126 
VARIATIONS OF MATERIAL. 
of the bed accumulating round them. In 
a few cases the place of a trunk is marked 
by a circular depression in the coal, the 
trunk having been probably removed with 
the overlying fire clay. In some of the 
stumps the thick diverging roots may be 
traced by clearing off the coal nearly a 
yard from the circle of bark.”* 
The beds of coal themselves, and those 
interstratified with them, vary horizontally 
in their contents; the coal sometimes thin¬ 
ning off, and being succeeded by sandstone 
or clay, and the reverse. The depth of the 
beds is also not constant, affording traces 
of the irregular action of floods. A stratum 
of fine mud, indicating a tranquil flow of 
fine sedimentary matter from a distance, 
preserving the delicate fern leaf in sharp¬ 
ness of outline equal to the living leaf of 
to-day, will be supplanted in another part 
by a confused mass of rolled ])ebbles, and 
crushed river shells. The extensive work¬ 
ings of these ancient flats and beaches, 
have disclosed their character as accurately 
as though they were but of yesterday, 
* Journal of the Geological Society, 1845, p. 43. 
