Deserts and dunes that turned the land red
Around 390 million years ago, when Hutton’s Unconformity was being formed, Laurentia, the continent of which Scotland was a part, lay in the southern tropics. The mountains that had built up were being worn down. The lowlands were an arid desert, like the Sahara today. There was no vegetation cover and flash floods caused rapid erosion. The result was coarse gravels of rounded boulders, cobbles and pebbles, which turned into the rock called conglomerate. The red colour is typical of rocks formed in deserts.
One of the best places to see this deposit is in the Lammermuir Hills above Oldhamstocks. The spectacular valley of the Back Water has ‘badlands’ topography known locally as the Fairy Glen, displaying the conglomerate almost in the way it was originally formed.
The finer sand was blown about the desert plains as dunes. The sand grains became rounded and the beds formed typical dune bedding.
Red conglomerates and sandstones occur all the way round the Merse as at Jedburgh, and round the East Lothian and Dunbar basins. The fertile red soils of these areas pay testimony to the desert past.