In the early Carboniferous, the portion of continental crust that now constitutes Scotland lay within the hinterland of a large continent that extended westwards to what is now the western parts of North America, eastwards to what is now the Urals and northwards towards what is now Arctic Canada, Greenland, Scandinavia and Russia. Open ocean probably lay at between 600 and 1000 km to the south. Whereas mountainous terrane lay to the north of the Highland Boundary fault, the Scottish Midland Valley, like the Northumberland Trough further south, was a region of low relief subject to periodic marine incursions.
A period of block faulting and concomitant basaltic volcanism commenced at the beginning of the Carboniferous at c. 350 Ma. This had manifestations in various regions of the British Isles from the south-west of England to the west of Ireland and as far north as the Midland Valley (Francis 1978, 1991; Upton 1982; Cameron and Stephenson 1985).