Sediments, mainly sandstones, conglomerates and shales, accumulated in small turbidite fans along the northern arc–trench margin of the Iapetus Ocean from middle Ordovician to Silurian time. These fans, together with the underlying pelagic facies and part of the oceanic crust, were sliced and accreted northward resulting in the Lower Palaeozoic accretionary prism which forms the Scottish Southern Uplands and the Longford-Down inlier in Ireland. North Down is the continuation of the Northern belt of the Southern Uplands of Scotland into Ireland, bounded to the S by the Orlock Bridge fault. Lithological and petrographical comparison with the rest of the Northern belt indicates closer affinities with the Southern Uplands of Scotland than with the western end of the Longford-Down inlier. Major ENE—WSW-trending Caledonian strike faults define five blocks, in which new formations of Caradoc and ? Ashgill age are defined. Pillowed spilitic rock, interpreted as a fragment of the ocean-floor, is only recognised in the Ballygrot block. Pelagic and hemipelagic black shales and cherts are overlain by arenaceous sediments in all blocks.

An evolving pattern of fluvial dispersal responsible for the Lower Old Red Sandstone magnafacies has emerged from a stratigraphical and geographical consideration of palaeocurrent structures, clast lithology and fauna, sandstone composition, and sandstone detrital heavy-mineral assemblages. The evidence suggests that the Post-Ludlow (Downton) and lower Gedinnian rocks formed mainly in the joined Dingle–Shannon and Anglo–Welsh basins, fed from metamorphic complexes in NW Britain or beyond. Contemporaneous sedimentation in the Caledonian basin was restricted to its northeastern end. Later in the Gedinnian, the Dingle–Shannon and Angle–Welsh basins appear to have become separated by the uplift of a broad and extensive belt of mainly Lower Palaeozoic sedimentary and volcanic rocks; included in this belt were outcrops of Post-Ludlow strata representing the earlier stream of metamorphic detritus. Granite intrusion, which reduced the density of and consequently uplifted the crust, occurred widely in the regions dividing and bordering these basins, and may be causally connected with their separation in the Gedinnian. The Caledonian basin appears to have remained a separate feature.

The K–Ar ages of 117 clay concentrates from samples associated with mineral deposits in Ireland indicate that most, if not all of the major ore deposits were formed during Carboniferous times or earlier. The Avoca orebodies are pre-400 Ma in age. Many of the vein deposits traversing Palaeozoic rocks were either formed or rejuvenated during the Hercynian orogeny c. 300 Ma ago. The SW Ireland Cu–Ba ores are 290 Ma old, and the major, frequently stratiform, base metal deposits stratabound in the Lower Carboniferous were, at least largely, formed during the Carboniferous period. In the case of the Navan orebody, an early Carboniferous age is indicated. Previous models invoking major mineralisations during Mesozoic or Tertiary times are rendered invalid. However, in some areas there appears to have been hydrothermal activity during the Triassic and possibly the Permian. The Triassic event is thought to be genetically related to coeval hydrothermal avtivity found throughout the N Atlantic regions. The data suggest that probably <10 km of cover has been removed from the majority of Ireland since Lower Carboniferous times. K–Ar dating of clays is shown to be a powerful method for constraining the ages of oredeposits.

The Midland Valley of Scotland was an arc–interarc region during most of Ordovician—Devonian time. This arc terrane extends beneath the allochthonous Southern Uplands and probably beneath the southern Highlands. Models of Caledonian plate tectonism which regard the Midland Valley as a fore-arc basin are rejected principally on the grounds that (i) the Ordovician sequence at Girvan, in the very SW of the Midland Valley, was generated in a proximal fore-arc basin to the immediate S of a contemporaneous plutonic–volcanic arc, and (ii) the source for Silurian sediments in the southern part of the Midland Valley could not have been a rising trench-slope-break, but igneous basement and conglomerates with clasts of metamorphic basement, i.e. the southward extension of the Midland Valley.

The Midland Valley arc first comprised mainly plutonic rocks, some of which may have been basic but most of which were certainly granitic. Little is known of the ages of volcanic clasts in Silurian conglomerates (this time may have been a period of relative volcanic quiescence), but the Silurian–Devonian sequence is considered to have formed in an interarc basin which, like many other basins of this kind, began as marine (Early Silurian) and ended as fluvial (Devonian). At this final Silurian–Devonian stage, the Midland Valley arc was dominated by effusive rocks which made a substantial contribution to the sediments.

