Coal and the coal mines

Front matter

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UNITED STATES OF AMERICA.

L V

Preface

In treating of so large a theme in so small a compass it is impossible to do more than make an outline sketch. It has been the aim of the author to give reliable information free from minute details and technicalities. That information has been, for the most part, gathered through personal experience in the mines. The literature of this special subject is very meagre, and the author is unable to acknowledge any real indebtedness to more than half a dozen volumes. First among these is the valuable treatise on " Coal Mining," by H. M. Chance of the Pennsylvania Geological Survey. Other volumes from which the author has derived considerable information are the State geological reports of Pennsylvania, the mine inspector's reports of the same State, and the " Coal Trade Annuals," issued by Frederick E. Saward of New York.

The author desires also to acknowledge his invi PREFACE.

debtedness for valuable assistance in the preparation of this work to John B. Law and Andrew Bryden, mining superintendents, and George Johnson, real estate agent, all of the Pennsylvania Coal Company, at Pittston, Pennsylvania, and to the officers of the Wyoming Historical and Geological Society of Wilkes Barre, Pennsylvania.

HOMER GREENE.

HONESDALE, Pa.,

Contents

CHAPTER PAGE

I. In the Beginning 1

II. The Composition of Coal . 6

Chapter II. The Composition Op Coal

The first question that would naturally be asked concerning the subject with which we are dealing is, What is coal?

In reply it may be said that it is a mineral. It is black or brown in color, solid, heavy, and amorphous. The specific gravity of the average Pennsylvania anthracite is about 1.6, and of the bituminous coal about 1.4. There are four varieties of mineral coal, namely : anthracite, bituminous, lignite or brown coal, and cannel coal. To this list it would not be improj)er to add peat, since it partakes of most of the characteristics of " mineral coal, and would doubtless develop into such coal if the process of transformation were allowed to continue undisturbed. The principal element contained in each of these different kinds of coal is carbon. An analysis of an average piece of Pennsylvania anthracite would show the following chemical composition : —

Fixed carbon . . . . . .86.4

Ash 6.2

Water 3.7

Volatile matter . . . . . 3.1 Sulphur .6

Total 100

THE COMPOSITION OF COAL.

The composition of the bituminous coals of Pennsylvania, as represented by the gas coal of Westmoreland County, is shown by analysis to be as follows : — -

Fixed carbon Volatile matter Ash .

Water Sulphur

37.5 5.4 1.4

.7

Total

An analysis of coal from the Pittsburgh region would show its percentage of carbon to be from 58 to 64, and of volatile matter and ash to be proportionately less.

There is no strict line of demarcation between the anthracite and the bituminous coals. They are classed generally, according to the amount of carbon and volatile matter contained in them, as : —

Hard-dry Anthracites,

Semi-Anthracite,

Semi-Bituminous,

Bituminous.

Coals of the first class contain from 91 to 98 per cent, of carbon, and of the second class from 85 to 90 per cent. The volatile matter in the third class is usually less than 18 per cent., and in the fourth class more than 18 per cent, of its composition.

The anthracite coal is hard and brittle, and has a rich black color and a metallic lustre. It ignites with difficulty, and at first burns with a small blue flame of carbonic oxide. This disappears, however, when ignition is complete. No smoke is given off during combustion. Semi-anthracite coal is neither so hard, so dense, nor so brilliant in lustre as the anthracite, though when once fully ignited it has all the characteristic features of the latter in combustion. It is found principally at the western ends of the anthracite coal basins.

Bituminous coal is usually deep black in color, with little or no lustre, having planes of cleavage which run nearly at right angles with each other, so that when the coal is broken it separates into cubical fragments. It ignites easily and burns with a yellowish flame. It gives off smoke and leaves a large percentage of ashes after combustion. That variety of it known as caking or coking coal is the most important. This is quite soft, and will not bear much handling. During combustion it swells, fuses, and finally runs together in large porous masses.

