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
Bolton Brown boulder of his selection. Bolton Brown Bolton Coit Brown (November 27, 1864 – September 15, 1936) was an American painter, lithographer, and mountaineer. He was one of the original founders of the Byrdcliffe Colony in Woodstock, NY, part of what is now referred to as the Woodstock Art Colony. Brown was born and raised in Dresden, in upstate New York. His sister was the scientific illustrator Anna B. Nash. After receiving his Masters in Painting from Syracuse University, he moved to California in 1891 to create the Art Department at Stanford University. Brown headed the department for almost ten years,