A model for the early Palaeozoic metamorphic history of the Midland Valley and adjacent areas to the S in Scotland, England and Ireland is based on the results of new field mapping, thin section petrography, electron probe microanalysis, X-ray diffractometry, conodont and palynomorph colouration and graptolite reflectance measurement.

The oldest metamorphic rocks of the Midland Valley of Scotland, excluding xenoliths in post-Silurian lavas, are possibly the blueschist occurrences in the melange unit of the Ballantrae complex. These may be tectonised remnants of (?)pre-Arenig ocean-floor subducted during closure of the Iapetus Ocean. In the early Ordovician, the melange terrane was dynamothermally metamorphosed during obduction of newly-formed ocean crust. The obduction process piled up a thick sequence of various ocean-floor types such that burial metamorphism in parts reached pumpellyite-actinolite facies; elsewhere prehnite-pumpellyite and zeolite facies was attained.

Whilst the Midland Valley acted as an inter- or fore-arc basin during the Late Ordovician and Silurian and experienced burial metamorphism, an accretionary prism was formed to the S. Accretion, tectonic burial and metamorphism of ocean-floor and trench sediment was continuous in the Southern Uplands and the Longford-Down massif of Ireland through Late Ordovician to Late Silurian times. Rocks at the present-day surface vary from zeolite facies to prehnitepumpellyite facies. Silurian trench-slope basin sediments can be recognised in part by their lower grade of burial metamorphism. Greenschist facies rocks of the prism probably lie close to the surface.

The Lake District island-arc terrane of Northern England has an early Ordovician history of burial metamorphism up to prehnite-pumpellyite facies. The Late Ordovician and Silurian metamorphic history is one of sedimentary burial complicated by tectonism and intrusion of granite plutons to a relatively high level. The Iapetus suture is marked by a weak contrast in metamorphic grade.

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.

This paper provides a comprehensive account of the small spore assemblages of coals in the Limestone Coal Group and Upper Limestone Group (Namurian) of the Lower Carboniferous of Scotland. The coals were obtained from boreholes sunk in the Lothians, Central, and West Fife coalfields. Over ninety species of small spores are figured. Of this number twenty-six are new species. Five new genera—Glomospora, Procoronaspora, Callisporites, Tholisporites and Remysporites—are described. Full descriptions are given of all new genera and species. The assemblages are compared with assemblages of similar age in North America, the U.S.S.R. and elsewhere, and it is shown that the Carboniferous pre-Westphalian microfloras were uniform over wide areas of the earth's surface.

The two major lineages of extant archosaurs, crocodylians and avians, diverged in the Triassic, but the details and timing of this event are incompletely understood. Fragmentary and phylogenetically uninformative specimens, in addition to poor temporal constraints on rock units from the Early and Middle Triassic, typify obstacles in identifying early archosaurs. This paper re-describes the partial skeleton of the only known specimen of Xilousuchus sapingensis Wu, 1981 from the Early Triassic Heshanggou Formation in north-central China. Originally assigned to the non-archosaurian archosauriform clade Proterosuchidae, an extensive phylogenetic analysis posits X. sapingensis as a crown-group archosaur within Suchia, thus making this taxon the unequivocally oldest known member of Archosauria. The age and phylogenetic position of X. sapingensis indicate that many archosaurs, including all major clades of non-archosaurian archosauriforms, the avianline, ornithosuchids, aetosaurs and paracrocodylomorph lineages, must have diverged by the end of the Early Triassic. X. sapingensis is part of a possible clade of sail-backed poposauroids that were common components of archosaur assemblages during the Early to Middle Triassic.

In two papers read before this Society, I have very fully described the Diatomaceæ of the Glenshira Sand, which is very remarkable both for the large number of species found in it, which is certainly more than 320, and for the circumstances in which it must have been deposited. There can be no doubt, from the nature of the locality, which I have lately visited, that this bed was formed in the bottom of the Dhu Loch, a shallow fresh-water lake, at that time extending about two miles farther up the valley than it now does, and being at a higher level. In consequence of a rise in the level of the land, or a fall in that of the sea (from which—that is, from Loch Fine, the lower end of the lake is separated by a narrow and low barrier, through which the waters of the lake pass to Loch Fine), the lake has long ago been drained, till its upper end is nearly two miles from the point it must have reached when the bed of sand was formed. The present level of the lake is considerably lower than it was then; the precise difference I had no means of ascertaining, but I believe it is about 30 feet.

