The negative P-T slope of the wet melting curve of granite sets limits on the degree of upward movement of granitic magma formed at particular partial pressures of water vapour. Wet granite magma cannot rise very far from its place of formation, and only dry granite magma can be erupted as a liquid. This observation leads to a better understanding of the granitic structure of orogenic belts, and explains some of the apparently paradoxical aspects of granites. Other wet magmas would also not be expected to be erupted as liquids.

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 detailed account is given of the structural features of the Strathspey Granite and Pegmatite Complex together with information about the metamorphic and tectonic environment of the surrounding metasediments. The evidence indicates that the granite core of the complex was intruded shortly after the latest phase of folding recorded in the area had taken place. The country rocks were still at relatively high temperatures at the time of intrusion and were deformed by the granite. The granite emplacement is also shown to be a separate event not directly connected with the formation of the regional migmatite complex, which extends for 48 km to the north-east.

Preliminary Rb-Sr whole-rock isotopic analyses of some East African granulites give the following ages and initial ratios:

The initial ratios, at the 0.705–0.706 level, conform with a world-wide pattern found for granulites and other deep crustal rocks. The whole-rock ages are the first such study on East African granulites. They confirm in West Nile the suspected early Pre-Cambrian age of the Uganda basement, and in Tanzania raise source rock problems which involve the Mozambique Front.

The Ethiopian Cainozoic volcanics associated with the African rift system comprise one of the world's most voluminous alkaline igneous provinces. The Simien Mountains are the remnants of a Miocene alkali olivine-basalt volcanic centre in the north-western part of this province. The end-phase activity at Simien featured intrusion of dyke-swarms of two trends, one parallel to the rift system, the other almost perpendicular to it. Dykes of the rift trend are typically alkaline, but a dyke sampled from the other trend proves to be an olivine-tholeiite. Its presence is interpreted, along with similar rocks from the Harar region in eastern Ethiopia, in terms of upper mantle rifting extending from the Gulf of Aden and Red Sea under the continental blocks of the Ethiopian swell.

An area is described in which the main rock type is a variable dioritic rock, thought to have been formed by the expulsion of the residual acidic liquid from a largely crystalline quartz-diorite magma. It contains xenoliths of pyroxenite and appinite. The latter consist largely of hornblende, with some diopside, quartz, orthoclase microperthite and oligoclase. They are considered to be the reaction products of the outer margin of a magma and the adjacent calcareous country rock.

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.

A continuous profile of 430 large sand waves shows a progressive decrease in height (with some increasing crest separation) in their inferred migration direction, as well as showing the changing effectiveness of the ebb and flood tidal currents to move sand. The height of these and other sand waves around the British Isles is virtually unrelated to the depth of the sea, contrary to what has been suggested elsewhere. However, most sand waves occur on the continental shelf broadly because it is there that the currents reach a suitable range of speeds and sufficient sand is available at the present time.

A study in the deformational patterns of oolites from the Krol Series of the Simla Himalayas has been made in the type area. The deformation in the oolites is the result of the tectonic phenomenon coupled with folding movements during the Himalayan orogeny. The deformation varies with the amount and type of the matrix surrounding the oolites. The angle between the long axis of the ellipse and the principal tectonic extension is smallest in the axial regions of the folds.

Geological discontinuities, lineaments, field observations, and interpreted π-girdles demonstrate a left lateral, NNW trending transcurrent fault in the Sarawak-kiri valley of West Sarawak. Topography and geology also suggest that the fault belongs to an important fracture zone that extends well into Indonesian Kalimantan, and continues in a northerly direction along the edge of the Sunda Shelf beneath the South China Sea.

Comparison with transcurrent faulting occuring in the Malay Peninsula and a probable wrench fault between Palawan island and Sabah (North Borneo) reveals the continental part of southeast Asia to have rotated counter-clockwise up to Lower Palaeogene time, probably as a response to spreading of the Pacific ocean floor.

Calcareous nannoplankton from the Brockenhurst Bed of Whitecliff Bay, Isle of Wight, belong to zone NP 20 of the standard Palaeogene calcareous nannoplankton zonation, indicating that the stratigraphic position of the Brockenhurst Bed is in the uppermost Eocene, and not equivalent to the type Lattorfian (Lower Oligocene).

Small trachyte and phonolite bodies are shown as eroded plugs on published geological maps of part of north-eastern Nigeria. Field relationships at two such ‘plugs’ strongly suggest them to be extrusive in origin, formed of an earlier tholoid-building phase, followed by extrusion of a spine (plug dome) of very viscous lava, now forming the central peak at each locality. Petrographic data show that the tholoid and spine-forming lavas are phonolites of contrasted composition. Eruption of salic lavas from scattered centres appears to have occurred intermittently between mid-Tertiary and Pleistocene times.

A dolomite locality in the Senonian chalk at Mullaghcarton shows a sequence of fabric variations between the unconformity with the Trias and a discontinuity surface marking the top of the basal beds. The four main variations are (1) xenotopic dolomite at the base, (2) hypidiotopic dolomite with zoned crystals and a calcite sealed intercrystalline porosity, (3) zoned dolomite rhombs scattered in a microspar micrite matrix, and at the top (4) micrite with rhombohedral pores. The xenotopic fabric is interpreted as being due to distant source dolomitization and the hypidiotopic fabric with zoned crystals to local source dolomitization. The dedolomitization phenomena are related to the mechanisms of dolomitization; for distant source dolomitization the dedolomitization fabric mimics the dolomite fabric, whereas for local source dolomitization the dedolomite regenerates the pre-dolomitization fabric.

The Highland Border Ridge is a present day positive physiographic element whose activity can be traced back to Devonian time. A change from a distant Lower Dalradian to a nearby Middle and Upper Dalradian source area during Lower Old Red Sandstone times reflects the initial development of the ridge. A model for ridge uplift is outlined and some of its implications discussed.

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).

Structures affecting certain bedding planes, and simulating sedimentary ripples, have been found at a number of horizons in the Wenlock and Ludlow rocks of Denbighshire, North Wales. The megascopic appearance of the ripples, including their association with linear structures and their miscroscopical fabric are described in detail; and it is concluded that they are of tectonic origin, being manifestations of bedding-plane slip. The orientations of the ripples and other minor structures suggest that the stress responsible was the regional stress that produced folding, faulting and cleavage.

Caledonian dolerite dykes in northwest County Mayo, Ireland, are differentially metamorphosed with volumes of largely unmetamorphosed dolerite grading into marginal amphibole schists with no preserved igneous textures. Deformation controlled the extent of the metamorphism. The lack of a significant differential strain in the volumes of preserved igneous rock is considered to be the cause of the preservation.