How Machair is formed

The generally received theory of the formation of drift sands and hillocks or downs is this: the fragments of the shells of molluscous animals inhabiting the sea near the coasts, are rolled by the waves toward the shore, where they are further broken and comminuted. . . The wind then blows them beyond water-mark, where, in progress of time, hillocks are formed. These hillocks are occasionally broken up by the winds, and blown inland, covering the fields and pastures. . .

William Macgillivray (1830)

William Macgillivray, who spent much of his youth on the machairs of Northton in Harris, became Professor of Natural History at Aberdeen University. Today scientists might view his remarks as a little simplistic but he is not too far off the mark.

At the end of the last Ice Age, meltwater from the glaciers swept vast amounts of sand and gravel into the sea. The oceans were lower and so the debris was spread over much of what is now the continental shelf. As the sea level rose the glacial sediment mixed with the crushed shells of masses of molluscs and other marine creatures were driven ashore by wind and wave action to form characteristic white beaches and coastal sand dunes. The prevailing southwest winds continued to wear away and rebuild the dunes, blowing the light shelly sand over grasslands, marshes and lochs, even reaching the peatland and rocks further inland.