Carboniferous rocks occupy much of the Midland Valley of Scotland, but are
commonly obscured at surface by Quaternary deposits. The succession occupies an
ENE-trending graben bounded by the complexes of the Highland Boundary Fault to
the northwest and the Southern Upland Fault to the southeast. Onshore, the graben is
about 90 km wide and extends some 150 km from the Ayrshire coast and Glasgow in
the west to the east Fife and East Lothian coasts in the east (Fig. 14.1). The basins
within the graben are associated with Carboniferous rocks more than 6 km thick. The
Highland Boundary and Southern Upland faults were active and helped control
sedimentation, initially during the Tournaisian as sinistral strike/oblique slip faults
and subsequently in the Visean to Westphalian a regime of dextral strike/oblique-slip
deformation (Browne & Monro 1989; Ritchie et al. 2003; Underhill et al. 2008).
Isolated exposures also occur on the Island of Arran and at Machrihanish in Kintyre.
The Midland Valley of Scotland was separated from basins to the south (Tweed and
Solway Firth basins and the Northumberland Trough- see Chapter 13) by the Lower
Palaeozoic rocks of the Southern Uplands block, which formed a positive, mainly
emergent area throughout the Carboniferous. However, this was breached during the
Carboniferous by narrow NW–SE trending basins, for example Stranraer and
Sanquhar to Thornhill. The Scottish Highlands to the north, of Lower Palaeozoic and
Precambrian rocks, were similarly a positive, mainly emergent area with outcrops of
Carboniferous (Johnstone 1966) limited to the west coast around Inninmore (Sound of
Mull), Bridge of Awe (Pass of Brander) and Glas Eilean (Sound of Islay)