A formal lithostratigraphy is erected for all the Ordovician rocks in the Southern Uplands of Scotland. At the base of the succession, the Crawford Group (Arenig–Llanvirn) encompasses the chert and lava sequences usually associated with the tract-bounding faults, and includes the only proven Arenig rocks in the Southern Uplands. The overlying Moffat Shale Group (Caradoc–Llandovery) is now restricted to the black and grey graptolitic shales which succeed the grey and red chert successions. The Leadhills Supergroup (Caradoc–Ashgill) forms the overwhelming bulk of the sedimentary succession and includes the thick Ordovician turbidite successions of the Northern Belt. Existing stratigraphical terminology is reviewed, revised or extended as appropriate to maintain maximum continuity with current usage. Type sections for each unit are either proposed, where newly defined or revised, or cited in the case of existing definitions.

There are three distinct Silurian successions exposed in South Mayo and North Galway, western Ireland, of which the Louisburgh-Clare Island succession is the most northerly. It is separated from the adjacent Croagh Patrick succession by the Emlagh Fault. Three of the formations (Strake Banded, Knockmore Sandstone, Bunnamohaun Siltstone) in this 1·5 km Louisburgh–Clare Island succession had previously been interpreted as intertidal to offshore marine deposits. Almost all the facies present display characteristics of fluvial sedimentation and there is evidence for a contemporaneous volcanic centre to the west of the present outcrop. The exceptions are some grey laminated mudrocks with a fragmentary fauna which are interpreted as lacustrine and which show striking similarities to parts of the Silurian inliers in the central Midland Valley of Scotland. Despite these similarities the evidence for direct connection between western Ireland and Scotland is unproven. Within western Ireland correlations are hindered by uncertainties of the age of the Louisburgh-Clare Island succession and the age span of the adjacent Croagh Patrick succession.

Marine shelf siliciclastics of the early Cambrian Buen Formation of North Greenland have yielded the earliest abundant, well localised Bradoriida (Arthropoda) from the Laurentian part of North America: the shelf-dwelling Petrianna gen. nov. Petrianna apparently has a fairly rigid, phosphatic shell. Its assignment to the Cambriidae, a family markedly dissimilar morphologically from the phosphatocopines (the only Bradoriida hitherto regarded as having a primary phosphatic shell), implies rejection of the criterion of carapace composition in the ordinal/subordinal classification of Bradoriida.

Petrianna confirms the Bradoriida as a consistent component of the earliest arthropod faunas. Cambriids are currently known only from the early Cambrian of Greenland, Siberia and China and offer potential for correlation. Cambriid occurrences span parts of the Redlichiid, Olenellid and Bigotinid trilobite faunal realms but are known only from tropical/subtropical regions, thus indicating possible palaeolatitudinal controls on their distribution.

In a recent paper Johnston et al. (1994) have provided an innovative interpretation of the tectonostratigraphic relationships between distinct terranes juxtaposed along the Intra–Sudetic Fault in the Sudetes Mountainsof the Polish Variscides. They identified this fault as a major crustal fracture between Gondwana and Baltica, rramed the Tornquist Suture, resulting from the closure of the Tornquist Sea during the Caledonian orogeny. This interpretation is based on new U/Pb ages on zircon and titanite from igneous and metamorphic rocks (Oliver et al. 1993), field observations and reassessment of pre–existing data. Previously, the Sudetes were generally thought to haveformed during the Hercynian orogeny, although Caledonian age deformation was also inferred (Oberc 1977, 1986; Don 1984, 1986, 1990).

One of the writers' main aims has been to help to prepare the way for a new approach to problems in which the natural occurrence of forsteritic olivines is a vital factor. Variation in their shapes and textural relations in minor intrusions, lavas and melts is examined and the historical development of concepts of their growth and resorption, particularly in magmas, is traced. Particular attention is focused on the olivines of picritic, minor intrusions. It is concluded that in the interpretation of olivine shapes there has been discrimination in favour of magmatic resorption rather than skeletal crystallization. From a wide and detailed survey of forsteritic olivines it is established that they tend to grow rapidly and that their phenomenal variation in habit and shape is probably due to a specific growth sensitivity to slight environmental differences. Concepts of the physical conditions leading to skeletal crystallization are briefly reviewed and discussed.

