Analysis of 17 samples for both major and trace elements reveals that, unlike most other Tertiary composite intrusions, the Creag Dubh sheet possesses silicic margins and a doleritic centre. The two rock types grade together rapidly without chilling at the upper and lower internal contacts. However, there is evidence for mixing of the two magma types prior to or during emplacement with the production of limited amounts of intermediate hybrids. The central dolerite appears to be later than the marginal felsites which in places back-vein the dolerite. The sequence of intrusion is tentatively related to the upward draining of a strongly zoned magma chamber.

By systematic sampling (including the drilling of orientated cores) new data are presented on the chemistry, petrography, mineralogy, K/Ar isotopic age and remanent magnetism of the Wolf Rock, Cornwall. The overall homogeneity of the Rock is confirmed as a fine-grained fluxioned microporphyritic phonolite. Major joints strike NNW–SSE and NNE–SSW and there is a pronounced floor jointing. New whole-rock and probe analyses of the constituent minerals are given. Nosean, previously recorded, is found to be replaced by analcime, cancrinite and other minerals. K–Ar determinations on nepheline and K-feldspar give mean ages of 112±2, and 130±6 Ma respectively. The mean pole position of 70° N, 6° E, suggests that the 130 Ma pole for stable Europe may have been somewhat closer to Europe than previously supposed. The significance of this Lower Cretaceous magmatism in the context of Mesozoic volcanism in Southern England and European alkaline provinces is discussed.

The generic composition of trilobite faunas around the perimeter of North America during the Medial Ordovician is related to the regional palaeogeography deduced from field evidence. Major divisions into shelf, shelf-edge (biohermal mounds) and slope (upper and lower) can be recognized. The Caradoc immersion of the N American plate resulted in landward invasion of pre-adapted slope forms. Some of these genera had European origins and their appearance is due to migration in deeper water facies accompanying closure of the Proto-Atlantic ocean. There is no obvious repeat of Cambrian biomere patterns in the Ordovician although some later Ordovician trilobites, especially shelf inhabitants, had their origins in earlier Ordovician biohermal or slope communities. The origin and composition of the Remopleuridid faunal Province is briefly discussed.

Structural evidence from the Kalak Nappe Complex suggests the operation of layer parallel shearing stresses during the translation of the nappes. A simple shear model invoking irregular areas of high cohesion within individual layer boundaries is used to explain the development of both intra-folial, cylindrical and non-cylindrical folds and a regular zone of syn-folding blasto-mylonite at the base of the nappe(s). Fold hinges that are initially developed parallel to the Y axis of the strain ellipsoid during layer parallel shearing may be rotated towards the X direction as a result of large strains concentrated at points of high cohesion within the layering boundaries.

The Middle and Upper Devonian limestone successions at Torquay and in the Lemon Valley SW of Newton Abbot are described. Lithostratigraphic units are proposed for the Torquay succession. The compositions of the coral faunas in both successions are outlined and contribute, together with the other available faunal evidence, towards a broad internal dating of these limestone sequences. Successions elsewhere in the limestones of eastern South Devon are briefly outlined. On the basis of this evidence facies variations from the margin towards the centre of the carbonate platform in eastern South Devon are demonstrated and interpreted as reflecting the development of barrier reefs along parts at least of the platform margin in Givetian times. The character of the reef-complex, named the Tor Bay Reef-Complex, is briefly compared with Devonian reefs elsewhere.

A discussion of geological description and an account of the Descriptive System LSDØ2 are given. It is shown that by examination of the aims of description and of its main instrument, the geological observer, a set of principles and objectives may be established in order to design descriptive systems. The application of these principles is demonstrated by an account of the theory and practical aspects of the Lithostratigraphic Descriptive System LSDØ2.

Mantle diapirism centred in Transylvania is suggested as the explanation of the Carpathian Arc and the Pannonian Depression, deviation of the Danube from a formerly straight course, and the trends of the Eastern Alps and horsts and troughs in the Bohemian Massif and Poland. Central location in Transylvania is at the crossing-point of deep fractures, parts of great circles, most conspicuously displayed in Transcaucasia and along the Zagros Main Thrust line. Mantle diapirism extended westward from Transylvania along each lineament in Hungary. Pannonian deep lithosphere may be a subcrustally thinned extension of the Bohemian Massif, with a relict unthinned fragment appearing as the Dobrogean Massif. This extended massif would originally have lain almost parallel to the western boundary of the Russian Platform and to the present Dinaride belt.

Although a root system has been discussed for the blastoid Pentremites, no cirri have been reported and no photographic illustrations have heretofore been given of the complete animal. Two specimens with complete stems with sporadic cirri along the entire length and distal attachment cirri, and one specimen with a long portion of stem, a few cirri and spiracle covering plates preserved in place, are reported herein. All three specimens are from the Fraileys Formation, Hombergian Stage, Chesterian Series, Upper Mississippian of southern Illinois, U.S.A. (Zone E1, Pendelian Stage, Namurian Series [A], Upper Carboniferous). An eleutherozoic or free life style is postulated.

Basic rocks from the West Mexican Batholith and the Coastal Batholith of Peru are described. These are considered representative of the whole range of basic rocks in batholiths and their crystallization and subsequent history is related to the fluid pressure of the magma. Their role in batholithic evolution is discussed.

