The extreme rarity of alkaline rock suites bearing both calcic plagioclase and magmatic carbonatites is believed to reflect a fundamental bifold division between Gabbroic and Carbonatitic types, plagioclase being present only in the former and carbonatite only in the latter. Alkali basalt magma may be parental to both lineages, the gabbroic lineage deriving from normal differentiation under low CO2 pressure, and the carbonatitic by suppression of plagioclase crystallization under high pressures of CO2, leading through pyroxene fractionation to a ‘secondary parental’ olivine-poor nephelinite magma. Support for this hypothesis is found in evidence for the suppression of plagioclase in CO2-rich alkali basaltic magmas and for the secondary origin of olivine-poor nephelinites, in the nature of xenoliths and cumulates at carbonatite complexes, in Sr isotopic data, and in major and trace element compositions of the magmas. The possible origin of melilitic rocks at carbonatite complexes is also briefly discussed.

Changes in the Upper Cretaceous faunas of northeastern Ireland point to rising Cenomanian temperatures, and to progressive falls in temperatures from early Santonian to Maastrichtian times. At first sight, these changes fit the Cretaceous climatic trends claimed from isotopic data; but comparison with faunas seen in England suggests that this fit is illusory. It is suggested that faunas were more directly controlled by the influence of contrasting Atlanto-West Tethyan and Russo-Germanic water masses, and by changes in their relative distribution. Changes seen through the Irish Senonian may reflect the progressive submergence of a Scotland—Pennines barrier, permitting an increasing westward spread of the Russo—Germanic (‘boreal’) water and fauna.

The structure of the partly exposed lower section of the Jimberlana Intrusion has been determined by combining the geophysical evidence with the available geological and diamond drill hole data. The results have been added to the wellknown upper section to show that Jimberlana is not a dyke-like body as had previously been thought, but is a horizontal pipe-like intrusion 180 km long, 2.5km wide and 5.5 km deep, with a V-shaped cross-section. A marginal series with ‘reversed’ fractionation and high primary dips, similar to the marginal series of the Muskox Intrusion, occupies the lower part of the intrusion. The rocks of this series display rhythmic layering and a variety of cumulate textural types indicating that cumulate processes can take place during deposition on near-vertical dipping surfaces.

A pebble lineation has been produced as a result of the first phase deformation that formed the Chamba syncline and the associated slaty cleavage. The lineation indicates the principal direction of maximum elongation of the finite tectonic strain ellipsoid of the first phase deformation and lies nearly normal to the axial direction of the Chamba syncline. The mineral lineation and the long axes of deformed crinoid ossicles show paralelism to subparallelism with the pebble lineation. The second and third phases of deformation, which are characterized by open style folds and associated crenulation cleavage, appear to be of weak magnitude and have not modified the orientations of pebble lineation.

A mid-Cretaceous cobble conglomerate in the Beer district, south Devon, is interpreted as a Lower Cenomanian beach deposit.

The epizoan Vermiforichnus Cameron (1969b) from the Upper Ordovician (Caradoc) of the Berwyn Hills and the Welsh Borders is host-specific, occurring in association with the strophomenid Macrocoelia and the orthid Heterorthis. The spionid polychaete probably responsible for the production of the Vermiforichnus borings inhabited both live and dead individuals. In live individuals Vermiforichnus was located at the anterior margin and oriented perpendicular to the commissure, this position affording both a means of protection and a more efficient feeding position. In dead individuals population density was lower and the borings were randomly oriented. Vermiforichnus was restricted to inner—outer sublittoral environments and, as such, is a useful palaeoenvironmental guide.

Petrological and geochemical features of recently discovered basalts of the Troodos Massif, Cyprus — a dyke in the Basal Group and altered pillow lavas in the Lower Pillow Lavas — suggest that all the lavas are part of a single volcanic suite.

Clastic dykes are described from a late Precambrian sequence of shallow water sediments — the Porsangerfjord Group of Finnmark, North Norway. The dykes are from one stratigraphic member of the Group and only occur where this member outcrops in a zone where sedimentation was thought to have been affected by recurrent earthquake shock. The dykes consist of poorly defined sandstone clasts in a muddy matrix. They exhibit no significant internal sedimentary structures. It is suggested that the dykes were intruded due to remobilization of sediment affected by a combination of tectonic shock and hydrostatic load. The dykes bear no genetic relationship to tectonic structures (cleavage and jointing) and evidence suggests that dewatering was virtually complete before the formation of the first cleavage.