Ice smoothes and moulds the landscape
During much of the last 2 million years, south-east Scotland was buried under an ice sheet many hundreds of metres thick. The ice sheet was not stationary but flowed from west to east across East Lothian and from south-west to north-east across the Borders.
The moving ice carried boulders embedded in its base which scratched the bedrock underneath. These scratches or striae can be seen in many places but particularly good examples occur beside Fenton Tower at Kingston, near North Berwick.
Moving ice also moulds the landscape. Thus an east-west grain of ridges and hollows is very marked in parts of East Lothian. That is why the north-south roads in the county go up and down like a roller-coaster. Much of the Merse has similar ridges or is covered by oval mounds called drumlins forming the ‘basket-of-eggs’ landscape typical of glaciated areas.
Crag-and-tail is a spectacular feature sculptured by ice. The Law at North Berwick is a fine example. The very hard rock of the volcanic plug resisted erosion much better than the softer sedimentary strata. The moving ice was forced over and round the obstruction, stripping away the softer rocks round the front (upstream) and the sides of the hard rock (forming the crag) while softer rocks, protected in the lee of the crag, formed the long ridge (tail). Almost every craggy volcanic hill in both East Lothian and the Borders has its ‘tail’ to the east.
Rivers carve valleys proportionate to their size. But some large valleys have only small streams and some valleys have no streams at all. These are called dry valleys.
When the ice was melting, towards the end of the ice age, the Lammermuir Hills emerged from the ice sheet as it retreated into the plain. Vast amounts of meltwater were produced and it escaped by the easiest route to lower ground or to the sea. This water eroded along the edge of the ice-sheet, down into the rock. As the ice retreated channels were abandoned and new ones cut at lower levels. Deep channels form dry valleys around Garvald, and all along the north side of the Lammermuirs and the Garletons. Similar valleys occur along the south slopes of the Lammermuirs, such as Raecleuch Head, and in many other places in the Borders, particularly Carlops.
Running water acts like a sieve and sorts sediment into different sizes. Thus the coarsest fragments form gravels which are only rolled a short distance along the river bed. The sand fraction forms banks, and the silts and clays are carried along in suspension to be deposited in lakes or the sea when the flow weakens.
The most vigorous water in recent times was the meltwater from the ice-caps. Hence there are deposits of sand and gravel where the edge of the ice stood, the same areas where meltwater carved out the dry valleys. The movement of the water can be seen in the internal structures preserved in the sands and gravel layers. Where meltwater flowed in tunnels under the ice it left sinuous ridges of gravel, called eskers, when the ice melted, as at Bedshiel, near Greenlaw.