Thrust-bound bodies of trondhjemite, showing variable intensity of deformation, contain micro-structural evidences which suggest that the mylonitic fabric in them had developed in stages. An initial shearing stage was followed by a flattening one when the characteristic mylonitic microstructures and banding developed. These stages were punctuated and overlapped by phases of recovery and recrystallization. Mineral parageneses and microstructures indicate that prograde metamorphism and ductile deformation characterize the flattening stage. The origin of mylonite is explained in a scheme of progressive deformation during which planes of maximum shear strain and flattening became almost parallel, so that brittle microstructures were either modified or obliterated by ductile ones. The sequence of microstructural development and mineral redistribution suggest that in mylonite formation mechanical process is accompanied with chemical mobility.

Scapolite occurs in the NE Mt Lofty area of South Australia in rocks of bulk compositions as diverse as sulphide-rich veins, meta dolerite, scapolite (pelitic) schists, calc-silicate rocks and impure marbles. Scapolites analysed from all these rocks show with increasing grade a linear to near-linear change in composition from Me50 and Me66. Some scatter around these values is attributed to local perturbations of fCl/fCo2 in the fluid phase during metamorphism. Sulphur values as SO3 are below the 0.02 level even when scapolite occurs in contact with sulphides in a vein in a small copper mine; here, however, an interpreted FeO value of 2.58 weight % was recorded. The values in this study are comparable with those of Heitanen (1967), and are believed to be representative of products of normal metamorphic fluids evolved from non-evaporitic metamorphic rocks under a greenschist–amphibolite facies gradient; they can thus be used as a standard in assessing the possible significance of meta-evaporites in other areas.

Analysis of the fracture pattern in the Coniston area of the Lake District indicates that copper mineralization is localized in a series of fractures produced during the main phase of deformation affecting the Borrowdale Volcanic Series. Three events are recognized on the basis of field and textural evidence obtained from polished sections: an early haematite mineralization, correlated with the low grade regional metamorphism affecting the rocks; the main phase of sulphide mineralization, with zoning, which is correlated with a granite intrusion at depth; and a late renewed movement on the veins, with carbonate mineralization, believed to be related to uplift of the granite.

A technique is described for direct analysis of rock-fabric, utilising hardness differences between various mineral constituents. This renders unnecessary the intermediate step of measuring optical orientations. The direct relation that exists between hardness of the components making up a particular fabric and the start of plastic deformation of each mineral can be measured quantitatively on the basis of polishing hardness differences. If the surface roughness signal is digitalised, then it is possible to automatically construct a microtopography, with contours delineating resistance of individual minerals.

Clay mineral analysis of shales in the early Liassic Lower Broadford Beds of the Hebrides reveals the presence of abundant quantities of montmorillonite whereas the Upper Broadford Beds contain illite, kaolinite and subordinate mixed layer minerals together with chlorite. Montmorillonite enrichment of the Lower Broadford Beds as a consequence of recent weathering contamination by doleritic sills can effectively be ruled out. It is argued that the montmorillonite may have been derived from the weathering of basic igneous rocks exposed in the sediment source area during Late Triassic times. By Upper Broadford Beds times, the igneous source was either eroded away or transgressed by the early Liassic sea.

The Larsen Harbour Formation of southern South Georgia is part of an ophiolite sequence of submarine lavas and sheeted dykes emplaced into metasedimentary country rocks. The metasediments are remnants of a pre-Cretaceous continental crust which had been subject to regional metamorphism and polyphase deformation prior to intrusion by a variety of acid and basic igneous rocks (roots of the ophiolitic sequence). It is proposed that the segment of continental crust and the Larsen Harbour Formation formed the floor of a back-arc basin which was infilled during Early Cretaceous time by a thick sequence of volcaniclastic sediments (Cumberland Bay Formation).

An occurrence of small diagenetic siderite concretions is described. They occur towards the top of a postulated shallowing sequence of cleaved Lower Palaeozoic siltstones and shales. The concretions occur as lenses and aggregates associated with horizontal grazing trails, and also as diffuse bands apparently unrelated to the latter. The concretions are compared with other similar structures described elsewhere, and an origin by diagenetic growth beneath the sediment–water interface in a marine environment is postulated.

K—Ar age measurements on Esquibel Island, southeastern Alaska yield a minimum age of about 433±3 Ma for the Zone of Monograptus cyphus of the Lower Silurian. An age of approximately 435—437 Ma is estimated for the Ordovician—Silurian boundary.

Abundant spherules of phengite, 50—150 μm in diameter and with a radial texture, occur in mudstones at the top of the lowest member of the Bonahaven Formation. They have smooth, sharp boundaries, show flattening next to desiccation cracks and exhibit a restricted, bi-or tri-modal size distribution. It is inferred that the spherules represent infilled voids in a sediment which was deposited entirely from suspension. Accordingly, it is considered likely that the spherules are microfossils, although characteristic morphological features are lacking. They were probably infihled by glauconite, which was transformed to phengite during diagenesis and low-grade metamorphism.

Three sets of kink bands occur in Campanian chalk, near the coast of the Gulf of Elat. The kink bands can be traced by a system of vertical joints, intersecting the chalk and filled with secondary crystalline calcite. The geometry and the development of these structures are described, suggesting a change of the stress regime during the opening of the rift along the studied area.

Phacops turco aff. praecedens Haas, from the Devonian (Eifelian) of Morocco, varies in the type of lens packing in the eye. Cubic close packing in trilobite eyes is described for the first time.