78
left after coal is burnt and its quantity also reflects
the quality of the coal. Typically coals contain
only a few percent of sulphur; however, both ash
yield and sulphur may indicate the conditions of
the depositional environment in which the coal
was formed (Püspöki et al. 2017). The ash conFig. 4.3 Area of virgin forest in the USA in 1620 and 1926 (Source: Greeley 1925)
4 Changes on Earth as a Result of Interaction Between the Society and Nature
left after coal is burnt and its quantity also reflects
the quality of the coal. Typically coals contain
only a few percent of sulphur; however, both ash
yield and sulphur may indicate the conditions of
the depositional environment in which the coal
was formed (Püspöki et al. 2017). The ash conFig. 4.3 Area of virgin forest in the USA in 1620 and 1926 (Source: Greeley 1925)
4 Changes on Earth as a Result of Interaction Between the Society and Nature