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. HOW COAL WAS MADE The broad, rounded dome of a maple tree shades my windows from the intense heat of this August day. The air is hot, and every leaf of the tree's thatched roof is spread to catch the sunlight. The carbon in the air is breathed in through openings on the under side of each leaf. The sap in the leaf pulp uses the carbon in making starch. The sun's heat is absorbed. It is the energy that enables the leaf-green to produce a wonderful chemical change. Out of soil water, brought up from the roots, and the carbonic acid gas, taken in from the air, rich, sugary starch is manufactured in the leaf laboratory.