will show some further increase.*

Two mines in the New River field, one in the Fire Creek bed and
the other in the Sewell bed, have a recovery which is considered
practically complete, t At those two particular mines the roof con-
ditions are very favorable; in other sections of the field where they
are not so good and where less attention is paid to recovery, it is
thought that a fair average extraction is about 90 per cent. J

The Pocahontas district, in the southern part of West Virginia,
is one of the most important coal producing regions in the country,
largely because of the high quality of the coal. Pocahontas coal is
low in volatile matter and therefore is nearly smokeless; it contains
little ash and little sulphur, and it makes an excellent coke. Because
of these characteristics there is large demand for it. It is extensively
used in coke production, in power plants, in the navy, and in domes-
tic heaters. For coking purposes, however, Pocahontas coal is not
used so extensively at present as it was a few years ago. Several
beds are being operated, but the principal mines are in the Poca-
hontas No. 3 bed. The seam varies in thickness from about 4 feet on
the west to about 10 feet on the east, but the change is gradual and
the thickness is quite uniform within the area of a single mine. This
seam has a fire-clay or slate bottom, and a draw-slate roof.fi It
always has one streak of bone about 2 inches thick to which the coal
adheres on both sides; consequently when a piece of bone is thrown
out, about twice as much coal is lost.

The No. 4 bed, which has two streaks of similar bone, is found
75 to 80 feet above the No. 3. Above this bed occurs a seam of inter-
stratified coal and slate locally termed a "black rash." This rash
contains on the average about 25 per cent of ash, and it is considered

* Keely, Josiah, Personal Communication,
t Personal Communication.

J Cunningham, J. S., Personal Communication.
fl Eavenson, H. N., Personal Communication.

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL 105

worthless, but sometimes over rather large areas there occurs in it
a streak of clean coal from 6 to 8 inches in thickness. Miners are
supposed to leave all this rash in their working places, and most of
it is left, but sometimes some of this clean coal is loaded out. This
fact will explain the higher yield from the No. 4 bed. In other
words, the coal actually mined and loaded sometimes has a thickness
greater than that considered in calculating the contents of the bed.
The fact that a considerable amount of good coal is lost with the
bone explains the smaller yield in mines in the No. 3 bed. It is
believed that if it were not for this loss the extraction would average
about 95 per cent.

As a rule, throughout southern West Virginia, the coal lands
are held by land-holding companies, which lease to operating com-
panies. The royalty is generally 10 cents per ton of coal and 15
cents per ton of coke, with a yearly minimum.

The beds are nearly flat and quite regular, of an almost ideal
mining height, generally with good roof and bottom, and with little
gas and water in the drift mines. It is possible, therefore, to lay out
a definite plan of mining in advance, and to follow such a plan more
closely than in sections where natural conditions are less favorable.
In many cases the landholders specify that the coal shall be mined
in accordance with certain plans, and prescribe a minimum of extrac-
tion. Certain departures from the standard methods, however, are
permitted where it seems advisable.

Fig. 33 illustrates the plan of development formulated by the
Pocahontas Coal and Coke Company,* which may be carried out by
one of three possible procedures as follows:

Panel No. 1. — Drive rooms on 3rd cross entry as soon as come to,
begin robbing as soon as second room is completed and rob advanc-
ing on 2nd and 3rd cross entries to within 100 feet of 2nd cross entry,
on 1st cross entry drive last room first and rob retreating as shown,
taking out the barrier pillar left on 2nd cross entry.

Panel No. 2. — Drive entries to the limit before turning rooms ex-
cept as shown, turn last room on 3rd cross entry first, begin robbing
at inside corner of panel, develop rooms only fast enough to keep in
advance of robbing and bring robbing back with uniform breakline
until completed to barrier pillars.

* Stoek, H. H., " Pocahontas Region Mining Methods," Mines and Minerals, Vol. 29.
p. 395. Stow, Audley H., "Mining in the Pocahontas Field," Coal Age, Vol. 3, p. 594, 1913.

106

ILLINOIS ENGINEERING EXPERIMENT STATION

Panel No. 3. — Continuous panel, drive entries to the limit before
turning rooms except as shown, turn last room on 1st cross entry
first, begin robbing as soon as second room is completed, develop

FIG. 33. PLAN OP WORKING OF POCAHONTAS COAL AND COKE COMPANY

rooms only fast enough to keep in advance of robbing, and bring
robbing back with uniform breakline until limit of mining is reached.
According to W. H. Grady, chief mine inspector of the Poca-
hontas Coal and Coke Company,* the essential advantages of this
plan of mining include: provision for tonnage during the develop-
ment period, provision for meeting the market demand, large barrier
pillars insuring against squeezes and rendering impossible the de-

* Grady, W. H.. " Some Details of Mining Methods with Special Reference to the Maxi-
mum of Recovery,'' W. Va. Coal Min. Inst., Dec. 1913; Coal Age, Vol. 5, p. 156, 1913.

PERCENTAGE OF EXTRACTION OP BITUMINOUS COAL.

107

struction of coal over an extended area, 4-entry system for all exten-
sive main entries with two as intakes and two as returns with, break-
throughs intervening only at the points where the cross entries turn
off, rendering unnecessary the building of expensive masonry brat-
tices every 80 feet, and insuring the maximum quantity of air for
ventilation at a minimum cost for brattices and ventilating power,
and cross entries with narrow chain pillars which permit the rapid
advance of the entry.

The success of this method, with regard to high output, is shown
by the values given in Table 7, taken from Grady's article. The
percentage of recovery is based on the thickness of the total seam,
including the portion rejected. The lower percentages of extraction
shown in Table 7 were reached where pillars were being robbed after
standing for many years. Operations had not proceeded far enough
at the date of the paper quoted to permit a definite statement as to
how great the final recovery would be. A later statement* has been
received to the effect that the mines of the lessees of the Pocahontas
Coal and Coke Company will probably show an average recovery of
90 per cent. Since some of these operations have extended over many
years and since they were not so well managed formerly as at present,
it is probable that the recovery now is more than 90 per cent.

In the Pocahontas district, much attention has been given to the
subject of recovery, and the values which have been supplied by
operating companies are as accurate as such values can be made. H.

TABLE 7
RECOVERY OF COAL IN MINES OF POCAHONTAS COAL AND COKE COMPANY

Plant

Thick-
ness of
Seam
in Feet

Acres
of
Entry
Mined

Acres
of
Rooms
Mined

Acres
of
Pillars
Mined

Total
Acres
Mined

Total
Tonnage
Mined

Tons
Mined
per Acre

Theoret-
ical Tons
per Acre

Per-
centage
of Re-
covery

Pro-
portion
of Seam
Reject-

6.15

3.06

4.57

11.03

18.66

165,254

8,856

9,922

89.3

0.24

5.65

4.40

4.80

14.80

24.00

188,391

8,185

9,115

89.79

0.22

5.16

2.68

6.52

15.80

25.00

180,386

7,215

8,325

86.6

0.22

4.42

5.88

8.65

13.09

27.62

192,437

6,960

7,131

97.6

0.23

5.94

7.00

10.09

19.20

36.29

334,005

9,203

9,582

96.0

0.22

4.32

2.11

3.64

9.20

15.04

94,427

6,278

6,969

90.0

0.31

5.34

3.31

6.34

0.00

9.65

83,000

8,601

8,614

99.8

0.20

5.42

3.72

6.06

9.72

19.50

144,769

8,181

8,777

93.2

0.20

4.65

8.10

16.80

2.34

27.24

201,044

7,380

7,534

98.0

0.18

8.03

5.20

8.47

10.09

23.76

262,975

11,068

12.923J

85.6

0.23

* Eavenson, Howard N., Personal Communication.

108

ILLINOIS ENGINEERING EXPERIMENT STATION

N. Eavenson, whose communication has already been referred to
with regard to the character of the beds mined, says that the measure-
ments of areas worked out are as close as it is possible to get them
on a large scale. The thicknesses given are those of the clean coal, and
do not include any bone or black rash. In many instances a record
has been kept of coal left in small areas, and the values shown by
these tests agree very closely with those given in Table 8. It will
be seen from the table that the amount of extraction for mines 9, 10,
and 11 is given as more than 100 per cent. This record is explained
by the statement previously made concerning the loading out of coal
supposed to be left in the mines. At No. 9, the rash is much cleaner
than at the other mines of the company, and while the seam is thicker,
it carries only a very small amount of dirt; thus a higher percent-
age of clean coal is given.

TABLE 8

STATEMENT OF THICKNESSES AND RECOVERIES, ALL MINES, UNITED STATES
COAL AND COKE COMPANY 1902 TO 1916, INCLUSIVE

Mine
No.

Area Worked Out
per Cent

Average
Thickness
Clean
Coal

Net Tons
Recovered
Per Acre
Foot

Percentage
of
Recovery

No. of
Seam
Worked

Date of
First
Shipments

Rooms
and

Pillars

Entries

45.5

54.5

5.52

1746

97.0

3&4

1903

59.7

40.3

5.67

1790

99.4

1902

61.2

38.8

4.56

1429

79.4

1903

57.3

42.6

6.19

1581

87.8

1904

63.5

36.5

6.88

1606

89.2

1904

63.6

36.4

6.09

1769

98.3

1903

66.9

33.1

6.27

1770

98.3

1905

70.8

29.2

5.98

1728

96.0

1905

74.2

25.8

7.24

1908

106.0

1908

85.1

14.9

5.31

1806

100.3

3&4

1907

73.3

26.7

5.26

1807

100.4

8*4

1907

69.8

30.2

8.22.

1622

90.0

1908

65.9

34.1

5.95

1738

96.5

At the No. 3 mine, which shows the lowest percentage of extrac-
tion, the roof is exceedingly bad. Above the coal there occurs a
layer of shale and slate, from 5 to 10 feet thick, which it is impossible
to support even by close timbering. The mining practice is fully as
good at this mine as at the others, but the yield is much less because
of the more difficult conditions. The table shows the areas worked
out at different mines and the percentages recovered. It is Eaven-
son's opinion that the average recovery in the larger mines through-

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL

109

out the Pocahontas field is fully 90 per cent, and that in many mines
even a higher figure is reached.

One of the landholding associations of the Pocahontas district
furnishes information* concerning some of the operations of its
lessees, and submits a table (Table 9) showing the percentage of re-
covery. It takes account of operations up to January 1, 1917.

TABLE 9

PERCENTAGE OF RECOVERY ON LIVE WORK AND ROBBING

POCAHONTAS DISTRICT

January 1, 1917

AREA MINED

PERCENTAGE OF RECOVERY

Net Robbing,

No.
of
Mine

Live Work,
Per cent

Robbing,
Per cent

Live Work
(Assumed)

Gross
Robbing

Assuming that
37H per cent of
Gross Robbing
was Mined as

Total
to
Date

Live Work

16.1

83.9

84.6

77. 21

86.6

99.7

73.4

59.2

73.5

9.4

90.6

81.2

71.7

82.7

24.2

75.8

80.6

70.7

84.6

38.3

61.7

76.9

64.8

84.6

12 . 1

87.9

87.0

81.0

88.2

15.5

84.5

77.5

65.8

80.6

15.4

84.6

79.3

68.7

82.0

51.8

48.2

83.3

73.9

90.4

53.7

46.3

83.4

75.2

90.7

63.5

36.5

86.0

79.4

93.0

51.7

48.3

81.9

72.8

89.7

1 Values obtained by assuming that 37 .5 per cent of the pillar work is done under the same con-
ditions as live work, i. e., with recovery of 97 per cent; thus 0 . 625 X + 0 . 375 X 97 = 84 . 6, X = 77 . 2.

It will be noted that the extraction at mine No. 2, the first of the
leases to exhaust the No. 3 Pocahontas seam, is not more than 73 or
74 per cent. In addition to the losses which will be mentioned, there
was a considerable loss here of top coal. A thickness of 18 to 24
inches was left up in the first mining with the expectation that it
would be recovered on the retreat, but most of this coal was ultimately
lost on account of the bad roof. It is also possible that the loss in
the coke yard at this plant, where the maximum number of ovens
was run in proportion to the output, amounted to almost double the
average tabulated amount.

An inspection of the table shows that, in most cases, the highest
percentage of recovery has been reached at those mines where the

* Lincoln, J. J., Personal Communication.

110 ILLINOIS ENGINEERING EXPERIMENT STATION

pillar work has been least in proportion to the live work, that is,
at those still in the earlier stages of working. Future operations in
these mines may be expected to lower these values, but it would seem
that 80 per cent would be a very conservative estimate of the average
amount of coal that should be won in the various mines of the prop-
erty up to the exhaustion of all properties under lease.

J. J. Lincoln has discussed losses in the Pocahontas field, and
the facts brought out are of general interest in connection with the
subject of coal recovery. It is said that losses may be considered
under three headings; (a) mixing of coal with refuse, (b) loss in
drawing pillars, and (c) loss in coke making.

There is loss in removing the bone and pyrite from the coal, as
some coal adheres to the refuse. Under the present mining methods,
this loss is from 2 to 4 per cent, and occurs in both new work and
robbing.

The following losses are to be expected in pillar drawing in
addition to loss of coal attached to refuse: (1) In drawing each
stumps are occasionally crushed by the pressure of the top before
broken rock from the adjacent gob from covering the coal. This
loss will run from 3 to 10 per cent, according to conditions. (2)
When the pillars are drawn by splitting, a similar loss, frequently
greater, occurs. (3) As the drawing progresses small sections of
stumps are occasionally crushed by the pressure of the top before
they can be removed. (4) Stumps, sections of pillars, or entire
pillars may be crushed by the weight before they can be removed,
or may be surrounded and cut off by the broken top. In the mines
where actual losses from this source are closely recorded they do not
reach 1 per cent, and there is no mine in which they will reach 2
per cent. The third loss is not directly chargeable to mining, but
occurs in the making of coke. Where the tonnage of coke produced
is used as a measure of the amount of coal taken out, this loss be-
comes significant in calculating the percentage of coal won. The
ratio used by the company in all calculations of tonnage has always
been 1.6 tons of coal to one ton of coke. This ratio assumes an actual
average yield of 62% per cent of coke, but in practice this yield is
not obtained, the average yield under existing conditions being
nearer 55 per cent. This loss has always been charged, with the other
losses, directly against the mining. This ratio cannot be used directly
in determining the actual amount of coal mined, because only a part

•A

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL 111

of the coal is coked. The loss varies in amount from 1 to 5 per cent,
according to the conditions in the different operations, and the ac-
tual percentage of extraction is slightly higher than that given in
the table because of this error.

Losses in mining and coke making may then be tabulated as
follows :

"(a) Removing Refuse — Coal thrown into gob with bone
and sulphur bands . . 2 per cent to 4 per cent

(b) Robbing:—

1. Stumping, or

Splitting pillars . . 2 per cent to 10 per cent

2. Sections or Stumps . 0 per cent to 2 per cent

3. Pillars lost .... 0 per cent to 2 per cent

(c) Additional coal consumed in coke making over and
above the amount covered by the constant of calculation,
1.6 tons equals 1 ton coke 1 per cent to 5 per cent

Total . . 5 per cent to 23 per cent"

A peculiar system followed by the Gay Coal and Coke Company
of Logan, West Virginia, and called a single-room system* has re-
sulted from an attempt to apply the long-wall method to a seam the
average thickness of which is 5 feet, 7 inches. This seam dips to the
southwest about 1% per cent, is practically free from partings, and
is of the nature of splint coal, the bottom bench being rather
strong, and the top bench somewhat friable. The average thickness
of cover does not exceed 500 feet while the maximum is less than
1,000.

A block of coal was cut by two entries 600 feet long, Nos. 4 and 5
(Fig. 34). These were connected at their extremities, which where
300 feet apart. The purpose was to take out the block of coal thus
formed in a retreating direction by commencing at the inner end
and by working outward with a face about 300 feet long. One
hundred beech or hickory posts were used to support the roof near
the face. The top of each was covered with 1-inch poplar, and the

* Gay, H. S., "A Single-room System," Proc. Coal Min. Inst. Amer., p. 157, 1906; Minea
and Minerals, Vol. 27, p. 325, 1906; Personal Communication.

112

ILLINOIS ENGINEERING EXPERIMENT STATION

bottom with 1/16-inch sheet steel. Each post was mounted on a hy-
draulic head weighing about 700 pounds and tested to a pressure
of 3,000 pounds per square inch. These were set along the face 6
feet apart in parallel rows 3 feet apart. The cost of the equipment
was approximately $5,000.

When the walls became more than 30 feet apart, rows of props
on 15-foot centers were set 8 to 10 feet apart. When the distance
between the walls had reached 60 feet, the portable posts were put
into use, a row of 50 posts on 6-foot centers being set 10 feet from

FIG. 34. SINGLE ROOM METHOD, LOGAN COUNTY, WEST VIRGINIA

the face. The heads were covered with wooden cap pieces, and the
plungers were raised by a pressure of 50 pounds per square inch.
When the face had advanced 6 feet farther, the other 50 posts were
put in ; as the work progressed, the first row was moved 6 feet ahead
of the second, the posts being moved one at a time. An occasional
row of posts similar to the first was also set as a precautionary
measure.

When the walls were 100 feet apart, it was thought advisable to
blast down the roof. The portable posts were set in a single row
6 feet from the face. Examination after the rock had fallen showed
that the immediate roof consisted of a seam of strong sand slate at
least 30 feet thick without any sign of a parting and that difficulty

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL

113

would be encountered in attempting to apply the long-wall method
in this mine.

The advantages to be derived by working on a long face were so
great that the company devised another plan which involved work-
ing out the remainder of the block by a system of rooms 80 feet wide,
parallel with the long-wall face and separated by 30-foot pillars. Each
room was to be opened by driving a sub-entry across from entry No.
4 to entry No. 5 (Fig. 34), and thereafter the manner of working
was to be identical in every respect with that of the long-wall system.

FIG. 35. BIG BOOM METHOD, LOGAN COUNTY, WEST VIRGINIA

From the experience gained it was thought that, with the roof
in normal condition, rooms could be worked 90 feet wide with 30-
foot pillars. Entries Nos. 4 and 5 were therefore continued east-
ward, and sub-entries were spaced for the rooms as shown on the
map (Fig. 35). The last of the sub-entries was widened to 40 feet,
and a single row of ordinary props, 8 to 10 inches in diameter, was
set close to the face on 15-foot centers. When the face had moved
10 feet farther, a second row was set. When the room had reached
a width of sixty feet, a row of portable posts was set on 10-foot cen-
ters, and at 70 feet another row was set. The ordinary props were
used for detecting the action of the roof.

114 ILLINOIS ENGINEERING EXPERIMENT STATION

One of the advantages of this system of mining is that a large
amount of coal per employee may be obtained. In fact the produc-
tion per man is considerably greater than with the room-and-pillar
method, and greater even than would be possible with the long-wall
method. The highest rating in this seam for car distribution, ex-
clusive of this mine, is 13 tons per loader; this mine is rated at 20
tons per loader. It is the opinion of Mr. Gay that it would be pos-
sible to produce about 11 tons per inside employee per 9-hour day
for five days a week. The method also results in the recovery of a
very high percentage of coal. A calculation based upon the number
of tons shipped and the area excavated, according to planimeter
measurement, indicates that the extraction was 85.9 per cent.

Since this description was published, the system has been mod-
ified to reduce the narrow work, but the general plan has been
followed. Instead of driving a single room to form the working
face, parallel rooms separated by an 18-foot pillar are driven; thus
the use of brattices is unnecessary, and ventilation is improved. The
hydraulic posts were soon abandoned, as posts without the hydraulic
heads are cheaper, and they are easily recovered. One of the most
important facts concerning the operation is that there has not been
a single fatal accident in the mine since work was begun.

