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
Rachel Fuller Brown additional minor contributions to the field of bacteriology until their retirement. Brown died on January 14, 1980 at the age of 81 in Albany, New York. Royalties for nystatin totaled $13.4 million. As Brown and Hazen did not want any of the money for themselves, the philanthropic Research Corporation used half for grants to further scientific research and the other half to support what became known as the Brown-Hazen Fund. Both Brown and Hazen received many awards for their collaborative work, the first major prize being the Squibb Award in Chemotherapy in 1955. Brown was also elected fellow of the