_Topographical Changes in the Lake-Dwelling Area during or subsequent
to the Period of their Development._
_Supposed Change in Climate, and its effects._--The arguments in
support of the theory that a material deterioration has taken place in
the climate of Britain since the Roman period are generally based on
the following considerations:--
(1.) _Historical Statements._
Roman historians agree in representing the climate as humid, but so
mild that the natives went about in a semi-nude condition, favourable
to luxuriant vegetation, and not so cold as that of Gaul. Thus Cæsar
expressly states that all kinds of trees grew in Britain, except the
_fir_ and the _beech_, and that the climate was more temperate than
in Gaul. Tacitus describes the climate as always damp with rains,
and overcast with clouds, without, however, intense cold being even
felt. In the speech attributed to Galgacus, previous to the battle of
Mons Grampius, he says that their "bodies and limbs were worn out by
cutting down woods, draining bogs, stripes, and outrages;" and the
same historian, in describing the result of a previous engagement in
Fifeshire, in which the Caledonians were beaten, states that "had not
the woods and marshes favoured their retreat, this victory in all
probability would have put an end to the war." Another writer (Dion
Cassius) describes the Caledonians as dwelling in tents, naked, and
without shoes; enduring hunger, cold, and all manner of hardships
with wonderful patience; and capable of remaining in bogs for many
days immersed up to the neck, and without food. In the woods they
lived on the bark of trees and roots, and had a certain sort of food
always ready, of which, if they took but the quantity of a bean, they
would neither be hungry nor dry for a long time after. Herodian also
describes them as going about partially naked to prevent the beautiful
figures painted on their bodies from being hidden. According to him,
they used iron as other barbarians did gold, both as an ornament and
sign of wealth. They wore neither coat of mail nor helmet to prevent
being encumbered in their marches through bogs and mosses, whence such
a quantity of vapours was exhaled that the air was always thick and
cloudy.
(2.) _The numerous remains of forest trees found in bogs and mosses in
localities where, at the present time, no such trees are found to grow._
As indicating the kind of evidence brought forward in support of this
argument, the following extracts will suffice:--
"Of old, in the parish of Croy, Inverness-shire, and before the
records of the kingdom, there were extensive forests of oak, birch,
fir, and hazel, which have been converted into moss, in some places
upwards of 20 feet deep. In a moss 400 feet above the level of the
sea, oaks of extraordinary size are dug up, some of them measuring
from 50 to 60 feet, and of proportional thickness; and even at the
height of 800 feet, where the parish joins the Strathdearn hills,
large blocks of fir are found, where now, from cold and storm, the
dwarf willow can scarcely raise its downy and lowly head."--(_New
Stat. Account_, vol. xiv. p. 449.)
A writer in the _Old Stat. Account_ (vol. xv. p. 484) referring to
moss in the parish of Kilbarchan, Renfrewshire, from 7 to 9 feet deep,
says:--
"The soil below is a deep white clay, where has formerly been a
forest. The oak is perfectly fresh; the other kinds of timber
are rotten. The stumps in general are standing in their original
position. The trees are all broken over at about the height of 3
feet, and are lying from south-west to north-east. So, wherever you
see a stump, you are sure to find a tree to the north-east. How an
oak-tree could break over at that particular place, I never could
understand. But we may be allowed to form a conjecture, that before
the tree fell, the moss had advanced along its stem and rotted it
there."
Mr. Aiton, in an excellent introduction to his treatise on Moss Earth,
thus writes:[44]--
"Trees of enormous dimensions have grown spontaneously in many
parts of Britain, where it would baffle the ingenuity of man to
rear a tree to the tenth part of the size. The mosses in all parts
of the island abound with trees of much greater dimensions than
any now to be found growing in this country. The late Mr. Browning
found an oak-tree under a moss in his lands of Benthall, in East
Kilbride, of such size and preservation as to floor a garret 20
feet long by 16 wide. The boards, more than an inch in thickness,
may still be seen at Benthall. Another oak-tree may be seen there
upwards of 60 feet in length. It has evidently been broken at both
ends, and the lower end not being completely covered with moss,
has rotted so much that the dimensions of the tree cannot now be
ascertained, but the upper end is more than 4 feet in circumference.
"At Thriepwood, in Dalserf parish, and county of Lanark, the trunk
of an oak-tree 65 feet in length was a few years ago dug from under
moss. It was as straight as the mast of a ship, and so equal in
thickness at both ends, that it was not easy to say which was the
root. Both these trees had grown at 500 feet of altitude above the
level of the sea, and on ground on which it would be difficult to
rear an oak to the twentieth part of the size.
"Many fir-trees 100 feet in length have been found under moss.
