It is in fact quite likely that most of our Highland and Scotch hills were at one time covered by fine forests of Scotch Fir, of which the Silva Caledonica spoken of by Tacitus was an example.
There is, moreover, evidence to show that this was the case. There is one strange peculiarity of peat which renders it a most useful substance to antiquarians.
Anything lost in a peat-moss does not decay away, but remains in a blackened but still recognizable condition for hundreds of years. Not long ago a basket containing the bones of a child was found in a Scotch peat-moss. There is also a story that an English trooper of the fourteenth or fifteenth century, and his horse, were discovered in Lochar Moss, near Dumfries. The man's features were traceable at first, but fell into powder when exposed to the air; but the weapons, stirrups, etc., were all perfectly preserved. Bones of the extinct Irish elk have often been found. Not merely so, but the piles of lake dwellings and the rough dug-out canoes which were used by the early inhabitants of Britain have been discovered in a great many places. Coins of Roman, medieval, and modern times have been unearthed, and indeed there is no doubt that if Britain is still inhabited two thousand years hence, boots, sardine tins, brass cartridges, clay pipes, and other characteristic products of our own days, will be disentombed from the peat by enthusiastic antiquarians, and displayed in museums to admiring crowds of our descendants.
The reason is quite simple: in peat neither those bacteria which cause ordinary decomposition, nor worms of any kind, are able to exist, so that the material does not decay but accumulates, though it may be blackened by peat, water, and humic acid. It is for this reason that a peat-moss is such a bad or rather an impossible soil. Neither roots nor bacteria can thrive in saturated peat; therefore the flora of a peat-moss is generally confined to the upper surface, where air and bacteria can reach the roots. Peat-mosses are also the home of insectivorous plants, which get their nitrogenous food from the insects which they catch.
In consequence of this preserving effect of peat, it is possible to trace the entire history of a peat-moss from the very beginning. Remains of the Dwarf Willow or Polar Birch have been found in England, showing that those now Arctic plants were then flourishing in Norfolk. These are generally in the lowest layers of peat-mosses. Next follow remains of the Birch and Aspen, which would be growing, as they do in places to-day, on mossy soil where the peat was still thin. Higher up in the peat one finds remains of Scotch Fir, showing that at that time regular forests of Scotch Fir existed, e.g. in Sutherlandshire and on Lochar Moss, where they do not grow at present.
Some hold that the goats, black cattle, and ponies which have been kept since the Roman occupation at any rate, are responsible for the destruction of these forests. Others hold that they were killed by a change of climate. But they certainly existed.
Trunks of Scotch Fir have even been found in peat at 2400 feet in Yorkshire, and at heights in Scotland which are above all the present plantations. About this time it seems that the newer Stone Age men must have been in Switzerland and Denmark, for their remains and characteristic weapons occur in those countries at the same level in the mosses as the Scotch Fir.
Still higher in the peat comes the Bog Oak. With it are in Denmark remains of the Bronze, Iron, and Roman times.
In Denmark the uppermost layers of the peat contain remains of Beech trees. As this last tree only entered the country in the historic period, it is not found except in the highest layers of all.
Unfortunately we have not yet obtained in our own country the same evidence from the peat-bogs as to the history of the flora of Britain. It is at least probable that it was on very much the same lines.