Another system in which an effort was made to obtain the advan-
tages of long-wall working was tried a few years ago in West Vir-
ginia.* In developing this system (Fig. 36) triple entries are driven
from the outcrop, near which double entries are turned off at right
angles. From these, entries are driven parallel with the main entry;
thus blocks of coal about 900 feet wide are cut off. Block entries
are turned from the main entry and from these side entries, parallel
with the cross entry, spaced about 500 feet apart, and driven for
about 800 feet; thus the coal is blocked into areas approximately
500 by 800 feet. In working these blocks, a room is turned first at
the end of the block entries to form a working face for the long-wall
machine. The blocks are then worked back toward the main entry
for 500 feet; thus a barrier of 300 feet protects each main entry.
Track is laid along the face as near the coal as possible, and is moved as
the face progresses. The roof is allowed to fall, but the line of break
is kept at the correct distance from the face by three or more rows

* James, W. E., "Block System of Retreating Long-wall," Proc. W. Va. Coal Min. Inst.,
p. 137, 1911; Cabell, 0. A., Personal Communication, and Patent Specifications.

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL

115

of props, the last row being moved forward after a cut is made. The
trolley wires are hung on hangers as usual, but to keep them tight
they are carried on portable drums. Current for the motor and
machines along the face is taken from the trolley wire on the entry

FIG. 36. BLOCK SYSTEM OF RETREATING LONG-WALL, WEST VIRGINIA

by means of a cable which is also coiled on a portable drum. Ventila-
tion is controlled by placing a regulator in the return air course of
each block. Each block or face is provided with a separate supply
of fresh air by having overcasts placed at the air courses to admit
the return air into the main air course entry. No doors are required
at any points in the mine.

116 ILLINOIS ENGINEERING EXPERIMENT STATION

It was claimed for this method that a block will produce 440 tons
per day with the use of only 500 feet of track in addition to that on
the entries, that practically all the coal is obtained, and that the
work of the rolling stock and cutting machines is concentrated. The
trial of this method was temporarily abandoned because of an inade-
quate car supply, but the work was considered successful. It was
not carried far enough to provide reliable data for an estimation of
total extraction.

26. Ohio. — The literature of coal mining contains little informa-
tion regarding conditions in Ohio. Some of the operations in the
Hocking Valley district have been described in articles which state
that large quantities of coal are left in the roof because of the poor
quality of the product. An article on Hisylvania Mine No. 23 states*
that the bed mined in the Hocking Valley district is the Middle
Kittanning, Hocking Valley, or No. 6. The bottom consists of a few
inches of fire clay overlying hard rock. The roof is of shale, 6 to 8 feet
thick. The coal bed consists of three benches. The thickness of good
coal is about 6 feet, and above this is about 5Vjj feet of a poorer coal
separated from the lower portion of the bed by a distinct parting.
This upper bed, with the upper bench of the lower bed, is known as
top coal. In this district all coal in excess of 6 feet, and in many
places in excess of 4% feet, is to be credited to this upper bench
which has a maximum thickness of 10 feet.

James Pritchardf estimates the percentages of extraction in the
districts as follows:

In the Pittsburgh vein district, the Cambridge field, and the
Hocking field, districts which produce approximately three-fourths of
the coal of the state, the rate of extraction will range from 60 to 70 per
cent. In the Massillon and Jackson fields, the rate of extraction may
reach 85 per cent. In the Deerfield and Mahoning districts, the rate
of extraction may reach 85 per cent. Throughout the remainder of
the state, the maximum percentage of extraction will run from 60 to
70 per cent. The average rate of recovery is approximately 60 per
cent, with a minimum of 55 per cent and a maximum of 75 per cent.

* Burroughs, W. G., " Hisylvania Mine No. 23," Coll. Eng., Vol. 34, p. 421.

tPritchard, James, Chief Deputy and Safety Commissioner of Mines, Personal Com-
munication.

PERCENTAGE OF EXTRACTION OP BITUMINOUS COAL 117

The average value represents the most common percentage of ex-
traction.

The conditions in the Pittsburgh vein district of eastern Ohio are
described by Roby* as follows :

The extraction is limited by various physical and commercial
conditions. The roof consists of a bed of weak coal of poor quality,
variable in thickness, and separated from the main bed by a layer
of drawslate which disintegrates on exposure. Overlying the roof
coal is an unstratified "soapstone" 4 to 8 feet thick, and above this
is a thick layer of hard limestone. The country is hilly, and the
total cover varies from 30 to 600 feet in thickness. The character
of the roof makes it necessary to leave larger pillars than would be
required under a good roof. The roof coal is left up, and as it is
poor in quality and not marketable, it is not considered in making
estimates of extraction. The room-and-pillar method is used. There
has been much discussion concerning the possibility of applying the
long-wall method, but the fragility of the roof and the tendency of
all rock below the limestone to shear off at the solid face have seemed
to make the method impracticable.

It is desirable that rooms be worked out as quickly as possible
because of the tendency of the roof and pillars to fail. Because of
these conditions, the numerous interruptions which have been caused
by strikes and business depressions have tended to make the rate of
recovery lower than would have been the case with uninterrupted
operation.!

J. C. Haring states that the recovery in the Massillon district has
not exceeded 75 per cent. The highest recovery in "the district is
probably at the Pocock No. 4 mine where it is estimated that fully
90 per cent of the coal has been obtained.

At Steubenville, the mine of the LaBelle Iron Works has been
operated on the long-wall system since 1913; prior to that time the
room-and-pillar method was employed, J The bed is the Lower Free-
port which is a little over 3 feet in thickness and has a good shale
roof.

At present a considerable amount of stripping is being done in
the No. 8 coal in the vicinity of Steubenville. The coal outcrops on

* Roby, J. J., Personal Communication.

t Haring, J. C., Personal Communication.

$ Burroughs, W. G., "Long-wall Mining at Steubenville, Ohio," Coal Age, Vol. 11, p. 69'

118 ILLINOIS ENGINEERING EXPERIMENT STATION

the slopes of hills, and the rapid increase in the thickness of the
overburden restricts the operations to a narrow belt, although they
may extend for a considerable distance along the outcrop.

27. Kentucky. — The development of coal mining in Kentucky
has been comparatively recent, and some of the Kentucky fields are
still so young that it is impossible to obtain estimates of recovery.
The state may be divided broadly into two districts, the western
district being closely allied with the fields of Indiana and Illinois,
and the eastern district with those of West Virginia and Virginia.

The statements presented in the following paragraphs concerning
the western district are made on the authority of N. G. Alford,* who
says that the fields contain about 38.3 per cent of the coal-bearing
areas of this state and that in 1912 47.7 per cent of the total pro-
duction came from this district. The smallness of many operations
is shown by the statement that 21 per cent of the mines produced
less than 10,000 tons per annum each; 51 per cent produced less
than 60,000 tons each; 23 per cent produced more than 100,000 tons
each; and two companies, operating 18 mines, produced 2,750,000
tons each.

Generally, the rate of recovery in the mines of western Kentucky
is about 66 2/3 per cent, although in some instances it is as low as 44
per cent. Without an exception the mines of this district are de-
veloped on the room-and-pillar system with double or triple entries.
With the exception of two or three isolated operations, all the coal is
produced from three seams.

Most of the coal comes from the No. 9 and No. 11 beds, the for-
mer producing about three-fourths of the total output of the field.
This bed is present in eight counties and approaches 5 feet in
thickness. In most places it is reached by shafts of 300 feet or
less in depth, although there are some local surface depressions
which permit access by slopes or drifts. It has a black shale roof
and a soft fire-clay bottom.

The No. 11 seam lies from 40 to 100 feet above the No. 9, and fol-
lows the latter in commercial importance. Its average thickness is
6 feet. Above the coal is a stratum of limestone of thickness varying
from a few inches to 40 feet. This limestone is usually separated

* Alford, Newell G., " Problems Encountered in Kentucky Coal Mining," Ky. Min. Inat.,
1913 ; Coal Age, Vol. 5, p. 674, and Personal Communication.

PERCENTAGE OP EXTRACTION 6P BITUMINOUS COAL 119

from the coal by a thin stratum of heavy laminated clay 6 to 24 inches
thick. This top adheres uncertainly to the limestone above it, and
presents a constant danger. Near the outcrop the top becomes very
treacherous. The bottom of this seam consists of soft fire clay which
frequently heaves in haulage entries that have been opened for some
time. About half the mines in this seam are shaft mines, and the
remainder are drift mines.

The third seam in commercial importance is No. 12, which is
found best developed in Clay and Webster Counties. Its approxi-
mate depth below the surface is 225 feet. Its average thickness is
7 feet. The bottom is of fire clay which is high in calcium and
which disintegrates rapidly when drainage water is directed through
it in ditches. The roof consists of light gray disintegrated shale
10 to 15 feet thick. If all the coal is removed, this top will fall
to a height of 6 or 8 feet, and heavy timber sets, thoroughly and
solidly lagged, are required to support it. Because of this condition
it has been found necessary to leave 16 inches of top coal as
a roof. Sixty per cent of this top coal is recovered from rooms, but
no attempt is made to recover it from entries. When the develop-
ment of the No. 12 seam was begun, rooms were driven 21 feet wide
on 33-foot centers; but this width of pillar was found to be too
narrow, and it has been increased to 20 feet, with rooms 21 feet wide.
Under these conditions a recovery of 44 per cent is the best which has
been reached up to this time. This low percentage of recovery is in
part due to physical conditions, and in part to over-development and
keen competition.

Several factors contribute to limiting the recovery in the No. 9
and No. 11 beds. The most important of these is probably inadequate
planning of future workings. Frequently pillars are left too small;
consequently the bottom heaves, and the pillars are crushed. Partial
recovery of pillar coal by taking slabs off the ribs is not general, and
the total recovery of pillars has not been attempted. The operators
in this district hold the opinion that pillar robbing in the No. 11
seam is particularly hazardous and impractical, because heavy lime-
stone overlies the seam; in the Connellsville district of Pennsyl-
vania, however, pillars are successfully drawn under a heavy lime-
stone. Alford expresses the opinion that if the workings in the
No. 11 seam were properly laid out and started, little difficulty
would be found in increasing the percentage of recovery.

120 ILLINOIS ENGINEERING EXPERIMENT STATION

In this district there is an over-production with a limited market ;
consequently competition is keen. When business conditions are
normal, the margin of profit is so small as to preclude any costly im-
provements, and little money has been expended in experiments.
Another source of loss lies in the waste at the tipples in the summer,
because the demands of consumers are more exacting in times of
dull markets. Good coal attached to lumps of pyrite is often dis-
carded in large quantities, and so far this waste has been accepted
as unavoidable. This district furnishes one of the best illustrations
of the effects of over-development and lack of harmony of interests.
There are, however, some operations which are carried out on a
considerable scale and with careful attention to the proper planning
of the work.

The estimates covering production mentioned previously are con-
firmed by a personal communication from another operator, S. S.
Lanier, who has been a close observer in the district for thirty years
and who estimates that the extraction is about 65 per cent.

The eastern Kentucky district is of such recent development that
estimates of production are not very reliable. H. D. Easton, oper-
ating in the southeastern part of the state, thinks it safe to say
that a recovery of 90 per cent is being reached in the Straight
Creek seam in Bell County, but much trouble has been experienced
from squeezes due to lack of systematic working.

Mines are operated on the room-and-pillar system with rooms
turned from both sides of the room entries. Rooms are generally
40 feet wide with 20-foot pillars. Cross entries are driven about
1,200 feet apart, and these usually extend to the property line or
to the outcrop. It has been the practice to extract the pillar coal on
the retreat, and so far as possible to keep the face lined up over
a sufficient distance to get a fall of roof. Room tracks are swung
across the face of the pillar and are moved as the pillar is drawn
back. If the pillars are narrow, the room tracks are not moved
even though the coal has to be shoveled 15 or 20 feet.

There has been no very systematic work in pillar recovery in the
southeastern part of the state, and pillars or stumps have been left
scattered promiscuously, with the result that many costly squeezes
have occurred. One company has lost an entire mine as a result
of this practice. It has been the general opinion that it would
be impossible to get a clean break in the overlying strata because

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL 121

of the solid sandstone above the coal, but such breaks have been
obtained very successfully, even in rather limited areas.

The Harland district, the Hazard district, and the Elkhorn dis-
trict are all too newly developed to provide a reliable basis for
estimating recovery, but it is possible that the percentage of recovery
will be very high.

In eastern Kentucky the surface is of no great value, and it is
almost invariably owned by the coal companies so that the necessity
for sustaining it is not a factor affecting the percentage of extrac-
tion.

There are some operations in the central southern part of the
state, but the mines are not yet sufficiently developed to yield ade-
quate data for reliable estimates of extraction.* The mines are
opened by drifts, and as the coal is irregular, the hills have been
entered at many points. A heavy sandstone occurs between the two
seams worked, and pillars have not been drawn in the lower seam,
because it has been feared that the upper seam would be damaged.
In the upper seam, pillar drawing has not been practiced to any
great extent, because when tried, it has resulted in breaks extending
to the surface through which considerable water has entered. It
is the intention of the operators to extract the pillars when the
mines have been worked out, and the final percentage of extraction
will probably be high.

28. Tennessee. — Little information is available on the percentage
of recovery in Tennessee, and the statements obtained are not alto-
gether in agreement. One operator, t formerly connected with the
industry in Tennessee, states that a few years ago the mining practices
were not good. On the first mining, about 50 per cent of the coal
was taken, and the ultimate recovery was probably about 80 per cent.
Because of the low value of coal lands, less effort is made to get a
maximum recovery than in some other districts where coal lands
are more valuable.

R. A. Shiflett,t Chief Mine Inspector, says that it would be diffi-
cult to give any general percentage for extraction since the coal
measures vary in dip from horizontal to 40 degrees, and in some

* Butler, J. E., Personal Communication.
t Coxe, E. H., Personal Communication.
$ Personal Communication.

122 ILLINOIS ENGINEERING EXPERIMENT STATION

cases from horizontal to vertical. In a large number of mines it
is impossible to map out any definite method of mining, and con-
ditions have to be met as they are encountered.

Nearly all the drift mines are developed on the double-entry
room-and-pillar system. Rooms are driven from 250 to 300 feet, and
room pillars are drawn as soon as the rooms are finished. If condi-
tions are favorable, the entry pillars and room stumps are recovered
on the retreat ; and where the coal is practically level, 40 to 50 inches
thick and with good roof and bottom, about 90 per cent is extracted
under careful management. This percentage is not reached in many
mines because of lack of attention to high extraction. It is thought
that the extraction in general does not exceed 65 per cent, but that
this percentage could be greatly increased by proper methods and
careful management.

One company,* whose method was to turn rooms on the advance
and immediately to draw room pillars back to within 65 or 70 feet
of the entry on completion of the room, obtained a recovery of
nearly 90 per cent up to about the beginning of 1916. At that time
four cross entries were lost from heaving of the soft bottom. The
cover is 500 to 800 feet in thickness, the coal is 56 inches in thick-
ness, and the bottom is of soft fire clay from 4 to 7 feet in thickness.
This company is planning the introduction of the long-wall method.
A face of about 300 feet will be formed by connecting the ends of
two entries. It is thought that the single stick timbering, with per-
haps an occasional crib, will be sufficient. It is expected that the bot-
tom will heave and reach the roof as the latter bends down. The
scarcity of labor and the irregularity of the car supply make the
success of long- wall operations somewhat doubtful ; and if it is neces-
sary temporarily to abandon this method, another which is illustrated
in Fig. 37 will be adopted. In this method apparently a little more
than 50 per cent of the coal would be taken out from rooms, and
the ultimate percentage of extraction should be almost complete.
The method will permit concentrated working, and much of the
trouble due to the conditions of the floor and roof will probably be
avoided.

29. Alabama. — Although Alabama t is an important producer

* Hutcheson, W. C., Personal Communication.

t Strong, J. E., "Alabama Mining Methods," Mines and Minerals, Vol. 21, p. 195, and
Personal Communication.

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL

123

of coal, the working conditions are not so good as those of Pennsyl-
vania, Kentucky, and some other states. One of the distinctive
features of the Alabama coal field is that although there are five
seams of coal, rarely more than one of them is workable at any one
place; in one portion of Jefferson County, for instance, the Pratt
seam, which is considered the topmost workable seam of the Alabama
coal measures, may have a working thickness of 4 feet, while at a
distance of two or three miles the same seam may not be more than

FIG. 37. PROPOSED PLAN OF WIND BOCK COAL COMPANY, TENNESSEE

2 feet thick. The coal beds, including the Pratt bed, vary rather
abruptly within a few miles with regard to thickness, impurities,
and character of roof.

The Pratt seam has been worked longer and more extensively
than any other seam in this district. It is probable that the recovery
from this seam, under the best methods of working with the room-
and-pillar system, is about 87 per cent. This percentage applies
only where the thickness is three feet or more; coal thinner than
this cannot profitably be removed.

The Mary Lee seam, which is supposed to contain the thickest
workable coal, lies about 300 feet below the Pratt seam, and is the
one that the operators of the Birmingham district expect to work
during the next twenty years. So far as it is known, the thickness
of the bed ranges from 6 to 10 feet. It is difficult to get reliable esti-
mates of the recovery of coal in this seam, but one operator reports,

124 ILLINOIS ENGINEERING EXPERIMENT STATION

on the basis of an experience of twenty years, that the recovery has
been about 90 per cent.

There are mines on lower seams in other localities, but little atten-
tion has been paid to the extraction of a high percentage of the coal.
The operation of these mines depends largely upon market condi-
tions, and they are probably not operated, on the average, more than
half the time. Under these conditions the loss of pillar coal caused
by falls of roof is necessarily large.

The Alabama mines, with the single exception of the Montavallo
mine, where a change is being made to the long- wall system, are
worked on the room-and-pillar system. The larger operations are
in the neighborhood of Birmingham, and in this district the car-
boniferous measures are tilted and broken to a great extent. This
condition affects the roof of the coal under cover for a considerable
distance. Both top and bottom are of variable character.

In the larger operations at least, the triple entry system is used.
Commencing at .a distance of 800 feet from the surface, cross entries
are usually driven about 350 feet apart. Until the entries have been
driven a few hundred feet, it is not possible to determine whether
they should be narrow or wide enough to provide storage for the
impurities of the bed and the brushing of the roof. Rooms are
generally opened narrow also, (30 feet wide) with 25-foot room pillars,
until it is determined whether the character of the overlying strata
and of the floor will permit the working of wider rooms.

Probably 75 per cent of the large operators in the district have
adopted the plan of immediate pillar drawing in preference to that
of driving the narrow work to the limit and pulling the pillars upon the
retreat. In a number of instances, rooms are driven 40 feet wide with
30-foot pillars and are worked for a distance of 300 feet, or to the
entry above; then a cut is taken across the end of the pillar, and the
pillar is drawn back to the entry stump. When the room pillars are
drawn on the advance, there is no difficulty in getting room stumps
and air-course pillars after the entry work is complete.

Strong estimates the recovery in mines operated by the larger
corporations to be from 87 to 90 per cent. Priestly Toulmin, another
operator,* confirms these values by stating that the average extrac-
tion in Alabama is not less than 75 per cent and not more than 80
per cent, so that possibly 77% per cent would be a fair value. In

Personal Communication.

PERCENTAGE OF EXTRACTION OP BITUMINOUS COAL , 125

some mines the extraction is less than 60 per cent, and in others it is
more than 95 per cent.

C. F. DeBardeleben* furnishes the following estimates:
At one operation where 768.6 acres had been worked over, assum-
ing the average thickness of coal to be 4 feet and that 25 cubic feet
of coal in place make a ton, the coal available was 5,356,834 tons

Tons mined 3,028,960

Extraction 56.5 per cent

Assuming that 12.5 per cent more will be obtained from pillars,
the extraction will amount to about 63 per cent. At another opera-
tion where the average thickness is 5 feet and 316.6 acres have
been worked over, the coal available was 2,758,219 tons

Tons produced 1,847,582

Extraction 67 per cent

Assuming a probable extraction of pillars, the final recovery
will amount to about 70 per cent. At a third mine, where conditions
were favorable because of level coal and the absence of gas, 25-foot
rooms were driven on 75-foot centers; the pillar was drawn back
half way to the entry as soon as a room was finished, the entry pillars
and room stumps being extracted when the entry was abandoned.
Under these conditions the recovery was about 85 per cent.

