The Dalradian rocks of the South-west Highlands-Introduction

Abstract

Introduction Dalradian rocks outcrop over a wide area in the Scottish Highlands immediately to the northwest of the Highland Boundary Fault. They form a very thick sequence of sediments, of late Precambrian to Cambrian age, which was deposited in part of the Caledonian geosyncline. Unlike the underlying sediments of the Moine Series, which are a monotonous sequence of impure sandstones and shales, the Dalradian Series is a lithologically diverse sequence of conglomerates, sandstones, limestones, dolomites and shales. The deposition of these sediments was interrupted on occasion by the eruption of volcanic rocks, accompanied by the voluminous intrusion of dolerite sheets and sills. These rocks were then deformed and metamorphosed during an early stage of the Caledonian orogeny, probably at the end of Cambrian times. Although an emphasis has been placed on the structure and metamorphism of the Dalradian rocks, there are many areas of low-grade metamorphism where the deformation is relatively slight. The rocks of such areas can still be studied to advantage as sedimentary rocks from a stratigraphic and sedimentological viewpoint. This is certainly true of the Dalradian rocks in the South-west Highlands, defined as extending from Ballachulish and Lochaber in the north-east, to Islay, Jura, South-west Argyll, Cowal and Rosneath in the south-west. It is this area which is covered by the present series of excursion guides. Stratigraphy and Depositional History The mapping of the South-west Highlands by the Geological Survey led to the recognition of a number of local successions for the Dalradian rocks. The correlation of . . .