Coal mining Coal deposits | Britannica
Coal deposits are known to have formed more than 400 million years ago. Most anthracite and bituminous coals occur within the 299 to strata of the Carboniferous Period, the socalled first coal age. The formation of coal deposits continued through the Permian, Triassic, and Jurassic periods into the second coal age, which includes the Cretaceous, Paleogene, and Neogene