A deep borehole drilled at Rookhope in Weardale, Co. Durham in 1960–61 proved the Weardale Granite below Carboniferous sediments at a depth of 390 m; an account of the Carboniferous rocks is presented. The boring commenced in the basal Namurian Great Limestone and entered the Dinantian at the bottom of the limestone at 25 m. Most of the ten Brigantian cyclothems sectioned in the borehole are compound and average 30 m thick. They consist of an initial cycle often more than 20 m thick and overlying minor cycles that are usuallyless than 6 m thick. Each of the cycles, both initial and minor, are coarsening upwards sequences from marine limestone or mudstohe to deltaic and fluvial mudstone, sandstone, seatearth and occasionally a thin coal seam. The underlying Asbian consists of seven cyclothems averaging 8 m thick. By contrast they are simple coarsening upwards sequences similar to the Brigantian initial cycles, but no minor cycles are developed.

Marine fossils are abundant in the majority of cyclothems and are listed against their stratigraphical horizon in the borehole. Special studies of miospores, conodonts and foraminiferans from the borehole are presented. A consensus of biostratigraphical evidence shows that the base of the Carboniferous succession in the borehole is of early Asbian age.

The upper Cambrian trilobite Olenus wahlenbergi Westergård, 1922 occurs abun- dantly in stinkstone concretions in the Alum Shales at Andrarum, in Skåne, southern Sweden (Olenus/Homagnostus obesus Zone). All growth stages from anaprotaspis onwards are represented, though the early stages are comparatively uncommon and complete specimens are rare. Fine details of structure are preserved, suitable for scanning electron microscopic study.

The protaspis has five axial rings, which in the adult become divided transversely and reduced to three, and the preglabellar field expands markedly in the holaspis. The librigena broadens during development and the eye, with its widely separated lenses is retained on the librigena throughout meraspid development. The visual surface dehisces during ecdysis from the early holaspid onwards, due to emplacement of the ocular suture. The hypostome apparently changes from a conterminant to a natant condition in the early holaspis, which is consistent with the growth of the preglabellar field at this stage. The transitory pygidium has a slightly serrated margin throughout development, but becomes entire when all thoracic segments have been liberated.

Cuticular sculpture changes dramatically throughout ontogeny. Large (Type A) tubercles appear on the fixigena in early meraspides; these become prominent and coalesce by the end of meraspid development. They are abruptly replaced by smaller (Type B) tubercles in the early holaspid, which link to form a rough network in mature specimens. Comparable Type A tubercles in early meraspid librigenae give rise to a strong polygonal caecal sculpture in holaspids, while a radial sculpture on the broadening anterior border develops independently. The significance of these cuticular changes remains obscure. A median occipital organ is described for the first time in the Olenidae.

Silurian and late Ordovician K-bentonites of the British Isles provide a record of prolonged volcanism during the convergence of terranes associated with closure of the Iapetus and Tornquist Oceans. In the Southern Uplands–Longford-Down and Midland Valley terranes, they range from late Caradoc to Telychian, withfurther early Homerian occurrences. South of the Iapetus suture, in Eastern Avalonia, the range is Hirnantianto early Ludlow in northern England and early Telychian to earliest Ludfordian in the Welsh Borderland and English Midlands. In both cases, the distributions indicate that volcanism was more long-lived and probably more extensive than is depicted in current plate tectonic reconstructions. Average intervals between K-bentonites are estimated, based on Harland et al. (1990), as: c. 65000 years at Dob's Linn (late Aeronian to early Telychian); c. 39000 years in the Cautley area (Telychian); c. 51000 years in a borehole at Walsall (late Llandovery to Sheinwoodian). Trace element geochemistry suggests mostly subalkaline dacitic to rhyolitic magmas in which LILE-enrichment accompanies variable enrichment in crustally derived elements (Ta, Nb). The geochemistry suggests comparison with continental arc volcanism of ‘withinplate, attenuated lithosphere’ character. Ta–Nb enrichment and an absence of Eu anomalies from REE profiles are consistently present northof the Iapetus suture, but trace element patterns are less consistent south of the suture where negative Eu anomalies are generally present. Discriminant function analysis successfully distinguishes Llandovery, Wenlockand Ludlow K-bentonites from south of the Iapetus suture, and Llandovery K-bentonites from north and south ofthe suture. Those from north of the Iapetus suture probably originated in volcanism along the southern marginof Laurentia before final closure of the Iapetus Ocean. Those from south of the suture may have been derived from volcanism associated with late destruction of Iapetus and Tornquist oceanic crust, although an alternative involving volcanism at the southern margin of Eastern Avalonia or Baltica may accord better with the distribution of K-bentonites and the geographical trend of the fragmentary outcrops of Silurian volcanic rocks from southern Ireland to Belgium.