The Indian summer Southwest Monsoon plays an important part in influencing, and regulating, the productivity and sedimentation in the northwest Arabian Sea at the present day, by driving coastal upwelling. This leaves permanent sedimentological and geochemical records in the accumulating deep-sea sediments. Cores 722B and 724C were raised from the Owen Ridge and Oman Margin, respectively, during Leg 117 of the Ocean Drilling Program and have been subjected to geochemical analyses and α-spectrometry. A comparative core, CD17–30, situated on the adjacent Indus Fan abyssal plain, has also been studied. The chronostratigraphy of the cores has been established with δ 18O stratigraphy, giving a 350 ka climate record. Changes in the total sediment mass accumulation rates occur on glacial/interglacial time scales, with maximum fluxes occurring during glacial episodes. The high fluxes are predominantly due to wind-transported dust at the ridge and margin sites. Compositional parameters (e.g. the Ti/Al ratio) indicating the proportion of heavy minerals present within the dust, suggests that strong winds associated with the Southwest Monsoon, occur with Milankovitch periodicities, and are dominated by the precession (23 ka) frequency. The wind strength controls the proportion of heavy minerals transported to the Arabian Sea, whilst continental aridity influences the timing of deflation from the Arabian and Somalian peninsulas. Tracers of palaeoproductivity (Ba/Al) indicate strong coherence and phase with the proxy ice volume (foraminiferal δ 18O) signal, suggesting global climate parameters (ice volume, continental aridity) determine coastal productivity by influencing nutrient supply. In relation to productivity, the roles of oceanic circulation/stratification and nutrient supply through continental runoff are discussed. This study shows that the Southwest Monsoon appears to only affect the shorter period (precession cycle, 23 ka band) productivity signal. Evidence from excess 230Th suggests deep oceanic circulation (at about 2000 m depth) was more intense 110 ka BP decreasing toward 40 ka BP. By the use of these various geochemical tracers a new, and comprehensive, view of the interaction of the Monsoon and global climate with marine productivity through the late Pleistocene has been obtained.

Diapirism has been discredited as a transport mechanism for magmas partly because diapirs seem to be unable to bring magmas to shallow crustal levels (<10km) and partly because recent developments in the theory of dyke propagation have shown that sufficiently wide dykes are able to efficiently transport felsic magmas through the crust. However, it is still unclear how felsic dykes grow to widths that allow them to propagate faster than they close by magma freezing. Ultimately, it may be the ability of felsic dykes to grow within the source that controls which mechanism dominates ascent.

The ability of dykes to propagate, from the top of rising diapirs depends among other factors on the changing temperature gradient of the wall rocks. The steep gradient around rapidly rising diapirs in the low viscosity lower crust will cause dykes to freeze. As diapirs rise to colder stiffer crust and decelerate, heat diffuses further from the diapir, resulting in shallower temperature gradients that favour dyke propagation. The mechanism may thus swap, during ascent, from diapirism to dyking. Calculations of the thermal evolution of diapirs and their surroundings show that basaltic diapirs may never form because they would be drained by dykes at a very early stage; felsic diapirs may be unable to give rise to successful dykes, whereas diapirs of intermediate magmas may propagate dykes during ascent.

Most natural systems display non-linear dynamic behaviour. This should be true for magma mingling and mixing processes, which may be chaotic. The equations that most nearly represent how a chaotic natural system behaves are insoluble, so modelling involves linearisation. The difference between the solution of the linearised and ‘true’ equation is assumed to be small because the discarded terms are assumed to be unimportant. This may be very misleading because the importance of such terms is both unknown and unknowable. Linearised equations are generally poor descriptors of nature and are incapable of either predicting or retrodicting the evolution of most natural systems. Viewed in two dimensions, the mixing of two or more visually contrasting fluids produces patterns by folding and stretching. This increases the interfacial area and reduces striation thickness. This provides visual analogues of the deterministic chaos within a dynamic magma system, in which an enclave magma is mingling and mixing with a host magma. Here, two initially adjacent enclave blobs may be driven arbitrarily and exponentially far apart, while undergoing independent (and possibly dissimilar) changes in their composition. Examples are given of the wildly different morphologies, chemical characteristics and Nd isotope systematics of microgranitoid enclaves within individual felsic magmas, and it is concluded that these contrasts represent different stages in the temporal evolution of a complex magma system driven by nonlinear dynamics. If this is true, there are major implications for the interpretation of the parts played by enclaves in the genesis and evolution of granitoid magmas.

