This Memoir reviews, revises and interprets the biostratigraphy, lithostratigraphy, process sedimentology, palaeoenvironments and sequence stratigraphy of the classic Cambrian succession of SW Wales. This 1250m thick clastic sedimentary succession, of Terreneuvian to Furongian age, was deposited in environments ranging from alluvial fan to mid–outer shelf. Two lithostratigraphical groups are distinguished, each comprising six formations; where possible and appropriate, original and well-known names are retained in harmony with current usage. High-resolution sequence-stratigraphical techniques, constrained by biostratigraphical data whenever possible, allow the revised lithostratigraphy to be integrated with the western Avalonian chronostratigraphy developed in maritime Canada. A twofold subdivision is recognized. Megasequence 1 (sequences 3-7) spans the Terreneuvian, C2 and much of C3, with deposition occurring in an extensional rift-like regime on an epeirogenically active platform. Sequence 8 lies at the base of Megasequence 2, which extends from late C3 into the early Ordovician, and represents passive margin sedimentation.

The Advanced Science Institute on which this publication is based took the somewhat unusual form of a geological field symposium held during late August 1984. It was designed to demonstrate to experienced earth scientists from the North Atlantic area the full range of geological phenomena encountered in the British Caledonian rocks. The ASl travelled from South Wales to the far northwest of Scotland by the route shown on the map and in doing so examined sedimentary, igneous and metamorphic rocks from Pembrokeshire (Dyfed), Cardigan (Ceridigian), Snowdonia, Anglesey, the English Lake District and the Southern Uplands and Highlands of Scotland. Thus the fifty or so participants in the ASl studied the geological history and major structures of rocks exposed on either side of the supposed Lower Palaeozoic Iapetus Ocean the British sector of which closed to the south of the present Southern Uplands. Wales (1-5) afforded insight into the nature of the late Precambrian basement of England and Wales and the relationship of sedimentary and volcanic cover sequences to this basement. The Ordovician sequence in Wales is a sample of the volcanic rocks typical of a marginal basin, and were examined in Pembrokeshire and Snowdonia. The English Lake District (6) displays rocks from an island arc also of Ordovician age.

The first book to cover geological excursions for the whole of the British Isles. Information on the best means of studying geology in the field in the British Isles is followed by descriptions of 194 geological itineraries based on a number of centres and a final chapter on the geology evident on 31 journeys by road, rail and coastal boat. Sketch maps indicate the routes of all the excursions with maps showing the geology of each region. These are detailed for those areas for which modern geological maps are not available.