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.