ABSTRACT
When the organic remains of plants and animals decompose under anaerobic conditions such as those found in deep wetlands and are subjected to compaction over a long period of time, they undergo a gradual lithification. The effects of microbial action, temperature, and pressure produce metamorphic changes with time, as indicated in the following sequence: plant material→peat→hgnite→sub-bituminous coal→bituminous coal→semi-anthracite→antoacite→grapthite→diamond.