Graptolite biostratigraphy affords a robust and relatively accurate means of correlating Ordovician and Silurian hemipelagite and turbidite sequences and has been used to establish the structural development of the regional thrust belt in the Southern Uplands of Scotland. The overall structural pattern has long been recognised: greywackes within individual thrust slices, deposited within a relatively short time-interval, become sequentially younger southwards; each overlies the basal Moffat Shale Group which was deposited over a longer time. However, recent refinement of the graptolite biozonal scheme has allowed the better assessment of along-strike variations within the thrust belt which are here illustrated by two transects; one, based on work in the Rhins of Galloway and the Kirkcudbright areas (SW Southern Uplands), and the other in the Peebles-Hawick area (NE Southern Uplands). The SW transect most closely approximates to the regular pattern wherein a southward-propagating thrust-front incorporated sequentially younger greywacke units. The uniform geometry is interrupted only locally, towards the southern margin of the thrust belt, by a system of back-thrusts producing structural pop-ups. The NE transect departs from this regular model: a northern sector shows the orderly initiation of the thrust belt, but towards the SE a more irregular distribution of the thrust-slice agescan be best explained by outof- sequence movement. This transect also shows more repetitive imbrication of the same biostratigraphic interval than is apparent farther SW. In both transects the fundamental changes in thrustbelt geometry took place from mid-Llandovery times onwards, with a reversion to forward-breaking, in-sequence thrusting at the beginning of the Wenlock. The cause is a matter for speculation, but may be linked withthe accommodation of an obstacle to forward-thrust propagation. However it is recognised that such variationsin thrust geometry are a fundamental feature of most thrust belts and do not require a single regionally significant cause.

The trace fossils of the Tumblagooda Sandstone (?late Silurian) of Kalbarri, Western Australia are spectacular in their variety and preservation. They provide a unique insight into the activities of the early invaders of terrestrial environments, and reveal the presence of a diverse fauna dominated by arthropods. Within the Formation trace fossil assemblages can be related to fluvial, aeolian and marine sand-dominated environments. Two distinct and diverse ichnofaunas are recognised.

The Heimdallia–Diplichnites Ichnofauna occurs in sandstones deposited in broad low sinuosity braided fluvial channels, between which were mixed aeolian and waterlain sandsheets, small aeolian dunes and flooded interdune and deflation hollows. Heimdallia is the major bioturbator, favouring shallow pools. Other burrows include Tumblagoodichnus (gen. nov.), Diplocraterion, Skolithos, Beaconites and Didymaulyponomos. Arthropod trackways (Diplichnites) occur on surfaces of waterlain sands and on foreset bedding of aeolian dunes, and represent some of the earliest reported terrestrial trackways. Other trackways include Paleohelcura and Protichnites, and the digging traces Selenichnites and Rusophycus are also present. At least ten types of arthropods are required to produce the observed traces. Myriapods, eurypterids, euthycarcinoids, xiphosurids and scorpionids are considered responsible for the trackway assemblage.

The Skolithos–Diplocraterion Ichnofauna occurs at the top of the exposed section in sandstones that overlie a thick fluvial sequence containing few traces. The strata are considered to represent marine influence at a fluvial/marine transition. They show variable trough cross-bedding, complex planar cross-bedding with down-climbing sets, ripple lamination, and fining-up sequences with bioturbated tops. Traces are dominated by crowded Skolithos up to 1 m long, together with two forms of Diplocraterion. Daedalus and Lunatubichnus (gen. nov.) burrows occur in a few beds and Aulichnites trails cover some foreset surfaces of cross-bedding.

The trace fossils and the sedimentology of the Tumblagooda Sandstone bear a remarkable similarity to those of the lower part of the Taylor Group of Antarctica, which is probably Devonian in age. It is suggested that the two represent a similar age, stratigraphy, and range of environments on the margins of Gondwana. Large unvegetated fluvial outwash plains with variable aeolian influence were essentially coastal in character and fluvial/marine transitions occur in sand-rich environments. The animals responsible for the traces inhabited coastal areas but many could survive outwith marine influence, and arthropods responsible for some types of Diplichnites trackways walked out of water.

The rich diversity of trackways attributable to arthropods illustrate that the invasion of terrestrial environments by arthropods, particularly large forms, was well-established by the beginning of the Devonian. The basis of the food chain was algal and bacterial films which bound the surface sediment in freshwater pools.

Mapping of striae trends, macro-scale erosion forms, drumlins, morainic ridges, eskers, till fabric and boulder fans has facilitated reconstruction of glacial dynamics in terms of ice streams, marginal ice lobes and interlobate zones. Data were recorded in a computerised geographical information system (GIS).

Data on oriented glaciogenic elements are compared with the evolving patterns of glacial flow. The oldest flow occurred at a distance of several hundred kilometres inside the ice margin, while the later flows were dependent on the dynamics of the ice streams and fan-shaped ice lobes. A model is developed for the zonation of subglacial processes such as erosion, deposition and till deformation beneath the ice sheet. Most of the glacial forms, as well as lower till, were generated in a zone of basal melting and fast ice flow which existed some hundred kilometres from the receding margin and was associated with the formation of ice streams. These results are consistent with recent reconstructions of basal hydrology using mathematical models.