But, what is still more surprising, oak-trees 100 feet long were
found on draining Hartfield Moss in Yorkshire. They were as black
as ebony, and some of them sold one hundred and fifty years ago
as high as £15 for one tree. One oak-tree was dug from under that
moss, which measured 120 feet in length, 12 feet in diameter at
the root, and 6 feet diameter at the top! Twenty pounds sterling
was then offered for that single tree. One of the same dimensions,
with its bark, would sell now at £300, but no such tree at present
exists in Europe....
"But the climate was then also more congenial to the growth of
fruits, grapes, etc., as we have seen, and also of grain, than it
is now. The records of the Religious Houses show that wheat was
paid as a tithe from lands on which human industry could not now
raise that species of grain. Wheat was paid annually as a tithe to
the Priory of Lesmahagow from lands in that parish, on which that
species of grain has not been sown for several centuries past, and
where it could not now be raised; where, under the present economy,
oats can scarcely be brought to perfection. The minister of
Glenluce, in the Statistical Account of his parish, mentions a farm
that paid to the monastery of Glenluce twelve bolls of wheat and
the same quantity of barley as a tithe. But such is the melancholy
alteration that, about thirty years ago, that very farm was set at
£12 of yearly rent. Similar instances might be pointed out in many
parts of Scotland."
The inferences derived from these and similar observations made on the
phenomena of peat bogs and their buried forests in many other parts
of Scotland, are somewhat conflicting. There can be no doubt that the
climatal conditions that permitted oaks to grow on the higher slopes of
the hills in the north of Scotland, as well as trees of considerable
size in the Orkney and Shetland Islands, where scarcely a stunted shrub
is now to be seen growing in a wild state, were more favourable to
the growth of forest trees than those which now prevail. On the other
hand, the large pines found in some of the Lowland mosses would seem
to indicate a colder climate. The probable explanation of this is,
that the pines and oaks belong to different periods of time, that the
former preceded the latter and flourished when Scotland stood higher
above the level of the sea, and, being thus more extensive, was under
a colder climate, somewhat analogous to that which now prevails in
Norway. These conditions gradually gave place to a more genial climate,
which also induced a corresponding change in its flora. This apparently
more temperate climate appears to have been succeeded by another change
in the climatal conditions, this time of a less genial character, and
not so favourable to the growth of the oaks, and to which they, in
their turn, gradually yielded in point of luxuriance, and ultimately
succumbed to the encroachment of the bogs and peat-mosses.
To discuss at greater length the climatal changes which may have
occurred since the great oaks and pines of our moss-covered forests
flourished, would be a digression from the main object of this work.
In geological and astronomical causes some scientists believe they
have a sufficient explanation of the strange, and sometimes severe,
oscillations that are known to have taken place in post-Tertiary times,
so that the disappearance of the ancient forests from the country, and
the subsequent increase of the peat bogs, may be looked upon as the
effect rather than the cause of our altered climate. There can hardly
be any doubt, however, that during prehistoric times, and towards the
dawn of European history, North Britain was extensively covered with
forests which were characterised by a luxuriance of growth which is
not now attained in the same latitudes. Hence the statements made
by Roman historians to the effect that the natives painted their
bodies and roamed about in a semi-nude condition must not necessarily
be stigmatised as fables. That the inhabitants themselves greatly
contributed to the clearance of the woods and jungles, as they became
practically acquainted with the advantages of systematic tillage of the
ground, is also probable. But this change was not produced all at once,
as it is proved by such numerous place-names as Woodlands, Woodend,
Woodside, Linwood, Fulwood, Oakshaw-side, Oakshaw-head, Walkingshaw,
Lainshaw, etc. etc., that the south-west of Scotland was well wooded
after the Celtic language had been superseded by the Saxon dialects.
Cosmo Innes thus alludes to the subject: "At the earliest period
illustrated by the Melrose charters there is sufficient evidence that
the southern division of Scotland was not a well-wooded country. On
the contrary, the right of cutting wood was carefully reserved when
pasturage or arable land was granted; and when that right was conceded
for some particular purpose, such as for fuel for a salt-work, or for
building, the use was limited in express terms. The high grounds
of Ayrshire may be an exception, where there seems to have existed
an extensive forest; but elsewhere wood was a scarce and valuable
commodity."[45]
Though the gradual extinction of our primeval forests, the growth of
peat bogs, and many other topographical phenomena, are thus distinctly
traceable in the long vista which extends backwards to prehistoric,
if not, indeed, to geological times, there are no definite landmarks,
beyond a certain chronological sequence, by means of which these
physical changes can be more directly measured on the scale of time.
