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VITRIFIED FORTS.
THE first observer of
vitrified forts was Mr. John Williams, who described them in a small
book entitled "On Highland Ruins," published in Edinburgh in 1877.
It contains the following letter:-
Letter from DR.
JOSEPH BLACK, Professor of Chymistry in the University of Edinburgh.
"SIR,—I am much
obliged to you for the sight of your letters concerning the
vitrified fortresses in the 'North. I had got formerly from some of
my friends, some accounts of extraordinary vitrified walls which
they had seen in the Highlands; and Mr. James Wyatt, who spent some
time in surveying a part of that country, communicated a number of
particular observations which he had made upon one of these ruins;
but we were not enabled to judge with any certainty, for what
purposes, or in what manner, these hitherto unheard-of buildings had
been erected. It is very probable that they were executed in some
such manner as you have imagined. There are, in most parts of
Scotland, different kinds of stone, which can, without much
difficulty, be melted or softened by fire, to such a degree, as to
make them cohere together. Such is the grey stone, called whin-stone,
which, for some time past, has been carried to London to pave the
streets. Such also is the granite, or moor-stone, which is applied
to the same use, and pieces of which are plainly visible in some
specimens of these vitrified walls, which I received from my
friends. There are also many lime-stones, which, in consequence of
their containing certain proportions of sand and clay, are very
fusible: and there is no doubt that sand-stone and pudden-stone when
they happen to contain certain proportions of iron mixed with the
sand and gravel of which they are composed, must have the same
quality. A pudden-stone composed of pieces of granite must
necessarily have it.
"There is abundance
of one or other of these kinds of stone in many parts of Scotland;
and as the whole country was anciently a forest, and the greater
part of it overgrown with wood, it is easy to understand how those
who erected these works, got the materials necessary for their
purposes.—I am, SIR, your obedient humble servant.
(Signed) "JOSEPH BLACK.
"Edinburgh, April 18,
1877.
"To Mr. John Williams."
From Remarks on the
Construction of Vitrified Forts, by JOHN HONEYMAN, F.R.I.B.A. (Read
at a meeting of the Archcological Society held at Glasgow on 10th
February, 1868.)
"The conclusion to
which the phenomena exhibited at Dunskeig pointed seemed to me to be
this—that the walls were constructed of loose materials, bound
together into a solid mass by being grouted with a liquid vitreous
'cement, composed chiefly of greenstone and other easily fused
materials, and that the process was effected on the wall, not on
either side of it. In this way it would be as easy to construct a
wall twelve feet thick as two, and as easy to carry it along the
verge of a precipice as on a plain. But, it may be asked, if the
agglutination is chiefly effected in this way, how is it that we
find so large a portion of the remains bearing the evidence of the
action of intense heat ? The reason, I think, is obvious. The
material could not have been melted at all without the action of
intense heat on whatever enclosed the fire, and these enclosures
must necessarily have been very numerous. It would, with our present
amount of information on the subject; be obviously absurd to
dogmatize as to the exact modus operandi, but I shall suggest a
possible method. Suppose that first a course of loose stones was
laid all round the enclosure the width of the proposed wall, across
this a series of furnaces about eighteen inches wide and two feet
high were formed, closed at each end, and separated by partitions
composed chiefly of trap, the ends would form the outside and inside
faces of the wall, and would be provided with holes for the passage
of air through the furnace. The whole was then covered over with
stones (to a considerable extent trap) and probably turf and
sea-weed were added. In such a furnace —the means of producing a
blast being satisfactory — an intense heat would be produced, and
the result would be that the partitions and top would be fused."
(Transactions of the Glasgow Archaeological Society. Part i., vol.
ii.)
Mr. Honeyman makes
the following addition to his paper:—
"Having extended my
observation much since the above was written, I am able to add that
the vitrifaction is generally less perfect towards the outside than
in the centre of the wall, that in some forts which I have examined,
the vitrified mass rests upon rough building which has never been
subjected to great heat, and that in these cases the centre of the
wall is vitrified to a greater depth than either of the sides. It
seems evident therefore that the vitrifaction was effected from the
top of the wall, not from the sides. In every wall I have examined
there is abundant evidence that the cementing material has run dozen
among the loose stones, and the same appearances prove that the dry
building above referred to occupies still its original position
under the vitrified mass. In the interstices among the unvitrified
stones, drops and small streams from above still remain as they
cooled.
1879. J. H.
It is, however, true
that some of the loose stones have been exposed to great heat. The
fort existing in Bohemia has been remarked to have had alternate
layers of wood and stone. |
