Thermal stresses due to contraction during cooling have been widely accepted as the origin of columnar structures in certain igneous rocks. It is proposed that these highly ordered structures could be the result of a double-diffusive convective process in the melt during cooling, a process analogous to salt fingers observed in the laboratory and the oceans. Salt fingers are driven by appropriate differences in heat and salt content at the top and bottom of a stably stratified water column. In molten basalts, temperature and chemical-compositional differences between the top and bottom of a stagnant melt could drive highly regular columnar ‘finger’ motions in the melt. When solidification takes place eventually, cracks due to contraction during cooling would then have preferred paths of propagation into the interior from the surface along the junctions of adjacent ‘basalt fingers’ giving rise to columnar jointing. Morphological evidence supporting the finger hypothesis is cited and useful ways of gathering further field data that would shed some light on the validity of the hypothesis are suggested. For the benefit of geologists not familiar with double-diffusive processes, an up-to-date review of these flow phenomena is included.

Eocambrian volcanic breccias of angular dacite and andesite clasts at Wadi Fatima, Kingdom of Saudi Arabia, contain perfectly preserved gas pipe structures. Only the latter identify them as lithic-rich, pyroclastic flow breccias of Pelean type. Without the gas pipes it would not be possible to identify them as pyroclastic and different from epiclastic breccias originating as mudflows, lahars or avalanches. The pyroclastic flow breccias constitute a minor component of the volcanic Fatima Group dominated by pumiceous water deposited sediments and subaerial welded tuffs.

The discovery of marine fossils in the Upper Palaeozoic of the Oslo Region suggests a previously unknown marine transgression of probable middle Carboniferous age. The fossiliferous sequence in the Oslo district was probably deposited in a very shallow marine environment as indicated by its fauna, ooids and the strong micritization of the fossils. The discovery of this sequence is consistent with the rift model for the Oslo Rift Zone, and suggests a connection with the Variscan Ocean.

Recently discovered specimens from the Portrane Limestone Formation of eastern Ireland are regarded as topotypes of Tretaspis radialis Lament and used to further characterize the species. The features shown by these specimens confirm the close relationship between T. radialis and forms from Zones 2–4 of the Cautleyan Stage of northern England and Wales and allow its differentiation from T. moeldenensis Cave and from another related form of low Rawtheyan age which is here erected as a new species, T. caritus sp.nov.

X-ray diffraction analysis of metamorphic rocks from the Start peninsula shows that the dominant mineral assemblage in the Start schists is quartz-muscovite-chlorite ± paragonite ± albite. The assemblage in the Devonian phyllites to the north of the Start boundary is quartz-muscovite-chlorite and the crystallinity of the white mica there is indicative of greenschist fades. The b0 parameter of white micas indicates that the metamorphism was of an intermediate facies series (Barrovian type), but of a lower pressure variety to the north of the Start boundary juxtaposed against a higher pressure variety to the south. No evidence exists of the high pressure metamorphism needed to support tectonic models in which the Start boundary is identified as a suture representing a Variscan subduction margin.

Sand grains enclosed in gypsum crystals which grew in otherwise uncemented sand commonly, either float in the gypsum, or, are arrayed in sand-bearing and sand-free zones in a manner which indicates that they were displaced during growth of the gypsum. Corroborative evidence of displacement of included sand grains is found in some sandy gypsum crystals from coastal sabkhas in Abu Dhabi, U.A.E. In these crystals, dust particles which formerly coated the sand grains are strung out as festoons behind the grains and thus record the directions and extent of the displacement. The direction of displacement was outwards, normal to the traces of what had been former crystal faces. The displacement also involved some pivoting of elongate grains which now lie with their long axes in the direction of movement.