Amidst the abundant traces of struggling humanity, by which the
whole line of this hazy vista is characterised, we see the remains
of these lake-dwellings. The topographical features and environments
of Loch Buston, when the crannog-builders commenced their structural
operations, were totally different from what they are now. Then a
stagnant lake, deeply encroached upon by a marginal zone of aquatic
plants, and surrounded by a forest of oaks[46] and other indigenous
trees, occupied the site of the present fertile basin; now the whole
country-side is laid out into regular and well-cultivated fields,
with encircling hedges, and scarcely a tree to mark the once wooded
locality, part of which is still significantly known as the Shaws. For
upwards of half a century the present farmer has been raising splendid
crops of grain, not only from the whole area of the dried-up lake, but
over the very site of the crannog. And as for the size of the trees
which formerly grew here, I question if there is an oak now growing in
the whole of Ayrshire from which a dug-out canoe, having dimensions
as large as the one found at Loch Buston, could be made. The scene
strongly reminds me of a visit to Ephesus, when, after inspecting the
ruins of its once busy harbour, I penned the following words:--
"This (the famous Panormus) consists of a stone-built quay,
overlooking what used to be the harbour, having behind it a series
of vaults and passages, which must have been used as stores. Now,
however, instead of gazing on the sea, studded with ships from all
nations, and a crowded harbour, as St. Paul did when he landed at
Ephesus, we had before us a rich green field of wheat just coming
into ear, dotted here and there with some ugly-looking fig-trees.
As for the sea, it was nowhere to be seen, being distant some
four or five miles. The alluvial deposits of fifteen centuries
have thus not only raised the general level of the valley, and
covered it with débris to the thickness of about 12 feet, but also
very considerably enlarged its area, and converted it now into an
unhealthy and marshy wilderness."[47]
_Increase of Lake Silt._--But is there nothing in the local phenomena
of these lake-dwellings to indicate, even approximately, the period
of their existence, or the changes that have taken place since, by
submergence, they have disappeared from the gaze of mankind? Dame
Nature retains many agents in her service who faithfully keep tally
of many passing events, though not always by days or years. The woody
rings of a tree, water-worn channels, strata in rocks, and accumulated
mud, are some of the piles of records which she freely places at our
disposal--though often only to baffle our limited and feeble efforts
to decipher them. Can we therefore elicit any reliable data from an
examination of the accumulated silt from which the remains of the
lake-dwellings are now and again disentombed? Let us see. A few yards
from the Buston crannog, where the canoe was found, the upper stratum
of the lake sediment, for about the thickness of 2 feet, consisted of
a brown clayey substance, but, underneath this, the stuff had assumed
a more peaty character, being softer, darker in colour, and not so
heavy. The line of demarcation between these layers was so well marked,
that Mrs. Anstruther, in taking a sketch of the canoe while still lying
in its original bed, shows this feature on the exposed wall of the
trench (Fig. 191). The lowest portion of the canoe was exactly 6 feet
below the surface, so that, since its final abandonment, 4 feet of this
dark substance gradually accumulated around it. Then however, some
sudden change appears to have taken place in its composition, and under
the altered circumstances another two feet were added.
It is strange that this phenomenon is identical with what has been
observed and recorded at Lochlee. In making a large trench, so as to
expose the deeper structures of the gangway, the following particulars
were noted (see page 100):--
(1.) The uppermost portion was a bed of fine clay rather more than
2 feet thick.
(2.) Below this was a soft dark substance, formed of decomposed
vegetable matters.
(3.) At a depth of 7 feet the first horizontal beams of the gangway
were encountered.
(4.) At 10 feet deep the base of the gangway was supposed to be
reached.
The canoe found at Lochlee, though in a different part of the lake-bed,
was also buried to a depth of from 5 to 6 feet.
Regarding the marked change in the upper portion of the sedimentary
deposits in both these lakes, perhaps no better explanation can be
offered than that already suggested at page 151, viz., that it is due
to the disappearance of the primeval forests which formerly covered
their drainage areas, and the conversion of the land to agricultural
purposes, when part of the broken-up soil and clay would be washed down
into the lake-basin, and so become mixed with ordinary silt. Another
possible explanation may be found in the gradual filling up of the
lakes, and their entire conversion into marshes, covered with rank
grasses and other aquatic plants whose decomposition would henceforth
take the place of their former mossy sediment.
The proximity of Buston and Lochlee, as well as the topographical
similarity in the surrounding landscapes, would indicate that this
great change took place about the same time in both these localities.
Long before this, however, both canoes were finally sunk or abandoned,
the interval of time being measured by no less than 4 feet of a
deposit. Again the entire time that has elapsed since the gangway at
Lochlee was laid down till the lake was drained, and tally ceased to be
kept, is represented by 10 feet.
_Subsidence of the Crannogs._--Before quitting this somewhat
speculative line of research, one other subject remains to be
discussed, viz., the submergence of the Lake-Dwellings. This phenomenon
is a uniform feature in all those hitherto examined, and though the
causes of it have not been much inquired into by previous writers, they
will, I think, be found of sufficient importance to merit the attention
of both the antiquary and the geologist. There are just two immediate
causes to which this result can be assigned: viz., either a subsidence
of the surface of the island, or a rising of the waters of the
surrounding lake; or, as may happen sometimes, a combination of both
causes. The physical agencies that are likely to operate in producing a
subsidence of the island may be categorically stated thus:--
(1.) A compression of the island due to consolidation or decay of
its structural materials.
