Although it is unlikely that the east of Sutherland will ever rival the west in geological renown, its varied interests have already furnished material for a considerable literature. Attention has been specially focussed upon a down-faulted coastal strip of Mesozoic rocks, which, starting at Golspie, extends north-eastwards for twenty miles through Brora and Helmsdale to the county boundary at the Ord (fig. 1). Golspie itself stands on a narrow outcrop of Trias. Jurassic follows, with a generally ascending sequence that leads up to Kimmeridgian at Kintradwell, a couple of miles north of Brora (fig. 2). Beyond this Corallian reappears, but only for a short distance. Then Kimmeridgian returns and holds the coast-line continuously for nearly nine miles, until, at the Ord, it disappears beneath the sea. The width of the Kimmeridgian exposures is occasionally three-quarters of a mile, but generally much less.

Bellerophontidæ occur in considerable numbers at certain horizons in the Scottish Carboniferous rocks. Many forms are represented, but few have been described or figured (see Historical Account, Section III). In undertaking the study of these fossils the writer's object was limited, primarily, to figuring and describing the Scottish forms and ascertaining their value as stratigraphical indices in the Scottish Carboniferous rocks. Many forms from the shaly facies have been recorded in Scottish stratigraphical literature under the names of English and Belgian species of limestone facies. Investigation proved that most of these records were invalid, the determinations being erroneous, and that revision of all the Anglo-Belgian Bellerophontidæ was necessary in order to define the Scottish forms. The present memoir embodies the results of the wider investigation.

The Moffat Shale Group is a condensed, variable and partly pelagic sequence of mudrocks of Llandeilo—Llandovery age. The sequence has a five-fold lithological subdivision based mainly on the occurrence of grey mudstones within a succession otherwise dominated by fully euxinic black graptolitic mudrocks. Associated with the black mudrocks, especially in the Llandovery, are metabentonite beds which achieve a climax, both in thickness and in number, within the top quarter of the mudrock sequence. A geochemical and mineralogical study has confirmed a volcanic origin for the metabentonites. Major element data highlight a carbonate-dominated environment above the gregarius—convolutus Zones boundary. Phosphorus levels reach a peak at the same boundary, as well as at the Caradoc—Ashgill boundary where phosphorite horizons are known from Wales and Norway. Immobile trace elements have highlighted regular changes in source magma composition. Prolonged periods of crystal fractionation in magmas of intermediate composition gave rise, on eruption, to large volumes of silicic ash which had a deleterious effect on graptolite species and led to local extinctions. Regular fluctuations in ash composition from silicic to intermediate are ascribed to alternating fractionation and magma mixing cycles.

Synopsis The rocks exposed in the coastal sections between Gatehouse and Creetown, Kirkcudbrightshire, are considered to belong to the Hawick Rocks (Upper Valentian), and have been affected by five main episodes of deformation, three of which are of Caledonian age. The first phase produced E.N.E.-W.S.W. similar folds and associated tensional strike faults, forming the structural basis of the area and determining the outcrop distribution. During the second phase these folds were modified, and a new set of concentric folds, comparable in strike but with axial surfaces dipping at around 45° S.S.E., was generated, along with a conjugate set of wrench faults. Folds of the third phase have E.-W. axes and steep eastward plunges. The three phases are equated respectively with F 1 F 2 and F 3 of the Whithorn area ( Rust 1965a ). The fourth phase gave rise to folds with near-horizontal axial planes, and frequently developed as minor thrusts, and the final deformation gave rise to dextral kink-bands trending N.-S. The two last are correlated with F 4 and F 5 of Whithorn, to which Hercynian and Alpine dates are provisionally allocated. A swarm of dykes was emplaced between the first and second phases, and further dykes were intruded after the second phase.

Synopsis The Lower Palaeozoic rocks around the Cairnsmore of Fleet pluton comprise representatives of the Moffat Shale Group, ranging from the Glenkiln or Lower Hartfell Formation (Llandeilo or Lower Caradoc) to the Upper Birkhill Formation (Fronian), conformably though diachronously overlain by greywackes of later Llandovery age. The Main folds ( f 1 ) display two contrasting styles. Two tracts of northwestward dips, mainly steep and locally inverted, are separated by a tract of concentric folds, upright or overturned to the NW, with wavelengths mostly less than 500 m. The first phase concluded with the generation of complementary wrench fault sets, certain of which were subsequently reactivated. An episode of compressional faulting supervened, generating the southeastward-translating and strike-parallel listric faults of the Central Belt, of which four lie within the area. The tracts of steep NW dips were simultaneously modified by SE-verging open folds having axial planes with moderate SE dips ( f 2 ). Later Caledonian movements, producing crossfolds associated with oblique-slip faulting ( f 3 ) and kink bands ( f 4 ), are of minor significance.