Diggers in the Earth.

by Eva March Tappan.

PREFACE

The four books of this series have been written not merely to provide agreeable reading matter for children, but to give them information.

When a child can look at a steel pen not simply as an article furnished by the city for his use, but rather as the result of many interesting processes, he has made a distinct growth in intelligence.

When he has begun to apprehend the fruitfulness of the earth, both above ground and below, and the best way in which its products may be utilized and carried to the places where they are needed, he has not only acquired a knowledge of many kinds of industrial life which may help him to choose his life-work wisely from among them; but he has learned the dependence of one person upon other persons, of one part of the world upon other parts, and the necessity of peaceful intercourse. Best of all, he has learned to see. Wordsworth's familiar lines say of a man whose eyes had not been opened,--

"A primrose by a river's brim A yellow primrose was to him, And it was nothing more."

These books are planned to show the children that there is "something more"; to broaden their horizon; to reveal to them what invention has accomplished and what wide room for invention still remains; to teach them that reward comes to the man who improves his output beyond the task of the moment; and that success is waiting not for him who works because he must, but him who works because he may.

Acknowledgment is due to the Lehigh Valley Railroad, Jones Brothers Company, Alpha Portland Cement Company, Dwight W. Woodbridge, the Utah Copper Company, the Aluminum Company of America, the Diamond Crystal Salt Company, T. W. Rickard, and others, whose advice and criticism have been of most valuable aid in the preparation of this volume.

EVA MARCH TAPPAN.

I

IN A COAL MINE

Did you ever wonder how beds of coal happened to be in the earth? This is their story.

Centuries ago, so many thousand centuries that even the most learned men can only guess at their number, strange things were coming to pa.s.s. The air was so moist and cloudy that the sun's rays had hard work to get through. It was warm, nevertheless, for the crust of the earth was not nearly so thick as it is now, and much heat came from the earth itself. Many plants and trees grow best in warm, moist air; and such plants flourished in those days. Some of their descendants are living now, but they are dwarfs, while their ancestors were giants. There is a little "horse-tail" growing in our meadows, and there are ferns and club mosses almost everywhere. These are some of the descendants; but many of their ancestors were forty or fifty feet high. They grew very fast, especially in swamps; and when they died, there was no lack of others to take their places. Dead leaves fell and heaped up around them. Stumps stood and decayed, just as they do in our forests to-day. Every year the soft, black, decaying ma.s.s grew deeper. As the crust of the earth was so thin, it bent and wrinkled easily. It often sank in one place and rose in another. When these low, swampy places sank, water rushed over them, pressing down upon them with a great weight and sweeping in sand and clay. Now, if you burn a heap of wood in the open air, the carbon in the wood burns and only a pile of ashes remains. "Burning" means that the carbon in the wood unites with the oxygen gas in the air. If you cover the wood before you light it, so that only a little oxygen reaches it, much of the carbon is left, in the form of charcoal.

When wood decays, its carbon unites with the oxygen of the air; and so decay is really a sort of burning. In the forests of to-day the leaves, and at length the trees themselves, fall and decay in the open air; but at the time when our coal was forming, the water kept the air away, and much carbon was left. This is the way coal was made. Some of the layers, or strata, are fifty or sixty feet thick, and some are hardly thicker than paper. On top of each one is a stratum of sandstone or dark-gray shale. This was made by the sand and mud which were brought in by the water. These shaly rocks split easily into sheets and show beautiful fossil impressions of ferns. There are also impressions of the bark and fruit of trees, together with sh.e.l.ls, crinoids, corals, remains of fishes and flying lizards, and some few trilobites,--crablike animals with a sh.e.l.l somewhat like the back of a lobster, but marked into three divisions or lobes, from which its name comes.

Since the crust of the earth was so thin and yielding, it wrinkled up as the earth cooled, much as the skin of an apple wrinkles when the apple dries. This brought some of the strata of coal to the surface, and after a while people discovered that it would burn. If a vein of coal cropped out on a man's farm, he broke some of it up with his pickaxe, shoveled it into his wheelbarrow, and wheeled it home. After a while hundreds of thousands of people wanted coal; and now it had to be mined. In some places the coal stratum was horizontal and cropped out on the side of a hill, so that a level road could be dug straight into it. In other places the coal was so near the surface that it could be quarried under the open sky, just as granite is quarried.

