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COAL AND THE COAL MINES.

IN THE BEGINNING.

Every one knows that mineral coal is dug out from the crust of the earth. But the question frequently is asked concerning it, How and under what conditions was it formed? In order to answer this inquiry it is necessary to have recourse to the science of geology.

A brief review of the geological history of the earth's crust will be of prime importance, and it will not be inappropriate to go back to the origin of the earth itself. But no man can begin at the beginning; that is too far back in the eternal mists; only the Infinite Mind can reach to it. There is a point, however, to which speculation can journey, and from which it has brought back brilliant theories to account for the existence of the planet on which we live. The most philosophic of these theories, as it certainly is the most popular, is the one known as the Nebular Hypothesis, propounded by Laplace, the great French astronomer, in 1796. This theory accords so well with the laws of physics, and with the human knowledge of the age, that most of the great astronomers have adopted it as the best that has been given to us, and the world of science may be said to have accepted it as final. Let us suppose, then, in accordance with this theory, that our earth was, at one time, a ball of liquid fire, revolving on its axis, and moving, in its orbit, around the parent sun with the motion imparted to it in the beginning. As cooling and condensation went on, a crust was formed on its surface, and water was formed on the crust. The waters, however, were no sooner spread out than they were tossed by the motion of the atmosphere into waves, and these waves, by constant friction against the rock crust of the earth, wore it down into pebbles, sand, and mud. The silt thus made being washed up on to the primitive rock and left there by the receding waters became again as hard and firm as before. Occasionally a subsidence, due to the contraction of the earth's body, would take place and the sea would again sweep over the entire surface, depositing another layer of silt on the one already formed, or possibly washing that again into sand and pebbles. This process continued through an indefinite period of time, forming layer upon layer of stratified rock, or excavating great hollows in the surface already formed.

That period in the history of the earth's crust before stratification began is known as Archean time. This was followed by the period known as Paleozoic time, which is divided into three ages. The first is the age of Invertebrates. It was during this age that life made its advent on the earth. The waters were the first to bring it forth, but before the close of the age it began also to appear on the land, in isolated spots, in the simplest forms of vegetation. The next age is known as the age of Fishes, during which vegetable life became more varied and abundant, winged insects floated in the air, and great sharks and gars swam in the seas. Then came the Carboniferous age or age of Coal Plants, in which vast areas of what are now the Middle, Southern, and Western States were covered with low marshes and shallow seas, and were rich and rank with multitudinous forms of vegetation. But these marshes were again and again submerged and covered with material washed up by the waves before the final subsidence of the waters left them as a continuing portion of the dry land. It was at the close of the Carboniferous age that great disturbances took place in the earth's crust. Before this the rock strata had been comparatively level; now they were folded, flexed, broken, rounded into hills, pushed resistlessly up into mountain ranges. It was at this time that the upheaval of the great Appalachian Range in North America took place. Following this came Mesozoic time, which had but one age, the age of Reptiles. It was during this age that the type of reptiles reached its culmination. The land generally brought forth vegetation, though not with the prolific richness and luxury of the Carboniferous age. Birds, insects, and creeping things were abundant, and monsters of the saurian tribe swam in the seas, roamed through the marshes, crawled on the sandy shores, and took short flights through the air. The last great division is known as Cenozoic time, and covers two ages, the age of Mammals and the age of Man. It was during the mammalian age that trees of modern types, such as oak, maple, beech, etc., first made their appearance, and mammalian animals of great variety and size, both herbivorous and carnivorous, roamed through the forests. True birds flew in the air, true snakes crawled upon the ground, and in the waters were whales and many kinds of fishes of the present day. But the marine monsters and the gigantic and ferocious saurians of an earlier age had disappeared. So the world became fitted to be the dwelling-place of the human race. Then began the age of Man, an age which is yet not complete.

Such, in brief, is the history of the earth as the rocks have told it to us. Without their help we could know but little of the story. Through all the periods of time and all the ages, they were being formed, layer upon layer, of sand and silt, of mud and pebbles, hardening with the passing of the centuries. But while they were still soft they received impressions of the feet of birds and of beasts, they were marked by the waves and were cracked in the fierce heat of the sun, and their surfaces were pitted by the rain-drops of passing showers. Shells, corals, and sponges were imbedded in them; the skeletons of fishes and the bones of animals that walked or crept upon the land or flew in the air were covered over by them; they caught and held the drooping fern, the falling leaf and twig and nut; they closed around the body of the tree itself and buried it from sight; and as the soil hardened into rock, bone and shell, leaf and stem, hardened with it and became part of it. To-day we find these fossil remains, sometimes near the surface of the earth, sometimes hundreds or thousands of feet below it. We uncover them from the soil, we break them from the rock, we blast them out in the quarries, we dig them from the mines of coal and ore. It is by them and by the structure of the rock which contains them that we read the history of the earth, a history covering so long a period of time from the beginning of the stratification of the rocks to the age when man appeared upon the globe that no one has yet dared to reckon the millions upon millions of years which intervened, and give the result of his computation to the world as true.

THE COMPOSITION OF 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 improper 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:--

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:--

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:--

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