This process, known also as distillation takes place as organic matter
slowly decays after burial. During the process of decomposition, the
organic matter gradually loses its gases and liquids leaving only a thin
film of carbonaceous material (Pl. 2, fig. 7). This is the same process
by which coal is formed, and large numbers of carbonized plant fossils
have been found in many coal deposits.
In Texas the carbonized remains of plants, fish, and certain
invertebrates have been preserved in this manner, and some of these
carbon residues have accurately recorded even the most minute structures
of these organisms.