Studies of the chemistry of Lower Carboniferous igneous rocks in the Midland Valley of Scotland throw light on the nature and magmatic evolution of transitional basaltic suites. Major oxide and trace element chemistry of least altered lavas of the Campsie Fells reveals a lower group of basalts, basaltic hawaiites and hawaiites, and an upper, more variable group, ranging from basalt to trachyte. Chemical composition of associated vent intrusions confirms their association with the lower group of flows. The magmatically evolved condition of the erupted material indicates high-pressure fractionation of clinopyroxene at depth followed by fractional crystallisation of olivine, plagioclase and Ti-Fe ores at lower pressures. In the case of the upper lavas, further differentiation appears to have taken place in a shallow magma chamber under a central volcano.

The observed chemical variations in the Campsie Fells and other areas of Lower Carboniferousvolcanic activity can be attributed to a number of different factors during the evolution of the magmas. Detailed studies of the cumulative phases of the lavas may throw further light on the various stages involved.

Pb- and Sr-isotope, major element and trace element analyses are presented for 38 Tertiary igneous rocks and older country rocks from Arran. Tertiary igneous rocks define silica-undersaturated and -oversaturated differentiation trends, but acidic and basic examples of the latter trend, exemplified in composite dykes, are separated by a wide Daly gap. In contrast, Pb-, and to some extent Sr-isotope compositions of these rocks display continuous variation, almost independent of major element composition.

Isotopic variations are interpreted as resulting principally from crustal contamination of the differentiation products of mantle-derived basic magma. A dominant rôle by mantle heterogeneity or crustal anatexis in producing the isotopic variation is ruled out. Contamination is believed to have occurred primarily after differentiation, but some rocks, such as the fine unit of the Northern Granite, display evidence of post-contamination differentiation.

Tertiary igneous rocks define an array on a Pb/Pb isochron diagram whose slope corresponds to an apparent age of 770±180 Ma (2σ). This points to the existence of a late Proterozoic basement complex under Arran.

Acidic and basic members of composite dykes are interpreted as basaltic differentiates which have been variably affected by contamination, yielding wide ranges of isotopic composition. Composite intrusion is ascribed to the simultaneous presence of acidic and basic magma in the crust.

Hyalotuff deltaic deposits, a high proportion of volcanogenic sediment and a repeated occurrence of conglomerate with well-rounded clasts constitute evidence for the shallow-water origin of spilitic lavas and volcanogenic sediments in an Ordovician ophiolite at Ballantrae, SW Scotland. One section, >1.5 km thick, shows repeated evidence for a shallow-water origin. This implies accumulation in a subsiding area. In this sense the sequence at Ballantrae is in marked contrast to those found in oceanic islands (hot spots) which are known to grow from deep into shallow water. Neither does it compare well with those from ocean ridges which usually begin in deep water and move, with cessation of vulcanicity, into even deeper water.

The lava sequence at Ballantrae compares well with oceanic island-arc and remnant arc deposits where uplift and subsidence is common. This, the occurrence of intermediate and acidic lavas and clasts, and the restricted palaeontological and radiometric ages support an arc-marginal basin origin for the lavas. Diversity in the chemical composition of the lavas may reflect diverse origins within the marginal basin.

An upward coarsening sedimentary sequence was built by a hyalotuff delta which formed in front of advancing lava flows. As the lavas advanced over the sediments so a sequence was generated where these sediments have a source in lava flows which were eventually to overlie them.

Clasts of tholeiite were derived from lavas which are now spilite. This, together with the presence of spilitic lava clasts and tuff immediately beneath the flow suggests that the spilitisation resulted from metasomatic activity associated with the convective circulation of trapped water, with the lava as a heat source.

In an attempt to establish a chronology for volcanic neck emplacement and so elucidate petrogenesis, isotopic studies have been carried out on various cumulate inclusions, blocks and megacrysts which occur chiefly in association with tuffs infilling several Scottish vents. K-Ar ages of 13 samples of low-pressure cumulate minerals (biotite, hornblende and pyroxene) from necks in East Fife indicate crystallisation at shallow depth at 314 Ma. U-Pb analyses of zircons are concordant at 318 Ma suggesting they are also members of this suite and their formation is penecontemporaneous with the Namurian volcanic activity which is welldocumented stratigraphically. By 295 Ma crystallisation of anorthoclase megacrysts had been completed, perhaps from the fractionated residuum. An eruption from considerable depth (within the stability field of garnet precipitation) then broke through to the surface bearing high-pressure megacrysts. This penetrated and disrupted the early cumulates carrying them to the surface and producing the diverse vent assemblages. K-Ar dating of basanites suggest that the Duncansby Ness neck in Caithness was emplaced around 270 Ma in the early Permian. For two Fife necks the balance of evidence favours an age of 290 Ma (Stephanian) for this final explosive activity associated with vent formation.

