This specimen I have myself
seen in the parsonage garden of Kilsyth, and this description is most
accurate. Sir George Mackenzie lately found a specimen precisely
similar, in the face of a sandstone rock in Lothian, and I have seen
numerous specimens of bamboos and reeds in the sandstone quarries of
Glasgow, with the bark converted into coal, and the centre filled with
sandstone.
_Edward_.--But would not this prove that sandstone, also, was
derived from wood?
_Mrs. R._--No: it would only prove that the centre had been
destroyed and removed; for the sandstone is not chemically composed of
vegetable substances, but the coal is.
_Edward_--Still, I cannot conceive by what process the conversion
is effected.
_Mrs. R._ By a natural process, evidently; being a continuation of
that which converts mosses and marshes into peat. Nay, it is supposed
not to stop at the formation of coal, but, by a continuation of the
causes, the coal becomes jet, and even amber. The eminent chemist,
Fourcroy, in proof of this, mentions a specimen in which one end was
wood, little changed, and the other pure jet; and Chaptal tells us, that
at Montpellier there are dug up whole cart-loads of trees converted into
jet, though the original forms are so perfectly preserved that he could
often detect the species; and, among others, he mentions birch and
walnut.
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