Consideration of the arctic configuration of the Caledonides leads to a distinction between eastern and western geosynclinal belts. The western belt, comprising the East Greenland, East Svalbard and southern Barents Sea Caledonides is postulated to continue northwards into the Lomonosov Ridge, whilst the western Spitsbergen Caledonides are thought to have originated as part of the North Greenland geosyncline which is also thought to continue northwards to form the western part of the Lomonosov Ridge. The eastern Caledonian geosynclinal belt comprising the Scandinavian Caledonides appears to swing eastwards to link with the Timan Chain and possibly the Urals.

The already postulated (‘Proto-Atlantic’) ocean concept is reviewed in the light of the Arctic Caledonides and named Iapetus. Faunal provincialism suggests that the ocean was in existence up to early Ordovician but had substantially closed by mid Ordovician times. Possible relics of the suture marking the closure of this ocean suggest that it lay to the west of the Arctic Scandinavian Caledonides trending NE to latitude 70° N and thence veered eastwards separating the southern Barents Sea Caledonides from those of Arctic Scandinavia, possibly connecting with the northern Uralian ocean. A previous branch of the ocean may have separated East Svalbard and East Greenland as an ocean-like trough. A further (pre-Arctic) ocean may have existed to the north of the North Greenland–Lomonosov Ridge geosynclines. This is named Pelagus.

The closure of these oceanic areas and the deformation of the bordering geosynclines delineates three principal continental plates, namely, Baltic, Greenland and Barents Plates. Their relative dominantly E–W motion up to Silurian times produced compression between the Greenland and both the Baltic and Barents plates but dextral transpression and transcurrence between the latter plates. In Late Silurian to Devonian times an increasing northward component controlled late Caledonian transpression and sinistral transcurrence between the Greenland plate and the combined Baltic and Barents plates.

The present paper deals with the Lower Ordovician–Silurian rocks between Fördefjord and Sognefjord on the western coast of Norway. During the Caledonian orogeny this sequence was subjected to several phases of Silurian deformation, the first of which resulted in the formation of a large-scale anticline (the Stavfjord Anticline), which now occupies part of an overthrust unit. On the basis of ‘way-up’ criteria in the partly well-preserved Lower Ordovician pillow lavas it has been possible to determine with some confidence the geometry of the Stavfjord Anticline, its probable regional extension and the position of the axial plane trace. Arcuate deflections in the trend of this axial plane trace are a result of large-scale refolding, the later fold axes having WNW–ESE trends.

From the distribution and orientation of final axial ratios of deformed elliptical pyrites and boudins, initial distributions are determined. A strain ellipse is then reconstructed using the shape factor grid. The long axis of the strain ellipsoid represents the trend of regional fold axis (the fold is of flexural slip type). The dimensional orientation (elongation) of the pyrites and the boudins is referred to the homogeneous strain components in the fold. Petrofabrics of the pyrite cubes indicate that they have a preferred orientation.

It is pointed out, with a few examples, that metamorphic rock compositions can be significantly modified by the stable mineralogy that itself may provoke metasomatic movement, as distinct from externally actuated metasomatism.

The average chemical composition of the biotite–gneisses of Rona is very close to that of similar gneisses in the Laxford area, and nearly as close to those of the Torridon area. The biotite–gneisses of Rona are slightly richer in Li, Ba and Zr, slightly lower in Mg and Sr and have a higher Fe2O3/MgO ratio than their mainland counterparts. Biotite mineral ages of 1400 m.y. and hornblende mineral ages of up to 1750 m.y. indicate a similar late-metamorphic history to that of the mainland Laxford assemblage.

Cynodonts from two localities in Lesotho have been assigned by earlier workers to the Triassic Molteno beds of the upper part of the Karroo (Gondwana) System. These are important inasmuch as they were thought to represent the only evidence of reptilian remains in an otherwise barren sequence and may help to bridge the palaeontological gap in this part of the Karroo succession. Critical examination of both localities during the course of a regional analysis of the Molteno basin showed discrepancies in stratigraphic interpretation. These discrepancies are pointed out and the stratigraphy revised as a result of which the cynodonts can no longer be assigned to the Molteno beds; one is in the underlying Cynognathus zone (confirmed by further finds of typical Cynognathus zone reptiles) and the other is in the Red beds above. At the Tsoaning River locality a pebble conglomerate resting on an eroded surface provides a good local marker for the base of the Molteno. The implications of this with respect to the fossil flora and fauna at these localities are briefly discussed.

A description is given of the numerous thin dolomitic sandstone dykes cutting dark marine shales of E1a age in Co. Leitrim. They are almost wholly confined to the Dough–Thur Mountain area, which is cut by the Caledonoid trending Ox Mountain and Belhavel Faults. It is thought probable that movement along one of these faults, possible in E1c times, conferred thixotropic properties to a sand horizon in the marine shales and also produced fractures in the shales up which the sand was intruded.