Orthopyroxene- and kyanite-lineage eclogites are distinguished on the basis of silicate and carbonate petrography and chemistry. Different textural and chemical types of magnesite, dolomite and calcite can be satisfactorily attributed to one of the three sequential metamorphic stages of eclogite history at anhydrous eclogite facies, hydrous eclogite facies and amphibolite facies. The chronological sequence of development of magnesite, dolomite and calcite matches the carbonate sequence found experimentally in synthetic peridotite-CO2-H2O systems during decompression. Magnesite and dolomite show reasonably regular Fe/Mg distribution relationships with silicates.

A new geothermobarometer based upon is provisionally calibrated. It yields T estimates for given P very similar to those given by the geothermobarometer, e.g. 759–829°C at 20 kb and 803–894°C at 40 kb. P is tentatively estimated at 30±10, 23±6 and 10 ± 3 kb respectively for the three metamorphic stages.

Fluid conditions after equilibration during each stage were either low or fluid-absent, but not low . A unique quartz-magnesite-dolomite vein represents an influx of CO2 in the P-T regime of instability of CO2 + pyroxene. Tectonic emplacement by deep-level obduction of diverse foreign source materials remains the petrogenetic model which best fits the data for these eclogites.

The top 9 m of Lower Hartfell Shale has been collected in 10 cm samples through a continuous sequence on the North Cliff at Dob's Linn. The boundary between the Dicranograptus clingani and Pleurograptus linearis zones is denned for the first time in a measured section, 5.0 m below the top of the Lower Hartfell Shale, with the excavation of the North Cliff proposed as stratotype. The late D. clingani Zone is characterised by Dicranograptus ramosus?, Dicellograptus moffatensis, D. flexuosus [= D. forchhammeri], Climacograptus dorotheus, Glyptograptus daviesi sp. nov., Diplograptus? pilatus sp. nov., Neurograptus margaritatus and Corynoides calicularis. The P. linearis Zone is characterised by Pleurograptus linearis linearis, Amphigraptus divergens divergens, Leptograptus capillaris, Dicellograptus elegans elegans, D. pumilis, D. carruthersi and Climacograptus tubuliferus. A range chart is provided and an attempt is made at a revised correlation of the Scottish succession with coeval zonal sequences in North America and Australia. Twenty-one taxa are described including the two new species noted above.

The Indus-Tsangpo suture and its adjoining tectonic zones are well displayed in the Ladakh Himalayas where four tectonic zones have been distinguished, viz. the Zanskar, Indus suture, Shyok suture and Karakoram zones. The Zanskar zone is made up of Precambrian basement of the Zanskar crystalline complex and overlying Phanerozic sediments including Upper Palaeozoic volcanic rocks of the Zanskar Supergroup; they form the northern margin of the Indian plate. The Indus suture zone consists of a remnant of tectonised oceanic lithosphere represented by the Shergol melange and the Nidar complex with a former volcanic arc indicated by the volcanogenic Dras and Khardung formations and the Ladakh plutonic complex. The Shyok suture zone does not represent a tectonic repetition of the Indus suture; it is interpreted as a relic of a back-arc basin. The Karakoram plutonic complex appears to be genetically related to the Ladakh plutonic complex; both were generated from the subducting Indian oceanic plate. It is proposed that the boundary between the Indian and Eurasian plates does not lie along the Indus and Shyok sutures, but is located further N at the junction of Central Pamir (Alpine-Himalayan) and North Pamir (Hercynian).

