The character and distribution of middle Devonian to upper Carboniferous facies in central SW England is described. These may be interpreted in terms of the simple model of a shelf extending from a continent to the north, across most of SW England in earliest Devonian times. Within it a major E-W trending basin developed during the middle Devonian, possibly as a half graben structure with an active northern hinge. On this shelf in mid and late Devonian times, argillite successions accumulated to the north and a carbonate complex on the now starved platform to the south of the basin. In the early Carboniferous, basinal conditions extended northwards over the shelf, but to the south, at first flysch and then paralic sediments with a southern origin were ponded against the carbonate complex. Flysch penetrated through and across the platform into the intra-shelf basin. This flysch prograded northward to cover the whole area by early late Carboniferous times.The western part of the main basin suffered structural inversion in late Visean times and semiconsolidated sediments spread northward across its margin. The eastern extension of the basin was not deformed until the late Namurian, at which time successions were folded and disrupted into nappe structures showing northward transport. The most far-travelled nappes are represented at the highest structural levels.The stratigraphy of the coastal section of N Cornwall, which has been used to devise a structural model involving a major autochthonous south-facing overfold, is reassessed. The nappe structures and successions recognized inland are identified on the coast, and the overfold model is disproved. The whole of central SW England forms part of southerly derived thrust and nappe terrane.

For many years the geology of north Cornwall has been interpreted in terms of a south-facing overfold model, which predicts a major confrontation at Padstow with the north-facing structures of south Cornwall. New evidence indicates the existence of contrasting successions separated by flat-lying thrusts. In upward succession the Port Isaac, Tredorn and Boscastle nappes are identified; the first appears to have been emplaced by gravity sliding in late Viséan times, followed by the Tredorn and Boscastle nappes in the early Namurïan. Strata represented in the inverted limb of the Port Isaac Nappe, not previously distinguished, are described as the Jacket's Point Slate Formation. Throughout the nappe pile there is consistent evidence of north-facing and northward transport for distances measured in tens of kilometres. Not more than 3 km of south-facing strata may now exist at the Padstow confrontation, and this feature is unlikely to be of great regional significance. The allochthon extends northwards to the Rusey Fault Zone where the autochthon was locally backfolded over the allochthon in late Westphalian times; this appears to be the only significant confrontation of facing directions in north Cornwall.

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The discovery of trilobites characteristic of the Gattendorfia Zone is described from the California Quarry, Boscastle. The possible stratigraphical implications are discussed and a comparison is made with beds of similar age at Launceston. It is suggested that there is no important stratigraphical break at the top of the Devonian and that there is a conformable passage from the Tintagel Volcanic Series into the Carboniferous. The Tredorn Phyllites are tentatively equated with the Woolgarden Phyllites. There is no evidence to support the contention that the Lower Culm contains an important greywacke sequence; these beds are probably of Upper Culm age.

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