Abstract The Hebridean Terrane is a fragment of the Laurentian craton made up mainly of Lewisian Gneiss and Torridonian sedimentary rocks of later Proterozoic age. These rocks were peneplaned and formed a broad but shallow marine shelf upon which a succession of Cambrian-Ordovician rocks was deposited. Durness Group carbonates of Cambrian to Ordovician age overlie conformably Lower Cambrian arenaceous rocks; the outcrop extends for nearly 200 km, from Eriboll in the north to Skye in the south. The Durness Group is most completely preserved in a half-graben at Durness. Peach et al. (1907) described the Geological Survey’s detailed mapping of the north-west highlands (see Oldroyd 1990), the basis for all subsequent work. Correlation of the upper parts of the group is dependent on faunal evidence. The stratigraphical succession adopted here is shown in Columns 86-89, the principal divisions of the Durness Group being treated as formations, following Cowie et al. (1972). The faunas are exclusively of Laurentian type and, having nothing in common with coeval faunas in England and Wales, gave some of the first-described and best evidence for the former existence of the Iapetus ocean.

Abstract The Cambrian–Ordovician succession of northwestern Scotland represents a fragment of a once-continuous southeastern Laurentian margin stretching between western Newfoundland and eastern Greenland. The subdivisions of the Sauk megasequence are recognized within the Scottish succession for the first time. The Sauk I supersequence corresponds to deposition of the Ardvreck Group, which is composed of a succession of arkoses, quartz arenites, and siltstones. The overlying Sauk II and III supersequences are represented by carbonates of the Durness Group. Within the Durness Group, several smaller sequences can be identified (interpreted as third order). The Sauk II supersequence can be divided into two sequences of 83- and 75-m (272- and 246-ft) thickness. These may correlate with Cambrian grand cycles recognized in other parts of Laurentia. The Sauk III supersequence contains four smaller sequences, some of which correlate with sequences observed in western Newfoundland. The top of the Sauk megasequence is not observed because of truncation of the available section by a thrust fault.

Abstract The Cambrian succession in the Hebridean Terrane extends for about 200 km from near Durness on the northern coast of the Scottish mainland SSW to Skye (Fig. 14). The classic account of the whole region is the memoir by Peach et al . (1907), which work had a great influence on British geological studies in the Lower Palaeozoic during the earlier part of the 20th century. The geology of the region was described by Park et al . (2002) and some critical localities were reviewed by Prigmore & Rushton (1999). Sedimentological studies by Swett and his collaborators (Swett 1969; Swett & Smit 1972) and by McKie (1990a-c, 1993) and new litho-and biostratigraphical work, including the study of microfossil faunas and floras, have led to a re-appraisal of the stratigraphical succession and its correlation. The Cambrian succession (Fig. 15, Column 22) consists of a generally upward-fining sequence of clastic deposits, the Ardvreck Group of early Cambrian age, followed by a succession of carbonate formations, the Durness Group, of Cambrian to early Ordovician age. The strata were deposited on a stable, gently sloping shelf, and because the facies represented are generally similar throughout the length of the outcrop, it is inferred that the trend of the shelf lay approximately parallel to the line of the present outcrop (Bluck 2007).