"The mineral kingdom consists of the fossil substances found in the earth. These are either entirely destitute of organic structure, or, having once possessed it, possess it no longer: such are the petrefactions."
"Fossils are of four kinds, viz. saline, earthy, inflammable and metallic; hence arise four classes."
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Source: William Withering, Torbern Bergman (1822). “The miscellaneous tracts of the late William Withering: to which is prefixed a memoir of his life, character, and writings”, p.15
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