C. H. Nesbitt, Chief Mine Inspector of Alabama, estimates the
average recovery to be 80 per cent, the highest percentages being
reached in the Pratt and Montavallo beds.t There has been great im-
provement in the percentage of extraction in the past twenty years, and
even in the past ten years. This improvement has been due largely
to more nearly complete and accurate mapping, and to more improved
and effective methods of controlling the water in slope and shaft
mines.

•.

30. Indiana. — Almost no information has been available con-
cerning the percentage of coal extracted in Indiana mines. W. M.
Zeller f reports that the extraction in the Brazil district is probably
about 60 per cent. This estimate agrees fairly well with the estimates
of operators in southern Illinois, and since such estimates have been
found to be too high in almost all instances, it is probable that the

* Personal Communication.
t Personal Communication.

126 ILLINOIS ENGINEERING EXPERIMENT STATION

average extraction in Indiana, as in southern Illinois, will not exceed
50 per cent.

31. Michigan. — The coal beds in Michigan are irregular in ex-
tent and decrease in thickness with depth. Sometimes they are
entirely cut out by erosion or replaced by sandstone and other mate-
rials. Usually the beds above the coal consist of black shale, and
they are often weak. Owing to erosion, coal is sometimes found
directly below clay, sand, or gravel, or below other unconsolidated
rocks, where it is practically unworkable. At several mines the
roof is of black bituminous limestone. In most instances the floor
is of fire clay or shale, although sandstone is sometimes found. The
thickness of coal varies from 2 feet, 6 inches to 3 feet, 10 inches, a
fair average at Saginaw being 3 feet. In the Saginaw Valley the
surface is level.*

R. M. Randall states t that the first company in the district oper-
ated within the city limits of Saginaw, and that because of the neces-
sity of leaving pillars to protect the surface the recovery was only
about 68 to 70 per cent. At present this company is operating in
farming districts where it is not necessary to maintain the surface;
and the recovery, within the last five years, has been about 90 per
cent. The room-and-pillar system is used with rooms projected 40-
feet wide on 50-foot centers and driven 150 feet, but the actual
dimensions vary according to the conditions of the roof. Short-wall
machines are used for undercutting. It is estimated that 75 per
cent of the room pillars and 95 per cent of the entry pillars are
recovered, and that the extraction on the advance is 70 per cent.
The conditions at the old and at the new mines have been so different
that it is impossible to give an average value for the extraction, but
it is believed that the extraction in the new mines in the area act-
ually worked will be from 85 to 90 per cent.

32. Iowa. — The physical conditions in the Iowa coal field are
not uniform. The cover ranges in thickness from a few inches to
300 feet, and consists of the coal measure beds and glacial drift,
the latter commonly constituting the larger part of the thickness.
The workable coal beds generally have a top of draw shale varying

* Lane, A. 0., Mich. Geol. Sur., Vol. 8 ; Mines and Minerals, Vol. 23, p. 148.
t Personal Communication.

PERCENTAGE OF EXTRACTION OP BITUMINOUS COAL 127

from a few inches to two feet in thickness. Above this is a bliack
shale, or sometimes a bituminous or argillaceous limestone. In the
latter case this rock is often strong enough to permit a reduction
in the amount of timber used and thereby to facilitate mining. This
condition makes it possible in Appanoose County to work a bed in
which the thickness of clean coal is only about 25 to 27 inches. The
bottom everywhere consists of plastic fire clay, and in the Appanoose
field the undercutting is done in this clay. Its occurrence is fre-
quently the cause of creep in room-and-pillar mines. The most un-
favorable conditions are found through the northern end of the
Iowa coal fields.

Even in single districts the percentage of extraction varies be-
tween wide limits. The maximum extraction, estimated at 90 per
cent or more, is reached in the Appanoose field, where the long-wall
system is employed. An operator* familiar with conditions in these
long-wall mines says that the extraction is complete, but that it is
less than the previously calculated amount of coal in the ground
because of the presence of faults.

In the room-and-pillar districts the extraction rarely if ever
exceeds 75 per cent, and under especially bad conditions of bottom
and top with an abundance of water, it may not exceed 50 per cent.
Probably a fair average of recovery for the state is 70 per cent. The
percentages given refer only to the bed mined and to the area of
actual mining operations. When larger areas are considered, the
percentage of recovery is less because of the loss of considerable quan-
tities of coal through lack of cooperation between owners, a loss
estimated to be at least 10 per cent.f

The engineer J of one of the operating companies says that in
the room-and-pillar mines with which he is familiar the recovery
will average about 75 per cent, and that a recovery of 80 per cent is
expected in the newer mines.

33. Missouri. — The coal fields of Missouri may be roughly
divided into three districts, the first district lying near the middle of
the state in Macon and Randolph Counties where operations are
conducted on the room-and-pillar method, the second district farther

* Taylor, H. N., Personal Communication.

t Beyer, Professor S. W., Personal Communication.

$ Jorgensen, P. P., Personal Communication.

128 ILLINOIS ENGINEERING EXPERIMENT STATION

west along the Missouri River in the vicinity of Lexington where
operations are conducted on the long-wall system, and the third dis-
trict in the southwestern part of the state, where the conditions are
similar to those of southeastern Kansas and northeastern Oklahoma
and where the room-and-pillar system has generally been followed.
Recently a considerable quantity of coal has been obtained in the
southwest district by stripping.

In Randolph and Macon Counties, in the neighborhood of Bevier,
the coal is considerably broken by faults and horsebacks, and recov-
ery does not exceed 50 per cent.* In the long-wall district the ex-
traction in the area worked out is practically complete, but most of
the operations are conducted on a small scale and no estimates cover-
ing the probable extraction over the whole area are available.

In the southwestern part of the state the continuity of the coal
is considerably broken by horsebacks, as in the neighboring parts of
Kansas and Oklahoma. Mining methods have not been highly devel-
oped, and no great attention has been paid to completeness of extrac-
tion. It is not probable that the extraction in this district, within
the areas worked, will be more than 50 per cent.

34. Arkansas. — Steel sayst that the ordinary waste of coal in
Arkansas is unusually great even for this country, a fact to be
accounted for partly by unfavorable geological conditions. In addi-
tion to the wastes common to all coal producing states there are
others due to local geological and physical conditions, which Steel
considers unusually unfavorable in Arkansas.

There is considerable loss because of irregularities of entries,
due to the varying dip of the bed. Entries which are turned from
the slope at standard distances measured along the coal seam will
have variable and perhaps severe grades if they are driven straight
or will be very crooked if they are driven on grade. If the dip in-
creases and the entries are driven on grade, the distance between
entries decreases and sometimes the rooms between entries become so
short that the entry from which they are turned is discontinued ; then
rooms from the entry below are driven long enough to take out all
the coal, or part of it, which would have been taken out through the
intermediate entry. Sometimes the length of rooms necessary to

* Taylor, H. N., Personal Communication.

t Steel, A. A., "Coal Mining in Arkansas," Ark Geol. Sur.

,-
PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL 129

extract all the coal would be so great that part of it is left. Some-
times this is won through the upper entry, and sometimes it is lost.

There are also losses due to irregularities in the coal, and entries
are frequently not extended through areas of low coal to get the good
coal lying beyond. Areas of thin coal are commonly abandoned.
The losses due to thin or poor coal are greater perhaps in Arkansas
than in other states, because the dip of the beds makes the driving
of entries around these poor areas considerably more expensive, and
it is not profitable to take out good coal lying beyond poor coal un-
less the area of the good coal is large. There is often considerable
loss from the abandonment of parts of beds. In many places the
different benches of thick beds are separated by thick partings; if a
single bench is thick enough to mine, it is worked separately, and
sometimes the bench above it or below it is lost. The loss of coal in
this form, though not so great as formerly, is probably greater in
Arkansas than in any other state, with the possible exception of
Colorado. Loss due to the need of protecting the surface is not
serious, because the value of the surface is low, and the rough topog-
raphy insures good drainage.

H. Denman,* an operator familiar with the district, expresses
the opinion that the recovery in both Arkansas and Oklahoma does
not exceed 50 per cent. In certain portions of a mine the recovery
may be as high as 70 per cent, but he believes if the whole area of
the mine is considered, the percentage of extraction will not, in any
case, exceed 55 per cent. These statements are applicable to both
Arkansas and the neighboring Oklahoma district, as the same system
of mining is used in both.

The system of mining in the Arkansas-Oklahoma field is practi-
cally the same that was used when the field was first opened about
forty years ago. There is no systematic attempt at laying out mines
with the view of drawing pillars, but the general plan is to get as
much coal as possible in the first working and to abandon the re-
mainder. There is one mine in which an attempt is being made to
plan the work so as to obtain the pillar coal, but this attempt is so
recent that it is impossible to foretell the degree of its success. The
widths of rooms and pillars are influenced by the charges for narrow
work and for yardage, which are so high that neither narrow rooms
nor long break-throughs can be driven. At present the average room

* Personal Communication.

130 ILLINOIS ENGINEERING EXPERIMENT STATION

neck is about 10 feet long, and if longer necks could be driven
without increased cost, it might be possible to prevent squeezing of
the entry and to obtain a considerable amount of coal from the entry
pillars, but the yardage cost is so high that this procedure seems un-
profitable.

35. Kansas. — The coal produced in Kansas comes from three
districts, the one in the southeastern corner of the state being by
far the most important. The others are the Leavenworth and the
Osage districts. The Leavenworth district lies in the northeastern
part of the state and may be considered as connected with the district
of northwest Missouri, although the strata dip toward the west and
the coal is found at greater depths in Kansas than in Missouri. All
operations in the Leavenworth district are on the long-wall system,
and the extraction, in the areas mined out, is practically complete.
Coal in this district ranges from about 19 to about 24 inches in thick-
ness. The depth is about 700 feet. A 3-foot bed lying at a depth of
1,000 feet was found at Atchison about ten years ago and was worked
by the long-wall method, but the work was not commercially success-
ful and was abandoned. The Osage district lies to the south of
Topeka and is not important commercially. The coal is about 20
inches thick, and is mined entirely by the long-wall method. The
extraction is practically complete within the area mined out. This
is the thinnest bed of bituminous coal worked in the United States.

In the southeastern district of the state the coal beds lie on the
west slope of the Ozark uplift and dip toward the west and north-
west. The beds contain numerous horsebacks which interefere with
systematic mining. The room-and-pillar method is followed, and
little attempt is made to extract pillar coal. Practically all coal in
Kansas, except that produced by the long- wall method and by
stripping, is shot from the solid, a method which unquestionably
leads to the production of small coal, especially where the holes are
greatly overcharged as they usually are. The recovery is in the
neighborhood of 50 per cent, although it may sometimes be greater
in limited areas, because the horsebacks may be made to serve as
pillars. H. N. Taylor, in a personal communication, confirms this
estimate of extraction. He says that in places a considerable loss is
experienced, because the rate for mining low coal is so high as to be
considered prohibitive, and even if the rate is paid it is difficult to

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL

131

get men to work the low coal. A. C. Terrill reports* that the closest
estimates of those most familiar with conditions place the recovery
at about 50 per cent.

The approaching exhaustion of the shallower mines has neces-
sitated the working of the northern part of the district where the

FIG. 38. PANEL LONG-WALL IN OKLAHOMA

cover is about 250 feet thick. At least one of the operators desired
to work these deeper mines by the panel method, but it has not as
yet been found possible to reach satisfactory arrangements with the
mine workers. Since a makeshift adopted to prevent the spread
of squeezes leaves two rooms out of seven unworked, the recovery has
been reduced about 1,000 tons per acre. The operators still hope that
they may be able to introduce the panel system and thus materially
increase the recovery, t

In recent years a large amount of coal has been taken from this
district and from the neighboring region in Missouri by extensive

* Personal Communication.

t Taylor, H. N., Personal Communication.

132 ILLINOIS ENGINEERING EXPERIMENT STATION

stripping operations. In the area worked over, the extraction by
this method is practically complete.

36. Oklahoma. — In Oklahoma the coal is produced largely by
individual operators, the land being owned by the Indian nations
and leased to operators in small tracts. * Elaborate plans for mining
are not to be expected under these conditions. Elliot estimated that
the recovery of the entire bed worked was not more than 55 per cent.
He said that the low percentage of recovery was due to the extrav-
agant system of room-and-pillar mining adopted, and that this system
could not be changed because of unfavorable labor conditions.

The Rock Island Coal Mining Company obtains an extraction of
48.18 per cent in the McAlester district. In the Hartshorne district
this company has five mines, their percentages of extraction being
56.6, 52.6, 55.0, 51.5, and 47.8, respectively. The average percentage
of extraction at these five mines is 52.7 and the average of all the
mines of the company in Oklahoma is 51.8. t

This company is now trying a panel long-wall plan (Fig. 38) with
the hope of increasing the extraction from about 57 to about 70 per
cent. The coal is about 3 feet, 4 inches thick, and dips from 5 to 8
degrees. The working face is parallel with the dip. The roof along
the face was at first supported by cribs built of 8-inch by 8-inch
timbers about 4 feet long and these cribs were withdrawn and moved
forward as the face advanced, the roof being allowed to fall. A row
of props was also used to support the top above a conveyor used for
carrying the coal along the face. At present the use of cribs has been
discontinued, except along the ribs of the entries, and 10-inch by
10-inch props are used to support the roof. These are drawn and
reset as the face advances. The necessity of using props on both
sides of the conveyor constitutes one of the difficulties of the opera-
tion. The roof breaks as the face advances. There seems to be no
great difficulty in the use of undercutting machines, but sometimes
the coal falls too soon for convenience in loading, and large lumps
clog the conveyor. While this operation must still be considered in
the experimental stage, the working face has been advanced about
130 feet without serious difficulty. It is planned that the pillars flank-

* Elliot, James, " Conditions of the Coal Mining Industry of Oklahoma," Proc. Amer
Min. Cong., p. 221, 1911.

t Scholx, Carl, Personal Communication.

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL 133

ing the long- wall panel, left during the advance, shall be taken out
on the retreat.

37. Texas. — There are three bituminous coal fields and one
lignite field in Texas. In one bitumionus field in the north central
portion of the state, practically all the mines are operated on the
long-wall plan, and the recovery is nearly complete. The two other
bituminous fields are located in the southwestern part of the state
along the Rio Grande. In this district the mines are operated on
the room-and-pillar plan, and the recovery is said to be about 75
per cent. The lignite field extends entirely across the state from the
northeast corner in a southwesterly direction to the Rio Grande. All
lignite mines are worked on the room-and-pillar method, and the
recovery varies greatly in different parts of the state, but 75 per
cent is probably the average.*

38. North Dakota. — J. W. Bliss, State Engineer, estimates that
the recovery in the coal mines of North Dakota is between 70 and
75 per cent. The manager of one mine claims a recovery of about
85 per cent, t

39. Colorado. — The principal producing districts of Colorado
are the bituminous district in the southeastern part of the state, near
Trinidad, and the lignite district just east of the mountains in the
northern part of the state. The bituminous district is the more im-
portant. In the Trinidad district { the average thickness of the
coal is about 6 feet. The top is strong, and the bottom is weak.
Entries are driven to a fixed boundary, and the rooms which are
needed to supply enough coal to keep the driver busy are turned.
When the boundary is reached, rooms are turned at the inby end of
the entry, and pillar drawing is commenced as soon as the rooms
reach their limits. Nearly all the coal is taken out on .the retreat.
Rooms have a maximum width of 18 feet, and room pillars are 32
feet wide. All work is done with picks. The coal is soft and occa-
sionally the pillars crush, but most of the difficulty encountered is
due to heaving of the bottom. The cover averages more than 600

* Gentry, B. S., State Inspector of Mines, Personal Communication.

t Personal Communication.

t Weitzel, B. H., Personal Communication.

134 ILLINOIS ENGINEERING EXPERIMENT STATION

feet in thickness. The output from mines in this district is used
largely in connection with steel making, and operations are very
regular, most of the mines being worked every day in the year. The
recovery at a typical mine in this district, calculated for operations
over a period of several years, is 87.2 per cent.

In the domestic coal district in the neighborhood of Walsenburg,
the average thickness of coal is 5 feet. It is stronger than the coal
in the Trinidad district, and a squeeze is very unusual. The cover
averages about 400 feet in thickness. As a rule the bottom in this
district is stronger than the top, and little difficulty is experienced
from heaving. The work is less regular than in the Trinidad district,
although it is fairly regular except in March and April when the
mines are usually worked about half time. Rooms are driven 25 feet
wide on 50-foot centers. There is little difficulty in drawing pillars.
The tendency in these districts has been to drive narrow rooms and
to leave wide pillars, and this has assisted in increasing the percent-
age of recovery. The extraction in a typical mine in this district,
calculated for operations over a period of several years, is 91.7 per
cent. The chief engineer* of another company operating in this
same district believes the extraction in certain portions of the mines
of his company will reach 80 per cent. In the Canyon district the
long-wall system is used, and the recovery is nearly complete.

40. New Mexico. — No information is available concerning the
percentages of extraction in New Mexico.

41. Utah. — The principal coal fields of Utah are located in
Carbon County.! The main coal horizon has from two to four work-
able beds, from 5 to 28 feet in thickness. The main workable bed,
known as the Castle Gate, varies in thickness from 5 to 20 feet, and
rests on a massive close-grained sandstone. The problem presented by
these deposits is one of mining thick seams, comparatively level or
slightly inclined. Formerly some seams 4% to 8 feet in thickness
were worked, but at present most of the mining is done in seams
varying from 8 to 28 feet in thickness. The physical features to be
taken into consideration in this district are: the number of work-
able seams, the thickness of seams and their relation to one another,

* Personal Communication.

t Watts, A. C., "Coal Mining Methods in Utah," Coal Age, Vol. 10, p. 214 and p. 258 ;
and Personal Communication.

.
PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL 135

the character of the coal, the dip of seams, the character of roof and
floor, cover, faults, dikes, wants, the flow of water, sometimes gas, and
the burned-out coal beds in place with their residual heat.

Throughout most of the fields there are at least two workable
seams, and these are generally found in one coal horizon. In several
sections, however, there are three and sometimes four workable seams
5 feet or more in thickness. The distances between these seams vary
considerably, so that in some sections there are no unusual problems
involved while in others two or more workable seams #re found with so
little intervening strata that the problem of successful extraction has
not yet been solved. There may be, for example, an 8- to 14-foot seam
underlying a 6- to 10-foot seam with about 200 feet of intervening
strata; in another instance a 5- to 8-foot bed lies 60 feet below one
5 to 11 feet thick, and this lies from 12 to 20 feet below a 22-foot
seam, which in turn lies 30 feet below a 6-foot seam. In still another
instance an 11-foot bed is found from 3 to 40 feet below a 6-foot bed.
There is considerable variation in the physical characteristics of
the beds, some being hard and brittle and others tough. In some
instances the cleavage is good, while in others it is not pro-
nounced. Almost without exception the coals are hard to cut, and
some are hard to shoot. The average dip does not exceed 10 per
cent, and in some places the beds are practically flat. As a rule the
floor consists of hard smooth sandstone from which the coal parts
rather readily. In many cases the roof is of shale varying in thick-
ness from a few inches to several feet. Where a sandstone roof is
found, it is generally too hard to break for easy mining. In some
places the cover is more than 2,000 feet thick, and there are only a
few localities in which it is less than 1,000 feet in thickness. This
heavy cover makes the mining of these flat thick seams a serious
problem in itself, but the additional complication of great irregu-
larity in depth and the unyielding qualities of the thick beds of
overlying sandstone make the problem still more serious. A con-
dition which modifies, at least locally, the laying out and working
of a mine is the fact that near the outcrop there are sometimes
found large areas of burned coal. These sometimes extend 2,500 feet
in from the outcrop. Mining in burned areas is often dangerous, if the
burning has been at the top, because of the disintegration of the roof.
With one exception all the mines of the district are opened from
the outcrop by means of slopes of drifts. Where conditions of topog-

136

ILLINOIS ENGINEERING EXPERIMENT STATION

raphy and property permit, main slopes are driven directly on the
pitch of the seams. All mining is by the room-and-pillar method.
An attempt to use the long-wall method in one case failed because
of the unyielding nature of the roof. The double-entry system is
almost universal, although in one case a triple entry is used, and in
some cases the double-entry system has been so modified by the con-
nection of the first rooms on the cross entries that it has become prac-
tically a 4-entry system. In the earlier workings rooms were

CROSSCUT

FIG. 39. PILLAR DRAWING IN UTAH

turned from the cross entries as these were driven, but the system
resulted in the occurrence of bounces, which seem to take the place
of the squeezes that occur with more yielding materials. In later
operations the panel system has been used, and the pillars are drawn
on the retreat.

