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CONVERSATIONS ON GEOLOGY.

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 specim