In this country, and in this age, who can doubt that coal is king? It is one of the few necessities of life. In various sections of the country, layers of coal have been discovered—some near the surface, others deep underground. These are the storehouses of fuel which the coal miners dig out and bring to the surface, and the railroads distribute. From Pennsylvania and Ohio to Alabama stretches the richest coal-basin. Illinois and Indiana contain another. From Iowa southward to Texas another broad basin lies. Central Michigan and Nova Scotia each has isolated coal-basins. All these have been discovered and mined, for they lie in the oldest part of the country.

In the West, coal-beds have been discovered in several states, but many regions have not yet been explored. Vast coal-fields, still untouched, have been located in Alaska. The Government is trying to save this fuel supply for coming generations. Many of the richest coal-beds from Nova Scotia southward dip under the ocean. They have been robbed by the erosive action of waves and running water. Glaciers have ground away their substance, and given it to the sea. Much that remains intact must be left by miners on account of the difficulties of getting out coal from tilted and contorted strata.

As a rule, the first-formed coal is the best. The Western coal-fields belong to the period following the Carboniferous Age. Although conditions were favourable to abundant coal formation, Western coal is not equal to the older, Eastern coal. It is often called lignite, a word that designates its immaturity compared with anthracite.

Coal formed in the Triassic Period is found in a basin near Richmond, Virginia. There is an abundance of this coal, but it has been subjected to mountain-making pressure and heat, and is extremely inflammable. The miners are in constant danger on account of coal gas, which becomes explosive when the air of the shaft reaches and mingles with it. This the miner calls "fire damp." North Carolina has coal of the same formation, that is also dangerous to mine, and very awkward to reach, on account of the crumpling of the strata.

There are beds of coal so pure that very little ash remains after the burning. Five per cent, of ash may be reasonably expected in pure coal, unmixed with sedimentary deposits. Such coal was formed in that part of the swamp which was not stirred by the inflow of a river. Wherever muddy water flowed in among the fallen stems of plants, or sand drifted over the accumulated peat, these deposits remained, to appear later and bother those who attempt to burn the coal.

You know pure coal, that burns with great heat and leaves but little ashes. You know also the other kind, that ignites with difficulty, burns with little flame, gives out little heat, and dying leaves the furnace full of ashes. You are trying to burn ancient mud that has but a small proportion of coal mixed with it. The miners know good coal from poor, and so do the coal dealers. It is not profitable to mine the impure part of the vein. It costs as much to mine and ship as the best quality, and it brings a much lower price.

The deeper beds of coal are better than those formed in comparatively recent time and found lying nearer the surface. In many bogs a layer of embedded root fibres, called peat, is cut into bricks and dried for burning. Deeper than peat-beds lie the lignites, which are old beds of peat, on the way to become coal. Soft coal is older than lignite. It contains thirty to fifty per cent. of volatile matter, and burns readily, with a bright blaze. The richest of this bituminous coal is called fat, or fusing coal. The bitumen oozes out, and the coal cakes in burning. Ordinary soft coal contains less, but still we can see the resinous bitumen frying out of it as it burns. There is more heat and less volatile matter in steam coal, so-called because it is the fuel that most quickly forms steam in an engine. Hard coal contains but five to ten per cent. of volatile matter. It is slow to ignite and burns with a small blue blaze.

From peat to anthracite coal I have named the series which increases gradually in the amount of heat it gives out, and increases and then decreases in its readiness to burn and in the brightness of its flame. Anthracite coal has the highest amount of fixed carbon. This is the reason why it makes the best fuel, for fixed carbon is the substance which holds the store of imprisoned sunlight, liberated as heat when the coal burns. Tremendous pressure and heat due to shrinking of the earth's crust have crumpled and twisted the strata containing coal in eastern Pennsylvania, and thus changed bituminous coal into anthracite. Ohio beds, formed at the same time, but undisturbed by heat and pressure, are bituminous yet.

The coal-beds of Rhode Island are anthracite, but the coal is so hard that it will not burn in an open fire. The terrible, mountain-making forces that crumpled these strata and robbed the coal of its volatile matter, left so little of the gas-forming element, that a very special treatment is necessary to make the carbon burn. It is used successfully in furnaces built for the smelting of ores.

The last stage in the coal series is a black substance which we know as black lead, or graphite. We write with it when we use a "lead" pencil. This is anthracite coal after all of the volatile matter has been driven out of it. It cannot burn, although it is solid carbon. The beds of graphite have been formed out of coal by the same changes in the earth's crust which have converted soft coal into anthracite.

The tremendous pressure that bears on the coal measures has changed a part of the carbon into liquid and gaseous form. Lakes of oil have been tapped from which jets of great force have spouted out. Such accumulations of oil usually fill porous layers of sandstone and are confined by overlying and underlying beds of impervious clay. Gas may be similarly confined until a well is drilled, relieving the pressure, and furnishing abundant or scanty supply of this valuable fuel. Western Pennsylvania coal-fields have beds of gas and oil. If mountain-making forces had broken the strata, as in eastern Pennsylvania, the gas and the oil would have been lost by evaporation.

This is what happened in the anthracite coal-belt.