The prosomal morphology of Baltoeurypterus tetragonophthalmus (Fischer) from the Baltic Silurian is redescribed and reconstructed. The first eurypterid labrum and new secondary sexual characters of Baltoeurypterus are described. The radially-arranged coxae of Baltoeurypterus were capable of adduction and abduction for food mastication, but not promotor-remotor movements for locomotion. Joint diagrams are presented for the first time for an extinct arthropod. Promotion and remotion of the limbs occurred about subvertical trochanteral pivots, as in all other chelicerates except xiphosurans. Baltoeurypterus probably walked in a “slow” gait; a method of choosing possible gaits for extinct arthropods is outlined. Swimming in Baltoeurypterus was effected by means of a rowing action of the posterior limb pair, which is provided with complex joints for collapsing the paddle during the recovery stroke. The limb arrangement and joint mechanisms of Baltoeurypterus are intermediate between those of the xiphosurans and the arachnids. It is possible that a sister relationship exists between the eurypterids and some arachnid groups, which would render Merostomata and Arachnida unnatural assemblages.

Two new species of Ordovician echinoderms are described: Pleurocystites mitratus from the Kiln Mudstones (Caradoc) at Craighead, and Homocystites beggi from the Starfish Bed (Ashgill) of Threave Glen. Description of the former necessitated a review of the composition and status of the family Pleurocystitidae. The genus Dipleurocystis Jaekel 1918 and the subgenera Pleurocystites s.s. and Pleurocystella Paul, 1967 are rejected. The number and type of pectinirhombs; size of the periproct, composition of its border and nature of its covering plates (periproctals), and the ornament of the thecal plates and proximal columnals, are the most useful taxonomic criteria within the Pleurocystitidae. Pleurocystites mitratus is characterized by three conjunct pectinirhombs, a symmetrical theca without a rectal lobe and small periproctals each with a central pit. Homocystites beggi is distinguished from the closely related H. constrictus by strong granular ornament on the thecal plates.

Other echinoderm remains include plates of a cheirocrinid cystoid from the Kiln Mudstones.

A new fossil elasmobranch from the Lower Carboniferous Oil Shale groups (Viséan) of the Edinburgh area shows a mosaic of characters typical of at least two groups of early sharks. Its most distinctive feature is the small bicuspid teeth of “Diplodus” type. This, together with the long dorsal fin and the structure of the single, shallowly inserted dorsal spine, form a suite of characters previously considered unique to late Palaeozoic xenacanth sharks. Other features, such as the large equilobate tail and the structure of the pectoral fins, may have been retained from an ancestor of a more typical Palaeozoic elasmobranch appearance found in anacanthous and ctenacanth sharks. It is suggested that the xenacanths evolved from an ancestor within the anacanth-ctenacanth assemblage early in Carboniferous times and became adapted to a freshwater environment. This ancestor probably possessed a complex dermal skeleton including growing scales with both thickened and thin concave bases.

The fauna of the fish-bearing nodules amongst which this shark has been found is interpretedas being lagoonal in origin. The shark was probably a medium sized (c. 0·75–2·0 m lng)predator inhabiting the surface waters of the lagoon.

Assemblages of acritarchs are described from the Fucoid Beds of Skiag Bridge, Knockan Cliff and Skye in NW Scotland, and Holmia Shales of the Mjøsen area of Norway, the Bastion Formation of Ella Ø in East Greenland, the Lower Cambrian of the Burin Peninsula in Newfoundland and from the Gog Formation of the Rocky Mountains of Banff National Park, Alberta. These are shown to be correctable on the basis of acritarchs and with the Lower Cambrian successions of the Russian Platform. Twenty-one genera and fifty-three species of acritarchs and one tasmanitid are described. These include the new genera Skiagia and Volkovia, and thirteen new species, Acrum cylindiferum, Micrhystridium coniferum, M. ellaensis, M. ellipticum, M. flexispinosum, M. gogensis, M. minutum, M. ordensis, Multiplicisphaeridium ? waltoni, Skiagia brevispinosa, S. scottica, Revinotesta ordensis and Evittia irregulare. A number of recombinations have also been made.

Accurate identification of iron and manganese oxides in soils presents great difficulty because, not only are they always in admixture, but the poor crystallinity of the species present leads to difficulties in interpretation of diffraction patterns. A method involving the combined use of electron microscopy, selected area electron diffraction and electron probe microanalysis on the same crystals gives unambiguous identification. Its application is described in relation to the various iron and manganese oxides found in a set of soils from all parts of the world. The occurrence of hausmannite in soils has been definitely established.

