Changes attributable to weathering have been detected in Quaternary sediments overlying an important aquifer in the Vale of York. Solution of carbonates is quantitatively the most important effect of weathering. The amount of carbonate dissolved can be estimated from whole rock analyses. The length of time of weathering is known and an equivalent surface lowering rate for limestone can be calculated which is consistent with rates obtained by other workers.The volume of water required to give the observed compositional changes is calculated from porewater analyses. The time period is known and hence the rate of infiltration and the average recharge rate of the aquifer can be determined. The calculated rate of recharge is consistent with rates determined using other methods.

The Numidian flysch unit is the largest tectonic unit in the western Mediterranean, extending from Gibraltar to southern Italy. Displacement of the unit is supposedly to the S, a result of either gravity tectonics or plate tectonics. Both interpretations have their adherents, and to solve this dilemma the Numidian flysch in Tunisia was studied. Field data indicate surprisingly that the Numidian flysch in northeastern Tunisia (Mogods–Hedil area) did not move at all, which renders the question of the emplacement mechanism irrelevant. In northwestern Tunisia (Kroumiria) the flysch moved presumably only a few km to the S, not 50 km as was thought previously. Analysing this small displacement it appears unlikely that gravity tectonics was of importance because move ment over the fault was probably upward; moreover, sedimentological data do not indicate a high area from which sliding could have occurred. A plate tectonic interpretation cannot explain, however, why flysch movement was spasmodic instead of continuous and contemporaneous with plate movement, or why plate deformation was restricted to the thin flysch unit.

Ultramafic and mafic nodules are abundant inclusions in Cainozoic alkali basalts at 7 localities in the Auckland Province. Nodule types show a gradation from dunites and pyroxenites through periodotites to eucrites. Bulk chemical variations in the nodules show a wide range in MgO/ΣFeO with a tendency for Al2O3, ΣFeO, CaO and Na2O + K2O to increase as this ratio decreases. These chemical trends, together with published data on the nodules mineralogy and fabric, are consistent with their being interpreted as fragments of the upper mantle.

An assemblage of benthonic Foraminiferida of late Palaeocene age is described from subsurface material from Halesworth, Suffolk. Twenty-two species are listed, and are compared with microfaunas which were described by Haynes (1954–8) from the type Thanetian.

Potassium–argon and rubidium–strontium isotopic age studies of the Wolf Rock phonolite of SW England confirm its age as 131 Ma, with an initial 87Sr/88Sr ratio of 0.703. The existence of a Mesozoic volcanic province of this age on the margin of the Labrador–Biscay rift is discussed with special reference to its implications for the early evolution of the N.Atlantic Ocean, and the general relationship of alkaline igneous activity to major periods of plate reorientation.

In the Moinian rocks of Scotland, epidote-bearing calc-silicates, distinct from the commoner garnet-zoisite-bearing calc-silicates, occur at several widely scattered locations. The major element geochemistry of the two types of calc-silicate is very similar, and their somewhat different petrology and trace element geochemistry may be explained by the preservation of grains of detrital epidote and heavy minerals in the epidotic calc-silicates. These grains were concentrated in the original sediment and remained stable under greenschist and epidote-amphibolite metamorphic facies conditions. While the garnet-zoisite bearing calc-silicates may be derived from calcareous marls, the epidotic calc-silicate bands are probably derived from epidotic grits similar to those recorded in the Torridonian.

The nature and timing of ‘spilitization’, and the original composition of ‘spilitized’ Precambrian lavas fron the Athapuscow aulacogen, Great Slave Lake (Canada) are investigated, using geochemical and Rb/Sr isotopic methods. Relationships and abundances of trace elements of petrogenetic significance suggest that the spilites were not derived from alkaline basaltic magmas, but show petrogenetic affinity with tholeiitic basalts from continental or volcanic island environments. This new interpretation conforms well with the supposed tectonic and geologic environment in which the lavas and pyroclastics were erupted. Assuming an ‘open system’ behaviour for Rb and Sr during intense metasomatism, the isochron age of 1872 Ma obtained for the lavas is considered as the time of ‘spilitization’. This age, when compared with geochrono metric data obtained by other techniques, suggests that the time interval between initial volcanism and subsequent ‘spilitization’ event was brief, and probably related to diagenesis or burial metamorphism during rapid subsidence and sedimentation commonly associated with rifting within aulocogens. A relatively low initial 87Sr/86Sr ratio of 0.7018±0.0005 obtained for the lavas either reflects the low Sr isotope values characteristic of diagenetic pore fluid in Precambrian seas, or suggests that the original ‘primitive’ initial ratio was not adversely affected by the ‘spilitization’ process. .

