Coal was known to man thousands of years ago. Ancient writings tell us that three thousand years ago the Chinese knew that certain kinds of black rock would burn, and in one part of the country where there was little wood they used to dig into the earth to find this black rock for their fires. This is the first evidence of coal being deliberately dug from the ground, but it is quite possible that even before this, coal was used for fuel in some parts of the world. Early man probably discovered it by accident, when he noticed that in some places the stones on which he built his fires would burn.

When the shortage of wood in some places forced men to look for other material to burn, they searched for coal in the banks of streams, or on the sides of the alleys and hills. Having found coal, they worked it by burrowing into the hillside, as they soon discovered that the coal occurred as a thick layer or 'seam' running into the hill. The burrows generally collapsed before they had reached far into the coal, and other burrows were then dug alongside. The place where a layer of coal or any other rock comes to the surface of the ground is known as its 'outcrop'. When as much coal as possible had been dug from one outcrop a search was made for another outcrop and it was often found that there were several seams one above the other, separated by layers of other kinds of rock.

It was noticed by these early coal diggers that the coal seams continued beyond the ends of their burrows, so when no more coal could safely be worked from the outcrops or edges of the seams, pits were dug to reach down to the coal further from the outcrop. These pits were like village wells near the top, but in order to uncover as much coal as possible they were made wider as they got deeper, and because of their shape they have been called 'bell pits'. It was not until hundreds of years later that the miners learned how to support the overlying rocks so that they could extend their workings a mile or more from the bottom of the pit, as they do today.

Coal was therefore known to exist as a series of layers called 'seams', separated by layers of other rocks. In Britain these rocks – sandstones, shales, fireclays and coal seams are called the Coal Measures, and they form the upper part of a large series of rocks to which the name Carboniferous, meaning 'coal bearing', has been given. Scientists say that the Carboniferous period began about 285 million years ago, and lasted for about 75 million years.

The greatest thickness of the Coal Measures in this country is about 10,000 ft. but they generally reach 2,000 to 3,000 ft. and are sometimes even thinner. Coal seams do not occur throughout the full thickness but are usually concentrated in or about 500 to 1,000 ft. of rocks, near the bottom of the Coal Measures in some coalfields and about the middle in others. Within this thickness there may be over one hundred layers or seams of coal, but many of them (from an inch or two up to 2 ft. in thickness) are too thin to be worked. Most British coal seams of workable thickness measure between 2 ft. and 10 ft., but in Staffordshire and Warwickshire there is a seam 25 – 30 ft. thick, and in Scotland there is another 100 ft. thick, but it is found only in a very small area. In Australia there is a seam 800ft. thick, and others about 200 ft. thick.