Nearly sixty years ago fossil fishes were first discovered at Glencartholm, since when so much material has been collected from this locality that very few museums in the British Isles are without some representative of this remarkable fauna; remarkable both for the number of specimens collected and for the variety of forms it contains. One of us (J. A. M.-T.) became interested in this fauna while studying some of its more problematical members, and spent a few weeks collecting at Glencartholm during the summers of 1933, 1934, 1935 and 1936. During these visits a large quantity of new material was amassed which, when studied by modern methods with a low-powered binocular microscope under liquids, particularly xylol, revealed far more of the anatomy than it had been possible for earlier workers to describe. Some of these results have already been published and the present paper deals only with the Actinopterygians. The new descriptions in this work are not intended to be exhaustive accounts of all that is known of these fishes, but merely to serve as a supplement and summary to the excellent descriptions of Traquair. In so doing an attempt has been made to re-define all the genera and species, and in some cases it has been necessary to repeat the existing description, but where this has been done care has been taken to be as brief as possible. The definitions of the genera are only intended to apply to the species here described, and are consequently confined to characters which are determinable in these species. In certain cases species have been found to exist on brief and inadequate descriptions, in two species the type specimens being unfigured; in these cases the types have been figured, and new and more complete accounts given. Where the shape or ornament of a bone was indeterminable, it has been omitted without comment, in order to make the text as short as possible.

Buddington (1959) pointed out that the construction of large crustal magma chambers involves complex internal processes as well as multiple country rock material transfer processes (MTPs), which reflect large horizontal, vertical and temporal gradients in physical conditions. Thus, we have attempted to determine the relative importance of different magmatic and country rock MTPs at various crustal depths, and whether country rock MTPs largely transport material vertically or horizontally, rather than seeking a single model of magma ascent and emplacement.

Partially preserved roofs of nine plutons and in some cases roof–wall transitions with roof emplacement depths of 1·5–11 km were mapped. During emplacement, these roofs were not deformed in a ductile manner, detached or extended by faults, or significantly uplifted. Instead, sharp, irregular, discordant contacts are the rule with stoped blocks often preserved immediately below the roof, even at depths of 10 km. The upper portions of these magma chambers are varied, sometimes preserving the crests of more evolved magmas or local zones of volatile-rich phases and complex zones of dyking and magma mingling. Magmatic structures near roofs display a wide variety of patterns and generally formed after emplacement. Transitions from gently dipping roofs to steep walls are abrupt. At shallow crustal levels, steep wall contacts have sharp, discordant, stepped patterns with locally preserved stoped blocks indicating that the chamber grew sideways in part by stoping. Around deeper plutons, an abrupt transition (sometimes within hundreds of metres) occurs in the country rock from discordant, brittle roofs to moderately concordant, walls deformed in a ductile manner defining narrow structural aureoles. Brittle or ductile faults are not present at roof–wall joins.

Near steep wall contacts at shallow to mid-crustal depths (5–15 km), vertical and horizontal deflections of pre-emplacement markers (e.g. bedding, faults, dykes), and ductile strains in narrow aureoles (0·1–0·3 body radii) give a complete range of bulk strain values that account for 0–100% of the needed space, but average around 30%, or less, particularly for larger batholiths. A lack of far-field deflection of these same markers rules out significant horizontal displacement outside the aureoles and requires that any near-field lateral shortening is accommodated by vertical flow. Lateral variations from ductile (inner aureole) to brittle (outer aureole) MTPs are typically observed. Compositional zoning is widespread within these magma bodies and is thought to represent separately evolved pulses that travelled up the same magma plumbing system. Magmatic foliations and lineations commonly cross-cut contacts between pulses and reflect the strain caused either by the late flow of melt or regional deformation.

Country rocks near the few examined mid- to deep crustal walls (10–30 km) are extensively deformed, with both discordant and concordant contacts present; however, the distinction between regional and emplacement-related deformation is less clear than for shallower plutons. Internal sheeting is more common, although elliptical masses are present. Lateral compositional variations are as large as vertical variations at shallower depths and occur over shorter distances. Magmatic foliations and lineations often reflect regional deformation rather than emplacement processes.

