Paper No. 1
Presentation Time: 1:00 PM
HISTORY OF COAL RANK THEORIES, WITH EMPHASIS ON EASTERN US EXAMPLES
The earliest Appalachian coal rank studies date to Mathew Carey Lea’s late-1830’s analyses of
coals in the Southern Anthracite Field. The interpretation of the data was sparse, but his data has
been used in a number of studies over the past 175 years. In spite of the implications of Hilt’s
Law, indicating that rank increased with depth, many workers in the Appalachians, including
David White, believed that tectonic pressures predominated as a cause of metamorphism. In
part, this interpretation was based on an 1880’s misinterpretation of chemical data from the
Bernice semianthracite field, Sullivan County, PA. Even though the original misinterpretation
largely vanished from the literature, the effects of it persisted into the 1960’s. By that time,
European influences, with an emphasis on the effects of heating, were taking hold in the eastern
US coalfields. Particularly for the Pennsylvania Anthracite, some of the discussion of coal rank
centered around the possibility of burial at substantial (perhaps approaching 10 km) depths.
Others, following Oliver’s 1980’s proposal of hydrothermal fluids as an influence on coal
metamorphism, which, in turn, revived Gresley’s 1896 hypothesis, unraveled the metamorphic
history through the examination of generations of cleat minerals. In this model, neither great
depths nor extraordinary geothermal gradients nor, necessarily, great amounts of time are
necessary to produce the observed coal rank.