Generally, however, if you wish to visit a coal mine, you go to a shaft, a square, black well sometimes deeper than the height of three or four ordinary church steeples. You get into the "cage," a great steel box, and are lowered down, down, down. At last the cage stops and you are at the bottom of the mine. The miners' faces, hands, overalls, are all black with coal dust. They wear tiny lamps on their caps, and as they come near the walls of coal, it sparkles as it catches the light. Here and there hangs an electric lamp. It is doing its best to give out light, but its gla.s.s is thick with coal dust. The low roof is held up by stout wooden timbers and pillars of coal. A long pa.s.sageway stretches off into a blacker darkness than you ever dreamed of. Suddenly there is a blaze of red light far down the pa.s.sage, a roar, a medley of all sorts of noises,--the rattling of chains, the clattering of couplings, the shouts of men, the crash of coal falling into the bins. It is a locomotive dragging its line of cars loaded with coal. In a few minutes it rushes back with empty cars to have them refilled.

All along this pa.s.sageway are "rooms," that is, chambers which have been made by digging out the coal. Above them is a vast amount of earth and rock, sometimes hundreds of feet in thickness. There is always danger that the roof will cave in, and so the rooms are not made large, and great pillars of coal are left to hold up the roof.

Not many years ago the miner used to do all the work with his muscles; now machines do most of it. The miner then had to lie down on his side near the wall of coal in his "room" and cut into it, close to the floor, as far as his pickaxe would reach. Then he bored a hole into the top of the coal, pushed in a cartridge, thrust in a slender squib, lighted it, and ran for his life. The cartridge exploded, and perhaps a ton or two of coal fell. The miner's helper shoveled this into a car and pushed it out of the room to join the long string of cars.

[Ill.u.s.tration: HOW A COAL MINE LOOKS ABOVEGROUND

All that shows on the surface is the machinery shed where the various engines work to keep the air fresh, and bring up the miners and the coal.]

That is the way mining used to be done. In these days a man with a small machine for cutting coal comes first. He puts his cutter on the floor against the wall of coal and turns on the electricity. _Chip, chip_, grinds the machine, eating its way swiftly into the coal, and soon there is a deep cut all along the side of the room. The man and his machine go elsewhere, and the first room is left for its next visitors. They come in the evening and bore holes for the blasting.

Once these holes were bored by hand, but now they are made with powerful drills that work by compressed air. A little later other men come and set off cartridges. In the morning when the dust has settled and the smoke has blown away, the loaders appear with their shovels and load the coal into the cars. Then it is raised to the surface and made ready for market.

Did you ever notice that some pieces of coal are dull and s.m.u.tty, while others are hard and bright? The dull coal is called bituminous, because it contains more bitumen or mineral pitch. This is often sold as "run-of-mine" coal,--that is, just as it comes from the mine, whether in big pieces or in little ones; but sometimes it is pa.s.sed over screens, and in this process the dust and smaller bits drop out.

The second kind of coal, the sort that is hard and bright, is anthracite. Its name is connected with a Greek word meaning ruby. It burns with a glow, but does not blaze. Most of the anthracite coal is used in houses, and householders will not buy it unless the pieces are of nearly the same size and free from dirt, coal dust, and slate. The work of preparation is done in odd-shaped buildings called "breakers."

One part of a breaker is often a hundred or a hundred and fifty feet in height. The coal is carried to the top of the breaker. From there it makes a journey to the ground, but something happens to it every little way. It goes between rollers, which crush it; then over screens, through which the smaller pieces fall. Sometimes the screens are so made that the coal will pa.s.s over them, while the thin, flat pieces of slate will fall through. In spite of all this, bits of coal mixed with slate sometimes slide down with the coal, and these are picked out by boys. A better way of getting rid of them is now coming into use. This is to put the coal and slate into moving water. The slate is heavier than the coal, and sinks; and so the coal can easily be separated from it. Dealers have names for the various sizes of coal. "Egg" must be between two and two and five eighths inches in diameter; "nut" between three fourths and one and one eighth inches; "pea" between one half and three fourths of an inch.

Mining coal is dangerous work. Any blow of the pickaxe may break into a vein of water which will burst out and flood the mine. The wooden props which support the roof may break, or the pillars of coal may not be large enough; and the roof may fall in and crush the workers. There are always poisonous gases. The coal, as has been said before, was made under water, and therefore the gas which was formed in the decaying leaves and wood could not escape. It is always bubbling out from the coal, and at any moment a pickaxe may break into a hole that is full of it. One kind of gas is called "choke-damp," because it chokes or suffocates any one who breathes it. There is also "white-damp," the gas which you see burning with a pretty blue flame over a hot coal fire. Worst of all is the "fire-damp." If you stir up the water in a marsh, you will see bubbles of it rise to the surface.

