Chemical examination of uralites and their parent pyroxenes from associated eucrites and bronzitites indicate that the alteration can proceed by diverse paths and yield differing actinolites. Alteration in eucrites can be interpreted as occurring in a near closed system but in the bronzitites an external source of Ca and Al is required.

The Miocene phonolite succession of the Uasin Gishu Plateau comprises seven flows totalling about 600 km3 in volume and covering an area of some 6500 km2. Each flow has a number of recognizable and laterally persistent features which permit it to be recognized over a wide area (thousands of square kilometres). These flows originated within the Rift Valley and flowed westwards for distances of up to 60 km across the marginal plateau area.

Field relations of Carboniferous lavas in Limerick indicate that flow took place in shallow water in many cases. A possible flow mechanism is proposed for these lavas. Brecciation of the flows took place after emplacement due to steam release from underlying limestones, which frequently became thixotropic and injected upwards into the denser lava.

Granodiorite stocks were intruded into the alpine peridotites of southern New Caledonia in the Eocene following overthrusting of the ultramafics onto the sialic core of the island. Strong zoning, from mela-diorite to granodiorite, is developed in one pluton and is believed to be the result of assimilation of ultramafic and mafic rocks by the calc-alkaline magma. Evidence in favour of a consanguineous relationship between the felsic and ultramafic rocks is largely circumstantial. In their petrography, mineralogy and chemistry, the rocks show few differences from other felsic plutonics of Tertiary age in the southwest Pacific.

Re-assessment of the idea that the Monian and Longmyndian accumulated along the margin of a palaeo-ocean suggests that Monian sedimentation occurred near the eastern shoreline of a micro-continent. If Monian igneous activity, metamorphism and deformation are attributed to an underlying subduction zone, this must have dipped northwestwards away from a small ocean basin to the southeast. Consumption of this ocean floor brought about collision with the continental shield and simple deformation of the Longmyndian.

The first European occurrence of ‘Didymograptus’ spinosus Ruedemann, 1904, is reported. A re-description of this species is provided, based on the lectotype and new material from the West of Ireland. ‘D.’ spinosus is shown to possess the essential characteristics of the genus Holmograptus Koztowski, 1954, to which it is accordingly referred.

Didymograptus nodosus Harris, 1926, and Tylograptus regularis Mu, 1957, together with certain other species of Tylograptus described by Mu (1957), are junior synonyms of Holmograptus spinosus. Holmograptus Kozlowski, 1954, is a senior synonym of Tylograptus Mu, 1957.

The northern part of the Guiana Shield consists of large tracts of basic and intermediate volcanic rocks and sediments which are thought to have formed under geosynclinal conditions. During the 2000 m.y. Trans-Amazonian Orogeny these rocks were subjected to tectonism and metamorphism resulting in a broad belt of green schist facies with local and isolated patches of high grade metamorphic rocks and gneiss complexes. In the early stages of orogeny during which folding and probable block faulting of the sediments and volcanics took place, these rocks were intruded by basic and ultra-basic rocks giving rise to metagabbro-amphibolite-peridotite associations, commonly in the areas of subsequent high-grade metamorphism. In an attempt to account for the frequent supply of basic magma during and after the orogeny it is postulated that mantle peridotites rose diapir-like below the sinking geosyncline, and by partial melting not only provided basic magmas but also thermal energy which spread upwards to metamorphose the already tectonized crustal rocks; recent gravity measurements indicate an upwarped ‘sima’ under the Bartica Assemblage gneiss complex.

Potassium-argon age determinations on rocks from the Sierra de San Carlos, State of Tamaulipas, México, which are petrographically very similar to other bodies in north-eastern México and the south-central U.S.A., indicate that a NW-trending zone of alkaline complexes, at least 1,400 km in length, stretches from the Gulf coast to southern New Mexico. This zone may be structurally related to the parallel, but somewhat younger, Rio Grande rift.

This note outlines some thoughts on the possible significance of the April 1972 Qir earthquake with respect to the geological structure of Fars Province, SW Iran. The area in which the disturbance occurred belongs to a belt of simple folds of the Zagros system. These folds exhibit localized anomalies of structure which are attributed both to renewed movements along deep-seated basement features and to the modifying effects of salt mobility in the subsurface. The absence of surface indications of rupture in the devastated area is puzzling, but the alignment of zones of maximum destruction to buildings suggests a shallow epicentre associated with a concealed N70°W trending thrust fault system. Such seismicity is indicative of the continued activity of the Zagros orogenic movements.