In this interpretation, the present Old Red Sandstone volcanic rocks are seen as the final stage of a volcanic arc which occupied the position of the present Midland Valley from at least Llanvirn to Early Devonian time.

Radiometrie evidence suggests a complex evolution for some parts of the Moine assemblage NW of the Great Glen fault in Scotland. Four generations of microdiorite sheet intrusions are distinguished and used as time- and strain-markers in this region. Two are found to record different tectonic episodes in the Morar and Glenfinnan divisions and their Loch Eil division cover during the c 750 Ma Knoydartian orogeny. These demonstrate that F1 and F2 (of the Grenvillian orogeny) and F3 folds (of the Knoydartian orogeny) in the Morar and Glenfinnan divisions are absent from the Loch Eil division. Two later generations of microdiorites record successive episodes (F4 and F5) of the c. 455 Ma Caledonian orogeny.

The tectonic history of the region is considered after a discussion of the use of microdiorite sheet intrusions as strain-markers. This is because, rather than fold or boudinage, they deformed as incompetent single layers and foliated, mullioned or thinned uniformly instead. The attitudes of different elements of the microdiorites and their internal foliation are used to construct strain ellipsoids for four tectonic episodes on scales of 4–400 m and >4000 m. Three of these episodes are found empirically to have involved irrotational plane strain and all are close to coaxial even though the principal axes of strain appear to have swapped one for another in space as well as time.

Two new genera and species of haplolepids (Chondrostei), Protohaplolepis scotica and Blairolepis loanheadensis, are described from the ironstones of Loanhead, Midlothian (Namurian A, E1); this represents the earliest known record of the family. Protohaplolepis scotica (= Traquair's nomen nudum “Eurylepis scoticus”) shows many features in common with Westoll's hypothetical haplolepid “common ancestor X”, and is possibly ancestral to the Haplolepis–Microhaplolepis line within the family. Blairolepis loanheadensis, known only from a skull roof, shows greater similarities to Parahaplolepis and Pyritocephalus, but differs from these genera in having separate dermopterotics and parietals. Two subfamilies, the Haplolepinae and the Parahaplolepinae, are suggested to reflect the distinct evolutionary lines within the family.

A new species, Parahaplolepis westolli, is also described from Newsham, Northumberland (Westphalian B). This species shows a close resemblance to the American species Parahaplolepis tuberculata from Linton, Ohio.

A brief discussion of the evolutionary history of the family is presented, along with a summary of its stratigraphical and geographical distribution.

The Recent Saefell tuff-ring on Heimaey, Iceland was formed by surtseyan activity in shallow seawater. The tuff-ring has a basal diameter of about 3 km, a maximum rim height of 188 m above sea-level and a crater diameter of 1300 m. Three tuff-units are recognised, separated by unconformities on and inside the crater rim due to syndepositional slumping. The crater contains a nested rim which was constructed above slumped crater tuffs. Directional data indicate strongly directed blasts to the SW at a late stage in the activity.

Throughout the volcanic activity, base-surges formed antidunes, U-shaped channels, vesiculated tuffs, small ripples and plastering structures. One antidune reflects a decrease in surge flow power during deposition and subsequent slumping due to base-surge drag and instabilities developed during growth. On the basis of field characteristics, the structures are divided into those deposited by hot, dry, fast-moving surges and those by cooler, wet, slow-moving surges. Base-surges are compared with turbidity currents and deposition of distinct structures by the head, body and tail regions is interpreted.

