Hyalotuff deltaic deposits, a high proportion of volcanogenic sediment and a repeated occurrence of conglomerate with well-rounded clasts constitute evidence for the shallow-water origin of spilitic lavas and volcanogenic sediments in an Ordovician ophiolite at Ballantrae, SW Scotland. One section, >1.5 km thick, shows repeated evidence for a shallow-water origin. This implies accumulation in a subsiding area. In this sense the sequence at Ballantrae is in marked contrast to those found in oceanic islands (hot spots) which are known to grow from deep into shallow water. Neither does it compare well with those from ocean ridges which usually begin in deep water and move, with cessation of vulcanicity, into even deeper water.

The lava sequence at Ballantrae compares well with oceanic island-arc and remnant arc deposits where uplift and subsidence is common. This, the occurrence of intermediate and acidic lavas and clasts, and the restricted palaeontological and radiometric ages support an arc-marginal basin origin for the lavas. Diversity in the chemical composition of the lavas may reflect diverse origins within the marginal basin.

An upward coarsening sedimentary sequence was built by a hyalotuff delta which formed in front of advancing lava flows. As the lavas advanced over the sediments so a sequence was generated where these sediments have a source in lava flows which were eventually to overlie them.

Clasts of tholeiite were derived from lavas which are now spilite. This, together with the presence of spilitic lava clasts and tuff immediately beneath the flow suggests that the spilitisation resulted from metasomatic activity associated with the convective circulation of trapped water, with the lava as a heat source.

The top 9 m of Lower Hartfell Shale has been collected in 10 cm samples through a continuous sequence on the North Cliff at Dob's Linn. The boundary between the Dicranograptus clingani and Pleurograptus linearis zones is denned for the first time in a measured section, 5.0 m below the top of the Lower Hartfell Shale, with the excavation of the North Cliff proposed as stratotype. The late D. clingani Zone is characterised by Dicranograptus ramosus?, Dicellograptus moffatensis, D. flexuosus [= D. forchhammeri], Climacograptus dorotheus, Glyptograptus daviesi sp. nov., Diplograptus? pilatus sp. nov., Neurograptus margaritatus and Corynoides calicularis. The P. linearis Zone is characterised by Pleurograptus linearis linearis, Amphigraptus divergens divergens, Leptograptus capillaris, Dicellograptus elegans elegans, D. pumilis, D. carruthersi and Climacograptus tubuliferus. A range chart is provided and an attempt is made at a revised correlation of the Scottish succession with coeval zonal sequences in North America and Australia. Twenty-one taxa are described including the two new species noted above.

Assemblages of acritarchs are described from the Fucoid Beds of Skiag Bridge, Knockan Cliff and Skye in NW Scotland, and Holmia Shales of the Mjøsen area of Norway, the Bastion Formation of Ella Ø in East Greenland, the Lower Cambrian of the Burin Peninsula in Newfoundland and from the Gog Formation of the Rocky Mountains of Banff National Park, Alberta. These are shown to be correctable on the basis of acritarchs and with the Lower Cambrian successions of the Russian Platform. Twenty-one genera and fifty-three species of acritarchs and one tasmanitid are described. These include the new genera Skiagia and Volkovia, and thirteen new species, Acrum cylindiferum, Micrhystridium coniferum, M. ellaensis, M. ellipticum, M. flexispinosum, M. gogensis, M. minutum, M. ordensis, Multiplicisphaeridium ? waltoni, Skiagia brevispinosa, S. scottica, Revinotesta ordensis and Evittia irregulare. A number of recombinations have also been made.

Calyptaulax brongniartii (Portlock) from the Caradocian Bardahessiagh Formation, Pomeroy, Northern Ireland is redescribed. Equivalent material from Scottish horizons (Balclatchie and Ardwell groups) is regarded as belonging to separate populations. Campbell's system of notation is used to describe variation in the arrangement and number of lenses in the eye. The most closely related species is C. strasburgensis (Ulrich & Delo) from the Edinburg Limestone of Virginia, U.S.A.