An account is given of coral patch reefs in the Bajocian of Lorraine, France, and a distinctive ecological association in the other invertebrate fauna recognized, which compares closely with that present in the late Oxfordian reef facies of southern England. The inference is made of a series of low mounds on the original sea bed, composed of coralline sheet structures interfingering with calcareous sediment which locally and periodically enveloped the coral colonies. Compared with Recent patch reefs in the Bahamas and around Bermuda, important differences can be inferred for the Jurassic structures, principally the lack of significant topographic relief, major internal cavities, erosion and algal incrustation.

Phlogopitization of pyroxenite is common in contact zones between clinopyroxenites and carbonatite dikes of the Cargill ultramafic rock—carbonatite complex near Kapuskasing, Ontario. The most typical development is a mica zone 1–10 cm wide but phlogopite is also developed in a more pervasive manner throughout the groundmass of several types of ultramafic rock. Fenitization is most commonly thought of as a process whereby aegirine and riebeckitic amphiboles are formed in the host rock while feldspar is recrystallized and silica progressively removed. Phlogopitization of pyroxenite can properly be referred to, however, as a type of fenitization. It is clearly related to the intrusion of carbonatite into pyroxenite and is further testimony to the fact that many carbonatite magmas are initially alkalic but lose alkalies to the surrounding rocks and crystallize as calcitic and dolomitic carbonatite with alkali contents restricted to the amounts that could be fixed as micas, pyroxenes or amphiboles. This in turn is controlled by the silica and alumina activity of the carbonatite magma. Abundant evidence for considerable amounts of fluorine in carbonatite magmas suggests that alkalies may be transported into the country rocks as fluorides. It is further suggested that late-stage feldspathization in carbonatite complexes is explained by the abstraction of potassic halide solutions from the crystallizing carbonatite magma. The conclusion seems inescapable that alkali carbonatite magmas, far from being the curiosity thought by many petrologists, are in fact very common during the evolutionary history of carbonatites. The common calcitic and dolomitic carbonatites have not generally crystallized from a magma of the same composition but are the residue remaining after the abstraction of an alkali-rich aqueous fluid. Consequently, there is a need to redesign the experimental phase equilibrium approach to problems of carbonatite genesis in order to take account of the presence of alkalies in most carbonatite magmas.

Continental Middle Devonian sediments of the Kvamshesten district have recently been interpreted as a thrusted block. However, although basal contacts in the E of the district are mylonitized, contacts in the W can be interpreted as depositional unconformities. Coarse alluvial-fan breccias (Markavatn Formation) in the district's northern margins interdigitate with fluviatile sandstones (Heilefjell Formation) towards the basin's centre. Syndepositional tectonism is demonstrated by the geometry of the coarse marginal deposits.

Three samples of low-grade metamorphic rocks from the Hazara Group, northern Pakistan, analysed as total-rock samples by the Rb—Sr method, give model ages of 765±20 and 950±20 Ma. The results are discussed in terms of the stratigraphy of Hazara, northwestern Iran, and certain other areas.

The sedimentology of a key locality in the Caradoc of SW Wales is discussed for the first time. Five facies are described and interpreted: mudstones and siltstones (A), turbidite arenites (B), rudites (C), a diamictite of massflow origin (D), and muddy arenites rich in shaleclasts (E) which show a transition from massflow deposits to immature turbidites. Closely adjacent sections illustrate considerable lateral variations within an assemblage suggested to be of proximal turbidite character and to represent deposits high on a Middle Fan environment.