Calc-alkaline lamprophyres are porphyritic dyke-rocks, richer in amphibole, biotite, ultramark elements (Mg, Cr, Ni) and incompatible elements (K, F, P, Rb, Sr, Zn, Nb, Ba, REE, Th, U) than other rocks of comparable colour index (35–67) or % SiO2 (46–57). Field and petrological criteria are suggested for identifying them uniquely. New average compositions, based on some 600 screened analyses, confirm the chemical variability but possible heteromorphism of vogesites, kersantites, spessartites and some minettes. Calc-alkaline lamprophyres probably crystallise from volatile-rich, crystal-laden fluids. Microdioritic ‘porphyrites’, K-rich syenites and quartz-feldspar porphyries commonly form from these fluids by acidic hybridisation, and more rarely by in situ differentiation. Calc-alkaline lamprophyres have close compositional equivalents among, for example, shonkinites and absarokites, but not among kimberlites or common plutonie or volcanic rocks. They are compositionally more ‘crustal’ than lamproites and leucitites, despite some overlap. They are far more widespread than other K-rich or alkaline rocks. Three genetic petrological associations are confirmed: with calc-alkaline granitoid plutons (A), with shoshonitic volcanic and subvolcanic suites (B), and with appinite—breccia-pipe complexes (C). Most calc-alkaline lamprophyres, from association A, perhaps form by crustal modification of primary lamproitic or leucititic magmas; a very few, carrying rare mantle-type xenoliths, may represent relatively unmodified, but otherwise similar, primary magmas. Those of association B may form merely by volatile enrichment of shoshonitic magmas during subvolcanic crystallisation. Different origins for minettes in these associations are suggested by compositional differences, revealed by discriminant analysis.

The chemical, physical and mineralogical characteristics of five soil profiles developed on volcanic material on the Anatolian plateau of Turkey have been studied. The soils, which are mainly Entisols, have high pH values in the range 7·5 to 8·0, low amounts of organic matter (usually <1·0%), low available water capacities and a low to medium ability to sorb phosphate. The soil parent materials are basalts and tuffs which often contain large proportions of volcanic glass. Weathering of this material in the prevailing semi-arid climate results in the development of a smectite-dominated clay fraction with small amounts of kaolinite. The smectite usually yields anomalously high X-ray spacings, probably due to interstratification and absorption of interlamellar material. The characteristics of the Anatolian soils are in marked contrast to those of Andepts which have formed on similar parent materials in humid, temperate climates.

Recent collections of Sawdonia ornata have been made from the Strathmore Group which crops out in the Midland Valley of Scotland. The sediments are Lower Devonian, probably Emsian, in age. New morphological features discovered include planar branching of vegetative and fertile axes, abaxial emergences close to branch points and H branching. Well preserved cuticles have permitted reinterpretation of the structure of stornata, rosettes (hair bases), papillae and spines, and striated cuticle is identified as S. ornata. The morphology of sporangia and in situ spores is described. Pyritised axes have revealed details of xylem shape, maturation, changes in the vicinity of branching, tracheidal structure and the arrangement of xylem and cortex in deformed axes.

The lichens growing on gravestones in 142 Scottish graveyards have been examined. Measurements were restricted to Section Rhizocarpon thalii. These data permit the development of lichenometric growth curves on acidic igneous, basic igneous, sandstone and slate substrates in most areas of Highland Scotland. The colonisation of gravestones, which is extremely erratic, takes place after a minimum of eight years. The ‘great period’ of growth lasts for approximately 20 years after the erection of the gravestone. The lichen factor (growth after 100 years) is correlated with the growth after 25 and 250 years indicating that it is a representative index of the growth rates. Growth rates are non-linear, decreasing with time. Calculated lichen factors for acidic igneous substrates range from 33 to 104 mm. The distributions of different types of gravestones are non-uniform in both time and space, making the comparison of growth rates on different rock types impractical. The results indicate that there may be a gradual decrease in the growth rates from W to E, reflecting the decreasing maritime influence towards the E.

Svecokarelian migmatites in the Jussarö area of the southern Finnish archipelago comprise tonalitic gneiss, amphibolite, metagabbro, microgranite, the metamorphosed derivatives of sediments, including carbonates and graded argillites, together with later-emplaced potassic granite, and basic and acidic pegmatites. The rock assemblage shows evidence of repeated deformation; a succession of 15 sets of folds (and fold-related structures) is identified and documented. There are two sets of early intraf oliai isoclinal folds (Faa and Fab), isoclinal folds (Fbr), recumbent folds (Fx), upright open folds (Fy), tight upright folds (Fbb), two sets of asymmetrical folds (Fc and Fd), ‘scar’ folds (Fb1, Fcb Fd1), slip folds Fb, conjugate shear folds (Fe), angular folds (Fn), open warps (Fw) and tight ductile shears (Fds). From isotopie evidence reported elsewhere, the evolution of this crustal segment of the Svecokarelides is known to have spread over a period of approximately 200 m.y. from c. 1900 m.y. to c. 1700 m.y.

