Craigvinean :: Chapter 1 - The Shaping of the Landscape

Chapter 1 - The Shaping of the Landscape

The shape of the landscape in any particular area is continually changing over a very long period of time. The change in any single year is infinitesimal and it is almost impossible to comprehend the vast time scale involved in geological processes. Mountain ranges may form as a result of massive folding or movements within the Earthís crust. Molten lava may pour from stress points in crust to form huge volcanoes or layers of great thickness. Over many millions of years the shape of the landforms is modified by various agencies, such as running water and moving ice. The eroded material may be carried out to sea or deposited elsewhere to form a different kind of landscape. The whole cycle of uplift, erosion and deposition may repeat itself in the course of geological time.

Deposition

At a very early stage in the earthís history the whole of the South of Scotland lay under the sea. Layer upon layer of fine muddy sediment was laid down on the sea bed, building up to a thickness of thousands of feet. The effect of this enormous weight of material was to compress the sediments into solid rock.

These rocks are good examples of sedimentary rocks and are called shales. Certain kinds of coarser sedimentary material are called greywackes.

Uplift

At a later stage the sedimentary rocks were crumpled on a vast scale and pushed upwards to form mountains of which the present-day Southern Uplands are but a small remnant. These crumpled shales occur over large areas in the Southern Uplands and are to be seen to the south of Towford in the vicinity of Nether and Upper Hindhope. Some of the shale beds contain small marine fossils but these are extremely difficult to find.

Volcanic Activity

At times molten rock from great depths forced its way through the damaged upper crust and spread out to form great sheets of lava over wide areas. Rocks called tuffs were also formed from thick deposits of volcanic ash. Most of the rocks in the Towford area are lavas, some of which contain agates (Scotch pebbles), formed by chemicals deposited in the spaces left by gas bubbles in the lavas. At places the successive lava flows have been re-exposed as well-marked terraces, probably best seen in the Bowmont Valley (e.g. Fasset Hill, O.S. Grid Reference 852207, north-east of Sourhope Farm). The Towford Centre building itself is made from lava type material. The lavas are examples of igneous rocks. They do not contain fossils.

Time Scale

The Southern Uplands did not rise out of the sea over-night but by a process which took millions of years. Similarly the volcanic activity which produced the lava sheets was not a simple event lasting a few days. It is hardly possible for us to appreciate how long ago all this took place - some four hundred million years - even before the coal seams were being formed. It is even possible that the whole area may have been submerged below the sea again and that other sedimentary rocks were laid down on the old land surface.

Erosion

For many, many millions of years frosts, rain, running water and moving ice have been wearing away the landscape and shaping it to its present form by the processes known collectively as erosion.

The first valleys were almost certainly formed by streams and rivers cutting very slowly downwards - a process which is still in progress at the present day. (The major work of downcutting is done by pebbles and boulders being rolled along the stream bed, not by the water itself). This very, very slow process has been going on for countless millions of years, reducing what was formerly a great mountain mass to low, rounded hills.

The Ice Age

One of the most important events in shaping the landscape as we see it now was the coming of the Ice Age about one million years ago. The ice melted away only about ten thousand years ago - a very brief moment in the long span of geological history. During the Ice Age one or more ice-sheets covered the whole of Scotland, similar to the ice-sheets presently covering Greenland or Antarctica. Its effects in the South of Scotland were very different to the effects of valley-glaciers such as those still at work in Norway or Switzerland.

The ice covering this area was coming from the higher ground to the south-west (the Moffat and Tweedsmuir Hills) flowing in a wide sweep round both sides of Cheviot and in conflict with ice moving down from Cheviot itself.

This great mass of ice, grinding its way over the land surface, wore down and carried off many metres of solid rock. The general effect was to round off outlines and produce smooth shapes in contrast to the work done by valley glaciers in gouging out the steep-sided valleys and rugged landscape of the Scottish Highlands. (The fact that shales and lavas are easily weathered, i.e. broken down by frost, etc., into smaller fragments, is another factor which tends to produce the rounded same-ness in outline of most of the hills).

The ice-sheet appears to have melted away relatively quickly from the Cheviot area and there seems to have been very little valley-glacier features should not be expected in this area. It will be noted that few of the valleys even begin to approach the conventional U-shape associated with local glaciation. The main ice movement was towards the NNE, diagonally across the Kale valley. This is shown by glacial striae (rock scratches) and fluting of the rock on the summit of the ridge between Chesterhouse Hill and Morebattle Hill, to the south of Morebattle.

(By contrast, very good evidence of valley-glaciers, with associated corries, hanging valleys, waterfalls, moraines, etc., are to be seen in the higher Tweedsmuir and Moffat Hills, in the vicinity of St. Maryís Loch, Loch Skene, the Grey Mareís Tail, Winterhope Burn, etc.)