The lack of evidence for horizontal displacement outside the narrow, shallow to mid-crustal aureoles and the lack of lateral or upwards displacement of pluton roofs indicate that during emplacement most country rock is transported downwards in the region now occupied by the magma body and its aureole. The internal sheeting and zoning indicate that during the downwards flow of country rock, multiple pulses of magma travelled up the same magma system. If these relationships are widespread in arcs, magma emplacement is the driving mechanism for a huge crustal-scale exchange process.

The beginning of dinosaur evolution is currently known based on a handful of highly informative Gondwanan outcrops of Ischigualastian age (late Carnian–early Norian). The richest Triassic dinosaur records of the southern continents are those of South America and South Africa, with taxonomically diverse faunas, whereas faunas from India and central Africa are more poorly known. Here, the known diversity of Gondwanan Triassic dinosaurs is increased with new specimens from central India, which allow a more comprehensive characterisation of these dinosaur assemblages. Five dinosauriform specimens are reported from the probable late Norian–earliest Rhaetian Upper Maleri Formation, including two new sauropodomorph species, the non-plateosaurian Nambalia roychowdhurii and the plateosaurian Jaklapallisaurus asymmetrica, a guaibasaurid and two basal dinosauriforms. The Lower Dharmaram Formation, probably latest Norian–Rhaetian in age, includes basal sauropodomorph and neotheropod remains, providing the second record of a Triassic Gondwanan neotheropod. The currently available evidence suggests that the oldest known Gondwanan dinosaur assemblages (Ischigualastian) were not homogeneous, but more diverse in South America than in India. In addition, the Upper Maleri and Lower Dharmaram dinosaur assemblages resemble purported coeval South American and European beds in the presence of basal sauropodomorphs. Accordingly, the current available evidence of the Triassic beds of the Pranhita–Godavari Basin suggests that dinosaurs increased in diversity and abundance during the late Norian to Rhaetian in this region of Gondwana.

Excavations in 1958 for the construction of a dam at Loch Droma, Ross and Cromarty, revealed a deep and extensive section in peat and Late-glacial silts. The section was surveyed, its environs studied, and samples of materials analyzed by the Macaulay Institute, Aberdeen, and the Sub-department of Quaternary Research, University of Cambridge. The watershed location of the site, the early radio-carbon date obtained for the basal silts (12,810 ± 155 B.P.), and the nature of their organic contents, make this a critical site for the elucidation of the deglaciation and vegetational history of the Atlantic seaboard of North-west Scotland. In Part I of this report, W. Kirk describes the site and its setting, and indicates some of the problems it raises for existing glacial chronologies of Northern Scotland, and in Part II, H. Godwin summarizes and comments upon the analyses of organic remains.

Deposits of windblown sand up to 4 m thick on the Torridon Sandstone massif of An Teallach are shown to be of predominantly niveo-aeolian origin, a form of sedimentation hitherto unrecognised in upland Britain. Sand grains weathered from bedrock and from exposed clasts on plateau areas are blown on to the winter snowpack on surrounding slopes. When the snow melts, the grains are lowered on to the underlying vegetation, which traps the sand and thus allows a stable deposit to accumulate. The deposits formed in this way are massive, poorly sorted and coarser than most aeolian deposits, comprising mainly medium sand (212–600μm) with a substantial proportion of coarse sand and even very small pebbles. The coarseness and poor sorting of the sands reflect the size of grains available for transportation, the strength of the wind, short transport distances and admixture of different grades of sand during deposition. Sand accumulation began in the Early Flandrian before c. 7900 BP, but was eventually much reduced by the establishment of vegetation cover over the plateau source area. Recent disruption of this vegetation cover triggered either by increased storminess or overgrazing resulted in extensive erosion of sand deposits on the plateau and their redeposition on surrounding slopes. Niveo-aeolian deposition continues on lee slopes at present, but is offset by erosion of unvegetated scarps at the margins of the deposits.

Devonian rhizodontid fishes from East Gondwana include Gooloogongia loomesi Johanson & Ahlberg 1998 from near Canowindra, New South Wales (NSW), Australia and Aztecia mahalae gen. nov., sp. nov. from southern Victoria Land, Antarctica. Gooloogongia loomesi is known from well-preserved cranial and postcranial material, and as such represents the most complete rhizodont known. Newly discovered elements (braincase, pelvic girdle) are described for the first time. Aztecia mahalae gen. nov., sp. nov. is based on shoulder girdle material formerly assigned to Notorhizodon Young et al. 1992, which, based on skull and lower jaw morphology, is a member of the Tristichopteridae. The presence of several plesiomorphic characters suggests that Gooloogongia occupies a basal phylogenetic position within the Rhizodontida, while Aztecia n. gen. possesses a more derived shoulder girdle. We argue that the Rhizodontida evolved on the Gondwanan landmass. Notorhizodon occupies a relatively derived position within the Tristichopteridae, but is contemporary with the earliest and phylogenetically most basal Laurussian members of the group. This shows that the tristichopterids achieved a worldwide distribution considerably earlier than previously thought.