(2.) A sinking of the whole mass of these materials in soft mud as
a direct result of weight.
(3.) A general compressing and sinking of the sedimentary strata of
the lake-bed.
When the deeper structures of the Lochlee crannog were examined, it
was particularly noted that there was no flattening of any of the large
logs, as if they had been subjected to great pressure. At Lochspouts
and Buston, so far as the water permitted of similar explorations being
made, this observation was equally applicable to them. Though quite
soft, the logs always preserved their original shape and contour. One
day, at Lochspouts, I was greatly puzzled by finding what was evidently
portion of a birch-tree, from 6 to 9 inches in diameter, quite flat,
and with scarcely any wood left inside the thick bark. In no instance
previously had I seen the evidence of pressure on logs of this size;
but after carefully considering the point, it was ascertained that
such effects occurred only in the upper portion of the mound, and
above the log pavement, where the wood had been exposed to atmospheric
influences, so that when the woody fibres rotted away, the flattening
of the bark was easily produced. All the logs found buried in water or
mud retained their original dimensions, and showed no traces of having
yielded to superincumbent pressure.
In calculating the pressure of the entire crannog on the lake bottom,
it is only necessary to take into account the weight of the materials
above the surface of the island, as the greater density of the
displaced water would act as an upward pressure sufficient, before the
mass attained its equilibrium, to allow the surface of the island to
project a few feet above the level of the water, the amount varying
according to the depth of the lake. After the island grounded, if
constructed on the principles suggested at page 262, any additional
structures would act as a direct weight on the bed of the lake; but in
estimating the final and total submergence due to this element, we must
consider the weight of rubbish gradually accumulated during the period
of occupancy. As the base of the island at Lochlee was only 4 feet
below the level of that of the gangway, it follows therefore that the
maximum result due to the weight of the island could not exceed this
amount.
But the most important cause of submergence is the gradual compression
or consolidation of the lake-bed due to the increase of its sediment.
The depth of this increase at Lochlee, at least since the gangway was
laid, was found to be not less than 10 feet. Independent altogether
of any chemical changes going on in the sediment, however gradually
formed, its own weight must have acted very considerably in pressing
the lower strata into less bulk. Its accumulated depth, however, is far
from giving a correct indication of the rise in the bed of the lake; in
fact, 10 feet of silt might not raise the latter to half this extent.
Another thing, which must not be forgotten in this discussion, is the
subsidence which takes place after bogs and marshes are drained. This
is a fact well known to those conversant with the effects of drainage.
In the _Old Statistical Account of Scotland_, vol. xi. p. 163, I find
it stated that in three years after the drainage of Kinordy Moss, its
surface sank 3 feet; and Sir George Grant Suttie, writing of a drained
marsh at Balgone, says that after drainage its level sank from 3 to 4
feet (see footnote, page 249). Bogs are in fact like sponges saturated
with water, swollen to such an extent that they occupy a much larger
space than their solid materials would otherwise do. It will also be
remembered (page 191) that, after the last and more careful drainage
of Loch Buston, some five years ago, the subsidence of the _Knowe_ was
sufficiently noticeable to attract the attention of the farmer.
To assign more accurately to these agencies the respective amount of
subsidence due to each is impossible, but that their combined effect
is sufficient to account for the total submergence of the principal
lake-dwellings hitherto examined is proved by the measurements and
observations made at Lochspouts (page 168), which show a minimum result
of 10 feet.
If the above reasoning be correct, little importance remains to be
attached to the rising of the waters as a cause of submergence, even
in the exceptional circumstances where the agencies that produce this
effect, such as the destruction of the forests and the increase of peat
bogs, are known to have been in operation. It occurs in localities
where the outlet is level and the flow of water sluggish. Those of the
Irish writers who have taken notice of the phenomenon generally assign
it to this cause. Sir W. R. Wilde thus refers to it: "We likewise learn
from their recent submerged condition how much water had accumulated
on the face of the country since their construction, probably owing
to the great decrease of forest timber and the increased growth of
bog. From the additions made to the height of the stockades, and also
from the traces of fire discovered at different elevations in the
sections made of these islands, it may be inferred that the rise of
the waters commenced during the period of their occupation."--(Wilde's
_Catalogue_, p. 221.)
The observations made at Lochlee led me to ascribe an exceptionally
large share to this element as a cause of the submergence of the
crannog, but since then further investigations have proved that
the phenomenon takes place to a similar, if not greater, extent in
localities where no rising of the surface of the waters could have
occurred.