ABSTRACT
Coal is the compacted and chemically matured form of peat, itself a compressed and partially decomposed accumulation of dead land plants. There are four main requirements for coal formation.
Land plants, the main raw ingredient, are found only from late Silurian time (about 425 Ma) onwards, putting a lower stratigraphic limit on the formation of coals. Most major coal deposits formed either in Carboniferous to early Triassic time or between the late Jurassic and Palaeogene. At these periods the global climate, the arrangement of the continents and the evolutionary state of the land flora combined to favour extensive coalforming swamps.