The Pleistocene Gargaresh Calcarenite is a series of fossil dunes parallel to the Mediterranean coast of Tripoli; it is composed of medium-grained skeletal carbonate sand with abundant cross-stratification. Analyses of 321 azimuthal readings show that the distribution is bimodal with modes in the NE and the SE sectors. The distribution of modes indicates that the morphology and the orientation of eolian dunes were largely controlled by the then prevailing winds, and that the overall palaeowind pattern, although generally similar to the present-day system, might have undergone periodic changes due to Pleistocene climatic ups and downs.

Quartz-plagioclase veins in staurolite schists often have margins depleted in the vein minerals. In some cases vein formation has simply involved recrystallization of groundmass grains into large vein grains in a closed system. The driving force for this process is reduction of strain energy and surface free energy. It is suggested that the veins initiate when grain boundaries have been opened up by hydraulic fracturing during medium grade metamorphism. The segregation process can be explained by a model of local equilibrium between grains and a continuous pore fluid similar to that commonly applied to metasomatic reactions; however, no phase change occurs.

Structures similar to the monticules of Palaeozoic trepostomatous Bryozoa which occur in the Jurassic cyclostome Reptomultisparsa incrustans are described. They are interpreted as having a function analogous to that inferred for monticules. A smaller proportion of zooecia open on the monticules than between them, and, of these a higher proportion are occluded.These observations lend support to the theory proposed by Banta, McKinney & Zimmer (1974) that monticules functioned as regions of exhalant current chimneys on the zoarial surfaces of Bryozoa.

The paper reports the occurrence in the 2.9–3.1 B.Y. old charnockitic terrains of Southern India of some basic charnockites that are strikingly similar, chemically, to basaltic komatiite from the 3.4 B.Y. old Barberton greenstone belt of Southern Africa, and suggests that the pre-metamorphic evolution of Archaean charnockitic terrains followed the same trends that characterized the development of Archaean greenstone belts. The main events in the evolution of one such terrain, the ‘Madras granulite belt’, before it was subjected to granulite facies meamorphism some 2.6 B.Y. ago, is outlined in Table 2.

The Nyika granite gives a U-Pb zircon age of 1970±30 Ma, which is a minimum age for the high-grade Ubendian metamorphism in Northern Malawi. Cordierite gneisses from the same region yield an Rb-Sr whole-rock isochron age of 1815±260 Ma. Because this age is believed to reflect the high-grade Ubendian metamorphism, the latter cannot be significantly older than about 2100 Ma.

An examination of narrow zones of bare sand, usually averaging 10 m in width, situated between the patch reef and the sea grass beds (Thalassia and Cymodocea), shows that they appear to be primarily the result of wave action. Experiments were conducted in the U.S. Virgin Islands over a period of 5 years, which show the effect of subsurface interference of wave patterns in the forming of these bare sand zones. It is thought by the present author that these sand zones are a major factor in the equilibrium balance of sand quantity necessary for on and offshore transportation, and also in the balance of sand retained behind the patch reefs of the West Indies.

Strain distribution inside an elliptical shaped boudin under normal compressive stress is calculated by photo-elastic methods following Frocht (1966). The strain magnitude varies horizontally within the boudin and the value increases gradually from the central part of the body to the margin. The magnitude is nearly constant along the vertical central part of the boudin. Around the margin, inside the body, it shows an average value of the vertical and horizontal stress magnitudes. No actual change in the direction of shearing stress in different parts within the boudin is noted, hence no directional change of strain. Petrofabric diagrams of different parts of natural boudins showing the quartz (0001) plots, indicate no variation in the pattern of orientation in different parts of the body. However, the elongation ratio of quartz grains shows a correspondent increase with the increment of stress magnitude as noted in the experiments.

The Palaeozoic rocks of Hydra consist of a sequence of limestones and dolomites with some interbeds of shales and sandstones. Fusulinid foraminifera indicate the sequence is entirely Permian in age and not Carboniferous and Permian as previously thought.