As the ice melted away, great torrents of water flowed over, through and under the ice masses. Meltwater, flowing downslope under the ice, cut channels such as the one entering the Towford grounds at the high gate on the western boundary. Two other similar meltwater channels may be identified between the Centre and Pennymuir Roman camp, on the west side of the road. These meltwater channels now form small dry valleys.

While the last of the ice was melting away, the whole landscape probably resembled a vast roadworks scheme in the middle of a severe winter hold-up. Bare rock was exposed on the highest ground, with shattered fragments and boulders lying on the hillsides. Sheets of clay plastered the lower valley slopes. Gravel and sand was washed downslope by heavy rain and landslips were probably common.

That bare landscape is now covered with vegetation but the basic pattern is still there, with rock exposures and occasional scree near the hill tops, clay with occasional boulders on the hillsides, unconsolidated material flanking either side of the valley bottom and recent alluvium on the actual valley floor. The hillock behind the Centre is a mound of gravel and sand, as shown in the little gravel quarry on its south side. Excavations for the pond in the Centre grounds revealed interbedded sands, clays and gravels on the flat valley floor.

The Kale Valley

The Kale Water of the present day winds its way in great loops and bends across its flood plain. It most certainly does not conform to the hill-stream of the geographical text books. One reason why it meanders so much is that it has little work to do. The main valley was reshaped by the ice and the present small river is merely resorting the sands, gravels and clays left behind when the ice melted. There is also no doubt that a much larger river was coursing down the Kale Valley in late-glacial times. It will be many thousands (or millions) of years until the river is again cutting down into bedrock near Towford. The river can be seen actively eroding bedrock at the small waterfall about half a kilometre above Hownam.

When the river floods the banks are worn away very rapidly on the outside of the bends; as much as half a metre being cut away in a prolonged flood. The stream banks near the large pool have had to be protected by stone-filled baskets to prevent further erosion. An ox-bow or cutoff is in process of formation (1979) near the Centre grounds, a feature which is common in this part of the Kale Valley.

When the river is in full flood it spreads over the whole valley floor near the Centre, losing much of its power in the process and spreading fine silt over the flat flood-plain. This may happen once or twice a year.

The steep banks which are such a marked feature of the Kale Valley near the Centre are the result of the Kale Water cutting into unconsolidated materials left behind after the Ice Age. Materials moving downslope over thousands of years have probably tended to accentuate the terrace effect.

The Course of the Kale Water

The whole course of the Kale Water is a most interesting one. For the first fifteen kilometres from its source the stream flows due north. Near Morebattle it swings abruptly to the west, changing its character completely. It appears probable that it formerly flowed by Linton Bog, Crookedshaws, Yetholm Loch and the Stank to join the Bowmont Water near Yetholm. It also appears likely that there may have been a large loch between Linton Bog and Caverton Mill which subsequently flowed out by Grahamslaw to join the Teviot. The gorge course of the Kale near Grahamslaw contrasts markedly with its course over the Morebattle flood-plain. The whole question of the evolution of the Kale and Bowmont drainage systems awaits further research before firm conclusions can be drawn.

Notes on Geological Sequence and Time Scale

The shales and greywackes in the Towford area were laid down about 410 million years ago in the Silurian period. Geikie noted the following fossil groups in local shales - graptolities, ceratiocaris and orthoceras - but these are very difficult to find.

The mountain ranges of which the present-day Southern Uplands are but the last remnant were uplifted about 400 million years ago, with the volcanic activity which produced the local lavas and ash beds coming in the Lower Old Red Sandstone period.

An impression of the great age of the Southern Uplands mountain mass may be gained by comparison with the Alps, Himalayas and Rocky Mountains, all of which were formed only about 60 million years ago.

Some idea of the vast time scale involved in these geological processes may be had from the following statement.

If the age of the earth - about five thousand million years - is compared to a single day, the first life appeared about mid-day; the first rocks with common invertebrate fossils about 9.00 p.m.; the first fish at about 9.45 p.m.; and the first amphibians at 10.00 p.m. The first reptiles appeared at about 10.30 p.m., to be followed by birds and mammals more or less together at 11.15 p.m., with manís first appearance at about seven seconds to midnight. Recorded history began after the chimes of midnight had rung, just on the first stroke of midnight.

Sources of Information

  1. The Scenery of Scotland, Geikie, A., 1887.
  2. Fragments of Earth Lore, Geikie, J., 1893.
  3. Geology Map, Roxburgh, Sheet 28, Old Series.
  4. The South of Scotland, British Regional Geology, H.M.S.O., 3rd Edition, 1971.
  5. The Evolution of Scotlandís Scenery, Sissons, J.B., 1967.
  6. Problems of the Deglaciation of Scotland, Symposium, Dept. of Geography, University of St. Andrews, 1972.