Pitlochry - Glaciers, Moraines, and Peat Mosses

During the period, known as the great ice age, which
occurred many thousands of years ago, the whole of Britain, as well as the greater part of the Continent of Europe, was covered with Ice. This ice sheet was of great thickness, overtopping the highest hills, and the conditions must then have resembled those that prevail in Greenland today, where the ice cap is estimated
as being from a mile to a mile ani a half in thickness.

Ice is not stationary, it flows slowly to the lowest level, usually the sea. In this district and throughout all of the Highlands, ice has wrought great changes, not only by the removal of the sandstone and carboniferous bearing rocks, which were previously on the surface, but by widening and deepening the valleys. The harder rocks, when torn away by the ice and broken into fragments,
were ground and rounded till they became gravel, which the glacial streams from the melting ice spread over the underlying rocky surface, and this gravel, with the accompanying sand and clay, now forms the soil of the district.

Many of the surface rocks still bear evidences of glacial action as they are polished by glaciation, and bear deep scars showing the direction of the ice flow. When the extreme cold had passed away, and more genial conditions set in, the ice began to melt and get thinner, till it became lower than the higher hills, though still
filling the valleys.

It will be noticed that boulders are much more numerous
on the hillsides than in the valleys, the reason being that rocks, when they fell on edge of the glacier, were carried along by it till it incited, and were deposited on the hillsides where its edges had touched. When the ice gradually retreated up the valleys, it made long pauses, usually below the junction of two valleys, where the flow of glacial ice was stronger, and there it formed a moraine
which is a bank of clay, sand, and gravel interspersed with boulders, the height and width depending on the size of the glacier.

Two glaciers of the great ice age seem to have descended by the valleys of the Tummel and Garry, and united near Faskally House, where they formed one glacier, which stretched across the valley. Its face must have been nearly 1,000 feet in height, as it has left a large moraine, the one end being the clay bank to the west of Craigower, and the other forming the Druimchaber ridge on the south side of the Tummel, where there is a corresponding bank of clay. At Balnaguard in the Tay valley above Logierait, there is a similar moraine of that period where the bank of clay is above 400 feet in depth.

At the time of the glacier age and for long afterwards the
land was at a much hIgher level than it is now. The estuaries of the Forth, the Clyde, the Tay, and the Moray Firth, as well as all the smaller firths were river valleys when Britain and Ireland were part of the Continent of Eürope, and the English Channel did not exist. The Hebrides formed the coast line facing the
Atlantic, and the North Sea was a great plain through which the Rhine and other rivers flowed northwards to the Arctic Ocean.

How much higher the land was then, can only be a matter of conjecture, but an estimate can he made of what must have been its minimum height. The old bed of the river Forth, where the bridge spans the estuary at Queensferry, is fully 400 feet below the mean level of the sea, and from there the river must have had a sufficient fall to take it to the Arctic Ocesn. A calculation, based
on that, brings out that the land must have been at least 1,300 feet higher than it is now. As no part of the North Sea exceeds 50 fathoms in depth, an elevation of 300 feet would again make it a plain.

After the great ice age this country, which was still joined to the Continent, enjoyed a climate that might be described as semi-tropical, but this was succeeded by three or more lesser glacial periods, and it is to these, that the numerous smaller moraines are to be attributed.

Just above Dalguise, there is a distinct terminal moraine of one of these lesser glacial periods, no doubt formed by the glaciers that had flowed down the valleys of the Tay and Tummel, and united a short distance above where the railway bridge spans the Tay. At the village of Pitagowan, near the Falls of Bruar, there is a moraine occupying almost the whole breadth of the valley, which had been formed by two glaciers, that had flowed down the valleys of the Garry and the Errochty, and higher up the Garry almost to the County March, there are moraines, which tell of the reluctance with which the ice loosened its hold, and the long years it held the valley in its grip as it gradually retreated before the increasing power of the sun

Previous to the last glacial period, the land sunk until
it was abaut 100 feet lower than it is at present. Another cold period had then set in, as forests that had sunk beneath the sea, are found buried under beds of clay in the Carse of Gowrie, in the Carse of Stirling and elsewhere, and some of these forests are still below the sea level. The glacial clay with which they are covered could only have been deposited by floating ice after
their submersion, because had the clay been deposited by a glacier, it would at the same time have swept away and destroyed all vestiges of trees.