Following the question of the composition of coal comes the question of its origin, of which, indeed, there is no longer any serious doubt. It is generally conceded that coal is a vegetable product, and there are excellent reasons for this belief. The fragments of which coal is composed have been

THE COMPOSITION OF COAL, 9

greatly deformed by compression and decomposition. Bat when one of those fragments is made so thin that it will transmit light, and is then subjected to a powerful microscope, its vegetable structure may readily be distinguished ; that is, the fragments are seen to be the fragments of plants. Immediately under every separate seam of coal there is a stratum of what is known as fire clay. It may, under the beds of softer coals, be of the consistency of clay ; but under the coal seams of the harder varieties it is usually in the form of a slaty rock. This fire clay stratum is always present, and contains in great abundance the fossil impressions of roots and stems and twigs, showing that it was once the soil from which vegetation grew luxuriantly. It is common also to find fossil tree-stems lying mashed flat between the layers of black slate which form the roof of the coal mines, also the impressions of the leaves, nuts, and seeds which fell from these trees while they were living. In some beds of cannel coal whole trees have been found, with roots, branches, leaves, and seeds complete, and ail converted into the same quality of coal by which they were surrounded. In short, the strata of the coal measures everywhere are full of the fossil impressions of plants, of great variety both in kind and size.

If a piece of wood be subjected to heat and great pressure, a substance is obtained which strongly resembles mineral coal.

That coal contains a very large proportion of carbon in its composition has already been noted. If, therefore, it is a vegetable product, the vegetation from which it was formed must have been subjected to some process by which a large part of its substance was eliminated, since "wood or woody fibre contains only from 20 to 25 per cent, of carbon. But wood can be transformed, by combustion, inix) charcoal, a material containing in its composition 98 per cent, of carbon, or a greater percentage than the best anthracite contains. This cannot be done, however, by burning wood in an open fire, for in that case its carbon unites with atmospheric oxygen and passes invisibly into the air. It must be subjected to a process of smothered combustion ; free access of air must be denied to it while it is burning. Then the volatile matter will be freed and expelled, and, since the carbon cannot come in contact with the oxygen of the air, it will be retained, together with a small percentage of ash. The result will be charcoal, or coal artificially made. The principle on which this transformation is based is combustion or decomposition out of contact with atmospheric air. But Nature is as familiar with this principle as is man, and she may not only be discovered putting it in practice, but the entire process may be watched from beginning to end. One must go, for this purpose, first, to a peat bed. This is simply an accumulation of the remains of

THE COMPOSITION OF COAL. 11

plants which grew and decayed on the spot where they are now found. As these remains were deposited each year, every layer became buried under its succeeding layer, until finally a great thickness was obtained. When we remove the upper layer we find peat with its 52 to 66 per cent, of carbon, and the deeper we go the better is the quality of the substance. It may be cut out in blocks with sharp spades, the water may be pressed from the blocks, and they may be stacked up, covered and dried, and used for fuel. In most peat bogs the process of growth is going on, and may be watched. There is a certain kind of moss called sphagnum, which in large part makes up the peat-producing vegetation. Its roots die annually, but from the living top new roots are sent out each year. The workmen who dig peat understand that if this surface is destroyed the growth of the bed must stop ; consequently in many instances they have removed the sod carefully, and after taking out a stratum of peat have replaced the sod in order that the bed may be renewed. There is little doubt that if these beds of peat could lie undisturbed and covered over through many ages they would take on all the characteristics of mineral coal.

A step farther back in geological history we reach the period of the latest formations of lignite or brown coal. This coal is first found in the strata of the glacial period, or first period in the age of Man. But it is found there in an undeveloped state. The woody fibre has not yet undergone the complete transformation into coal. The trunks and branches of trees have indeed become softened to the consistence of soap, but they still retain their natural color. Going back, however, to the strata of the Miocene or second period of the Tertiary age or age of Mammals, we find that this wood has become black, though it has not yet hardened. But when we reach the upper cretaceous or last period of the age of Reptiles, the transformation into coal has become complete. The woody fibre is now black, hard, and compact, though it may still be easily disaggregated by atmospheric action, and we have the true lignite, so called because of its apparent woody structure.

