This issue marks the departure of the longest-serving of the current editors of Geological Magazine, Dr Chris Hughes, and his replacement by Dr Tim Palmer (University of Wales, Aberystwyth). The Geological Magazine has always had a strong content of palaeontology and biostratigraphy, and Chris Hughes has efficiently maintained the quality of these contributions since 1973. He is moving on from his lectureship in the Cambridge Earth Sciences Department to head the Associated Examining Board, based in Guildford. The other editors thank him warmly for his experienced guidance over the past 24 years and wish him success in his new post.

The editors welcome Tim Palmer, whose appointment from outside the Cambridge department represents a significant and deliberate departure from custom. Some 13 years ago, the Magazine broadened its editorial advice in a major way by appointing an Editorial Board, most of whose members have come not just from outside Cambridge, but from beyond the UK. Our new editorial appointment signals an extension of this same policy.

An important advantage of having all the Magazine's editors under one roof has been the efficiency and speed of communicating with each other. However, with the Cambridge editors now talking to each other as much by Email as face-to-face, geographical proximity has become a less crucial asset. The spread of Email is changing many other aspects of the editorial practice and the Geological Magazine office, run by Jane Holland, is now on-line at [email protected]. The editors now encourage the use of Email for all business except for submission of manuscripts, and in particular for contributors' queries and for referees' reports.

The horizontal opening of vertical fractures during emplacement of pegmatite-dyke swarms is an important mid-crustal mechanism of large-scale horizontal extension. This is documented in the south-western Grenville Province, a deeply eroded part of the collisional Grenville orogen. In the Georgian Bay region of central Ontario, Grenville gneisses host c. 990 Ma old, angular dykes which attest not only to horizontal extension but also to vertical thinning. The original dilation dykes probably varied in strike and were statistically vertical. However, many dykes had subhorizontal or inclined segments that were oblique or quasi-concordant to the gneissic foliation in the host rocks. The number of dykes exposed per 0.25 km2 varies on the scale of a few kilometres, and this is indicative of heterogeneous late orogenic extension of the Grenville gneisses. The apparent absence of regional gradients of peak palaeo-pressure, at the present erosion level, suggests that the extension was horizontal and initially unaccompanied by vertical contraction of the host gneisses. Subsequent buckling of the pegmatite dykes led to gentle, open or close folds with vertical enveloping surfaces. The geometric effects of gentle buckling of pegmatite dykes can be difficult to recognize in the field, especially where the late-stage vertical thinning is relatively weak. Among the geometric indicators of buckle-shortened dykes, the characteristic deflection (‘fanning’) of coplanar, inherited folia in gneissic host rocks is most sensitive. Systematic changes in the local degree of vertical shortening are indicative of heterogeneous vertical thinning, and may be associated with pull-apart structures at the horizontal scale of several kilometres.

The collision of India and Asia can be defined as a process that started with the closing of the Tethyan ocean that, during Mesozoic and early Tertiary times, separated the two continental plates. Following initial contact of Indian and Asian continental crust, the Indian plate continued its northward drift into Asia, a process which continues to this day. In the Ladakh–Zanskar Himalaya the youngest marine sediments, both in the Indus suture zone and along the northern continental margin of India, are lowermost Eocene Nummulitic limestones dated at ∼54 Ma. Along the north Indian shelf margin, southwest-facing folded Palaeocene–Lower Eocene shallow-marine limestones unconformably overlie highly deformed Mesozoic shelf carbonates and allochthonous Upper Cretaceous shales, indicating an initial deformation event during the latest Cretaceous–early Palaeocene, corresponding with the timing of obduction of the Spontang ophiolite onto the Indian margin. It is suggested here that all the ophiolites from Oman, along western Pakistan (Bela, Muslim Bagh, Zhob and Waziristan) to the Spontang and Amlang-la ophiolites in the Himalaya were obducted during the late Cretaceous and earliest Palaeocene, prior to the closing of Tethys.

The major phase of crustal shortening followed the India–Asia collision producing spectacular folds and thrusts across the Zanskar range. A new structural profile across the Indian continental margin along the Zanskar River gorge is presented here. Four main units are separated by major detachments including both normal faults (e.g. Zanskar, Karsha Detachments), southwest-directed thrusts reactivated as northeast-directed normal faults (e.g. Zangla Detachment), breakback thrusts (e.g. Photoksar Thrust) and late Tertiary backthrusts (e.g. Zanskar Backthrust). The normal faults place younger rocks onto older and separate two units, both showing compressional tectonics, but have no net crustal extension across them. Rather, they are related to rapid exhumation of the structurally lower, middle and deep crustal metamorphic rocks of the High Himalaya along the footwall of the Zanskar Detachment. The backthrusting affects the northern margin of the Zanskar shelf and the entire Indus suture zone, including the mid-Eocene–Miocene post-collisional fluvial and lacustrine molasse sediments (Indus Group), and therefore must be Pliocene–Pleistocene in age. Minimum amounts of crustal shortening across the Indian continental margin are 150–170 km although extreme ductile folding makes any balancing exercise questionable.

The first British Pleistocene record of Larix (Larch) is described from the Brays Pit near Mathon in the English West Midlands. This new record is the most westerly from the European Pleistocene and is also beyond the western limit of the distribution of any extant species of Larix within Europe. Today there are no native species of Larix in the British Isles. The fossil remains comprise of macrofossils and pollen, which are not, however, well enough preserved to allow determination to species level. The fluvial sediments which yielded the fossils were probably deposited in the early Anglian Stage or possibly during an earlier Pleistocene event.