Methods of drawing pillars are of particular interest, since they
show how almost complete extraction can be attained under condi-
tions which seem unfavorable. These are described by Watts sub-
stantially as follows:

In one method (Fig. 39), the block at the end of the pillar on
the inby side of the cross-cut is divided by another cross-cut driven
through its center, and from the center of this new cross-cut a narrow

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL

137

room which splits the stump into two parts is driven to the gob. The
upper inside stump is taken out first by slices beginning at the inby
end ; then the remaining stump is removed. The lower half of the
original block or pillar meanwhile is split by a narrow road, and the
process is thus continued down the pillar, each block being divided
into four parts.

Pillar drawing in a flat seam 12 to 14 feet thick under a cover
800 feet thick and under a roof which broke fairly well when posts
were removed has been successful! y accomplished by the following

FIG. 40. PILLAR DRAWING IN UTAH

method: 20-foot rooms were driven with 50-foot pillars (Fig. 40),
and a cross-cut was driven through the pillar; thus a 30-foot stump
was left. This 30- by 50-foot stump was then split by a 12-foot room
which left a 24- by 30-foot stump next to the room and a 14- by 30-
foot stump on the other side. The latter stump was then taken out
in slices which begin at the gob, and the roof was supported by props
set every 4 feet. The coal was undercut by hand and shot with
black powder. When this block had been removed, the track was
taken up, and all props were drawn except a row adjacent to the
rib of block No. 3. These blocks were numberd in the order of their
extraction, 1, 2, 3, and 4. Block No. 3 was then taken out from the

138

ILLINOIS ENGINEERING EXPERIMENT STATION

cross-cut to the gob, track was laid in the space, and block No. 4 was
taken out in the reverse direction, that is, beginning at the gob. In
this mine 3 to 6 feet of top coal are left up to protect the roof on the
advance, but this coal is taken down on the retreat. When cross-
cuts are made in pillars preparatory to drawing them the whole
height of the seam is taken.

Pillar drawing in 16-foot coal with a cover of 400 to 1,000 feet,
with no top seam and with the roof breaking well when props are
drawn, is accomplished as follows: Rooms about 400 feet long are

Pillar Line 45°

to Entry
Height of Coal 14 nit

FIG. 41. PILLAR DRAWING IN UTAH

driven straight up the pitch which averages about 10 per cent.
Pillars are drawn 011 the retreat, and the line of break is kept at an
angle of 45 degrees with the entry ; thus work is done on six or seven
pillars at a time. Kooms are about 20 feet wide, and pillars are 50 feet
wide. A cross-cut is driven through the pillar 30 to 35 feet from
the end (Fig. 41) ; thus a block about 25 to 30 feet by 50 feet is cut
off. This block is then split by a room about 12 feet wide. Blocks
1 and 2 are drawn by slicing which begins at the end next to the gob.
The top is supported by means of props at 4-foot intervals, and after
the two blocks have been removed and the track has been taken out,
these props are pulled, and the area is allowed to cave. The track
is then laid in the main room, and blocks 3 and 4 are taken out by

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL

139

end slicing from the room ; then the track is taken out, and the props
are pulled. Another cross-cut meanwhile has been made through
the pillar nearer the entry, and a room has been driven through the
stump so that by the time the first stumps have been extracted, work
is being begun on the lower stumps.

In this mine the size and the systematic placing of props have
an important bearing on the successful recovery of the pillars. Until
heavy pine props were used, trouble was likely to occur at any time.
Now props as large as 10 inches in diameter at the small end with

FIG. 42. PILLAR DRAWING IN UTAH

correspondingly heavy caps and, in some places, cross bars are used.
Props are set at regular distances. Many of these props are recov-
ered and re-used three or four times. By the adoption of this method,
the safety factor is largely increased, the percentage of recovery is
greater, and the product is of better quality. In some cases it is
customary to mark pillars at regular distances so that the mine fore-
man or pillar boss may easily determine the progress of the pillar
work daily and may keep the ends of the stumps in proper align-
ment.

Another method of pillar drawing sometimes used is similar to
that last mentioned, although the stump left is a little shorter. This
stump is then split into quarters, and the work of extraction pro-
ceeds from the cross-cut toward the gob, a thin section of coal being

140 ILLINOIS ENGINEERING EXPERIMENT STATION

left to the last around the edges of the block to prevent the mixture
of fallen roof with clean coal.

A plan which has proved satisfactory, partly because it does not
split the pillar into many small stumps, is illustrated by Fig. 42.
The original block of pillar coal 100 feet wide by 120 feet long is
divided into equal parts by a cross-cut, and the upper half is takeii
out by slicing beginning at the inner side, a curtain of coal being
left to prevent the loading of gob, and one or two rows of props being
put along the side of the coal. Before the track and props are pulled,
most of this section of coal is loaded out. In this case the rooms are
18 feet wide and the pillars 100 feet wide.

Little information is available regarding the percentage of ex-
traction in Utah. There is probably only one mine in the state which
has been worked out, and no reliable information can be obtained
concerning this mine. It is believed, however, that the extraction
was probably about 75 per cent. In coal 12 to 16 feet thick and under
cover varying from 200 to 2,000 feet an extraction as high as 90
per cent has been made, if marketable coal alone is considered. If
all the coal in the bed is considered, the recovery is about 80 per
cent. In beds ranging from 15 to 30 feet in thickness, retreating
work has hardly been started so that no information on total recovery
is available. It is possible that it will be rather low. It could be
made higher if the filling method could be used, but the price of coal
does not warrant the use of this method.

A condition largely influencing the percentage of extraction is
the presence of more than one workable seam with little intervening
material. Under present conditions the percentage of extraction from
an area containing seams with 3 to 12 feet of intervening rock is at
best only 65 per cent of all the coal. In one mine an attempt was
made to take out the coal from two beds, the lower being 11 feet thick
and the upper 5 to 6 feet thick with intervening rock 2% to 12 feet
thick. The workings were in the lower bed, and frequently the roof
caved as soon as the pillars were drawn and practically all the upper
seam was lost.

A. B. Apperson* gives the percentage of extraction in two mines
as nearly 95 per cent of the total seam, while the extraction at another
mine is about 85 per cent. At the mines yielding the lower percent-
age of extraction, the cover is about 800 feet. At one of the mines

Personal Communication.

PERCENTAGE OP EXTRACTION OP BITUMINOUS COAL 141

yielding the higher percentage of extraction, pillar drawing was
commenced at the middle of the mine under a cover of approximately
1,700 feet. A good break is obtained about 50 feet behind the pillar
extending the full length of line. Only small areas have been worked
out in these mines.

42. Washington. — No reliable information is available concern-
ing the percentage of extraction in Washington. Conditions are
somewhat unusual in that most of the coal has been badly folded and
faulted and consequently crushed, and the deposits have been steeply
tilted.* It is impossible to separate the refuse in the mines, and a
large percentage of it has to be washed.

* Daniel, Professor Jos., Personal Communication.

142

ILLINOIS ENGINEERING EXPERIMENT STATION

APPENDIX

DEVELOPMENT OF MINING METHODS IN ENGLAND

AND ON THE CONTINENT

43. Brief History of Coal Mining Practice in England. — It is
interesting to review briefly the history of the coal mining methods
of England, because the mining methods employed in this country
are largely applications of methods developed in England and brought
over by miners.

The many methods of obtaining coal may be grouped on the basis
of recovery under two main headings : one in which the whole of the
coal seam is taken out in the first working, and another in which

FIG. 43. BELL PIT

only a part of the seam is removed in the first working. These may
be called the no-pillar, or long-wall, system and the pillar system.

The earliest mining was naturally done on the outcrop of the
seams, and as this practice became difficult or. impossible, the use of
"bell-pits" (Fig. 43) was developed. These were holes or shafts,
from 3 to 4 feet in diameter, which were sunk through the shallow
overburden near the outcrop and widened out at the bottom in order
to allow the excavation of as much coal as possible without permit-
ting the roof to fall in. It was of course impossible to extract much
coal from a pit of this kind, and in order to obtain the coal even
from a small area it was necessary to dig a large number of pits.
This method was gradually abandoned, and the coal was worked
by means of galleries driven out from the bottom of the shaft, usually
in an unsystematic manner; thus began the use of pillars to sustain
the roof. The driving of galleries permitted the working of much

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL

143

greater areas than could be reached from the bell-pits; however, no
areas of more than a few acres were worked from one shaft, nor
were systematic ventilation and regularity in laying out the work-
ings introduced until the exhaustion of the shallow coal made neces-
sary a study of methods to be employed in deeper workings. Until
the introduction of the Newcomen engine, when pumping by steam
power became possible, shafts were rarely as deep as 200 feet; they

FlG. 44. BORD-AND-PlLLAR

were 7 or 8 feet in diameter, and the area worked from one shaft was
seldom more than 600 feet in radius.*

The structure of many coal seams is such that there are two direc-
tions, determined by the cleat of the coal, in which the seams can be
most easily worked. The direction at right angles to the face cleats
is known as "bordway," while the other direction approximately at
right angles to the first is known as "headway." The excavations
made in a direction at right angles to the principal or face cleats

* Bulman and Redmayne, " Colliery Working and Management," p. 3, 1906.

144 ILLINOIS ENGINEERING EXPERIMENT STATION

were called bords, and, as the coal was most easily taken out in this
direction, these excavations were made wider than the connecting
passages or headways. The coal left in place to sustain the roof
was called pillars; thus originated the term, "bord-and-pillar"
method, which in its various developments is commonly known in
this country as the room-and-pillar method. This method was
developed in different forms in England and was variously called
"bord-and-pillar," " bord-and-wall, " ' ' post-and-stall, " and "stoop-
and-room. ' '

In early times the "pillars" were probably made very small and
square measuring from 3 to 6 feet each way. In the eighteenth cen-
tury the bords were usually made 9 feet wide and the pillars 12 feet

FIG. 45. STOOP-AND-KOOM

wide, though they were of course irregular. The bords were com-
monly widened out between the headways (Fig. 44), and the pillars
were thus gouged to as great an extent as was considered safe, it
being desirable, in view of the comparatively small area which could
be reached from a single shaft and in view also of the inadequate ven-
tilation, to extract as much coal as possible within the area worked.
This method of working was essentially wasteful as not much more
than 50 per cent of the coal was obtained, and since the pillars left
were unable to bear the weight of the cover, they were soon crushed
and further working was made impossible.* Possibly a larger per-
centage of coal was taken out in some places as Redmayne t says it
was rare that more than 65 per cent of the available area could be

* Boulton, W. S., " Practical Coal Mining," Vol. 1, p. 296.

t Redmayne, Rr A, S., "Modern Practice in Mining," Vol. 3, p. 82.

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL 145

extracted; but he refers to John Buddie as saying, at a somewhat
later period when the pillars were 18 by 66 feet, that not more than
45% per cent of the contents of a fiery seam could be obtained under
any method of working then known. It was not until much later
that the exhaustion of the most easily worked deposits directed atten-
tion to the desirability of higher extraction.

A system with square pillars and working places of almost uni-
form width (Fig. 45) has continued in common use at Whitehaven
and in Scotland down to the present time. In the north of England
the pillars were usually oblong, probably because the highly devel-
oped face cleat of the coal made the extraction in one direction much
easier than in others.* The lengthening of the pillars reached its
greatest extent in South Wales where cross holing was so little em-
ployed as scarcely to form a part of the system of working.

The date at which the extraction of pillar coal was begun is not
known, but it seems certain that pillars were removed in the north
of England before 1740. The following statement! is made concern-
ing the removal of pillars: — "The documentary evidence cited goes
to show that, previous to 1708, the general practice was to leave
small pillars of coal standing for the support of the roof; 30 years
later pillars were being partially, sometimes entirely, removed; and
during the remainder of that century, in mines free from gas, a
second working of the pillars was frequently carried out. In the
deeper and fiery collieries, which began to be developed about the
middle of the eighteenth century, the risk of creep as well as of gas ex-
plosions prevented the removal of the pillars. The invention of
the safety lamp, improvements in ventilation, and the formation
of much larger pillars in the first working .... were introduced
during the first 30 to 40 years of the present (nineteenth) cent-
ury .... which enabled the pillars to be removed in a second work-
ing."

Concerning the size of pillars, Jars, a French engineer who pub-
lished "Voyages Metallurgiques " in 1774, says in "A Journey
Through the North of England," that underground pillars of coal
were made from 39 to 54 feet square, and that working places were
from 5 to 16 feet wide. At this time the pillars were left until all the
coal was. exhausted. Another traveler who made a tour of Scotland in

* Galloway, R. L., "Annals of Coal Mining and the Coal Trade," p. 18i, 1898.
t Bulman and Redmayne, "Colliery Working: and Management." p. 14. 1906.

146 ILLINOIS ENGINEERING EXPERIMENT STATION

1772 said that pillars 45 feet square were left and that not more than
one-third of the coal was worked.*

The extraction of a portion of the pillars in gassy mines by a
second working was just beginning to be a regular part of the bord-
and-pillar system at this period. It could, however, be effected only
in a very incomplete manner so long as the miners had to depend
upon candles and steel mills for light. At this time also the extensive
adoption of the long- wall system began, t

In the early part of the nineteenth century little change seems
to have been made in the size of pillars used in the Newcastle district,
according to a statement of an author who speaks of them as being

60 by 27 feet or, in some instances, 27 feet square. About this time
the drawing of pillars seems to have become common in Northumber-
land, as Mackenzie, who wrote a "View of Northumberland" in
1825, speaks of the mode of working coal as being much improved
in the last few years. He says (second edition, page 90), "from
seven-eights to nine-tenths of the coal is at present raised, whilst
formerly but one-half, and frequently less, was all that could be ob-
tained." No doubt this statement refers to the general practice of
removing pillars, which had been made practicable in gassy mines
by the invention of the Davy lamp.

Conflicts of interests between coal producers and owners of the
surface are of early record. It was, of course, the desire of the
colliers to remove as much of the coal as possible, even where the
surface was supposed to be maintained, and the result of making
pillars too small was subsidence. There is probably no definite rec-
ord of the first occurrence of subsidence, but one of the earliest
mining leases written in the English language, dated 1447, indicates
that it was the custom to leave pillars to sustain the surface and that
subsidence had already taken place. J

In the latter part of the eighteenth century the working of pillars
in a fiery mine, such as Wallsend Colliery, was not considered prac-
ticable, and only about 39 per cent of the coal was obtained while

61 per cent was permanently lost. This coal was at a depth of 600
feet, and the workings represent the best practice of the bord-and-
pillar system at that period.fi

* Galloway, R. L., "Annals of Coal Mining and the Coal Trade," p. 353, 1898.
t Ibid, p. 362.
t Ibid, p. 69.
I Ibid, p. 393.

PERCENTAGE OF EXTRACTION OP BITUMINOUS COAL 147

Until about the end of the eighteenth century an extraction of
45.5 per cent was considered the maximum which could be obtained
in the deep collieries of the Tyne.* The first person to offer a par-
tial remedy for this very unsatisfactory condition was Thomas
Barnes, viewer of Walker Colliery, who projected a scheme in 1795
for recovering a portion of the pillars without causing loss of the mine.
This system provided for dividing the workings into small sections
of 10 to 20 acres and isolating these with artificial barriers formed by
filling the excavated spaces with stones and refuse for a breadth of 120
to 150 feet. By this method one-half of alternate pillars, or one-quarter
of the remaining coal, was removed, and the percentage of extraction
was increased from about 39 to about 54 per cent. Wherever pillars
were thus removed, a squeeze was brought on, but the barriers kept it
from spreading. This method proved to be successful, and it was
adopted at other collieries.

Probably about this time the pillars at Wallsend Colliery were
left larger as a preparatory step toward a second working. Buddie
said that after about one-third of the colliery had been worked by
means of 36-foot winnings (12 feet to the bord, 24 feet to the wall or
pillar) in which no more coal was left in pillars than was consid-
ered sufficient to support the roof, the size of the winnings was in-
creased to 45 feet (15 feet to the bord and 30 feet to the pillar).
"This change of size," he said, "was not made for the purpose of
obtaining a greater produce in the first working of the seam. But the
notion of the future working of the pillars then began to be enter-
tained, and the increased size of the winnings was considered a more
favorable apportionment of the excavation and pillar for the attain-
ment of this object." This is the first record found of a second
working in the deep Tyne Collieries, t Pillars seem to have been
worked in the northern part of England about the middle of the
eighteenth century.

44. Ventilation. — The distance to which workings could be driven
and the extent to which pillars could be drawn, especially in gassy
mines, were found to depend largely upon ventilation. In the latter
half of the eighteenth century improvements in ventilation, which
had been used earlier in the Cumberland field, were introduced into

* " Trans. Nat. Hist. Soc. of Northumberland," Vol. 2, p. 323.

t Galloway, R. L., "Annals of Coal Mining and the Coal Trade," pp. 315-318, 1898.

148 ILLINOIS ENGINEERING EXPERIMENT STATION

the north of England, where the frequency of explosions made better
ventilation necessary. Until this time it had been considered suffi-
cient to conduct the air current along the working face, an arrange-
ment known as " face-airing;" consequently, the worked-out places,
which were behind the miners in advancing work, were left without
ventilation. As long as the extent of workings was very limited,
this method was not attended with great danger; but, as the mines
became deeper and more gassy, workings were made larger and the
danger from this inadequate ventilation increased, because the worked-
out places became magazines for the accumulation of fire damp.

The improved method of ventilation, which was known as "cours-
ing the air," consisted in so directing the air that the whole current
passed through all the openings in the mine. While this method was
effective in preventing the accumulation of standing gas, it intro-
duced a great danger in that the air took up constantly increasing
quantities of gas in its passage through the mine, and, since it was
constantly exposed to the lights of miners, it became dangerous in
the latter part of its course. It was, moreover, constantly contami-
nated by the breathing of men and animals and by the smoke from
the candles. This method was introduced in the north of England
about 1765 or 1766, and it was about this date that the steel mill
also was introduced for the purpose of giving light.* Though this
method was fairly satisfactory in small mines, it was very unsatis-
factory in large ones. At Walker Colliery, although the pits were
only half a mile apart, the air current traversed a line exceeding
thirty miles in length. At Hebburn Colliery the air course was also
said to be not less than the same length. Not only was it difficult to
keep the air passages open and the doors and stoppings tight, but
the friction of the air limited the velocity of the ventilating current,
which would have been low at best since the force causing this cur-
rent was supplied only by a furnace. At this colliery the circulation
of five or six thousand cubic feet of air per minute was considered
sufficient, and the velocity was about three feet per second.

