The brachiopod Orthisocrania divaricata (M'Coy) is generally considered to be a fairly long-ranging form occurring in both the Caradoc and Ashgill Series. The latter age is based principally on records of its common occurrence from the Chair of Kildare, Ireland, but the species is not present in the Ashgill beds at this locality. It does occur there, however, in association with a fauna whose age is here judged to be Longvillian on the basis of its strong similarities to that of the Gelli-grin Calcareous Ashes. Examination of other records and occurrences suggests that this inarticulate is restricted to the Longvillian in the British Isles, and is therefore of some importance stratigraphically.

Study of the punctation mosaics of Moorellina granulosa (Moore) and Moorellina ornata (Davidson), revealed by serial sectioning and stereoscan photomicrographs, shows that the apparent random distribution of punctae may be reconciled to two superimposed regular insertion patterns. Careful plotting of the endopunctae of M. granulosa from serial, cellulose acetate peels, reveals the presence of impersistent punctae. A new model is proposed, based on superimposed insertion patterns and offering an explanation for impersistence of punctae.

The Pre-Cambrian rocks of north-eastern Botswana comprise two major geotectonic domains: the south-western extremity of the Rhodesian craton, and the surrounding mobile belts– namely the Limpopo Mobile Belt to the south and the Shashi Mobile Belt to the west-southwest. The Mosetse-Matsitama area bears affinity to both these environments and this contribution attempts to assess the relationships of the area within the context of the regional geological framework. The area is underlain by a supracrustal schist belt which is interfolded with an infracrustal basement of gneisses and granitic rocks. The schist belt includes metasedimentary and probably metavolcanic rocks of low metamorphic grade and, therefore, contrasts sharply with the rocks of higher metamorphic grade which comprise the basement. Only in the south-west of the belt does a transitional relationship between the two major units occur. Geographical and geological criteria characteristic of both the major geotectonic environments are described, and it is concluded that the area shows a transition from a cratonic to a mobile belt environment. Involvement in a developing mobile belt would initially affect the infracrustal basement, allowing the supracrustal rocks to retain their cratonic characteristics to a more advanced stage.

Quartz-trachytic differentiates characterise volcanic islands on or near mid-ocean ridges, while phonolitic trends are found on islands rising from ocean basins. A large part of the Kenya Rift Valley is dominated by Plio-Pleistocene quartz-trachytes, which are underlain and flanked by variably nepheline-rich Miocene and Plio-Pleistocene lavas.

Phonolitic and nephelinitic lavas dominate the assemblages of Miocene age, trachytes and olivine basalts those of Plio-Pleistocence age. This change in petrographic character with time is attributed to two stages of sub-crustal pressure relief corresponding to Lower Miocene and late Pliocene elevations of the Kenya dome. The result was a change in partial melting products from less to more silicic, especially along the axial rift valley.

The doming movements and related vulcanism are believed to have originated because of lateral compression, induced by sea-floor spreading movements in the Atlantic and Indian oceans.

A résumé of the stratigraphy, sedimentation and volcanism of the Lower Palaeozoic rocks in the northern Trondheim region is presented. Spatially the Caledonian rocks occupy a shallow trough which plunges south-west. Within the trough the rocks have been subject to four episodes of deformation; the essential structure of the region is an anticline flanked by recumbent fold nappes (F1) which spill outwards on either side of the NE-trending spine. These are deformed by further major folds (F2). The F3 folds, developed widely but only on a mesoscopic scale, show a constant down-dip sense of overturning. It is thought that they were formed in response to gravitational sliding. F4 is represented only by local kink bands. It is probable that large areas of these Cambro-Silurian rocks are allochthonous, the marginal thrust being of late-F2 age. Examination of the structures is illuminating many other aspects of the geology of this segment of the Caledonian chain, making it possible to visualize the changing sequences of deformation, the relationship of metamorphism to tectonic level and the tectonic behaviour of domal granitic masses. In conclusion, comments are made on the relative significance of the orogenic ‘disturbances’ described from this part of Norway.

Statistical sampling of the Aberystwyth Grits, using a method previously employed in an analogous study of Tyee Formation, Oregon, shows an overall decrease in the ratio of sandstone to shale from south-west to north-east, away from the supposed source of depositing currents. Comparison with other methods of proximality evaluation in turbidite sequences indicates that at least in this case the ratio of sandstone to shale is the most sensitive indicator of palaeogeography.

The lectotypes of the Devonian tabulate corals Roemeria infundibulifera (Goldfuss), Roemeripora minor (Schlüter) and Fovosites goldfussi d'Orbigny are redescribed from new thin sections. It is confirmed that Roemeria Edwards & Haime and Roemeripora Kraicz are best regarded as two separate genera of the Roemeriidae Pocta and that R. minor is best referred to Roemeripora. It is shown that internal characters of the lectotype of F. goldfussi are reasonably consistent with those taken as diagnostic for the species by Jones (1936) and Lecompte (1936, 1939).