The fossil fuels comprise the coal family — coal, lignite, and peat — and the petroleum family — crude oil, natural-gas liquids, natural gas, tar — sand deposits, and oil shales (see Figs. 1-16).

Coal is reported to have been used to a limited extent by the ancient Chinese, and by the Romans during their occupation of the British Isles. It was not until about the twelfth century, however, that the mining of coal as a continuous enterprise was begun near Newcastle in northeast England. Until the beginning of the eighteenth century, coal was used al­most exclusively for heating. Then, shortly after 1700, the use of coal was extended to the production of power by the development of the steam en­gine. The first use of steam power was for the pumping of water. Then fol­lowed the use of the steam engine to drive industrial machinery, by steam locomotives and steam-driven ships, and eventually, about 1880, by steam-powered central electric power plants.

Also, about the middle of the eighteenth century it was found possi­ble to use coal to supplant charcoal for the smelting of metals, particularly iron. Subsequently, this use of coal has become so large that during the last century in the heavily industrialized areas the curves of coal consump­tion and of iron production are barely distinguishable from each other.

In Romania in 1857 and in the United States in 1859, the use of the second major class of fossil fuels, petroleum, was initiated. Since that time, owing in large measure to the development of the internal-combus­tion engine, the production and consumption of oil and gas have increased spectacularly. In fact, half a century ago only a small fraction of the total industrial energy was supplied by oil and gas, whereas now the fraction has risen to about three-quarters in the United States, and to somewhat more than half for the world as a whole.