Ice streams were important for deglaciation dynamics. In the course of deglaciation, decreased shear stress on the water-saturated substratum resulted in ice-bed uncoupling which lowered the profile and accelerated flow in the ice streams. This did not happen in interstream areas as reflected by the glacial geomorphology typical of inactive ice.

Palaeocene volcanic activity is represented in west-central Skye, Inner Hebrides, Scotland, by a laterally extensive and thick pile of sub-aerial lavas mainly belonging to the alkali olivine basalt—hawaiite—mugearite—benmoreite—trachyte suite. The lavas are typical of many continental flood basalt suites and were principally fed from fissure eruptions similar to those of present day Iceland. Intercalated with the lavas are rare beds of heterogeneous volcaniclastic material, including breccias, conglomerates, sandstones and mudstones. The sequence forms a major portion of a larger volcanic field preserved within the NNE-SSW-elongated ‘Sea of the Hebrides’ sedimentary basin.

Significant hiatuses in the volcanic activity are marked by deep-weathering profiles and thin sedimentary sequences comprising mudstones, ironstones, coals, sandstones and conglomerates. Palaeocurrent indicators and clast lithologies within the clastic sedimentary rocks indicate that erosion of a massif dominated by the Palaeocene Rum Igneous Complex and its roof rocks, c. 20 km to the S, provided abundant detritus to a river system which drained towards the N. Such sedimentary intercalations aid the stratigraphical subdivision of the lava field. Eight lava groups, each most likely with a different focus of fissure eruption, and divisible into mappable formations, together with two sedimentary formations, are recognised.

The alkali olivine basalts are typically thin, with a tendency to form compound flows with limited lateral extents, whilst the hawaiites and mugearites are considerably thicker and cover large areas. Only very rarely are flow terminations observed. The original extents of the single benmoreite and rare trachytes cannot be determined from their limited erosional remnants. The more evolved flows tended to occur after brief hiatuses in the volcanic activity, indicated by well-developed lateritic tops to the underlying flows.

The youngest preserved lava is a columnar-jointed olivine tholeiite with a MORB-like composition. The flow is at least 120 m thick and apparently ponded in a steep-sided palaeo-valley within the lava field.

Three fault trends are recognised: parallel, normal and marginally oblique to the main NW-SEtrending regional dyke swarm, and dissect the lava field into a number of discrete blocks. The more significant of these faults may have been active during the development of the lava field, and in some instances instrumental in controlling the distribution of the flows.

Later Tertiary erosion has removed an unknown thickness of material from the upper part of the lava field, the preserved thickness of which is estimated to be about 1·5 km.

Small phosphatised fossils from late Cambrian limestones of Västergötland, Sweden, share major external features with larval extant Pentastomida, such as a prominent head with two pairs of stumpy limbs adapted for attachment, and a slender trunk of four portions. Even such details, as paired forehead structures, pores on the inner edges of the head limbs and paired papillae at the rear of the trunk correspond with structures of extant pentastomid larvae. Neither the fossils nor the Recent pentastomids add any additional body segments during growth (segment constancy). Since characters of this kind and in this combination do not occur elsewhere, the fossils are recognised as true Pentastomida. Major differences, such as distinctly divided head limbs, partial occurrence of vestigial trunk limbs, and a different mode of trunk development during growth can be explained as representing merely the plesiomorphic state of characters of Pentastomida, indicating that the fossils are representatives of its stem-group prior to branching into the two Recent lineages. The fossils clearly document the marine origin of the Pentastomida, and that their specific morphology and parasitic life style were already established in the late Cambrian at a high degree of diversification, long before the terrestrialisation of their present final hosts, the tetrapods. General arthropod affinities are recognisable not least in the nature of the limbs, but the morphology of stem- and crown-group pentastomids gives no clues for closer relationship with any of the major (eu)arthropod taxa.

Cyclotron lapworthi (Groom, 1902), one of the few British Cambrian bradoriid ostracod species known from a large number of specimens, is redescribed. It has an interdorsum, thus indicating a hesslandonid affinity. The ontogeny of C. lapworthi does not demonstrate a clear distinction of its individual moult stages but does show marked changes in the development of nodes and lobes. C. lapworthi shows wide variation in carapace shape possibly indicating that its valves were thin and relatively flexible. In England and Canada C. lapworthi is restricted to the Upper Cambrian Olenus Zone. C. lapworthi may also occur coevally in the Upper Cambrian of Sweden.