At Skiag Bridge, atypically for the Assynt district, the lower most imbricates and Sole Thrust of the Moine Thrust Belt are clearly displayed and very accessible. As ever, the area was originally mapped for the Geological Survey (Peach et al., 1907) and has been much-visited since (e.g. MacGregor and Phemister, 1948; Johnson and Parsons, 1979). The importance of the area, as recognised by Elliott and Johnson (1980), is that it links the rather weakly developed imbricate systems in the footwall to the Glencoul thrust in its type area to the much more extensive systems around Inchnadamph.
The site was remapped by Coward (1985) as part of a major research programme that reassessed thrust belt evolution. By tracing thrust linkages and establishing the internal arrangement of imbricate thrusts and major detachments, Coward identified three main duplexes. The uppermost one consists of imbricated Durness Group carbonates and lamprophyre sills. The floor thrust to this system lies a few metres above the base of the carbonates and it acts as a roof to the underlying middle duplex, formed in Fucoid Beds, Salterella Grit and with a few metres of Durness Group carbonates. The lowest duplex contains a few metres of Pipe Rock and Fucoid Beds and its floor is the regional Sole Thrust. There are over twelve repetitions of individual units exposed in stream sections, giving rise to complex thrust belt geometries. Higher imbricate systems are folded by underlying ones suggesting an overall foreland-directed (piggy-back) thrusting sequence. Comparison between different transects through the site implies that an important lateral ramp exists on the regional Sole Thrust, climbing upsection from north to south, from the base of the Fucoid Beds to just within the Grudaidh Formation of the Durness Group. This ramp zone was long-lived during the formation of thrust structures hereabouts and strongly-influenced the geometry of thrust-related folds, inferred thrust ramps and associated culminations aligned oblique to the thrusting direction.
A few minor thrusts occur beneath, within the underlying Pipe Rock, and some of these have been the focus of microstructural investigations aimed at studying processes of cataclastic faulting in quartzites (Lloyd and Knipe, 1992; Knipe and Lloyd, 1994). All fault zones at Skiag Bridge are characterised by cataclastic deformation, in contrast to the mylonites that occur along the structurally higher parts of the Moine Thrust Belt (e.g. at the Stack of Glencoul, see Glencoul site). Detailed studies of faults within the Pipe Rock have been particularly important for understanding the microstructural processes of fracturing and cementation that typically accompany brittle faulting in the upper continental crust (Lloyd and Knipe, 1992).