45. The Panel System. — There was great difficulty in carrying
on work in the deep collieries of the North, because squeezes occurred.
A method of working described as common in the North at this
period consisted in having bords 12 feet wide and 24 feet apart

*Galloway, R. L,., "Annali of Coal Mining and the Coal Trade." p. 279, 1898

PERCENTAGE OF EXTRACTION OP BITUMINOUS COAL 149

connected by headways 60 feet apart, thus leaving pillars of coal
24 by 60 feet. Another size of pillar given is 30 by 72 feet.*

Early in the nineteenth century, John Buddie, Jr., who had suc-
ceeded his father as manager at Wallsend and who was responsible
for important improvements in coal mining methods, devised and
put into practice improved methods of working and ventilation
whereby squeezes were effectually kept in check, and the existing
system of ventilation was greatly improved. He effected these im-
provements by dividing the workings into independent districts or
panels, as Barnes had done. Buddie's idea, however, was to provide
for confining the movement by separating the districts or panels
with barriers of solid coal left in the first working. This method
was adopted in developing the Wallsend G pit in 1810. Buddie's
improvement in ventilation involved dividing or splitting the cur-
rent. This method of ventilation proved successful and was quickly
adopted at other mines to which it could be applied, but the air
currents employed were still very feeble.

From the preceding descriptions it will be seen that all the essen-
tials of the room-and-pillar system as now practiced in this country
had been developed in Great Britain prior to 1810.

46. Square Work of South Staffordshire. — In the Thick seam of
South Staffordshire where the coal varies in thickness from 18 to
36 feet, a method which bears a close resemblance to the panel method
was developed. The district had been greatly troubled with fires
due to spontaneous combustion, and in order to extinguish these
fires easily or to confine them within the immediate vicinity of their
origin this method, known as " square work," was developed. It
consists in dividing the area to be worked into a number of large
chambers termed ' ' sides-of -work, " surrounded on all sides by panels
of solid coal known as "fire ribs." The only openings in these
panels are those necessary for the extraction of coal and for venti-
lation. The panels are nearly square, and from four to sixteen pil-
lars, the number varying according to the size of the chamber, are
left to support the roof. Fig. 46 shows an old form of square work.
Under the system in its simple form and in the first working, only
from 40 to 50 per cent of the available coal is recovered, but
the larger portion of that left is recovered by second or even third

*Ibid. p. 395.

150 ILLINOIS ENGINEERING EXPERIMENT STATION

workings carried out after the lapse of some years. The final loss
in working may, therefore, not exceed 10 per cent of the available
coal ; the coal recovered in these later workings, however, is frequently
badly crushed.*

47. The Long-wall System. — The other general method of coal
mining, the long-wall method, has been from early times prevalent
in Shropshire, from which district it has spread into others. The
date of the origin of this method is doubtful, but it is said to have
been in general use in the Shropshire district about the middle
of the nineteenth century, t

Fio. 46. OLD SQUARE WORK

The long-wall method of mining has been highly developed in
England and Scotland and has been applied at greater depths
and to thicker beds of coal than it has been in this country. Con-
sidered from the point of view of completeness of extraction, the
system fulfills the highest requirements: It not only permits, but
requires the excavation of the whole bed of coal. Whether all
the coal shall be taken out of the mine depends of course on whether
it is marketable.

This method of working has not been as generally applied in
the United States as have the various forms of the room-and-pillar
system. There are, however, certain districts in which it is used
almost exclusively. Among the most prominent of these is the
long-wall district of Illinois which has been described as District I
in Chapter II. The other districts in which the long-wall method
is used are those of northwest Missouri, nprtheast Kansas, the

* Redmayne, R. A. 8., " Modern Practice in Mining," Vol. 3, p. 116.
t "Trans. North of Eng. Inst. Min. Engrs.," Vol. 2, p. 261.

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL 151

Osage district of Kansas, the Appanoose district of Iowa, the north-
central district of Texas, and the Canyon district of Colorado.
Scattering applications of the method are found elsewhere, but
the physical conditions in the regions mentioned have been best
suited to its use. It seems probable that the long-wall system, with
modifications perhaps, will be more widely used in this country in
the future.

48. Percentage of Recovery in England. — The methods followed
in England have not been developed with the purpose of obtaining
a high percentage of recovery. It was not until 1854* that a special
department for collecting and publishing mineral statistics was cre-
ated, and not until 1861 that any systematic estimate of coal re-
sources was made. About this time predictions forecasting the
exhaustion of the coal supply within a century caused a great dis-
turbance, and a royal commission was appointed in 1866. A report
of this commission was made public in 1871.

The part of this report which deals with waste in working is of
special interest. The commission estimated the " ordinary and un-
avoidable loss" to be about 10 per cent, though they said, "In a
large number of instances, when the system of working practiced
is not suited to the peculiarities of the seams, the ordinary waste
and loss amount to sometimes as much as 40 per cent." The princi-
pal part of this unavoidable waste arises from the crushing of pillars.

In addition to this unavoidable loss, there is waste or loss, variable
in amount, but sometimes very great, arising from the following
causes :t

(1) The leaving below ground or consuming in large heaps of
small coal on the surface (presumably the loss from this source is
much less at present because of the greater consumption of small
sized coal, as in this country).

(2) Undercutting, often wastefully made, in good coal.

(3) The leaving, either wholly or in part, of an adjoining or
neighboring bed when it becomes crushed and unworkable, because
it is not wanted at the time, or because if it should be worked, the
cost per ton of the coal extracted is increased.

* Digest of the Evidence given before the Royal Commission on Coal Supplies, Vol. I..
p. IX., 1905.

t Ibid, p. XXXIII.

152 ILLINOIS ENGINEERING EXPERIMENT STATION

(4) Existence of coal on properties which are too small to be
worked alone or in small parts of colleries cut off by a large fault.

(5) Disputes over the cost of drainage.

(6) The breaking in of water from the sea or from a river
estuary.

(7) The leaving of barriers around small properties or crooked
boundaries.

(8) Lack of plans or records showing the extent of old work-
ings, operations of seams not sufficiently proved to justify expendi-
ture for sinking pits; sufficient information might have been
obtained if records of previous explorations had been preserved in
available form.

(9) The piercing of water-bearing strata by shafts and bore
holes which are not protected by water-tight casings, or are not care-
fully filled and puddled when temporarily left or abandoned.

(10) The cutting through of main faults serving as natural
barriers to keep back water and the consequent flooding of the coal.

(11) The leaving of large areas of coal in populous and manu-
facturing districts to support the surface and the buildings.

While some of the causes mentioned do not apply directly to con-
ditions in this country, the list furnishes a complete synopsis of
reasons for coal losses.

Since the issuance of the report of 1871, there have been great
improvements in the methods of getting coal. At the present time
the long-wall system is in general use, and the waste has been
lowered; yet in some parts of the United Kingdom, notably North-
umberland, the pillar-and-stall system is still in general use.

Among the factors contributing to a higher rate of recovery is
the greatly increased value of small sizes of coal. It was computed in
1871 that the average value of the small coal mined in Great Brit-
ain was only 60 cents per ton, while in 1905 the small sizes of steam
coal from the South Wales district brought about $1.90 per ton; in
all the other coal fields the value has been doubled and even trebled.
The principal cause of this change lies in the improved preparation
of coal. The manufacture of producer gas on a large scale and
the growth of the briquet industry have also increased the possible
uses of the small sizes. One of the effects of the increase in the
value of small coal has been some decrease of the comparative ad van-

PERCENTAGE OP EXTRACTION OF BITUMINOUS COAL 153

tage of the long-wall system, since the production of a large amount of
fine coal with the pillar-and-stall system is less objectionable than
formerly.*

Interest in the subject continued, and another investigation, more
exhaustive than the earlier one, was made by the Koyal Com-
mission on Coal Supplies which organized in 1902 and presented
its report in 1905. The Royal Commission of 1905 adhered to the
limit of depth, namely 4,000 feet, established by the earlier com-
mission. It was thought that, although there might be no insuperable
physical or mechanical difficulties in the working of beds at greater
depths, the expense would be so great that imported coal could be
obtained more cheaply. . < f

With regard to thickness, the commission which reported in 1871
had included seams exceeding one foot in thickness as workable. The
question is largely a commercial one, and thinner seams are being
worked now than formerly. Mr. Gerrard, inspector of mines for
the Manchester district, obtained from all the inspection districts
returns which showed that in 1900 17.7 per cent of the entire output
was taken from seams not exceeding three feet in thickness, t In
the United States, limits of 3,000 feet in depth and of 14 inches in
thickness have been decided upon by the Department of the Interior
as factors determining what portions of the remaining public lands
shall be considered coal lands. J

The Royal Commission took evidence also on the cost of working,
and gave figures which show how greatly the labor cost rises and the
individual output declines as thinner beds are mined. Mr. Gerrard
gave the underground wages as ranging from $1.68 to $2.28 per ton
in seams up to 12 inches, and from 63 cents to $1.36 in all under-
ground seams in his district from 1 foot, 1 inch to 3 feet, while
the daily output ranged from one-half ton to 3!/4 tons. It was
estimated that the cost of digging, loading, and hauling in Scotland
was $1.24 for a seam 14 to 15 inches thick, and 65 cents for one from
2 to 2y2 feet thick, while the daily output varied from 22 hundred-
weight to 1% tons. In Somersetshire the average cost of working
thin seams has been about $1.92 per ton for a number of years, while

*Digest of the Evidence given before the Royal Commission on Coal Supplies. Vol. I.,
p. XXV., 1905.

t Digest of the Evidence given before the Royal Commission on Coal Supplies, Vol. I.,
p. XXXV., 1905.

t Fisher, Cassius A., "Standards Adopted for Coal Lands of the Public Domain." U. S.
Geol. Sur., Bui. 424, Ashley and Fisher, p. 63, 1910.

154 ILLINOIS ENGINEERING EXPERIMENT STATION

in Yorkshire the cost in 1900 varied from about 96 cents to $1.68.*
The Commission of 1905 finally decided to retain the figure of one foot
as the limit of thickness.

In connection with the subjects of depth and thickness, it should
be noted that it is not the practice in Europe to work single thin
beds at great depths. The thin beds are worked in conjunction with
thicker ones, and it is the lower cost of production in the latter which
makes the working of the thin ones commercially possible. The high
cost of working thin beds is partly responsible for the high cost of
European coal. The American practice is distinctly different, for
there are few, if any, districts in this country in which any bed of
bituminous coal is worked unless it is believed that such working
shows a profit without reference to other workings. Instances of
the working of more than one bed of bituminous coal from the same
shaft are rare in the United States.

49. Percentage of Coal Lost. — A detailed inquiry was made by
the Royal Commission into the various sources of loss. The points of
greatest interest in connection with the present study were covered
as follows :t

"Coal left for Support. — It is evident, that, except in very special
cases, it is not possible to remove all the coal. A certain amount must
be left in order to maintain shafts, etc., and to support the surface
— as, for instance, under houses, railway, canals and rivers — and there
seems little hope under existing circumstances of avoiding this source
of loss. The amount of coal left for support depends largely upon
whether its value is greater than the damage, which would be caused
by its removal. .

"Barriers. — We have evidence that much coal has been and is
lost through the practice of leaving unnecessary barriers between roy-
alties and properties; but the present tendency to take large areas
under lease is reducing the loss from this cause, and in many cases
barriers between properties are now worked out by mutual arrange-
ments.

"Thick Seams. — Where the seams are of abnormal thickness much
coal is, in some cases, wasted, and for various reasons. Sometimes it

* Digest of Evidence given before the Royal Commission on Coal Supplies, Vol. I., p. 178
et seq., 1905.

t Digest of the Evidence given before the Royal Commission on Coal Supplies, Vol. I.,
p. XXXVI., 1905.

PERCENTAGE OF EXTRACTION OP BITUMINOUS COAL

155

is considered that the whole seam cannot be taken out with safety,
and part is therefore left to form a roof. Further, such thick seams are
more difficult to work, and when the whole of the seam is not of the
same quality, there is a temptation to take out the best coal first and
to leave the rest for possible future working. Suggestions have been
made by some of the witnesses as to the best method of working such
thick seams, and there is little doubt that improved methods com-
bined with the increasing use of inferior coal will to a large extent
obviate the difficulties mentioned.

"Inferior and Small Coal Left in Mines. — According to the evi-
dence inferior coal is frequently left in the mine owing to its being
unsalable, and in some districts considerable quantities of small coal
are also left. In recent years there have been vast improvements in
the methods of, and the appliances for, preparing and utilizing small
and inferior coal, and the higher appreciation of such coal should
£0 far to put an end to this waste. "

Table 10 presents the conclusions of the commissioners of different
districts regarding the deductions which should be made to cover
losses in calculating the amount of coal remaining available.* It is
to be understood that the values given do not refer merely to the losses
within a definite mined-out area but to the total losses which are to be
expected in extracting the total coal remaining available. Since both
amounts of losses and reasons for them are governed largely by local
conditions, it is unnecessary to go into details, especially since it was
found impossible there, as it has been here, to arrive at definite state-
ment for the losses in all cases. Values, however, are founded upon
the opinions of men familiar with the practice in the districts, and
they are at least approximately correct.

TABLE 10

PERCENTAGES OF COAL LOSSES AS ESTIMATED BY THE
ROYAL COMMISSION OF 1905

District

Per Cent
lost

District

Per Cent
lost

District

Per Cent
lost

South Wales and
Monmouthshire

20 68

Warwickshire
Leicestershire

2.20
26.00

Northumberland
Durham

22.61
20.23

15 50

Lancashire

20 70

Cumberland

28.20

North Staffordshire

17 00

18 70

Scotland

26 20

1 o oo

27 60

South Staffordshire

27 50

33 30

Average . .

21.28

Ibid, p. XXV.

156 ILLINOIS ENGINEERING EXPERIMENT STATION

In the introduction to the report of the Commission, prepared by
the editor of the " Colliery Guardian, " it is stated (p. xxvi), " Much
of the evidence goes to show that the more general adoption of the
long-wall system in recent years has resulted in an increased yield of
coal. But there are many localities where the conditions are not con-
sidered favorable to long-wall working, and where pillars are still left.
In the worst cases, in exceptionally bad ground, as much as 50 per
cent of the coal is often left behind for this purpose, only to be crushed
and oxidized and rendered unfit for future recovery. In the under-
sea workings in Cumberland as much as 75 per cent is thus left behind.
Perhaps the most interesting point brought out in the evidence is
that which concerns thick seams. It certainly does seem unfortunate
that where there are 9 feet of good coal in a single seam, nearly one-
third of this should be left behind. Yet this happens in many of our
thickest seams, and the loss threatens to be still more serious as the
depth increases."

50. Mining Conditions on the Continent. — In the Franco-Belgian
basin the beds are for the most part thin, and they are worked, to
a considerable extent, at greater depths than those reached in the
United States. In Westphalia the beds are mostly steeply dipping,
and in Upper Silesia there are combinations of steep dip with great
thickness of coal. The development of mining methods in the United
States up to the present time has not been affected by practice in
these districts.

51. Percentage of Extraction on the Continent. — In France it
is the custom to extract as much coal as possible from the bed and to
fill the resulting space with rock or other material. The filling mate-
rial is usually transported to its destination in cars, and the method
of packing depends largely on the inclination of the bed. In steeply
dipping beds the material is allowed to run into place by gravity, but
where the slope is not sufficient to permit this method of packing, it
is packed by hand. This custom does not entirely prevent subsidence,
but it permits the extraction of nearly all the coal without serious
disturbance of the surface. While the method of packing followed
in these districts permits the removal of nearly all the coal, the re-
moval is accomplished at an expense which would be regarded as pro-
hibitive in the United States in view of the narrow margin between

PERCENTAGE OF EXTRACTION OP BITUMINOUS COAL 157

cost of production and selling price here. The method of filling by
flushing is coming into use in France, but has not yet displaced dry
filling in most of the mines. Whatever system of filling is used,
and whether the coal is taken out by pillar or long-wall method, the
extraction is nearly complete.

Some of the most difficult problems found in any coal mining dis-
trict have been encountered in Belgium. There is no other country
in which such thin seams are worked and in which coal is generally
mined at such great depths. At Quaregnon a series of thirty-three
seams is worked, the average useful thickness being 1 foot, 3% inches,
while the greatest thickness is 2 feet, 2 inches. These beds vary in
dip from 8 to 90 degrees. The flatter portions of the bed are worked
by long-wall, and the steeper parts by inverted steps forming an
interrupted long-wall face. Other beds of nearly the same thickness
are being worked, and it appears in all cases that those thin beds
are attacked by some form of long-wall working in which, of course,
the extraction is practically complete.* The discussion of these
districts is much briefer than their importance as coal mining dis-
tricts would warrant were it not for the fact that the methods used
would not in general be adaptable to physical and commercial condi-
tions in this country. They furnish interesting illustrations of high
percentages of extraction under difficult conditions, but can hardly be
regarded as indicative of what it would be possible to do in the
United States.

In the Westphalian district in Germany large amounts of coal
have been lost, not so much as the result of poor mining methods or
lack of attention to completeness of extraction as because of the neces-
sity of preventing subsidence of the surface. This region is one of
great industrial activity, and surface values have so increased within
the last half century that high extraction without filling has become
impossible. At first, hand filling was employed, the material used
being the waste produced in the large amount of rock excavation neces-
sary in beds lying at various angles combined with slack from collieries
where coke was not made. More recently the method of hydraulic
filling has been introduced. Where the packing is well done and the
mining conditions are favorable, the loss of coal is possibly not more
than five per cent, which may be considered a fair estimate of the

* Digest of the Evidence given before the Royal Commission on Coal Supplies, Vol. I.,
pp. 41, 76, 393, 1905.

158 ILLINOIS ENGINEERING EXPERIMENT STATION

loss even where the long-wall method is followed. There is, however,
a greater loss in some of the thicker steeply dipping beds, though it
has not been possible to obtain estimates of the amount.

The Upper Silesian coal field,* situated in the southeast corner of
Prussia and extending into Austria and into Russian Poland, has an
area of 2,160 square miles. The character of the seam varies consid-
erably both in composition and in thickness, and thick seams occur
only in the northern portion of the field where they are very numerous
and many of which are of great thickness.

In this coal field, the problem of removing coal beds of great aggre-
gate and individual thicknesses without serious disturbance of the
surface has been met by the development of sand flushing processes
of filling. This method of filling was borrowed from the anthracite
district of the United States where it had first been used.

The mines are worked with and without sand filling. In the method
without sand filling much coal is left unworked in the form of pillars
and as support under towns or villages. There is a considerable loss
resulting from the -difficulty of extracting coal left as barriers between
the working places and in the old workings. There is also a consider-
able loss because of fire. The estimated total loss under this method is
25 per cent.

At present sand filling is being used more or less extensively in
most of the mines in the thick beds. It is especially advantageous
where spontaneous combustion is prevalent and where surface support
is necessary. With sand filling when only a part of the coal is re-
placed by sand it is estimated that the loss of coal is 10 to 15 per cent ;
with complete replacement of coal by sand filling, the loss is only from
3 to 5 per cent. Smaller and cheaper timber is used in this case, and
the greater portion of this timber is recovered for future use. In four
mines in Upper Silesia in which sand filling is used extensively and
in sufficient quantities to suit the conditions of the mines, the cost in
the seams is between 12 and 18 cents per ton. The cost is variable,
however, and is calculated in different ways. The average working
cost per ton of coal at the surface in this district is $1.51, of which
37 cents is for underground labor.

A report by J. B. Hadesty f shows that the sand filling system has
not yet been adopted on a large scale in the western part of Europe,

* Gullachsen, Berent Conrad, " The Working of the Thick Coal Seams in Upper Silesia,"
Trans. Inst. Min. Engrs., Vol. 42, p. 209, 1911.

t " Pennsylvania State Anthracite Mine Cave Commission Report," Journal Pa. Legis
lature, Appendix, 1913.

PERCENTAGE OF EXTRACTION OF BITUMINOUS COAL 159

and the statements on cost of filling show that it would be impossible
to adopt the process in the United States without materially increasing
the cost of production.

It is unnecessary to go into the methods of mining and the results
obtained in other coal producing districts. While there are great
coal deposits in other parts of the world, and while large quantities of
coal are produced, these regions have not been developed sufficiently
to work out what may be called a settled practice. No other districts,
moreover, are really large producers of coal in the same sense as those
already considered. The problems to be considered in connection with
districts only partially developed, or districts which though well devel-
oped supply only a limited market, are different from those in this
country, and the results in such districts are no indication of what
can be accomplished here.