It is harmless in a marsh, but quite the opposite in a mine. When it unites with a certain amount of air, it becomes explosive, and the least bit of flame will cause a terrible explosion. Even coal dust may explode if the air is full of it, and it is suddenly set in motion by too heavy a blast of powder.

Miners used to work by candlelight. Every one knew how dangerous this was; but no one found any better way until, about a hundred years ago, Sir Humphry Davy noticed something which other people had not observed. He discovered that flame would not pa.s.s through fine wire gauze, and he made a safety lamp in which a little oil lamp was placed in a round funnel of wire gauze. The light, but not the flame, would pa.s.s through it; and all safety lamps that burn oil have been made on this principle. The electric lamp, however, is now in general use. The miner wears it on his cap, and between his shoulders he carries a small, light storage battery. Even with safety lamps, however, there are sometimes explosions. The only way to make a mine at all safe from dangerous gases is to keep it full of fresh, pure air. There is no wind to blow through the chambers and pa.s.sages, and therefore air has to be forced in. One way is to keep a large fire at the bottom of the air shaft. If you stand on a stepladder, you will feel that the top of the room is much warmer than the floor. This is because hot air rises; and in a mine, the hot air over the fire rises and sucks the foul air and gas out of the mine, and fresh air rushes in to take its place. Another way is by a "fan," a machine that forces fresh air into the mine.

[Ill.u.s.tration: MINERS AND THEIR MINE

Notice the safety lamps in the men's caps, and the little railroad on which the cars of coal and ore travel, hauled by the useful mule.]

So it is that by hard work and much danger we get coal for burning.

Now, coal is dirty and heavy. A coal fire is hard to kindle and hard to put out, and the ashes are decidedly disagreeable to handle. And after all, we do not really burn the coal itself, but only the gas from it which results from the union of carbon and oxygen. In some places natural gas, as it is called, which comes directly from some storehouse in the ground, is used in stoves and furnaces and fireplaces for both heating and cooking; and perhaps before long gas will be manufactured so cheaply and can be used so safely and comfortably that we shall not have to burn coal at all, but can use gas for all purposes--unless electricity should take its place.

II

DOWN IN THE QUARRIES

When walking in the country one day I came to a beautiful pond by the side of the road. The water was almost as clear as air, and as I looked down into it, I could see that the bottom was made of granite.

The farther sh.o.r.es were cliffs of clean granite thirty or forty feet high and coming down to the water's edge. The marks of tools could be seen on them, showing where blocks of stone had evidently been split off. I picked up a piece of the rock and examined it closely. It proved to be made up of three kinds of material. First, there were tiny sparkling bits of mica. In some places there are mica mines yielding big sheets of this curious mineral which is used in the doors of stoves and the little windows of automobile curtains. With the point of a knife the bits in my piece of granite could be split into tiny sheets as thin as paper. The second material was quartz. This was grayish-white and looked somewhat like gla.s.s. The third material was feldspar. This, too, was whitish, but one or two sides of each bit were flat, as if they had not been broken, but split. This is the most common kind of granite. There are many varieties. Some of them are almost white, some dark gray, others pale pink, and yet others deep red. It is found in more than half the States of the Union.

This quarry had been given up and allowed to fill with water; but it was a granite country, and farther down the road there was another, where scores of men were hard at work. This second quarry was part-way up a hill; or rather, it was a hill of granite which men were digging out and carrying away. When they began to open the quarry, much of the rock was covered with dirt and loose stones, and even the granite that showed aboveground was worn and broken and stained. This is called "trap rock." The easiest way to get rid of it is to blast with dynamite and then carry away the dirt and fragments. Next comes the getting out of great ma.s.ses of rock to use, some of them perhaps long enough to make the pillars of a large building.

[Ill.u.s.tration: OPENING A GRANITE QUARRY

_Courtesy Jones Brothers Company._

The first thing to do is to strip off the soil from the stone. Then, as the blocks are cut out, the big derrick lifts and loads them on waiting cars.]

