the coal analyses is the increase in
coal rank and metamorphic grade resulting from the higher pressure
and temperature gradients associated with two factors: (a) depth of
burial and geologic time and (b) structural deformation. The coal samples
from the area of investigations in Virginia and West Virginia
increase in rank by a reduction of volatile matter from 29 to 22 percent
through about 244m (800ft) of stratigraphic distance or depth in this
case.