The next step takes us back to the bituminous coal of the Carboniferous age, the character and consistency of which has already been noted, and finally we reach the complete development in anthracite. It is, however, the opinion of the best geologists that the bituminous and anthracite coals are of the same age, and were originally of the same formation and character. That is, they were all bituminous ; but during the violent contortions and upheavals of the earth's crust at the time of the Appalachian revolution at the close of the Carboniferous age, the bituminous coals involved in that disturbance were changed by heat, pres-

THE COMPOSITION OF COAL. 13

sure, and motion, and the consequent expulsion of volatile matter, from bituminous to anthracite.

Cannel coal is a variety of bituminous coal, burning with great freedom, the flame of which affords considerable light. It was called " candle coal " by the English people who first used it, as it often served as a substitute for that household necessity. But the name soon became corrupted to "cannel," and has so remained. It is duller and more compact than the ordinary bituminous coal, and it can be wrought in a lathe and polished. A certain variety of it, found in the lower oolitic strata of Yorkshire in England, is manufactured into a kind of jewelry, well known by its popular name of jet.

Chapter III. When Coal Was Formed

It becomes of interest now to examine briefly into the causes and process of the transformation from vegetable substance into coal, to note the character of the vegetation which went to make up the coal beds, and to glance at the animal life of the period.

As has already been said, the plants of the Carboniferous age were exceedingly abundant and luxuriant. They grew up richly from the clayey soil, and formed dense jungles in the vast marshes which covered so large an area of the earth's surface. Ferns, mosses, and tufts of surface vegetation, and the leaves, branches, and trunks of trees fell and decayed on the place where they grew, only to make the soil more fertile and the next growth richer and more luxuriant. Year after year, century after century, this process of growth and decay went on, until the beds of vegetable matter thus deposited had reached a great thickness. But condensation was still in progress in the earth's body, and in consequence of it her crust, of necessity, at times contracted and fell. When it did so the land sank throughout vast areas, these beds of incipient coal went down, and over the great marshes the waters swept again, bringing drift of vegetation from higher levels to add to that already buried. Then over these deposits of vegetable matter the sand and. mud and gravel were laid up anew, and the clayey soil from which the next rich growth should spring was spread out upon the surface. This process was repeated again and again, as often, indeed, as we find seams of coal in any coal bed. Thus the final condition for the formation of coal was met, the exclusion of atmospheric air from this mass of decaying vegetation was complete, and under the water of the ocean, under the sand and silt of the shore, under the new deposits of succeeding ages, the transformation went on, the wood of the Carboniferous era became the coal of to-day, while above and below it the sand and clay were hardened into rock and shale.

The remarkable features of the vegetation of the coal era were the size and abundance of its plants. Trees of that time whose trunks were from one to three feet in diameter, and which grew to a height of from forty to one hundred feet, are represented in our day by mere stems a fraction of an inch in diameter and but one or two feet high. A comparison of quantity would show differences as great as does the comparison of size.

But at that time all the conditions were favorable for the rapid and enormous growth of vegetation. The air was laden with carbon, which is the principal food for plants ; so laden, indeed, that man, who is eminently an oxygen-breathing animal, could not have lived in it. The great humidity of the atmosphere was another element favorable to growth. Vegetation never lacked for an abundance of moisture either at root or leaf. Then, too, the climate was universally warm. Over the entire surface of the earth the heat was greater than it is to-day at the torrid zone. It must be remembered that the internal fires of the globe have been constantly cooling and receding, and that the earth, in the Carboniferous age, was subjected to the greater power of a larger sun than shines upon us to-day.

