The sequence sits unconformably either on rocks of lower Paleozoic age or Carboniferous strata.

[1] Rocks of the Stewartry Group form the fill of a series of extensional basins trending NW-SE to N-S across the Southern Uplands.

[2] The northwestern part of the Lochmaben Basin also has lavas of the Carron Basalt Formation at the base of the sequence.

These are overlain by interbedded silty sandstones and breccio-conglomerates of the Hartfield Formation.

[2] The Stranraer Basin contains thick breccio-conglomerates with variable amounts of interbedded sandstones of the Loch Ryan Formation.