We have already spoken in favourable terms of this volume. It consists
of 15 conversations of a family circle, comprising a familiar explanation
of the Huttonian and Wernerian systems; the Mosaic geology, as explained
by Penn; and the late discoveries of Buckland, Humboldt, Macculloch, and
others. By way of specimen, we take a portion of a conversation which
introduces the very interesting subject of the _formation of coal_:
_Edward_.--As the Huttonians evidently fail in proving coal to be
produced by fusion, I hope the Wernerians may succeed better, for I
should be sorry if so interesting a subject were left unexplained.
_Mrs. R._--To understand their account, it will be requisite for
you to recollect the process of the formation of bogs and marshes, as it
is from these that Werner derives coal. What I told you, also, of the
change produced on wood by being long exposed to moisture and kept from
contact with the air, will be of use here, as wood, in all stages of
change, is often found in coal-fields, in the same way as in peat-bogs.
_Edward_. That is a very strong circumstance in favour of the
alleged origin.
_Mrs. R_. There are some facts, indeed, connected with this, which
prove this origin beyond question, as you will admit, when I tell you
that specimens of wood are often found partly converted into coal and
partly unchanged, or petrified by some other mineral.
_Edward_. This will, at least, be direct proof that wood may be
converted into coal.
_Mrs. R_. One instance of this kind is mentioned by Brand, in his
"History of Newcastle," as having been brought from Iceland, by Sir
Joseph Banks. Dr. Rennie, in his "Essay on Peat Moss," gives a still
stronger example. In the parish of Kilsyth, he tells us, there was
found, in a solid bed of sandstone, the trunk of a tree in an erect
position, the indentations of the bark and marks of the branches being
in many parts of it still obvious. It rose from a bed of coal below the
sandstone, and the roots which reached the coal, as well as the bark for
an inch thick round the trunk, were completely converted into coal,
while the centre consisted of sandstone. 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. What is even more remarkable, he found a wooden pail and a
wooden shovel converted into pure jet.
_Edward._ Then I suppose, from all these details, that coal might
be formed artificially, by imitating the natural process.
_Mrs. R._ Mr. Hatchett made many ingenious and successful
experiments with this design, and Dr. Macculloch has more recently
succeeded in actually making coal. One of the strongest instances of the
process, is the existence of a great quantity of wood only half
converted into coal, at Bovey, near Exeter; this has been much discussed
by the geologists; but there is a bed of coal found at Locle, on the
continent, which is said to have been formed almost within the memory of
man, though I have not yet seen any good account of it.
Altogether, we have been much gratified with these Conversations. As a
hint, _en passant_, we remind the editor of such an oversight as
that at p. 350-1, "Order in which the _strata lies_ in the Paris
basin."
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