With all these circumstances in its favor, warmth, moisture, and an atmosphere charged heavily with carbon, vegetation could not help but flourish. That it did flourish amazingly is abundantly shown by its fossil remains. The impressions of more than five hundred different species of plants that grew in the Carboniferous era have been found in the coal measures. There are few of them that bear any direct analogy to existing species, and these few have their counterparts only in the torrid zone. The most abundant of the plants of the coal era were the ferns. Their fossil remains are found in great profusion and variety in most of the rocks of the coal-bearing strata. There was also the plant known as the tree fern, which attained a height of twenty or thirty feet and carried a single tuft of leaves radiating from its top. Probably the species next in abundance, as it certainly is next in importance, to the ferns is that of the Lepidodendrids. It doubtless contributed the greatest proportion of woody material to the composition of coal. The plants of this species were forest trees, but are supposed to have been analogous to the low club mosses of the present. Fossil trunks of Lepidodenclrids have been found measuring from one hundred to one hundred and thirty feet in length, and from six to ten feet in diameter.

Similar in appearance to the Lepidodendrids were the Sigillariae, which were also very abundant. The Conifers were of quite a different species from those already named, and probably grew on higher ground. They were somewhat analogous to the modern pine.

The Calamites belonged to the horsetail family. They grew up with long, reed-like, articulated stems to a height of twenty feet or more, and with a diameter of ten or twelve inches. They stood close together in the muddy ground, forming an almost impenetrable thicket, and probably made up a very large percentage of the vegetation which was transformed into coal,

One of the most abundant species of plants of the coal era is that of Stigmaria. Stout stems, from two to four inches in diameter, branched downward from a short trunk, and then grew out in long root-like processes, floating in the water or trailing on the mud to distances of twenty or thirtyfeet. These are the roots with which the under clay of every coal seam is usually filled.

The plants which have been described, together with their kindred species, formed the largest and most important part of the vegetation of the Carboniferous age. But of the hundreds of varieties which then abounded, the greater portion reached their highest stage of perfection in the coal era, and became extinct before the close of Paleozoic time. Other types were lost during Mesozoic time, and to-day there is scarcely a counterpart in existence of any of the multitude of forms of plant life that grew and flourished in that far-off age of the world.

The animal life of the Carboniferous era was confined almost entirely to the water. The dry land had not yet begun to produce in abundance the higher forms of living things. There were spiders there, however, and scorpions, and centipedes, and even cockroaches. There were also land snails, beetles, locusts, and mayflies. Reptiles, with clumsy feet and dragging tails, prowled about on the wet sands of the shore, leaving footprints that were never effaced by time or the elements, and are found to-day in the layers of the rocks, almost as perfect as when they were formed, millions of years ago. But the waters teemed with animal life. On the bottom of the shallow seas lay shells and corals in such abundance and variety that from the deposits of their remains great beds of limestone have been formed. Broken into minute fragments by the action of the waves and washed up by the sea during periods of submergence, they were spread over the beds of carboniferous deposits, and became the rock strata through which the drills and shafts of to-day are sunk to reach the veins of mineral coal.

Fishes were numerous. Some of them, belonging to species allied to the modern shark, were of great size, with huge fin spines fully eighteen inches in length. These spines have been found as fossils, as have also the scales, teeth, and bones. Complete skeletons of smaller fishes of the ganoid order were preserved in the rock as it hardened, and now form fossil specimens which are unequaled in beauty and perfection.

Besides the fishes, there were the swimming reptiles ; amphibian monsters, allied to the ichthyosaurs and plesiosaurs which were so abundant during the Reptilian age that followed. These animals are known as enaliosaurs. They attained great size, being from twenty-five to fifty feet in length ; they had air-breathing apparatus, and propelled themselves through the water with paddles like the paddles of whales. Their enormous jaws were lined with rows of sharp, pointed teeth, and their food was fish, shell-fish, and any other kind of animal life that came within their reach. They devoured even their own species. Living mostly in the open seas or fresh-water lagoons, they sometimes chased their prey far up the rivers, and sometimes basked in the sunshine on the sands of the shore. Frightful in aspect, fierce, and voracious, they were the terror and the tyrants of the seas.