After this last glacial period the climate again became warmer and the land rose about 50 feet, and round the coast can be seen, what is known as the 100 feet terrace, which marks the sea beach of what had been the lowest land level. After a further period, the land rose about 25 feet, forming the 50 feet sea terrace, and it again rose 25 feet to its present level when the last or
terrace was formed.

The valley of the Moulin burn between Moulin and the mill
dam above Pitlochry, presents a puzzle for geologists. This burn is a diversion of the Kinnaird Burn, the only natural flow of outer being the small stream that rises in the hill face above Baledmund. But the valley of the burn below Moulin is much wider and deeper than any other side valley in the neighbourhood, so it is evident, it must at one time have had a considerable stream flowing through it. Looking at the configuration of the ground, it seems probable that ages ago, both the Edradour and
Kiiinaird burns flowed into the lake from which Moulin takes its name, and that the exit was by what is now the valley of the Moulin burn. There is a small moraine at the lower end of this valley above Pitlochry, immediately below the mill dam, and as this is the only moraine on the burns having their source in Ben Vrackie, it would seem that it was the only valley at the time of the last glacial period. The curious circumstance in connection with this valley is, that the lower part of it between Moulin and
the moraine above Pitlochry is occupied by a buried forest. This forest lies from five to ten feet below the surface, and the trees are not imbedded, but occupy a space of from two to three feet and support the overlying soil. Underneath the trees is an open space of fully a foot, and the ground beneath is covered in some parts to the depth of six inches with hazel nuts of large size resembling filberts. The trees are chiefly hazel, of a much larger size than can now be grown, with some oak and birch, and they are covered with large slabs of mica schist, weighing from 50 lbs. to a quarter of a ton,
above that is large gravel, then boulder clay mixed with small stones, and the surface soil consists of about 18 inches, of loam.

It is evident, that this was not the result of glacial action, as the trees would have been carried away and destroyed by the ice. It looks, as if a deluge of water, had suddenly descended from the face of the hill, carrying with it, slabs of mica schiist torn from the
outcrop of that rock above Baledmund, and levelling the trees as it tore down the valley. The stone slabs, bring the heaviest, would be the first to sink, and as they covered the trees, they prevented the gravel and clay from filling up the spaces between and beneath them. There is a magnificent specimen of an oak lying buried
in this valley, at the foot of the Lettoch larin. It was discovered some years ago, when laying the Pitlochry water pipe, the part then uncovered being upwards of 20 feet in length, with a diameter of 3 feet.

The climate, after the last of the glacial periods, must have been much warmer than it is now, though it never reached the semi-tropical heat that succeeded the Great Ice Age. This is shown by the remains of large fir and other trees that are found imbedded in peat mosses at an altitude of from 2,ooo to 3,000 feet, where at present it would be hopeless to attempt afforestation of any description, and there is evidence that the climate became colder within historical times.

The Romans, when they invaded Scotland described it is
densely wooded and so called it Caledonia, which means
and the inhabitants Caledonians“ or wood dwellers

There is no record or description of the state of Scotland, from the time the Roman s left, till some 400 years a afterwars, but in that interval the forests had almuest entirely disappeared. It was at one time thought this was owing to the trees being burnt down by the inhabitants, but the appearance (If the roots and the
absence of charred wood prove, that the forests were killed by the formation of peat. It will he noticed that the roots of trees iimibedded in peat are always found resting on the hard till underneath. Sometime after the Romans left, the climate became colder and more humid, and this change encouraged the growth of heath and mosses and other peat forming plants, and as peat, when it attains a thickness of a low inches, becomes imperVious to air, it had the effect off cutting of all ventilation from the roots, and so causing the death of the trees. The roots being buried under the peat, which is antiseptic, have been preserved, but as the trees fell on the surface, they disappeared from natural dlecay.

The growth of peat varies with the situation. On a dry moor the growth is slow, but with favourable conditions, and especially where sphagnum mosses abound, the growth is rapid. When the bog of Allan near Stirling was drained, about the beginning of the last century, a Roman Road was uncovered under 14ft of peat, which would show that peat had been forming at the rate of about one foot in the century.

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