The transition from diagenesis to very low-grade metamorphism has been characterized by conodont colour alteration index (CAI), illite crystallinity (IC), clay-mineral assemblages and rock fabric in a transect (Cape Peñas–Cape Torres) located in the Cantabrian Zone (northwest Spain). IC values show a northwest to southeast change from epizonal to diagenetic values. CAI values show a general congruence for low- and high-grade areas. This correlation indicates that CAI values for the epizone are >5.5, the anchizone 5.5≥CAI>4, and the diagenetic zone ≤4. Cleavage develops in incompetent rocks with CAI values greater than 3, mainly by pressure solution. Temperature increases towards the inner parts of the orogen (towards the northwest) and is considered to be related to the tectonic superposition caused by thrusting and folding. A gradient of 35°C/km is inferred for the transect. In the southeastern sector of the section there are several thermal anomalies that are attributed to the presence of epithermal fluids.

The Bainmedart Coal Measures constitute the middle portion of the Permian–Triassic Amery Group, which represents the only substantial Palaeozoic–Mesozoic sedimentary succession exposed in eastern Antarctica outside the Transantarctic Mountains. The coal measures disconformably or unconformably overlie alluvial fan deposits of the Radok Conglomerate and are conformably overlain by the dominantly fluviatile Flagstone Bench Formation. The coal measures were deposited within alluvial settings dominated by north to northeasterly flowing, low-sinuosity rivers chiefly confined to broad, fault-bounded, valleys of the Lambert Graben, a major late Palaeozoic to early Mesozoic failed rift system. Both climatic and local tectonic factors are considered to have been the major influences on the pattern of coal measure sedimentation. Recent mapping has identified a much greater thickness of sediments within the coal measures than had been inferred previously. The Bainmedart Coal Measures are formally subdivided into six members. In ascending stratigraphic order these are: Dart Fields Conglomerate Member (<3 m thick), Toploje Member (c. 300 m thick), Dragons Teeth Member (15–25 m thick), Glossopteris Gully Member (c. 670 m thick), Grainger Member (c. 350 m thick) and McKinnon Member (c. 530 m thick).

Mafic dykes (Groups A–D) intruded into Mesoproterozoic basement amphibolites, gneisses, and granitoids of the Cape Meredith Complex on the southern tip of West Falkland, provide an important record of at least three periods of lithospheric extension during Palaeozoic and Jurassic times. Group A dykes are calc-alkaline lamprophyres that were generated by partial melting of an enriched subcontinental lithospheric mantle in Cambro-Ordovician times. Group B dykes are Ordovician dolerites derived from an asthenospheric mantle source, perhaps during the same extensional episode as Group A dykes. Group C dykes were also derived from an asthenospheric source and are possibly of Silurian age. The youngest, Group D, dykes are part of the widespread Jurassic Gondwana province. This group contains an oceanic island basalt-like sample and an enriched sample similar to both Group A lamprophyres and to the Jurassic Ferrar province in Antarctica. These correlations have interesting implications for the composition and evolution of mantle sources through time; the co-existence of Cambrian lamprophyres and Jurassic Ferrar-type magmas in the Cape Meredith Complex demonstrate for the first time that the enriched lithospheric mantle source postulated for the Ferrar magmas existed as far back as Cambrian times.

Four new specimens of phalangiotarbid (Arachnida: Phalangiotarbida) from the Upper Carboniferous (upper Westphalian A) of Westhoughton, Lancashire, UK, are referred to Mesotarbus peteri sp. nov. An additional Lancashire phalangiotarbid, Phalangiotarbus subovalis (Woodward, 1872), from the Upper Carboniferous (lower/middle Westphalian A) of Burnley, is redescribed and designated the neotype of this species. This material allows new interpretations of the opisthosomal segmentation and respiratory organs of phalangiotarbids, and a reconstruction of Mesotarbus peteri is presented.

The South Orkney Islands are the exposed part of a continental fragment on the southern limb of the Scotia arc. The islands are to a large extent composed of metapelites and metagreywackes of probable Triassic sedimentary age. Deformation related to an accretionary wedge setting, with associated metamorphism from anchizone to the greenschist facies, are of Jurassic age (176–200 Ma). On Powell Island, in the centre of the archipelago, five phases of deformation are recognized. The first three, associated with the main metamorphism, are tentatively correlated with early Jurassic subduction along the Pacific margin of Gondwana. D4 is a phase of middle to late Jurassic crustal extension associated with uplift. This extension phase may be related to opening of the Rocas Verdes basin in southern Chile, associated with the breakup of Gondwanaland. Upper Jurassic conglomerates cover the metamorphic rocks unconformably. D5 is a phase of brittle extensional faulting probably associated with Cenozoic opening of the Powell basin west of the archipelago, and with development of the Scotia arc.

Sedimentological evidence suggests that sea-water chemistry has oscillated between ‘Aragonite’ and ‘Calcite’ seas during the course of Phanerozoic time. During ‘Calcite’ sea periods aragonite was soluble and dissolved on the sea-floor. Here we propose, using a survey of familial diversity, that during times of such corrosive seas bivalved molluscs which secreted their shells entirely of aragonite were at a selective disadvantage compared to those with calcitic outer shell layers. This is the first case in which it has been suggested that there was a dynamic link between sea-water chemistry and the evolution of a particular taxon throughout Phanerozoic time.