No less than thirty, some
of them four or five feet in diameter, were visible within an area of 50 yards
square, the interior being sandstone, and the bark having been converted into
coal. Such vertical stems are familiar to our coal-miners, under the name of
coal-pipes. They are much dreaded, for almost every year in the Bristol,
Newcastle, and other coal-fields, they are the cause of fatal accidents. Each
cylindrical cast of a tree, formed of solid sandstone, and increasing gradually
in size towards the base, and being without branches, has its whole weight
thrown downward, and receives no support from the coating of friable coal which
has replaced the bark. As soon, therefore, as the cohesion of this external
layer is overcome, the heavy column falls suddenly in a perpendicular or oblique
direction from the roof of the gallery whence coal has been extracted, wounding
or killing the workman who stands below. It is strange to reflect how many
thousands of these trees fell originally in their native forests in obedience to
the law of gravity; and how the few which continued to stand erect, obeying,
after myriads of ages, the same force, are cast down to immolate their human
victims.
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