Now, granite is a hard stone, but there is no special difficulty in cutting it if you know how. In the old days, when people wished to split a big boulder, they sometimes built a fire beside it, and when it was well heated, they dropped a heavy iron ball upon it. King's Chapel in Boston was built of stone broken in this way. To break from a cliff, however, a block of granite big enough to make a long pillar is a different matter, and this is what the men were doing. First of all, the foreman had examined the quarry till he had found a stratum of the right thickness. He had marked where the ends were to come, and the men had drilled holes down to the bottom of the stratum. Then he had drawn a line at the back along where he wished the split to be, and the men had drilled on this line also a row of holes. Next came the blasting. If one very heavy charge had been exploded, it would probably have shattered the whole ma.s.s, or at any rate have injured it badly. Instead of this, they put into each hole a light charge of coa.r.s.e powder and covered it with sand. These were all fired at the same instant, and thus the great block was loosened from the wall.

Sometimes there seems to be no sign of strata, and then a line of horizontal holes must be drilled where the bottom of the block is to be. After this comes what is called the "plug-and-feather" process.

Into each hole are placed two pieces of iron, shaped like a pencil split down the middle. These are the "feathers." The "plug" is a small steel wedge that is put between the iron pieces. Then two men with hammers go down the line and strike each wedge almost as gently as if it was a nut whose kernel they were afraid of crushing. They go down the line again, striking as softly as before. Then, if you look closely, you can see a tiny crack between the holes. There is more hammering, the crack stretches farther, a few of the wedges are driven deeper and the others drop out. The block splits off. A mighty chain is then wound about it, the steam derrick lifts it, lays it gently upon a car, and it is carried to the shed to be cut into shape, smoothed, and perhaps polished.

In almost every kind of work new methods are invented after a while.

In quarrying, however, the same old methods are in use. The only difference is that, instead of the work being done by muscle, it is done by compressed air or steam or electricity. Compressed air or steam works the drill and the sledgehammer. The drill is held by an arm, but the arm is a long steel rod which is only guided by the workman. Not the horse-sweep of old times, but the steam derrick and the electric hoist lift the heavy blocks from the quarry. Polishing used to be a very slow, expensive operation, because it was all done by the strength of some one's right arm, but now, although it takes as much work as ever, this work is done by machinery. To "point" a piece of stone, or give it a somewhat smooth surface, is done now with tools worked by compressed air. After this, the stone is rubbed--by machinery, of course--with water and emery, then by wet felt covered with pumice or polishing putty. A few years ago two young Vermonters invented a machine that would saw granite. This saw has no teeth, but only blades of iron. Between these blades and the piece of granite, however, shot of chilled steel are poured; and they do the real cutting.

Granite has long been used in building wherever a strong, solid material was needed; but until the sand blast was tried, people thought it impossible to do fine work in this stone. There was a firm in Vermont, however, who believed in the sand blast. They had a contract with the Government to furnish several thousand headstones for national cemeteries. Cutting the names would be slow and costly; so they made letters and figures of iron, stuck them to the stones, and turned on the blast. If a sand blast is only fast enough, it will cut stone harder than itself. The blast was turned upon a stone for five minutes. Then the iron letters were removed. There stood in raised letters the name, company, regiment, and rank of the soldier, while a quarter of an inch of the rest of the stone, which the iron letters had not protected, had been cut away. By means of the sand blast it has become possible to do beautiful carving even in material as hard as granite.

Granite looks so solid that people used to think it was fireproof; but it is really poor material in a great fire. Most substances expand when they are heated; but the three substances of which granite is made do not expand alike, and so they tend to break apart and the granite crumbles.

A marble quarry is even more interesting than a granite quarry. If you stand on a hill in a part of the country where marble is worked, you will see white ledges cropping out here and there. The little villages are white because many of the houses are built of marble. Then, too, there are great marble quarries flashing in the sunshine. Sometimes a marble quarry is chiefly on the surface. Sometimes the marble stretches into the earth, and the cutting follows it until a great cavern is made, perhaps two or three hundred feet deep. A roof is often built to keep out the rain and snow. It keeps out the light, too, and on rainy days the roof, together with the smoke and steam of the engines, makes the bottom of the quarry a gloomy place. Everywhere there are slender ladders with men running up and down them. There are shouts of the men, clanking of chains, and puffing of locomotives.

Marble is cut out in somewhat the same way as granite, but a valuable machine called a "channeler" is much used. This machine runs back and forth, cutting a channel two inches wide along the ends and back and sometimes the bottom of the block to be taken out.