Extent of coalfields

Spread of primeval forests

Laying down of peat bogs

  The map shows the extent of the British coalfields that have been proved.
 There are also large areas where coal is  known to be present but has not yet been confirmed as feasible to be worked.
 This coal was formed millions of years ago, far back in time, long before great reptiles and long before the British Isles was the shape that it is now. It was formed about 300 million years ago when the worlds surface was  quite different to what it is today from forests that formed a huge swamp  that is now Great Britain and Ireland.
 Before it became a swampland this area was a great inlet of the sea fed by rivers from high ground far to the north and south and to the west where  the Atlantic ocean is now.

 Where there are hills rainwater will collect forming streams which join to  form rivers and then raging torrents moving vast quantities of rocks and debris  in their wake. As these rivers get nearer to their mouth they slow down and it  becomes more and more difficult for them to carry their load of solid matter.  This material settles as sediment in the shallow water of the river's mouth  which gradually builds up a delta forming land where plants can grow. This process occurred over many hundreds of years until the land formed covered many  thousands of square miles. Conditions were just right for plant growth, the climate was sub tropical, damp and hot so that growth was very fast. These vast forests were eventually to turn into coal. The plants and trees that grew in these forests were not the plants of today but from fragments preserved in the coal seams and overlying strata it is possible to see exactly what they were  like. As they grew in water they were quick growing and very soft which meant  they decayed easily. For century after century dead leaves, branches and whole  trees fell into the swamp decayed and formed a base upon which a new generation  of forest could grow. As the weather was damp and hot the amount of dead matter was enormous and the action of bacteria turned it into peat.            How then did this peat become coal??

The surface of the planet constantly changes shape due to the tremendous movements that take place in the centre. Below the solid crust of the earth there is great heat from radioactive materials and from the molten core and it  is thought that

movements here caused changes to the earths surface. For example for a long time throughout the seventy million years when the coal bearing rocks were formed one  part of the earths crust was sinking steadily but occasionally rather faster  than usual. It was happening over the whole area where the British Isles are now  and it was this sinking that made the formation of coal possible.
 The peat was forming on a layer of sand and mud which was slowly sinking  but so slowly that all the dead matter dropping from the forest above kept  the conditions of the swamp just right with the surface of the peat at about water level. While the sinking was steady the peat beds grew thicker and thicker because the forests were growing fast enough to equal the rate of sinking.
 It was this length of time of steady sinking that determined the  eventual thickness of the coal seams but occasionally the deep seated movements caused the earths crust to sink faster.
 When this happened it meant that the forest could no longer build itself a  base to grow on fast enough to keep itself above water consequently all the plants and trees were drowned.
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