Conventional K—Ar age determinations are frequently discrepant. A major factor is the failure of rocks to conform to the basic simplifying assumptions made in the total fusion method. Many rocks incorporate initial argon with an isotopic composition different from the present atmosphere and others have not remained closed systems.By careful sampling and the application of isochron geochronometry more reliable and geologically acceptable K-Ar ages can be obtained. K-Ar step heating isochrons from Kenyan Miocene volcanic sanidines are used to illustrate the accumulating evidence for the presence in ancient rocks of initial argon with an isotope ratio unlike that of the modern atmosphere. Single whole rock total fusion K-Ar isochrons from the Olduvai basalt, Tanzania and the Upper basalts of Antrim are presented to illustrate a new version of the K-Ar isochron technique. Special circumstance multiple rock K-Ar isochrons from the Belfast section of the Antrim basalts and from an ignimbrite-ash flow unit in Bed I, Olduvai Gorge, are used in a further discussion of the general applicability and usefulness of K-Ar isochrons.

The three species of Placoparia; P. (Placoparia) cambriensis Hicks, P. (Coplacoparia) tournemini (Rouault) and P. (Coplacoparia) borni Hammann have been recognized from the Ordovician of North Portugal. New subspecies of P. (Placoparia) cambriensis have been established on the basis of differences in the pygidium and suggests the presence of two, broadly coeval, populations in western Europe during the Llanvirn. Quantitative analyses have provided information on growth patterns.

Ordovician echinoderms from Greenland include: Glyptocystites groenlandicus sp.nov. which is distinguished from other Glyptocystites by a very coarse slit spacing in its pectinirhombs (1 slit per 0.365 mm) and by its ambulacral structure; ?Macrocystella sp.; Cheirocystella sp and ?Carabocrinus sp. A variety of unidentified stem and cup plates of crinoids is described and illustrated.

Ceratitic ammonoids from the Greville Formation in the Nelson Regional Syncline, South Island of New Zealand, were described as a new genus and species of the Ophiceratidae, Durvilleoceras woodmani, and dated as ‘late Middle Permian’ (Waterhouse, 1973). In fact, Durvilleoceras differs from all known Permian ammonoids in both conch form and sutural pattern, but closely resembles lower Triassic ceratites. Structural and sedimentologic complexities within the Nelson Syncline are such that stratigraphic interpretations are questionable, and the fauna of both the Greville and adjacent formations is sparse. Consequently, we consider that Durvilleoceras is best interpreted as a middle Scythian ceratite of the family Flemingitidae.

Three-dimensional coastal exposures of the Middle Jurassic (Bathonian) Scalby Formation in Yorkshire, England, exhibit a complex, exhumed meander belt. The lateral accretion surfaces (epsilon-cross stratification) of individual meander loops are described. Field and aerial photograph measurements of accretion-surface dimensions have enabled direct determination of channel bankful depths and widths and meander wavelengths. Values for mean annual discharge of the channel system are derived using existing empirical equations. Palaeocurrents measured in the meander belt sandstones show a wide dispersal due to many periods of meander migration and cut off.

An Archaean greenstone belt, occupied by rocks of the Nyanzian System, rests apparently unconformably on a basement composed of the metamorphites of the Dodoman System in the central part of the Tanganyika shield. The latter were originally metamorphosed in granulite facies. Two episodes of migmatization were imposed on this earlier crust producing two complexes of anatectic granitoids (Puma and Ikungi) which locally have a charnockitic character. Differences in structural setting suggest that they were developed in connection with two major tectonic events. A basin-like structure was built up during the second – Ikungi – in which the Nyanzian System occurs. The Nyanzian rocks are not migmatized and their juxtaposition with the migmatites suggests that they are of younger age. Another tectonism took place after deposition of the greenstones as a result of which they were intensely deformed. Two types of intrusive granites were emplaced in the greenschists upgrading them to hornfelses during this tectonism. An interesting feature is the coincidence of the general tectonic axes of these three events. For the successively established metamorphic processes in this Archaean nucleus a gradual downgrading of metamorphic facies is characteristic, showing its irreversible development.

The ultramafic—mafic complex at North Cape lies in a Mesozoic—Lower Tertiary tectonic belt linking New Zealand with New Caledonia and Papua New Guinea. The complex is faulted against Cretaceous submarine tholeiites and contains (1) serpentinized harzburgite and lherzolite of probable cumulus origin (and intruded by more Fe-rich wehrlitic veins and dykes), overlain by (2) layered olivine- and orthopyroxene-gabbro subvolcanic cumulates which are themselves host for (3) a sheeted dyke swarm of mainly quartz-diorite composition. It is suggested that the complex was emplaced with the Cretaceous volcanics by obduction of Mesozoic oceanic crust during the Lower Tertiary.

A vertical channel structure within a layered dolerite dyke resulted from differential magmatic flow. Layering in both dyke and channel is formed of more feldspathic dolerite attributed to fluctuations in water vapour pressure and supercooling during crystallization.