Near Tintagel, southerly verging kink bands cut flat-lying Upper Palaeozoic Plates and schists. The bands are about 2 cm wide and most of them terminate by a Decrease of amplitude but not wavelength. The length of the kinked limb and the frequency of the bands were probably determined by lithology when the deformation began, The bands may have formed under a N-S directed maximum principal stress which was Slightly oblique to the layering.

The alkali syenites of the Mundwara magmatic suite, Sirohi district, Rajasthan, in north-western India, are chiefly developed in the Musala hill of the complex. They comprise three principal varieties representing different stages of crystallization, viz. nepheline-sodalite syenite, nepheline-barkevikite microsyenite, and nepheline poor leucosyenite. The dominant constituent of these hypersolvus syenites is alkali feldspar, an orthoclase microperthite showing a variable degree of exsolution. The chief mafic mineral is a distinctly green and zoned sodic pyroxene, close to aegirine-augite in composition. A brown calciferous amphibole, identified as a barkevikite, is developed in addition in the microsyenites. Reddish brown biotite of the phlogopite-annite series is common to all the syenites. The petrography and mineralogy of the syenites are discussed, and a comparative study of the Mundwara syenites with similar rocks of the Deccan volcanic province is presented. Chemistry and mineralogy of the syenites of the Mundwara suite suggest that they are related to those associated with the Deccan volcanic province.

Regional mapping in the eastern escarpment of the Ethiopian plateau indicated Precambrian block-faulted structures which have been felt in sedimentation and tectonics for more than 1000 m. y. and which controlled to some extent the opening of the Afar.

The two pits expose Pliensbachian silty shales and ferruginous limestones and sandstones. Fossils collected in situ are listed and two new morphospecies of fossil bivalve mollusc are described—Hippopodium tuffleyensis and Hettangia aperta. A taxonomic discussion is followed by palaeoecological inferences drawn from the essentially bivalve-dominated molluscan fauna. The conclusions indicate that the silty shales were deposited in well oxygenated waters, probably not exceeding 100 m, and the limestones at even shallower depths. Pebbles in the limestones indicate that some erosion preceded each of the limestones in the Margaritatus zone.

A lithostratigraphy is described and related to that in the adjacent Corris-Machynlleth district. Thickness of the Formation is estimated to be c. 500 m near Towyn rather than c. 1000 m as generally accepted, although poor exposure precludes accurate determination. Palaeocurrent data are given for a prominent interval of turbidite arenites, here termed the Llyn Barfog Member. Sedimentary facies are interpreted as slope-base and deep basinal deposits and are consistent with control of sedimentation by the Bala and Corris ‘basement faults’.

Characteristics of mineralogy and texture, together with systematic changes in the enstatite content of orthopyroxene and in the anorthite content of plagioclase, indicate that intrusions of pyroxenite, norite and gabbro, and diorite and leucocratic diorite in the Dahomeyan gneiss of Ghana are genetically related, and that they belong to a subalkaline comagmatic series derived from a parental mafic magma. Partial recrystallization (deuteric) of the igneous rocks during and after intrusion and protoclasis produced minerals characteristic of temperatures higher than those that existed during the medium-grade regional metamorphism of the Dahomeyan gneiss, thus indicating that emplacement of the igneous rocks occurred late during, or perhaps after, the metamorphism. Contact metamorphism appears to have resulted in higher than normal anorthite contents of the plagioclase in the surrounding Dahomeyan gneiss.

A conventional trend surface is symmetrically placed between the observed values of a dependent variable. The proposed median surface is symmetrically placed between the ranks of the observed values. The use of a median surface is illustrated by its application to the distribution of silver in a granodiorite stock.

The bankfull width (w) of modern meandering rivers (sinuosity >1.7) is related to bankfull depth (h) by the equation w = 6.8h1.54. The equation may be used to calculate limits for the bankfull widths of palaeochannels that deposited alluvial fining-upwards cycles. Calculated bankfull widths and measured bankfull widths from epsilon cross stratification are further used to state ranges of values for meander wavelength and mean annual discharge using existing empirical equations. The empirical equations directly relating width/depth ratios to sediment load and sinuosity are shown to be generally valid only for small rivers because of the increase of width/depth ratios as meandering rivers increase in size.