Such were the animals, such were the plants, that lived and died, that flourished and decayed, in the age when coal was being formed and fashioned and hidden away in the crust of the earth. That the fauna and flora of to-day have few prototypes among them should be little cause for regret. There was, indeed, hardly a feature in the landscape of the coal era that would have had a familiar look to an inhabitant of the world in its present age. In place of the hills and valleys as we have them now, there were great plains sloping imperceptibly to the borders of the sea. There were vast marshes, shallow fresh-water lakes, and broad and sluggish rivers. Save bj^ isolated peaks the Rocky Mountains had not yet been uplifted from the face of the deep, and the great West of to-day was a waste of waters. In the wide forests no bird's song was ever heard, no flashing of a wing was ever seen, no serpent trailed its length upon the ground, no wild beast searched the woods for prey. The spider spun his web in silence from the dew-wet twigs, the locust hopped drowsily from leaf to leaf, the mayfly floated lightly in the heavy air, the slow-paced snail left his damp track on the surfaces of the rocks, and the beetles, lifting the hard coverings from their gauzy wings, flew aimlessly from place to place. In seas and lakes and swampy pools strange fishes swam, up from the salt waters odd reptiles crawled to sun themselves upon the sandy shore or make their way through the dense jungles of the swamps, and out where the ocean waves were dashing, fierce monsters of the sea darted on their prey, or churned the water into foam in savage fights with each other.

But in all the world there were no flowers. Stems grew to be trunks, branches were sent out, leaves formed and fell, the land was robed and wrapped in the richest, most luxuriant foliage, yet the few buds that tried to blossom were scentless and hidden, and earth w T as still void of the beauty and the fragrance of the flowers.

Chapter IV. How The Coal Beds Lie

The process of growth, deposition, submergence, and burial, described in the preceding chapter, continued throughout the Carboniferous age. Each period of inundation and of the covering over of beds of vegetable deposit by sand and silt is marked by the layers of stratified rock that intervene between, and that overlie the separate seams of coal in the coal measures of to-day. The number of these coal seams indicates the number of periods during which the growth and decay of vegetation was uninterrupted. This number, in the anthracite coal regions, varies from ten to thirty or thereabouts, but in the bituminous regions it scarcely ever exceeds eight or ten. The thickness of the separate coal seams also varies greatly, ranging from a fraction of an inch up to sixty or seventy feet. Indeed, there are basins of small extent in the south of France and in India where the seam is two hundred feet thick. It is seldom, however, that workable seams of anthracite exceed twenty feet in thickness, and by far the largest number of them do not go above eight or ten, while the seams of bituminous coal do not even average these last figures in thickness. Neither is the entire thickness of a seam made up of pure coaL Bands of slate called "partings" usually run horizontally through a seam, dividing it into " benches*" These partings vary from a fraction of an inch to several feet in thickness, and make up from one fifth to one seventh of the entire seam.

The rock strata between the coal seams range from three feet to three hundred feet in thickness, and in exceptional cases go as high as five or six hundred feet. Perhaps a fair average would be from eighty to one hundred feet. These rock intervals are made up mostly of sandstones and shales. The combined average thickness of the coal seams of Pennsylvania varies from twenty-five feet at Pittsburgh in the western bituminous region to one hundred and twenty feet at Pottsville in the eastern anthracite district, and may be said to average about one fiftieth of the entire thickness of the coal measures, which is placed at 4,000 feet.