160 ILLINOIS ENGINEERING EXPERIMENT STATION

BIBLIOGRAPHY

Books

Boulton, W. S. " Practical Coal Mining. ' ' Vol. 1, 1913.
Bulraan and Bedinayne. " Colliery Working and Management." 1906.
de la Goupilliere, Haton. " Cours d' Exploitation des Mines." 1907.
Galloway, B. L. "Annals of Coal Mining." Series I., 1898.
Galloway, R. L. "Annals of Coal Mining." Series II., 1898.
Galloway, W. " Lectures on Mining." 1900.
Heise-Herbst. " Bergbaukunde. "

Hughes, H. W. "A Text Book of Coal Mining." 1904.
Mayer, L. W. " Mining Methods in Europe." 1909.
Pamely, Caleb. ' ' Colliery Managers ' Handbook. ' ' 1891.

Redmayne, B. A. S. " Coal — Its Occurrence, Value, and Methods of Boring.'
Modern Practice in Coal Mining." Vol. I., 1908.

GENERAL

Chance, H. M. "A New Method for Working Deep Coal-Beds. ' ' Trans. Amer.

Inst. Min. Engrs., Vol. 30, p. 285, 1900.
Conner, Eli T. ' ' Anthracite and Bituminous Mining. ' ' Coal Age, Vol. I., pp. 2,

42, 76, 170, 277, 1911-12.
Edwards, J. C. and Gibb, H. M. "An Ideal Method of Mining." Coll. Eng.,

Vol. 33, p. 665, 1913.
Edwards, J. C. " Machine Mining in Room Pillars." Coll. Eng., Vol. 34,

p. 591, 1914.
Grady, Win. H. " Cost Factors in Coal Production." Trans. Amer. Inst. Min.

Engrs., Vol. 51, p. 138, 1915.
Grady, W. H. " Some Details of Mining Methods with Special Reference to

the Maximum of Recovery." W. Va. Coal Min. Inst., Dec., 1913; Coal Age,

Vol. 5, pp. 126, 156, 1914.
Gresley, W. S. " Rib Drawing with Machines. ' ' Mines and Minerals, Vol. 21,

p. 82, 1900.

Hall, R. D. " Permanent Roof Sustention." Coal Age, Vol. L, p. 481, 1911.
Hall, B. D. " Squeezes in Mines and Their Causes." Mines and Minerals,

Vol. 30, p. 286, 1909.

Hesse, A. W. " Maximum Coal Becovery. ' ' Coll. Eng., Vol. 35, p. 13, 1914.
Knox, George. " Hydraulic Filling as Boof Support." Coll. Eng., Vol. 34,

p. 225, 1913.
Knox, George. ' ' Belation of Subsidence to Packing. ' ' Coll. Eng., Vol. 34,

p. 87, 1913.
Parker, E. W. " Conservation of Coal in the United States. ' ' Trans. Amer. Inst.

Min. Engrs., Vol. 40, p. 596, 1909.
Payne, Henry M. "American Long-wall Mining Methods." Eng. and Min.

Jour., Vol. 90, p. 1020, 1910.

PERCENTAGE OF EXTRACTION'1* OF BITUMINOUS COAL 161

Eice, George S. " Mining Costs and Selling Prices of Coal in the United States
and Europe with Special Reference to Export Trade. " Second Pan-Ameri-
can Scientific Congress.

Unsigned. " Width of Room and Pillar." Mines and Minerals, Vol. 26, p. 107,
1905. (Gives dimensions of workings, characteristics of beds, percentage
of extraction, etc.)

Weeks, Joseph D. " Some Fuel Problems." Trans. Amer. Inst. Min. Engrs.,
Vol. 25, p. 943, 1895.

SUBSIDENCE

Knox, George. " The Relation between Subsidence and Packing, with Special
Reference to Hydraulic Packing of Goaves." Trans. Inst. Min. Engrs.,
Vol. 44, p. 527, 1912-13.

UNITED STATES

ALABAMA

Hutchins, Neill. ' ' Kellerman Mine, Kellerman, Alabama. ' ' Mines and Min-
erals, Vol. 31, p. 204, 1910.

Strong, J. E. "Alabama Mining Methods." Mines and Minerals, Vol. 21,
p. 195, 1900.

Unsigned. ' ' Mine of Birmingham Fuel Company at Townley, Alabama. ' ' Coal
Age, Vol. 5, p. 524, 1914.

ALASKA

Payne, Henry M. " Coal Mining in Yukon Territory." Coll. Eng., Vol. 35.
p. 133, 1914.

ARKANSAS
Steel, A. A. " Coal Mining in Arkansas." Ark. Geol. Sur.

CALIFORNIA

Horsewill, F. J. " Tesla Coal Mines." Mines and Minerals, Vol. 19, p. 146,

1898.

COLORADO

Herrick, R. L. " Coal Mining at Primero, Colorado." Mines and Minerals,
Vol. 30, p. 598, 1910.

Whiteside, F. W. " The Delagua Mines. ' ' Mines and Minerals, Vol. 29, p. 317,
1909.

ILLINOIS

Andros, S. O. " Coal Mining in Illinois." 111. Coal Min. Invest., Bulletin 13,

1915.
Andros, S. O. " Coal Mining Practice in District I. (Long-wall)." 111. Coal

Min. Invest,, Bulletin 5, 1914.
Andros, S. O. " Coal Mining Practice in District II." 111. Coal Min. Invest.,

Bulletin 7, 1914.

Andros, S. O. " Coal Mining Practice in District III." 111. Coal Min. Invest.,

Bulletin 9, 1915.
Andros, S. O. " Coal Mining Practice in District IV." 111. Coal Min. Invest.,

Bulletin 12, 1915. -

162 ILLINOIS ENGINEERING EXPERIMENT STATION

Andros, S. O. " Coal Mining Practice in District V." 111. Coal Min. Invest.,

Bulletin 6, 1914.
Andros, S. O. " Coal Mining Practice in District VI." 111. Coal Min. Invest.,

Bulletin 8, 1914.
Andros, S. O. ' ' Coal Mining Practice in District VII. ' ' 111. Coal Min. Invest.,

Bulletin 4, 1914.

Andros, S. O. " Coal Mining Practice in District VIII. (Danville)." 111. Coal
Min. Invest., Bulletin 2, 1914.

Cady, G. H. " Coal Resources of District I. (Long-wall.) " 111. State Geol. Sur.,
Bulletin 10, 1915.

Cady, G. H. " Coal Eesources of District VI." 111. State Geol. Sur., Bulletin
15, 1916.

Cartlidge, Oscar. " Mine No. 3, Saline County Coal Co." Mines and Minerals,
Vol. 32, p. 387, 1912.

Kay, Fred H. ' ' Coal Resources of District VII. ' ' 111. State Geol. Sur., Bul-
letin 11, 1915.

Kay, Fred H., and White, K. D. " Coal Resources of District VIII. (Dan-
ville)." 111. State Geol. Sur., Bulletin 14, 1915.

Rice, George S. " Mining-Wastes and Mining-Costs in Illinois." Trans. Amer.
Inst. Min. Engrs., Vol. 40, p. 31, 1909.

Roberts, Warren, and Cartlidge, Oscar. " Buckner No. 2 Mine." Coll. Eng.,
Vol. 33, p. 121, 1912.

INDIANA

Ashley, Geo. H. " Coal Mining in Indiana." Mines and Minerals. Vol. 20,

p. 202, 1899.

Hall, R. D. " Method of Working in Indiana." Coal Age, Vol. 7, p. 94, 1915.
Parsons, Floyd W. " Mining Coal in South Indiana." Eng. and Min. Jour.,

Vol. 90, p. 869, 1910.
Price, Wm. Z. ' ' The J. K. Dering Coal Co. ' ' Coll. Eng., Vol. 35, p. 65, 1914.

IOWA
Price, Wm. Z. " The Electra Mine." Coll. Eng., Vol. 35, p. 11, 1914.

KENTUCKY

Alford, Newell G. " Problems Encountered in Kentucky Coal Mining." Coal
Age, Vol. 5, p. 674, 1914.

MARYLAND

Hall, R. D. " Georges Creek Coalfield, Maryland." Coal Age, Vol. 1, p. 10,
1911-12.

Hesse, H. V. " Maximum Recovery of Coal." Mines and Minerals, Vol. 29,
p. 373, 1909.

Jenkins, Jonathan. lt Pillar Drawing." Mines and Minerals, Vol. 30, p. 151,
1909.

Rutledge, J. J. " Ocean No. 7, or ' Klondyke Mine,' " Mines and Minerals,

Ige, J. J.
ol. 26, p. 5,

Vol. 26, p. 5, 1905.

MICHIGAN

Lane, Alfred C. " Coal of Michigan." Mich. Geol. Sur., Vol. 8, Pt. 2, 1902;
Mines and Minerals, Vol. 32, p. 148, 1911.

PERCENTAGE OF EXTRACTION**OF BITUMINOUS COAL 163

OHIO

Burroughs, W. G. " Black Diamond Concrete Tipple." Coll. Eng., Vol. 34,

p. 475, 1914.

Burroughs, W. G. " The High Shaft Mine." Coll. Eng., Vol. 35, p. 69, 1914.

Burroughs, W. G. " Hisylvania Mine No. 23." CoU. Eng., Vol. 35, p. 421,

1914.

Burroughs, W. G. " The Panel System in Ohio." Coll. Eng., Vol. 34, p. 562,

OKLAHOMA

Elliot, James. ' ' Conditions of the Coal Mining Industry of Oklahoma. ' ' Proc.
Amer. Min. Cong., p. 221, 1911.

PENNSYLVANIA

Baton, G. S. " Rib Drawing in the Connellsville Coke Eegion. " Mines and

Minerals, Vol. 27, p. 561, 1907.
Beeson, A. C., and Parsons, F. W. " Model Coal Mine at Marianna. ' ' Eng. and

Min. Jour., Vol. 91, p. 177 et seq., 1911.
Claghorn, Clarence R. "A Modified Long-wall System. ' ' Mines and Minerals,

Vol. 22, p. 16, 1901.
Cunningham, F. W. " Best Methods of Removing Coal Pillars." Proc. Coal

Min. Inst. Amer., p. 275, 1910; p. 35, 1911 j Mines and Minerals, Vol. 31,

p. 495, 1911.
Cunningham, J. S. " The Windber Mine. ' ' Mines and Minerals, Vol. 21,

p. 340, 1901.
Dixon, Charlton. ' ' A New Method of Coal Mining. ' ' Mines and Minerals,

Vol. 27, p. 32, 1906.
Goodale, S. L. " Safety Through Systematic Timbering." Coll. Eng., Vol. 32,

p. 195, 1911.
Howarth, H. W. ' ' Mining by Concentration Method. ' ' Coal Age1, Vol. 9,

p. 125, 1916.
Jennings, S. J. ' ' The Panel Retreating System. ' ' Mines and Minerals, Vol. 27,

p. 532, 1907.
Keighley, Fred C. " Mining Coal with Friable Roof and Soft Floor." Coal

Age, Vol. 7, p. 1008, 1915.
Mullen, Patrick. " New Mining Method in the Connellsville Region." Coal

Age, Vol. 10, p. 700, 1916.
Phelps, H. M. " The Marianna Coal Mines." Mines and Minerals, Vol. 31,

p. 523, 1911.
Phillips, Elias. * ' Late Methods of Rib Drawing. ' ' Mines and Minerals, Vol. 26,

p. 380, 1906.

Report of Commission Appointed to Investigate the Waste of Coal Mining, 1893.
Schellenberg, F. Z. (l Systematic Exploitation in the Pittsburgh Coal-Seam."

Trans. Amer. Inst. Min. Engrs., Vol. 41, p. 225, 1910.

TENNESSEE

Hutchinsou, W. S. " The Wind Rock Coal Mine. ' ' Mines and Minerals, Vol. 31,
p. 65, 1910.

UTAH

Manley, B. P. " The Somerset Mines." Coll. Eng., Vol. 34, p. 667, 1914.
Turner, R. J. " Consolidated Fuel Co., Utah." Mines and Minerals, Vol. 31,

p. 385, 1911.
Watts, A. C. " Coal-Mining Methods in Utah." Coal Age, Vol. 10, pp. 214,

258, 1916.

164 ILLINOIS ENGINEERING EXPERIMENT STATION

WASHINGTON

Ash, Simon H. ' ' Working a Steep Coal Seam by the Long-wall Method. ' ' Coal

Age, Vol. 9, p. 742, 1916.

Evans, Geo. W. " Working an Inclined Coal Bed." Coll. Eng., Vol. 35, p. 18,
1914.

WEST VIRGINIA

Beebe, James C. ' ' Protection of Mines and Miners. ' ' Mines and Minerals,

Vol. 28, p. 554, 1908.
Cornet, F. C. " Proposed Method of Long-wall Mining." Coal Age, Vol. 4,

p. 120, 1913.
Evans, Geo. D. " E. E. White Coal Co. Klines." Coll. Eng., Vol. 35, p. 401,

1915.
Gay, H. S. "A Single Room System. ' ' Mines and Minerals, Vol. 27, p. 325,

1907.
Hall, R. D. " The Fairmont, West Virginia Coal Region." Coal Age, Vol. 1,

p. 138, 1911.
Hesse, A. W. " Pillar-Drawing Methods in Fairmont Region." Coal Age,

Vol. 4, p. 762, 1913.
Hesse, Hr V. " Mining Methods for Maximum Recovery of Coal. ' ' W. Va.

Min. Inst., p. 75, 1908; Mines and Minerals, Vol. 29, p. 373, 1909.
Stock, H. H. " Coal Fields of West Virginia." Mines and Minerals, Vol. 29,

pp. 219, 283, 1908.
Stoek, H. H. " Coal Fields of Central W. Va." Mines and Minerals, Vol. 30,

p. 188, 1009.
Stoek, H. H. " The Kanawha Region, W. Va." Mines and Minerals, Vol. 30,

p. 70, 1909.
Stoek, H. H. " New River Coal Field, West Virginia." Mines and Minerals,

Vol. 29, p. 509, 1909.
Stoek, H. H. " Pocahontas Region Mining Methods." Mines and Minerals,

Vol. 29, p. 394, 1909.
Stoek, H. H. " Raleigh County Mining Methods. ' ' Mines and Minerals, Vol. 29,

p. 471, 1909.
Stow, Audley H. ' ' Mining in the Pocahontas Field. ' ' Coal Age, Vol. 3, p. 549,

1913.
Unsigned. ' ' The Boissevain Plant. ' ' Mines and Minerals, Vol. 28, p. 497, 1908.

OTHER COUNTRIES
CANADA

Jacobs, E. (i The Blairmore-Frank Coal Field." Mines and Minerals, Vol. 25,

p. 359, 1905.

Leblanc, E. E. " Long-wall Mining in Alberta." Coal Age, Vol. 7, p. 712, 1915.
Quigley, J. S. ' < Methods of Drawing Pillars in Pitching Seams. ' ' Trans. Amer.

Inst. Min. Engrs., Vol. 17, p. 406, 1888-9.

FRANCE

Dean, Samuel. "A Tour Through European Coal Mines — III." Coal Age,
Vol. 7, p. 110, 1915.

PERCENTAGE OF EXTRACTION *OF BITUMINOUS COAL 165

GERMANY

Annett, Hugh Clarkson. ' l Hydraulic Stowing of Gob at Shamrock I. and II.,
Colliery, Herne, Westphalia, Germany." Trans. Inst. Min. Engrs., Vol., 37,
p. 257, 1908-09.

Young, Geo. J. "Brown Coal Mining in Germany." Trans. Amer. Inst. Min.
Engrs., Vol. 54, p. 327, 1916.

GREAT BRITAIN

Charlton, Wm. « ' A Method of Working the Thick Coal Seam in Two Sections. ' '

Trans. Inst. Min. Engrs., Vol. 21, p. 264, 1900-01; p. 110, 1902.
Dean, Samuel. ' < Bentley Colliery. ' ' Coll. Eng., Vol. 35, p. 71, 1914.
Holland, Laurence. "Notes on Working the Thick Coal of South Staffordshire

and Warwichshire. ' ' Trans. Inst. Min. Engrs., Vol. 37, p. 46, 1908-09.
Jackson, J. H. "Notes on Early Mining in Staffordshire and Worcestershire."

Trans. Inst. Min. Engrs., Vol. 27, p. 98, 1903-4.
Meachem, Isaac. l ' Notes on the Loss of Mineral Areas in South Staffordshire. ' '

Trans. Inst. Min. Engrs., Vol. 43, p. 11, 1912.
O 'Donahue, T. A. " Notes on the Valuation of Mineral Properties. ' ' Trans.

Inst. Min. Engrs., Vol. 43, p. 19, 1912.
Smith, Alexander. ' ' Brief History of Coal-Mining in Warwichsire. ' ' Trans.

Inst. Min. Engrs., Vol. 34, p. 355, 1907-08.

INDIA

Adamson, T. " Working a Thick Coal Seam, Bengal." Trans. Inst. Min.
Engrs., Vol. 25, p. 10, 1902-03.

McCale, C. H. " Pillar Working in the Raniganj and Jharia Coal Fields."
Min. and Geol. Inst. of India, Vol. 7, p. 42, 1912.

Simpson, F. L. G. " Goaf Packing at the Mohpani Mines. ' ' Trans. Min. and
Geol. Inst. of India, Coll. Guard., Vol. 112, p. 1213, 1916.

Stonier, Geo. A. " The Bengal Coal-Fields, and Some Methods of Pillar-Work-
ing in Bengal, India." Trans. Inst. Min. Engrs., Vol. 28, p. 537, 1904-05.

JAPAN

Yonekra, K. " Japanese Coal Mines." Mines and Minerals, Vol. 24, pp. 349,
508, 1904.

MEXICO

Brown, E. O. Forster. " Coal Mining in Mexico." Trans. Inst. Min. Engrs.,
Vol. 49, p. 381, 1915.

SILESIA

Gullachsen, Berent Conrad. " The Working of the Thick Coal Seams of Upper
Silesia." Trans. Inst. Min. Engrs., Vol. 42, p. 209, 1911-12.

SPAIN

Louis, Henry. " Coal Mining in Asturias, Spain." Trans. Inst. Min. Engrs.,
Vol. 28, p. 420, 1904-05.

INDEX

Accidents, 36, 114; liability to, 78.

Affelder, W. L., 73.

Alabama, 122-125; Birmingham district,
123, 124; coal losses in, 124; extraction
in, 123, 124-125; Jefferson County, 123;
long-wall method used in, 124; Mary Lee
seam, 123 ; Montavallo Mine, 124, 125 ;
pillar drawing in, 124; Pratt seam, 123,
125 ; room-and-pillar system used in, 123,
124; triple entry system used in, 124.

Alford, N. G., 118, 119.

Andros, S. O., 31, 32, 36, 38, 39, 40, 41, 54,
58.

Annabelle Mine (W. Va.), 70.

Appanoose field (la.), 127.

Apperson, A. B., 140.

Arkansas, 128-130; coal losses in, 129;
coal wastes in, 128; extraction in, 129;
pillar drawing in, 129; production (1910)
in, 13; strike (1910) in, 13.

Arkansas-Oklahoma field, 129.

Atchison (Kan.), 130.

Auchmuty, H. L., 63.

Barnes, Thomas, 147, 149.

Baton, G. S., 68.

B bed (Pa.), see Lower Kittanning bed.