The massive pyrite-pyrrhotite-chalcopyrite-sphalerite deposit of Outokumpu, comprising the Keretti and Vuonos orebodies, is a deformed and metamorphosed strata-bound mass associated with mineralised stockworks. Mobilisation of much of the ore followed formation of large recumbent isoclinal folds that are the major structures of the surrounding rocks and associated with the modification of originally flat saucer-shaped ore lenses into elongate ruler-shaped masses. Further modification of shape took place at the mobilisation stage with much of the pyrrhotitic ore, particularly, now occupying the thickest parts of the orebodies in the form of breccia or microbreccia. In many parts gross original characters still exist and the pyritic and pyrrhotitic constituents of the ore have survived as separate entities while locally the pyritic ore retains pre-deformational characteristics and consistent stratigraphic position within a thin horizon.

Both ore and country rocks show evidence of extensive polyphase deformation with the effects of six fold phases shown in the ore. Mineral assemblages in the country rocks indicate a middle amphibolite facies peak of metamorphism. The serpentinite-black schist-carbonate-quartzite rock assemblage, with which the ore is associated, was tectonically incorporated within the regionally extensive mica schist by even earlier subhorizontal thrusting. This is related to the movement of a thrust nappe with the interdigitation of an ocean-floor ophiolite assemblage and flysch deposited during ocean closure associated with Svecokarelian tectonism.

The original formation of the Keretti and Vuonos sulphide masses took place in a marine exhalative environment with a pyritic layer overlying a pyrrhotitic layer in each of the two c. 4 km diameter irregularly oval-shaped depressions whose centres were c. 8 km apart. The mineralised stockwork below each mass represents the upper parts of the conduit for metalbearing fluids in a convective system.

Calyptaulax brongniartii (Portlock) from the Caradocian Bardahessiagh Formation, Pomeroy, Northern Ireland is redescribed. Equivalent material from Scottish horizons (Balclatchie and Ardwell groups) is regarded as belonging to separate populations. Campbell's system of notation is used to describe variation in the arrangement and number of lenses in the eye. The most closely related species is C. strasburgensis (Ulrich & Delo) from the Edinburg Limestone of Virginia, U.S.A.

Analysed compositions of coexisting phases from cordierite-amphibole-bearing rocks (cordierite-orthoamphibole-cummingtonite-garnet-staurolite-spinel-opaque ores) and mica schists (garnet-staurolite-biotite-muscovite-plagioclase-andalusite-quartz) have been used in conjunction with experimentally determined equilibria to estimate pressures and temperatures of metamorphism for the rocks of the Outokumpu district. The data do not determine a single point in P-T space, but bracket an area such that T ≈ 600 ± 50°C and P ≈ 3·5 ± 1 kb. These conditions represent the maximum temperature attained by the rocks, and the associated sulphide ore bodies, during the Svecokarelian orogeny and are consistent with a regional palaeogeotherm of c. 50°C/km.

Assessment of the composition of the coexisting phases in the cordierite-amphibole-bearing rocks, particularly the Fe-Mg-bearing phases, indicates that it is unlikely that either iron or magnesium was mobile during metamorphism and that the equilibrium assemblage represents essentially isochemical metamorphism of a rock composition that predates the metamorphism. A similar genesis is considered likely for the cordierite-anthophyllite rocks of Orijärvi in southern Finland which forms the basis of the classic statement of the magnesium-metasomatism hypothesis.

The late Carboniferous quartz dolerite suite of Scotland consists mainly of quartz tholeiites, with subordinate olivine tholeiites and tholeiitic andesites. The low pressure evolution of the magmas was controlled by fractionation of olivine–plagioclase–pyroxene–oxides assemblages from more magnesian compositions and plagioclase–pyroxene–oxides–apatite removal from intermediate compositions. A higher pressure stage dominated by olivine fractionation is suggested by the presence of olivine nodules in a magnesian basalt dyke from Fife.

The suite is of high-Fe-Ti type, closely comparable to certain basalts erupted in areas of active lithospheric spreading or “hot spots”, such as Iceland and Hawaii. The ppO2 can be inferred to have been rather higher in the Scottish rocks than in comparative suites, promoting earlier separation of Fe-Ti oxides, with the consequent effects on trace element distribution.

Apart from varying degrees of fractionation, chemical variations in the dykes are of three types: rather minor variations along individual dykes, variations across certain thicker dykes, and minor and trace element variations reflecting chemical heterogeneities in the mantle sources. The dykes and sills are inferred to have been fed from a plexus of small, partly independent, magma reservoirs.

New trace element data on tholeiitic lavas from the Oslo Rift confirm recently revived suggestions that the Scottish and northern English quartz dolerites are part of a larger province extending into Scandinavia.