Some conception may be had of the enormous vegetable deposits of the Carboniferous era by recalling the fact that the resultant coal in each seam is only from one ninth to one sixteenth in bulk of the woody fibre from which it has been derived, the loss being mainly in oxygen and hydrogen. It is probable that the coal seams as well as the rock strata had attained a comparative degree of hardness before the close of the Carboniferous age. It was at the close of this age that those profound disturbances of the earth's crust throughout eastern North America took place which have already been referred to. Hitherto, through the long ages of Paleozoic time, there had been comparative quiet. As cooling and contraction of the earth's body were still going on, there were doubtless oscillations of surface and subsidence of strata in almost continuous progress. But these movements were very slow, amounting, perhaps, to not more than a foot in a century. Yet in Pennsylvania and Virginia the sinking of the crust up to the close of the Carboniferous age amounted to 35,000 or 40,000 feet. That the subsidence was quiet and unmarked by violent movement is attested by the regularity of strata, especially of the carboniferous measures, which alone show a sinking of 3,000 or 4,000 feet. Neither were the disturbances which followed violent, nor were the changes paroxysmal. Indeed, the probability is that they took place gradually through long periods of time. They were, nevertheless, productive of enormous results in the shape of hills, peaks, and mountain ranges.

These movements in the earth's crust were due, as always, to contractions in the earth's body or reductions in its bulk. On the same principle by which the skin of an apple that has dried without decay is thrown into folds and wrinkles, the earth's crust became corrugated. There is this difference, however : the crust, being hard and unyielding, has often been torn and broken in the process of change. Naturally these ridges in the earth's surface have been lifted alons: the lines of least resistance, and these lines seem to have been, at the time of the Appalachian revolution, practically parallel to the line of the Atlantic coast, though long spurs were thrown out in other directions, isolated domeshaped elevations were raised up, and bowlshaped valleys were hollowed out among the hills. The anthracite coal beds were in the regions of greatest disturbance, and, together with the rock strata above and below them, assumed new positions, which were inclined at all angles to their old ones of horizontality. More than this, the heat and pressure of that period exerted upon these beds of coal, which up to this time had been bituminous in character, resulted in the expulsion of so large a portion of the volatile matter still remaining in them as to change their character from bituminous to anthracite. Although the strata, in the positions to which they have been forced, are at times broken and abrupt, yet as a rule they rise and fall in wave-like folds or ridges. These ridges are called anticlinal s, because the strata slope in opposite directions from a common plane.

The valleys between the ridges are called synclinals^ because the strata slope from opposite directions toward a common plane. One result of this great force of compression exerted on the earth's crust was to make rents in it across the lines of strata. These rents are called fissures. Sometimes the faces of a fissure are parallel and sometimes they inclose a wedge-shaped cavity. This cavity, whatever its shape, is usually filled either with igneous rock that has come up from the molten mass below, or with surface drift or broken rock fragments that have been deposited there from above. Where there is displacement as well as fracture, that is when the strata on one side of a fissure have been pushed up or have fallen below the corresponding strata on the other side, we have what is known as a fault. Sometimes the displacement seems to have been accomplished with little disturbance to the sides of the fissure ; at other times we find, along the line of fracture, evidences of great destruction caused by the pushing up of strata in this way. A fault may reach a comparatively short distance, or it may traverse a country for miles. The vertical displacement may be only a few inches, or it may amount to hundreds or thousands of feet. In the bituminous coal regions, where the strata lie comparatively undisturbed, faults are but little known. In the anthracite districts they are common, but not great.

Besides the great folds into which the earth's crust was crowded, there are usually smaller folds

VERTICAL SECTION THROUGH SOUTHERN COAL FIELD.

VERTICAL SECTION THROUGH NORTHERN COAL FIELD.

corrugating the slopes of the greater ones, sometimes running parallel with them, oftener stretching across them at various angles. A marked instance of this formation is found in the Wyoming coal basin, the general coal bed of which is in the shape of a canoe, about fifty miles long, from two to six miles broad, and with a maximum depth of perhaps one thousand feet. Running diagonally across this basin, in practically parallel lines from one extremity to the other, is a series of gentle anticlinals, dividing the basin into some thirty smaller synclinal valleys or sub-basins.