Beds, B (Pa.), 83, 86; Castle Gate (Utah),
134; Fire Creek (W. Va.), 104; Free-
port (W. Va.), 99; Hocking Valley (O.),
116; Kittanning (W. Va.), 99; Lower
Freeport (O.), 117, (Pa.), 89; Lower
Kittanning (Pa.), 83, 86, (W. Va.), 101;
Middle Kittanning (O.), 116; Miller
(Pa.), 83, 86; No. 1 and No. 2 beds
(District III., HI.), 33-34; No. 2 (Dis-
trict I., 111.), 31; No. 5 (Districts IV. and
V., 111.), 36, 38; No. 6 (111.), 15, 40, 46,
53, (O.), 116; Pittsburgh (Pa.), 61.
(W. Va.), 98, 101-102; Pocahontas No. 3
(W. Va.), 104, 105, 108, 109; Poca-
hontas No. 4, 105; Sewell (W. Va.), 104.

Belgium, long-wall system used in, 157;
Quaregnon, 157.

Bell County (Ky.), 120.

Bell-pits, 142, 143.

Bevier (Mo.), 128.

Beyer, S. W., 127.

Big Pillar system, 83, 84.

Big Room method, 113.

Big-vein seam (Md.), 90-97.

Birmingham district (Ala.), 123, 124.

Bischoff, J. W., 101, 102.

Black jack, 43.

Black rash, 104.

Bliss, J. W., 133.

Block long-wall system, 86, 87.

Block room-and-pillar system, 37.

Block system, 44.

Block system of retreating long wall, 114-

115.

Bord-and-pillar method, 143, 144, 146.
Bord-and-wall method, 144.
Bordway, 143.
Boulton, W. S., 144.
Bounces, 136.
Brackett, G. S., 97, 99.
Braxton County (W. Va.), 101.
Brazil district (Ind.), 125.
Buddie, John, 145, 147.
Buddie, John, Jr., 149.
Bulman, H. F., 143, 145.
Burroughs, W. G., 116, 117.
Bush, B. F., 13.
Butler, J. E., 121.
Cabell, C. A., 103, 114.
Cabin Creek (Kanawha district, W. Va.).

104.

Cady, G. H., 41, 43.
Cambria County (Pa.), 83.
Cambridge field (O.), 116.
Carbon Coal Company (W. Va.), 86.
Carbon County (Utah), 134.
Canyon district (Colo.), 134, 151.
Carterville (111.), 40.
Castle Gate bed (Utah), 134.
Cement seam (Pa.), 88.
Claghorn, C. R., 86.
Clay County (Ky.), 119.
Clearfield County (Pa.), 89.
Coal, abandonment of, 10, 21-22, 54, 129;

cost of, 14, 15, 36, 74; cost of production

of, 13; demands for, 53; pillar, 9, 34, 66,

67, 101, 102; room, 9, 101, 102; value

of, 9, 14.

Coal beds, see Beds.
Coal extraction, see Extraction.
Coal losses, 8, 10, 16-17, 20, 32, 36, 42-43,

65, 77, 109-111, 119, 124, 127, 129,

130, 146, 151-152, 154-156, 157, 158;

conditions causing, 15—16.
Coal mining industry, development of, 12;

over-development of, 12-13, 119, 120.
Coal recovery, see Extraction.
Coal rights, cost of, 16; price of, 16; value

of, 15-16, 28.
Coal seams, see Seams.

166

167

Coal Valley Mining Company (111.), 35-36.

Coal Waste Commission (reported in 1893),
11.

Coal wastes, 34, 41, 128; see also Coal,
abondonment of, and Coal losses.

"Colliery Guardian, The," 156.

Colorado, 133-134; bituminous district of,
133; Canyon district, 134, 151; extraction
in, 134; lignite district of, 133; long-wall
method used in, 134; pick work in, 133;
pillar drawing in, 133, 134; squeezes in,
134; Trinidad district, 133, 134; Walsen-
burg, 134.

Concentration method, 78-83 ; extraction
under, 83, 89; maximum plan of, 80-82;
medium plan of, 80 ; minimum plan of,
80.

Connellsville district (Pa.), 65, 66, 75-83;
bore hole records of, 41 ; coal losses in,
77 ; coke of, 75 ; concentration method
used in, 78; extraction in, 77, 83, 89;
H. C. Frick Coke Company, 78, 89; in-
tensive methods of production in, 75 ; pil-
lar drawing in, 77, 119 ; room-and-pillar
system used in, 78 ; squeezes in, 76-77.

Connellsville seam, see No. 8, Pittsburgh

Cooperative Coal Mining Investigations, 11,

29, 31, 41, 56.
Coxe, E. H., 86, 121.
Creeps, 20, 77, 92, 127, 145; see also

Squeezes.

Cross entry system, 61.
Culm filling, cost of, 21.
Cumberland field (Eng.), 147, 156.
Cunningham, F. W., 64, 66, 68, 77.
Cunningham, J. S., 104.
Daniel, Joseph, 141.
Danville (HI.), 56.
Davy lamp, 146.
Dawson, T. W., 83, 89.
DeBardeleben, C. F., 125.
Deerfield district (O.), 116.
Delaney, E. A., 89.
Delano, Warren, 86.
Denman, H., 129.
De Wolf, F. W., 7.
District I., 31-32, 150; description of No.

2 bed in, 31; coal losses in, 32; extraction

in, 32; La Salle field, 31; long-wall system

used in, 32; Wilmington field, 31-32.
District II., 32-33; description of No. 2

seam in, 32 ; extraction in, 32, 33 ; panel

system used in, 32 ; pillar gouging in, 32 ;

pillar slabbing in, 33 ; subsidence in, 32 ;

unmodified room-and-pillar system used in,

32.
District III., 33-36; coal losses in, 36; Coal

Valley Mining Company, 35-36; coal

wastes in, 34; cost of coal in, 36; des-
cription of No. 1 and No. 2 beds in, 33-
34; double-entry room-and-pillar system
used in, 34; extraction in, 34; Matherville,
33, 36; No. 3 mine, 36; pillar drawing in,
34-35; subsidence in, 36.

District IV., 36-38; block room-and-pillar
system used in, 37; description of No. 5
coal in, 36; extraction in, 38; Fulton
County, 36; Knox County, 36; Logan
County, 36; long-wall system used in, 37;
Macon County, 36; McLean County, 36;
panel system used in, 37; Peoria County,
36; pillar drawing in, 38; pillar gouging
in, 37, 38; semi-panel system used in, 37;
squeezes in, 37; unmodified room-and-
pillar system used in, 37.

District V., 38-39; description of Bed No. 5
in, 38 ; extraction in, 39 ; Gallatin County,
38; pillar gouging in, 39; room-and-pillar
system used in, 39; Saline County, 38;
squeezes in, 39.

District VI., 40-53 ; block system used in,
44; Carterville, 40; coal losses in, 42-43,
coal wastes in, 41 ; description of the
No. 6 coal in, 40 ; Duquoin anticline, 40 ;
extraction in, 42-43, 45, 46-47, 48-49,
50-51; Franklin County, 43-47; Marion,
40; panel long-wall system used in, 51,
52; panel system used in, 41, 44, 47, 49,
51; Perry County, 51; pillar drawing in,
41, 44, 45, 47, 48, 49, 50, 51; pillar
gouging in, 42, 50 ; pillar slabbing in, 44,
48, 50; room-and-pillar system used in,
41 ; Sesser, 40 ; squeezes in, 40, 41, 42,
47, 48, 49, 50; Williamson County, 47-51.

District VII., 53-56; description of No. 6
bed in, 53; extraction in, 54, 55, 56;
panel system used in, 56; squeezes in, 54-
55, 56; subsidence in, 54-55, 56.

District VIII., 56-58; descriptions of seams
6 and 7 in, 56, 57; Danville, 56; extrac-
tion in, 58 ; Georgetown, 56 ; pillar draw-
ing not systematic in, 58 ; pillar gouging
in, 58 ; room-and-pillar system used in,
57; squeezes in, 58; stripping operations
in, 56; Westville, 56.

Districts, Appanoose (la.), 127; Arkansas-
Oklahoma, 129; Birmingham (Ala.), 123,
124; Brazil (Ind.), 125; Cambridge (O.),
116; Connellsville (Pa.), 65, 66, 75-83;
Cumberland (Eng.), 147, 156; Deerfield
(0.), 116; Elk Garden (W. Va.), 93;
Elkhorn (Ky.), 121; Fairmont (W. Va.),
98, 99; Harland (Ky.), 121; Hartshorne
(Okla.), 132; Hazard (Ky.), 121; Hock-
ing (O.), 116; Jackson (O.), 116; Johns-
town (Pa.), 89; Kanawha (W. Va.), 102-
104; La Salle (111.), 31; Leavenworth

168

INDEX

(Kan.), 130; Mahoning (O.), 116; Man-
chester (Eng.), 153; Massillon (O.), 116;
McAlester (Okla.), 132; New River (W.
Va.), 104; Newcastle (Eng.), 146; No. 8
Ohio, 13; Osage (Kan.), 130, 151; Pan-
handle (Pa.), 75; Piedmont (W. Va.),
99; Pittsburgh (O.), 116, 117; (Pa.),
61-75; Pocahontas (W. Va.), 104-111;
Shropshire (Eng.). 150; similar condi-
tions of Illinois, 29; Somerset County
(Pa.), 86, 89; Trinidad (Colo.), 133,
134; Wilmington (111.), 16, 31-32.
Dixon, Charlton, 62, 64.

Double-entry room-and-pillar system, 34, 122.
Double entry system, 61, 62, 136.
Drawing pillars, see Pillar drawing.
Duquoin anticline (111.), 40, 53.
Easton, H. D., 120.
Eavenson, H. N., 104, 107. 108.
Edwards, J. C., 69.
Elk Garden district (W. Va.), see Piedmont

district.

Elkhorn district (Ky.), 121.
Elkins (W. Va.), 101.
Elliot, James, 132.

England, bell-pits used in, 142, 143; bord
and-pillar method used in, 143, 144, 146;
bord-and-wall method used in, 144; coal
losses in, 146, 151-152, 154-156; Cum-
berland field, 147, 156; early mining in,
142; extraction in, 144, 146, 147, 151-
154; Hebburn Colliery, 148; long-wall
system used in, 142, 145, 150-151, 152-
153, 155-156; Manchester district, 153;
miners of, 60-61; Newcastle district, 146;
no-pillar system used in, 142; North-
umberland, 146, 152 ; panel system used
in, 148-149; pillar system used in, 142;
pillar-and-stall method used in, 152, 153 ;
post-and-stall method used in, 144; re-
covery of pillars in, 145, 146, 147 ; room-
and-pillar system used in, 144, 149, 150;
Royal Commission of, 151—156; Shrop-
shire, 150; Somersetshire, 153; square
work in South Staffordshire, 149-150;
squeezes in, 147, 148; stoop-and-room
method used in, 144; subsidence in, 146;
Thick seam, 149; Whitehaven, 145;
Walker Colliery, 147, 148; Wallsend Col-
liery, 146, 147, 149; Wallsend G pit,
149; ventilation of mines in, 143, 144,
145, 147-148, 149; Yorkshire, 154.
European War, 53.

Extraction, best results of, 9; conditions
affecting, 9, 31; conditions necessary to
obtain high, 14-15 ; estimating, 10, 11-
12, 31; importance of, 17; increase in,
14; low percentage of, 17; meager atten-
tion given to, 11; methods involving low,

12 ; only accurate method of estimating,
12; percentage of, 11, 12, 13, 15, 23, 24,
25-27, 156; see also Alabama, Arkansas,
Colorado, England, Illinois, Indiana, Iowa,
Kansas, Kentucky, Maryland, Michigan,
Missouri, Ohio, Oklahoma, Pennsylvania,
Tennessee, Texas, Utah, and West Vir-
ginia.

Face airing, 148.

Fairmont district (W. Va.), 98, 99.
Fields, see Districts.
Fire Creek bed (W. Va.), 104.
Fire ribs, 149.
Fisher, C. A., 153.

Four States Coal Company (W. Va.), 70.
France, filling methods used in, 157.
Franco-Belgian basin, beds in, 156.
Franklin County (111.), 43-47; block system
used in, 44 ; extraction in, 43-45, 46-47 ;
panel system used in, 44, 47; pillar draw-
ing in, 44, 45, 47; pillar slabbing in, 44;
squeezes in, 47.
Franklin County Coal Operators' Association

(111.), 46.

Freeport bed (W. Va.), 99.
Fulton County (111.), 36.
Gallatin County (111.), 38.
Galloway, R. L., 145, 146, 147, 148.
Gay Coal and Coke Company (W. Va.), 111.
Gay, H. 8., Ill, 114.
Gentry, B. S., 133.
Georges Creek region, see Maryland.
Georgetown (111.), 56.
German Empire, average value of coal in,

14.

Germany, mining profits in, 14.
Gerrard, J., 153.
Gibb, H. M., 69.
Gilmer County (W. Va.), 101.
Grady, W. H., 106, 107.
Great Britain, average value of coal in, 14,
152; mining profits in, 14; similar con-
ditions in United States as in, 61 ; United
States, a colonial possession of, 60 ; see
also England, Scotland, and Wales.
Gullachsen, B. C., 21, 158.
Hadesty, J. B., 158.
Half advancing and half retreating system,

70.

Haring, J. C., 117.
Harland district (Ky.), 121.
Hartshorne district (Okla.), 132.
Hazard district (Ky.), 121.
Hazel mine (Pa.), 69.

H. C. Frick Coke Company (Pa.), 78; ex-
traction of, 89.
Headway, 143, 144.
Hebburn Colliery (Eng.), 148.
Hesse, A. W., 11, 24.

INDEX

169

Hesse, H. V., 90.

Hisylvania Mine No. 23 (O.), 116.

Hocking Valley bed (O.), see Middle Kit-
tanning bed.

Hocking Valley district (O.), 116.

Howarth, W. H., 78.

Hutcheson, W. C., 122.

Illinois, 29-59 ; block room-and-pillar system
used in, 37; block system used in, 44;
Carterville, 40 ; Central, 18 ; coal costs in,
36; coal losses in, 36, 42-43; Coal Valley
Mining Company, 35—36; coal wastes in,
34, 41; conditions affecting extraction in,
31; Danville, 56; district I. of, 31-32,
150; district II. of, 32-33; district III.
of, 33-36, district IV. of, 36-38; district
V. of, 38-39; district VI. of, 40-53; dis-
trict- VII. of, 53-56; district VIII. of,
56-58; districts of, 29-58; double-entry
room-and-pillar system used in, 34;.Du-
•quoin anticline, 40, 53 ; extraction in, 9,
(1910) 13, 15, 16, 25-27, 32, 33,
34, 38, 39, 42-43, 45, 46-47, 48-49,
.50-51, 54, 55, 56, 58; filling method in,
21; Franklin County, 43-47; Fulton
-County, 36; Gallatin County, 38; George-
town, 56; Knox County, 36; La Salle
field, 31; Logan County, 36; long-wall
method used in, 32, 37; McLean County,
36; Macon County, 36; Marion, 40;
Matherville, 33, 36; panel long-wall
method used in, 51, 52; panel system
used in, 32, 37, 41, 44, 47, 49, 51, 56;
Peabody Coal Company, 47, 54, 58;
Peoria County, 36; Perry County, 51;
pillar drawing in, 35, 38, 41, 44, 45, 47,
48, 49, 50, 51, 58, 59; pillar gouging in,
32, 37, 38, 39, 42, 50, 58; pillar slabbing
in, 33, 44, 48, 50; room-and-pillar system
used in, 39, 41, 57; Saline County, 38;
semi-panel method used in, 37; Sesser,
40; squeezes in, 10, 20, 37, 39, 40, 41,
42, 47, 48, 49, 50, 54-55, 56, 58; State
Geological Survey, 40, 46; strike (1910)
in, 13; stripping operations, 56; sub-
sidence in, 10,18, 20, 32, 36, 54-55, 56;
unmodified room-and-pillar system used
in, 32, 37; value of coal rights in, 15—16,
28; value of farm lands in, 18, 28; West-
ville, 56; Williamson County, 47-51; Wil-
mington field, 16, 31-32.

Indiana, 125-126; Brazil district, 125; ex-
traction in, 125-126; strike (1910) in,
13.

Iowa, 126-127; Appanoose field, 127; coal
losses in, 127; creeps in, 127; extraction
in, 127; long-wall system used in, 127;
room-and-pillar system used in, 127.
.Jackson field (O.), 116.

James, W. E., 114.

Jars, 145.

Jefferson County (Ala.), 123.

Jefferson County (Pa.), 89.

Johnstown district (Pa.), 89.

Jorgensen, F. F., 127.

"Journey through the North of England, A,"
145.

Kanawha region (W. Va.), 102-104; Cabin
Creek portion of, 104; extraction in, 103,
104; No. 2 Gas Seam, 103; pillar draw-
ing in, 103 ; room-and-pillar system used
in, 103.

Kansas, 130-132 ; Atchison, 130 ; coal losses
in, 130; extraction in, 130, 131; Leaven-
worth district, 130 ; long- wall system used
in, 130; Osage district, 130, 151; panel
method unsatisfactory in, 131; room-and-
pillar system used in, 130 ; squeezes pre-
vented in, 131; stripping operations in,
130; Topeka, 130.

Keely, Josiah, 104.

Keighley, F. C., 75.

Kentucky, 118-121; Bell County, 120; Cflay
County, 119; coal losses in, 119; Elkhorn
district, 121; extraction in, 118, 119,
120; Harland district, 121; Hazard dis-
trict, 121; No. 9 seam, 118, 119; No. 11
seam, 118, 119; No. 12 seam, 119; pillar
drawing in, 121 ; pillar recovery in, 119,
120; room-and-pillar system used in, 118,
120; squeezes in, 120; Straight Creek
seam, 120; Webster County, 119.

Kittanning bed (W. Va.), 99.

Knox County (111.), 36.

La Belle Iron Works (O.), 117.

La Salle field (111.), 31.

Lamps, Davy, 146; locked safety, 66; open.
66; safety, 145.

Land, value of, 18, 28.

Lane, A. C., 126.

Lanier, S. S., 120.

Leavenworth district (Kan.), 130.

Lexington (Mo.), 128.

Lincoln, J. J., 109, 110.

Link-Belt Company, 88.

Logan (W. Va.), 111.

Logan County (111.), 36.

Logan County (W. Va.), 113.

Long-wall system, 18, 32, 37, 86-88, 117,
122, 124, 127, 128, 130, 133, 134, 136,
142, 145, 150-151, 152-153, 156, 157;
failure of, 62, 111, 113, 117, 136.

Lower Freeport bed (O.), 117; (Pa.), 89.

Lower Kittanning bed (Pa.), 83, 86; (W.
Va.), 101.

McAlester district (Okla.), 132.

Machines, breast, 57, 74; chain, 52; chain
breast, 71; cutting, 116; extracting pil-

170

INDEX

lars with, 51, 66, 68-69, 71; long-wall,
114; mining, 17, 46; pick work replaced
by, 73, 78; rolling stock, 116; short-wall,
71, 72, 73, 83, 126; undercutting, 132.

Mackenzie, 146.

McLean County (111.), 36.

Macon County (111.), 36.

Macon County (Mo.), 127, 128.

Mahoning district (O.), 116.

Majer, John, 86.

Manchester district (Eng.), 153.

Marianna mine (Pa.), 69.

Marion (111.), 40.

Marshall, J. J., 103.

Mary Lee Seam (Ala.), 123.

Maryland, 61, 90-98; Big Vein seam, 90-
97; coal losses in, 92; creeps in, 92; ex-
traction in, 98; Georges Creek region,
90-98; methods used in, (1850) 90-92,
(1870-1880) 92, 93, (1890) 92, 94,
(1900) 92, 95, (1904) 96, 97; pillar
drawing in, 91; room-and-pillar retreating
method used in, 98 ; squeezes in, 92 ;
wasteful early methods in, 90.

Maryland Coal Company (Pa.), 88.

Massillon district (O.), 116, 117.

Matherville (111.), 33, 86.

Michigan, extraction in, 126; machines used
in, 126; recovery of pillars in, 126;
room-and-pillar system used in, 126;
Saginaw, 126.

