Coal the heat and pressure of deep burial causes the loss of water, methane and carbon dioxide and an increase in the proportion of carbon. Thus first lignite (also called "brown coal"), then sub-bituminous coal, bituminous coal, and lastly anthracite (also called "hard coal" or "black coal") may be formed. The wide, shallow seas of the Carboniferous Period provided ideal conditions for coal formation, although coal is known from most geological periods. The exception is the coal gap in the Permian–Triassic extinction event, where coal is rare. Coal is known from Precambrian strata, which predate land plants—this coal is presumed to
A-class destroyer (1913) tons and had a length of around . All were powered by triple expansion steam engines and had coal-fired water-tube boilers (although initially, some had "locomotive type" fire-tube boilers in lieu). Armament was generally one QF 12 pounder on a bandstand on the forecastle, up to five QF 6 pounder and 2 single tubes for torpedoes. The "Daring" and "Havock"-class ships initially had a third tube in the bow, fixed to fire straight ahead, but this was found to weigh down the bows and it was possible for the ship to run over its own torpedo when moving at high