Serpentinites are a major component in a distinctive suite of metasedimentary and metamorphosed igneous rocks, the Outokumpu association, in the early–middle Proterozoic Svecokarelides of eastern Finland. Like the adjacent mica schists and associated supracrustal rocks, they show the effects of at least six phases of deformation (D1–D6). The tectonic history began with the emplacement of the Outokumpunappe (pre-D1), but a study of relict assemblages in the serpentinites and theirenvelope rocks reveals evidence for a complex pre-nappe history involving ultramaficmagmatism with extensive high-temperature hornfels development, and low-temperature serpentinisation contributing to sea-floor exhalation of sulphide ores.

The serpentinites subsequently underwent recrystallisation during several phases of regional metamorphism giving rise to mineral fabrics, including a pressure-solution initiated segregation (M1–D1), anthophyllite growth during the thermal climax (D2–M2—600–680°C, 2·5–4 kb), and steatitisation (D2c–M2c). Steatitisation is structurally controlled, occurring where serpentinite bodies impinge upon localised shear zones (wrench faults—D2c). Talc–carbonate–brucite assemblages reflect the influx of CO2 in this environment. Deformation during late metamorphic retrogression (greenschist—D3–D4) has a dichotomous expression with crenulations developed in strongly anisotropic phyllonitised serpentinite and irregular fracturesin massive rock.

The implications of such polyphase reconstitution for geochemical and isotopic studies are assessed and discussed.

Pyrite textures are described and illustrated and stable S-isotope data are presented from the Alton (Gastrioceras listen) marine horizon of the Westphalian Lower Coal Measures, from sections near Penistone in central northern England, with the object of relating the paragenetic sequence of pyrite formation to the conditions of sediment deposition and diagenesis. The earliest diagenetic pyrite is dispersed as framboidal and related textures. It is followed in the marine shale, coal and ganister by more localised but more intense pyrite deposition and replacement in a variety of textures. Most of this is precompactional in age, but some, together with pyrite in veinlets and cleat, is postcompactional. Marcasite is rare and mainly late. δ34S ratios range between −35·31‰ and +20·39‰. There is a definite trend from lighter values (−1·15 ± 6·47‰) in the marine part of the sequence to much heavier values (+12·73 ± 7·66‰) in the sediment below the coal. This allows the relationship of the earliest pyrite deposition in the coal-peat and ganister to the chemistry of their own depositional fresh water to be seen but then relates the main pyrite deposition to the influx of the marine-water sulphate of the Alton horizon, and shows the penetration of this influence downward into the coal-peat and its seat-bed.

For much of its length in eastern Finland, the contact between the late Archaean granitoid terrane and early Proterozoic supracrustal rocks is that of a depositional unconformity tectonically modified during the Svecokarelian orogeny. In the Kaavi district, this modification has been extensive, particularly because of thrusting which resulted in tectonic slices of basement being present as inliers within the cover rocks and cover rocks as outliers within the main basement outcrop. Both basement and cover have undergone repeated deformation and metamorphic recrystallisation reflected by the presence of multiple tectonic fabrics and sequential mineral growths. However, it is only locally in major zones of movement that the basement rocks of the Presvecokarelides show major modification as the result of the deformation which had such a profound effect on the cover rocks during the development of the Svecokarelides. Over large areas, the products of four phases of deformation (DI–IV) remain in the basement gneisses together with the products of basic and acidic intrusion whose positions in the deformational sequence can be established‥

In the cover rocks, early nappe emplacement (Outokumpu nappe) was followed by the development of isoclinal folds associated with prograde metamorphism (D1). Regionally expressed asymmetrical folds, overturned to the E, with attenuation of overturned limbs and thrusting, involving basement, followed (D2). Subsequent deformation related to wrench faulting (D2c) was followed by the development of more open folds associated with declining geotherms (D3, D4); F3–F4 interference structures are expressed as domes, some of which were a locus of granitoid emplacement (Maarianvaara granitoid suite). D5 and D6 are expressed as cleavages and fractures.

Correlation of the structural features in the Kaavi district with those in the Outokumpu and adjacent districts forms the basis both for establishing the regional disposition of basement and cover units and for determining the structural evolution of this part of the Svecokarelides.