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
William Procter Prize for Scientific Achievement a principal event at the Sigma Xi Annual Meeting, where the recipient delivers the Procter Prize Address. The Prize is named for William Procter, an heir of one of the founders of the Procter and Gamble Company. He was active in Sigma Xi and its affiliated organization, the Research Society of America (RESA), and endowed the award that bears his name in 1950, the year before he died. William Procter Prize for Scientific Achievement The William Procter Prize for Scientific Achievement is an award given by Sigma Xi, a scientific-research honor society. The Procter Prize is presented annually to a