The Clyde Mystery. Lang Andrew
in diameter) had no woodwork, and the circular cavity thus formed, when cleared of fallen stones, showed indications of having been walled with stones and clay. Surrounding this walled cavity – the so-called ‘well’ of the explorers, there was a kind of coping, in the form of five or six ‘raised mounds,’ arranged ‘rosette fashion,’ in regard to which Mr. Donnelly thus writes:
‘One feature that strikes me very much in the configuration of the structure in the centre is those places marked X, fig. 20, around which I have discovered the presence of soft wood piles 5 inches in diameter driven into the ground, and bounding the raised stone arrangement; the stones in these rude circular pavements or cairns are laid slightly slanting inwards.’ 25
From this description, and especially the ‘slanting inwards’ of these ‘circular pavements’ or ‘cairns,’ it would appear that they formed the bases for wooden stays to support a great central pole, a suggestion which, on different grounds, has already been made by Dr. David Murray.
The surrounding piles were also attached to the horizontal logs by various ingenious contrivances, such as a fork, a natural bend, an artificial check, or a mortised hole; and some of the beams were pinned together by tree-nails, the perforations of which were unmistakable. This binding together of the wooden structures is a well-known feature in crannogs, as was demonstrated by my investigations at Lochlee and elsewhere. 26 It would be still more necessary in a substratum of timbers that was intended (as will be afterwards explained) to bear the weight of a superincumbent cairn. Underneath the layers of horizontal woodwork some portions of heather, bracken, and brushwood were detected, and below this came a succession of thin beds of mud, loam, sand, gravel, and finally the blue clay which forms the solum of the river valley. 27 The piles penetrated this latter, but not deeply, owing to its consistency; and so the blue clay formed an excellent foundation for a structure whose main object was resistance to superincumbent pressure.
Outside the circle of piles there was, at a distance of 12 to 14 feet, another wooden structure in the shape of a broad ring of horizontal beams and piles which surrounded the central area. The breadth of this outer ring was 7 feet, and it consisted of some nine rows of beams running circumferentially. Beyond this lay scattered about some rough cobble stones, as if they had fallen down from a stone structure which had been raised over the woodwork. The space intervening between these wooden structures was filled up in its eastern third with a refuse heap, consisting of broken and partially burnt bones of various animals, the shells of edible molluscs, and a quantity of ashes and charcoal, evidently the débris of human occupancy. On the north, or landward side, the outer and inner basements of woodwork appeared to coalesce for 5 or 6 yards, leaving an open space having stones embedded in the mud and decayed wood, a condition of things which suggested a rude causeway. When Mr. Donnelly drew my attention to this, I demurred to its being so characterised owing to its indefiniteness. At the outer limit of this so-called causeway, and about 25 feet north-east of the circle of piles, a canoe was discovered lying in a kind of dock, rudely constructed of side stones and wooden piling. The canoe measures 35½ feet long, 4 feet broad, and 1½ foot deep. It has a square stern with a movable board, two grasping holes near the stem, and three round perforations (2 inches in diameter) in its bottom. On the north-west border of the log-pavement a massive ladder of oak was found, one end resting on the margin of the log-pavement and the other projecting obliquely into the timberless zone between the former and the outer woodwork. It is thus described in the Proceedings of the Glasgow Philosophical Society:28
‘Made of a slab of oak which has been split from the tree by wedges (on one side little has been done to dress the work), it is 15 feet 3 inches long, 2 feet broad, and 3½ inches thick. Six holes are cut for steps, 12 inches by 10 inches; the bottom of each is bevelled to an angle of 60 degrees to make the footing level when the ladder is in position. On one side those holes show signs of wear by long use.’
An under quern stone, 19 inches in diameter, was found about halfway between the canoe and the margin of the circle of piles, and immediately to the east of the so-called causeway already described.
I carefully examined the surface of the log-pavement with the view of finding evidence as to the possibility of its having been at any time the habitable area of this strange dwelling-place; but the result was absolutely negative, as not a single particle of bone or ash was discovered in any of its chinks. This fact, together with the impossibility of living on a surface that is submerged every twelve hours, and the improbability of any land subsidence having taken place since prehistoric times, or any adequate depression from the shrinkage of the under-structures themselves, compels me to summarily reject the theory that the Dumbuck structure in its present form was an ordinary crannog. The most probable hypothesis, and that which supplies a reasonable explanation of all the facts, is that the woodwork was the foundation of a superstructure of stones built sufficiently high to be above the action of the tides and waves, over which there had been some kind of dwelling-place. The unique arrangement of the wooden substructures suggests that the central building was in the form of a round tower with very thick walls, like the brochs and other forts of North Britain. The central space was probably occupied with a pole, firmly fixed at its base in the ‘well,’ and kept in position by suitable stays, resting partly on the stone ‘cairns’ already described, partly in wooden sockets fixed into the log-pavement, and partly on the inner wall of the tower. This suggestion seems to me to be greatly strengthened by the following description of some holed tree-roots in Mr. Bruce’s paper to the Scottish Antiquaries: 29
‘Midway between the centre and the outside piles of the structure what looked at first to be tree-roots or snags were noticed partly imbedded in the sand. On being washed of the adhering soil, holes of 12 inches wide by 25 inches deep were found cut in them at an angle, to all appearance for the insertion of struts for the support of an upper structure. On the outside, 14 inches down on either side, holes of 2 inches diameter were found intersecting the central hole, apparently for the insertion of a wooden key or trenail to retain the struts. These were found at intervals, and were held in position by stones and smaller jammers.’
The outer woodwork formed the foundation of another stone structure, of a horseshoe shape, having the open side to the north or landside of the tower, which doubtless was intended as a breakwater. By means of the ladder placed slantingly against the wall of the central stone building access could be got to the top in all states of the tides.
The people who occupied this watch-tower ground their own corn, and fared abundantly on beef, mutton, pork, venison, and shell-fish. The food refuse and other debris were thrown into the space between the central structure and the breakwater, forming in the course of time a veritable kitchen-midden.
Besides the causeway on the north side, Mr. Bruce describes ‘a belt of stones, forming a pavement about six feet wide and just awash with the mud,’ extending westwards about twenty yards from the central cavity, till it intersected the breakwater. 30 These so-called pavements and causeways were probably formed during the construction of the tower with its central pole, or perhaps at the time of its demolition, as it would be manifestly inconvenient to transport stones to or from such a place, in the midst of so much slush, without first making some kind of firm pathway. Their present superficial position alone demonstrates the absurdity of assigning the Dumbuck structures to Neolithic times, as if the only change effected in the bed of the Clyde since then would be the deposition of a few inches of mud. At a little distance to the west of these wooden structures there is the terminal end of a modern ditch (‘the burn’ of Mr. Alston), extending towards the shore, and having on its eastern bank a row of stepping-stones; a fact which, in my opinion, partly accounts for the demolition of the stonework, which formerly stood over them. So far, the facts disclosed by the excavations of the structures at Dumbuck, though highly interesting as evidence of the hand of man in the early navigation of the Clyde basin, present nothing very remarkable or improbable. It is when we come to examine the strange relics which the occupants of this habitation have left behind them that the real difficulties begin.”
Dr. Munro next describes the
See
Vol. xxx. 270.
Vol. xxxiv. p. 438.
Mr. Alston describes this causeway, and shows it on the plan as “leading from the ‘central well’ to the burn about 120 fee to west of centre of crannog.”