Middle Kittanning bed (O.), 116.

Middle West, extraction in, 9.

Miller bed (Pa.), 89; see also Lower Kit-
tanning bed.

Mines, Annabelle (W. Va.),70; Hazel (Pa.),
69; Hisylvania No. 23 (O.), 116; Mari-
anna (Pa.), 69; Montavallo (Ala.), 124,
125; No. 3 (District III., 111.), 36; No. 9
(W. Va.), 108; No. 10 (W. Va.), 108;
No. 11 (W. Va.), 108; Pocahontas No. 2
(W. Va.), 109; Pocock No. 4 (O.), 117.

Mining methods, 37, 55-56; choice of, 9,
12, 13, 15; early, 60, 61, 142; low cost
of production of, 31; prejudices against
newer, 9 ; plan of Pittsburgh-Buffalo and
Four States Coal Companies, 69-70; plan
of Pocahontas Coke and Coal Company,
105-106; plan of Wind Rock Coal Com-
pany, 123; variation of, 10; wasteful
early, 90; see also Big Pillar, Big Room,
Block, Block long-wall, Block method of
retreating long-wall, Block room-and-pil-
lar, Bord-and-pillar, Bord-and-wall, Con-
centration, Cross entry, Double entry,
Double entry room-and-pillar, Half ad-
vancing and half retreating, Long- wall,
No-piUar, Panel, Panel long-wall, Pillar,
Pillar-and-stall, Post-and-stall, Room-and-

pillar, Semi-panel, Single entry, Single
room, Stoop-and-room, and Triple entry
systems, and Maryland.

Mining profits, see Germany, Great Britain,
United States.

Mining systems, see Mining methods.

Missouri, 127-128; Bevier, 128; extraction
in, 128 ; Lexington, 128 ; long-wall system
used in, 128; Macon County, 127, 128;
production (1910) in, 13; Randolph
County, 127, 128; room-and-pillar method
used in, 127, 128; strike (1910) in, 13;
stripping in, 128.

Montavallo mine (Ala.), 124, 125.

Moore, H. G., 89.

Moore, M. G., 88.

Moorshead, A. J., 13.

Mullen, Patrick, 78.

Nesbitt, C. H., 125.

New Mexico, 134.

New River field (W. Va.), 104.

Newcastle district (Eng.), 146.

Newcomen engine, introduction of, 143.

Niggerheads, 36, 38.

No-pillar system, 142.

North Dakota, recovery in, 133.

Northumberland (Eng.), 146.

No. 6 bed (O.), nee Middle Kittanning bed.

No. 2 Gas seam (Kanawha dist., W. Va.).
103.

No. 8 Ohio district, production in, 13.

No. H Pittsburgh spam (Pa.), 76.

No. 9 mine (W. Va.), 108.

No. 9 seam (Ky.), 118, 119.

No. 10 mine (W. Va.), 108.

No. 11 mine (W. Va.), 108.

No. 11 seam (Ky.), 118, 119.

No. 12 seam (Ky.), 119.

Ohio, 116-118; Cambridge field, 116; Deer-
field district, 116; extraction in, 116-117;
Hisylvania Mine No. 23, 116; Hocking
Valley bed, 116; Hocking Valley district,
116; Jackson field, 116; La Belle Iron
Works, 117; long- wall method used in,
117; Lower Freeport bed, 117; Mahoning
district, 116; Massillon district, 116, 117;
Middle Kittanning bed, 116; No. 6 bed,
116; Pittsburgh vein district, 116, 117;
Pocock No. 4 mine, 117; room-and-pillar
method used in, 117; Steubenville, 117;
stripping in, 117.

Oklahoma, 132-133 ; extraction in, 129,
132; Hartshorne district, 132; McAlester
district, 132 ; panel long-wall method used
in, 131-132; production (1910) in, 13;
Rock Island Coal Mining Company, 132 ;
room-and-pillar system used in, 132 ;
strike (1910) in, 13.

Osage district (Kan.), 130, 151.

f*
INDEX

171

Panel long-wall system, 51, 52, 86, 131,
132.

Panel system, 32, 37, 41, 44, 47, 49, 51,
56, 70, 86, 98, 136, 148-149; failure of,
131.

Panhandle district (Pa.), 75.

Parr, S. W., 51.

Peabody Coal Company (111.), extractions
of, 47, 54, 58.

Pennsylvania, 61-90; anthracite district of,
11; Cement seam, 88; Clearfield County,
89 ; extraction in, 9 ; Hazel mine, 69 ;
Jefferson County, 89 ; Johnstown district,
89;. Lower Freeport bed, 89; Maryland
Coal Company, 88 ; panel system used in,
86; Pittsburgh-Buffalo Company, 69; St.
Michael, 88 ; Somerset County, 86, 89 ;
South Fork, 89.

Central, 83-88; B bed, 83, 86; big
pillar system used in, 83, 84; Cambria
County, 83; Miller bed, 83, 86; Lower
Kittanning bed, 83, 86; pillar drawing
in, 85; squeezes in, 84; see also Con-
nellsville district and Pittsburgh district.

Peoria County (111.), 36.

Perry County (111.), 51; extraction in, 51;
panel long-wall system used in, 51, 52 ;
panel system used in, 51; pillar drawing
in, 51.

Pick work, 17-18, 43, 46, 50, 66, 68, 75,
100, 103, 133; average price for, 74; sub-
stituting more machine work for, 73, 78.

Piedmont district (W. Va.), 99.

Pillar-and-stall system, 152, 153.

Pillar drawing, 9, 10, 34-35, 38, 41, 42,
44, 45, 47, 48, 49, 50, 51, 62, 63, 64,
65, 67, 68, 69, 77, 85, 98, 100, 103,
110, 119, 121, 122, 124, 129, 133, 134,
136-141; accidents with, 36; unsystema-
tic, 58, 59.

Pillar gouging, 32, 37, 38, 39, 42, 50, 58,
144.

Pillar slabbing, 33, 44, 48, 50.

Pillar system, 61, 142.

Pillars, extraction of stump and chain, 65 ;
recovery of, 65, 66, 68, 69, 71, 72, 73,
119, 120, 126, 145, 146, 147; tapered,
68.

Pittsburgh bed (Pa.), 61; (W. Va.), 98,
101-102. ,

Pittsburgh-Buffalo Company (Pa.), 69.

Pittsburgh district (O.), 116, 117; (Pa.),
61—75 ; block long-wall system used in,
86; coal losses in, 65; cross entry system
used in, 61 ; double entry system used in,
61, 62; extraction in, 66, 67, 88; half
advancing and half retreating system used
in, 70 ; improved room-and-pillar method
used in, 63 ; long-wall system tried in, 62,

used in, 86-88; panel long-wall system
used in, 86; panel system used in, 70;
Panhandle district, 75 ; pillar drawing in,
62, 63, 64, 65, 67, 68-69; production in,
13 ; room-and-pillar system used in, 62-
63 ; single entry system used in, 61 ;
squeezes in, 63 ; substituting machines for
pick work in, 73 ; ventilation in mines of,
61, 63, 64, 66.

Pocahontas Coal and Coke Company (W.
Va.), 105-107; extraction in, 107;
method used by, 105-106.

Pocahontas district (W. Va.), 104-111;
characteristics of coal in, 104; coal losses
in, 109-111; coke of, 104; extraction in,
109, 110; No. 2 mine, 109; No. 3 bed,
104-105, 108, 109; No. 4 bed, 105; No. 9
mine, 108; No. 10 mine, 108; No. 11
mine 108; pillar drawing in, 110.

Pocahontas No. 2 mine (W. Va.), 109.

Pocahontas No. 3 bed (W. Va.), 104-105,
108, 109.

Pocahontas No. 4 bed (W. Va.), 105.

Pocock No. 4 mine (O.), 117.

Post-and-stall method, 144.

Pratt Seam (Ala.), 123, 125.

Pritchard, James, 116.

Quaregnon (Belgium), 157.

Randall, R. M., 126.

Randolph County (Mo.), 127, 128.

Redmayne, R. A. S., 143, 144, 145, 150.

Rice, G. S., 7, 14, 15, 18, 32.

Richmond basin (Va.), 61, pillar system
used in, 61.

Roby, J. J., 117.

Rock Island Coal Mining Company (Okla.),
132.

Room-and-pillar system, 39, 41, 57, 62—63,
78, 102, 114, 117, 118, 120, 123, 124,
126, 127, 128, 130, 132, 133, 136, 144,
149, 150; objections to the, 63, 86; re-
treating, 97; unmodified, 32, 37.

Royal Commission on Coal Supplies, 151—
156, 157; report (1871), 151, 153;
(1905), 153, 154.

Saginaw (Mich.), 126.

St. Michael (Pa.), 88.

Saline County (111.), 38.

Sand filling, 21.

Savage, T. E., 40.

Schellenberg, F. C., 66.

Schluederberg, G. W., 88.

Scholz, Carl, 15, 35-36, 132.

Scotland, 145-146, 150, 153 ; miners of,
60-61.

Seams, Big- Vein (Md.), 90-97; Cement
(Pa.), 88; Connellsville (Pa.), 76; Mary
Lee (Ala.), 123; Miller (Pa.), 89; No. 2
(District II., 111. ), 32; No. 2 Gas

172

INDEX

(W. Va.), 103; No. 6 and No. 7 (Dis-
trict VIII., 111.), 56; No. 8 Pittsburgh
(Pa.), 76; No. 9 (Ky.), 118, 119;
No. 11 (Ky.), 118, 119; No. 12 (Ky.),
119; Pratt (Ala.), 123, 125; Straight
Creek (Ky.), 120; Thick (S. Stafford-
shire), 149.

Semi-panel system, 37.

Sesser (111.), 40.

Sewell bed (W. Va.), 104.

Shaw, E. W., 40.

Shiflett, R. A., 121.

Shropshire district (Eng.), 150.

Silliman, W. A., 83.

Smgle-entry system, 61.

Single-room system, 53, 111-113.

Smyth, J. G., 12, 98.

Somerset County district (Pa.), 86, 89.

Somersetshire (Eng.), 153.

South Fork (Pa.), '89.

South Staffordshire, square work of, 149-
150.

Southwest, strike (1910) in, 13.

Square work, 149-150.

Squeezes, 20-22, 37, 39, 40, 41, 42, 47,
48, 49, 50, 54-55, 56, 58, 63, 76-77,
84, 92, 100, 106, 120, 134, 147, 148;
pillars crushed through. 10; prevention of.
10, 21, 22, 59, 130, 131.

State Geological Survey (HI.), 40, 46.

Steel, A. A., 128.

Steubenville (O.), 117.

Stock, H. H., 7, 8, 11, 23, 105.

Stoop-and-room method, 144.

Stow, A. H., 105.

Straight Creek seam (Ky.), 120.

Strike (1910), 13.

Stripping operations, 56, 117, 128, 130.

Strong, J. E., 122, 124.

Subsidence, 9-10, 18-20, 36, 54-55, 56,
146, 156; damages obtained for, 20; in-
vestigation of, 56; need of law regulating
damages for, 20, 59; prevention of, 10;
relation of surface values and, 18.

Surface rights, values of, 18, 28.

Surface, subsidence of the, see Subsidence.

Surface values, relation of subsidence and,
18.

Syndicates (European), regulation of out-
put of mines and selling price of coal by,
15.

Taylor, H. N., 127, 128, 130, 131.

Tennessee, 121-122; double entry room-and-
pillar system used in, 122 ; extraction in,
121, 122; long-wall method used in, 122;
pillar drawing in, 122; proposed plan of
Wind Rock Coal Company, 123.

Terrill, A. C., 131.

Texas, extraction in, 133 ; long-wall system
used in, 133 ; room-and-pillar system used
in, 133.

Thick seam (South Staffordshire), 149.

Thirty-first Annual Coal Report of Illinois.
36.

Thomas, J. I., 86.

Topeka, (Kan.), 130.

Toulmin, Priestly, 124.

Trade conditions (1907), 87.

Trinidad district (Colo.), 133, 134.

Triple entry system, 124, 136.

Tyne Collieries, 147.

United States, average value of coal in the,
14; early methods in the, 60; land prices
no inducement to save coal in the, 9 :
miners of the, 60—61 ; mining profits in
the, 14; similar conditions in Great
Britain as in the, 61 ; standards adopted
for coal lands in the, 153.

United States Coal and Coke Company, 108.

Upper Silesia, beds of, 156; coal losses in,
158; cost of coal in, 158; cost of filling
method used in, 21, 158; filling method
used in, 158.

Utah, 134-141; bounces in, 136; Carbon
County, 134; Castle Gate bed, 134;
double-entry system used in, 136 ; extrac-
tion in, 140-141 ; long-wall system failed
in, 136; panel system used in, 136; pillar
drawing in, 136-141; room-and-pillar
system used in, 136; triple-entry system
used in, 136.

Van Horn, H. M., 89.

Ventilation, 45, 51-52, 61, 63, 64, 107, 114,
115, 143, 144, 145, 147-148; cost of, 17.

"View of Northumberland," 146.

"Voyages M6tallurgiques," 145.

Wages, underground, 153.

Wales, average value of coal in, 14, 152;
miners of, 60-61; South, 145.

Walker Colliery (Eng.), 147, 148.

Wallsend Colliery (Eng.), 146, 147, 149.

Wallsend G pit (Eng.), 149.

Walsenburg (Colo.), 134.

Washington, 141.

Watts, A. C., 134, 136.

Webster County (Ky.), 119.

Weitzel, E. H., 133.

West Virginia, 61, 98-116; Annabelle mine.
70; big room method used in, 113; block
system of retreating long-wall, 114-115;
Braxton County, 101; Cabin Creek, 104;
Carbon Coal Company, 86 ; central dis-
trict, 101; coal losses in, 109-111; Elk
Garden district, 99 ; Elkins, 101 ; extrac
tion in, 9, 98-99, 100, 101, 102, 103,
104, 105, 107, 108, 109, 110, 114;
Fairmont district, 98, 99; Fire Creek bed,

,v
INDEX

173

104; Four States Coal Company, 70;
Freeport bed, 99; Gay Coal and Coke
Company, 111; Geological Survey, 98;
Gilmer County, 101 ; Kanawha region,
102-104; Kittanning bed, 99; Logan,
111; Logan County, 113; Lower Kit-
tanning bed, 101 ; most advanced methods
used in, 98 ; New River field, 104 ; No. 2
Gas Seam, 103 ; No. 9 mine, 108 ; No. 10
mine, 108; No. 11 mine, 108; panel sys-
tem used in, 98 ; pick work in, 100, 103 ;
Piedmont district, 99 ; pillar drawing in,
98, 100, 103, 110, 111; Pittsburgh bed,
98, 101-102; Pocahontas Coal and Coke
Company, 105-107; Pocahontas district,
104-111; Pocahontas No. 3 bed, 104-105,
108, 109; Pocahontas No. 4 bed, 105;
Pocahontas No. 2 mine, 109 ; production
(1910) in, 13; room-and-pillar system
used in, 102; Sewell bed, 104; single

room method used in, 53, 111-113;
squeezes in, 100, 106.

West Virginia Geological Survey, 98.

Westphalia, average value .of coal in, 14 ;
beds of, 156; coal losses in, 157; filling
methods in, 157; long-wall system used
in, 158.

Westville (111.), 56.

Whitehaven (Eng.), 145.

Williamson County (111.), 47-51; descrip-
tion of mines in, 47, 48, 49 ; extraction
in, 48—49, 50—51; panel system used in,
49 ; pillar drawing in, 48, 49, 50 ; pillar
gouging in, 50 ; pillar slabbing in, 48, 50 ;
squeezes in, 48, 49, 50.

Wilmington field (111.), 16, 31-32.

Wind Rock Coal Company (Tenn.), 123.

Yorkshire (Eng.), 154.

Young, L. E., 18, 28.

Zeller, W. M., 125.

PUBLICATIONS OF THE ILLINOIS COAL
MINING INVESTIGATIONS

Bulletin 1. Preliminary Report on Organization and Method of Investiga-
tions, 1913. (Out of print.)

Bulletin 2. Coal Mining Practice in District VIII. (Danville), by S. O. An-
dros, 1914.

Bulletin 3. A Chemical Study of Illinois Coals, by Prof. S. W. Parr. (In

press.)

Bulletin 4. Coal Mining Practice in District VII. (Mines in bed 6 in Bond,
Clinton, Christian, Macoupin, Madison, Marion, Montgomery, Moultrie,
Perry, Eandolph, St. Glair, Sangamon, Shelby, and Washington Counties),
by S. O. Andros, 1914.

Bulletin 5. Coal Mining Practice in District I. (Long- wall), by S. O. Andros,
1914. (Out of print.)

Bulletin 6. Coal Mining in District V. (Mines in bed 5 in Saline and
Gallatin Counties), by S. O. Andros, 1914.

Bulletin 7. Coal Mining Practice in District II. (Mines in bed 2 in Jackson
County), by S. O. Andros, 1914.

Bulletin 8. Coal Mining Practice in District VI. (Mines in bed 6 in Frank-
lin, Jackson, Perry, and Williamson Counties), by S. O. Andros, 1914.

Bulletin 9. Coal Mining Practice in District III. (Mines in beds 1 and 2 in
Brown, Calhoun, Cass, Fulton, Greene, Hancock, Henry, Jersey, Knox,
McDonough, Mercer, Morgan, Bock Island, Schuyler, Scott, and Warren
Counties), by S. O. Andros, 1915.

Bulletin 10. Coal Eesources of District I. (Long- wall), by G. H. Cady, 1915.

Bulletin 11. Coal Eesources of District VII. (Counties listed in Bulletin 4),
by Fred H. Kay, 1915.

Bulletin 12. Coal Mining Practice in District IV. (Mines in bed 5 in Cass,
DeWitt, Fulton, Knox, Logan, Macon, Mason, McLean, Menard, Peoria,
Sangamon, Schuyler, Tazewell, and Woodford Counties), by S. O. Andros.
1915.

Bulletin 13. Coal Mining in Illinois, by S. O. Andros, 1915.

Bulletin 14. Coal Eesources of District VIII. (Danville), by Fred H. Kay
and K. D. White.

Bulletin 15. Coal Eesources of District VI., by G. H. Cady, 1916.
Bulletin 16. Coal Eesources of District II., by G. H. Cady, 1917.

Bulletin 17. Surface Subsidence in Illinois Eesulting from Coal Mining, by
L. E. Young, 1916.

Bulletin 18. Tests 011 Clay Materials Available in Illinois Coal Mines, by
E. T. Stull and E. K. Hursh.

*Bulletin 72. U. S. Bureau of Mines, Occurrence of Explosive Gases in Coal
Mines, by N. H. Darton, 1915.

*Bulletin 83. U. S. Bureau of Mines, The Humidity of Mine Air, by E. Y.
Williams, 1914.

174

PUBLICATIONS OF THE ILLINOIS COAL MINING INVESTIGATIONS 175

^Bulletin 99. U. S. Bureau of Mines, Mine Ventilation Stoppings, by E. Y.
Williams.

^Bulletin 102. U. S. Bureau of Mines, Inflammability of Illinois Coal Dust,
by J. K. Clement and L. A. Scholl, Jr.

^Bulletin 137. U. S. Bureau of Mines, Use of Permissible Explosives in the
Coal Mines of Illinois, by James R. Fleming and John W. Koster.

^Bulletin 138. U. S. Bureau of Mines, Coking of Illinois Coals, by F. K.
Ovitz.

Bulletin 91. Engineering Experiment Station, University of Illinois, Sub-
sidence Resulting from Mining, by L. E. Young and H. H. Stock.

Bulletin 100. Engineering Experiment Station, University of Illinois, The
Percentage of Extraction of Bituminous Coal, with Special Reference to
Illinois Conditions, by C. M. Young.

* Copies may be obtained by addressing the Director, U. S. Bureau of Mines, Washing-
ton, D. C.

OVERDUE.

YD 00278

UNIVERSITY OF CALIFORNIA LIBRARY

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