Late Cretaceous (90–100 Ma) A-type granites are widespread in the coastal area of the Zhejiang and Fujian Provinces, SE China. According to mineralogical and geochemical characteristics, the A-type granites in this belt can be further divided into aluminous and peralkaline subgroups. The aluminous subgroup often contains aluminous-rich minerals (e.g. spessartine and Mn-rich muscovite), while the peralkaline subgroup usually contains riebeckite, arfvedsonite and aegirine. Geochemically, the aluminous A-type granites show lower Nb, Zr, Ga, Y and REE abundances, and lower FeO*/MgO and Ga/Al than the peralkaline subgroup. When they occur in the same area, the two subgroups of A-type granites display quite similar initial Nd isotopic compositions, which are indicative of mixing of ancient basement crustal rocks with variable amounts of mantle materials. Integrated geological and geochemical investigations indicate that both the aluminous and the peralkaline magmas are highly evolved and reflect the residual liquids left after high degrees of fractional crystallisation in a deep magma chamber. The present authors suggest that the mineralogical and geochemical differences between the aluminous and peralkaline subgroups are likely to have been generated via different differentiation paths controlled by varying fluorine contents of the parent magmas.

Past work on the genus Pitus is reviewed and evidence adduced in favour of the view that it was a genus of arborescent Pteridosperms bearing the sterile bifurcate fronds known as Lyginorachis papilio Kidston. These probably resembled Sphenopteris affinis L. & H. in the compression state. Fertile organs were probably borne on trifurcate fronds in which a stemlike median rachis (Tristichia ovensi Long) bore synangia (Telangium sp.) composed of eight microsporangia, or alternatively seed-cupules of Stamnostoma huttonense Long. Branching in Pitus produced single branches at a wide angle, or pseudo-whorls (close spirals) of about five branches. An anomalous ring of medullary xylem was sometimes associated with branching as in Lyginopteris. This supports the view that Pitus should be classified in the Lyginopteridaceae although it was arborescent and in some respects more advanced than many of the more shrub-like Pteridosperms.

During the “Challenger” Deep-Sea Exploring Expedition a great many peculiar-looking manganese nodules or concretions were dredged from the floor of the ocean at great depths, chiefly in the Red Clay areas of the Pacific, but also in less abundance in the Red Clays of the Atlantic. In the other varieties of Deep-Sea deposits these nodules were much less abundant than in the Red Clays.

In still more recent soundings, both American and British ships have discovered in many regions of the Pacific and Indian Oceans a dark-brown coloured deposit containing a large amount of manganese dioxide, similar in character to the Red Clays from which the “Challenger” procured the largest hauls of manganese nodules. There is then every reason for supposing that manganese deposits and nodules are very widely distributed over the ocean's bed, especially in deep water at great distances from land. It was only occasionally that manganese nodules were present in any abundance in a Globigerina Ooze, and in these exceptional instances there was always much volcanic debris associated with the deposit. In the Blue Muds surrounding continental shores manganese nodules were rarely observed; still, on some rocks and boulders dredged from terrigenous deposits, a coating of manganese dioxide was observed on that portion of the stone which had projected above the surface of the mud.

The work described in this paper was carried out in the Department of Zoology of Birkbeck College, University of London, and at the Marine Laboratories at Plymouth and Port Erin. I wish to acknowledge my indebtedness to the University of London for the use of their table at Plymouth, to Birkbeck College for a grant of £5 towards the illustrations, and, in particular, I would express my gratitude to Mr Graham, under whose direction the work was carried out, for his continued kindness and help.

The specimens of Lepidochitona cinereus which were used for the investigation were collected at Bangor, Plymouth and Port Erin, and also obtained from Cullercoats. Most of the material from Plymouth and one specimen from Cullercoats was infected with the Haplosporidian parasite Haplosporidium chitonis (Debaisieux, 1920) and was therefore unreliable for histological and physiological work. Specimens of Acanthochitona crinitus were collected at Plymouth, and showed no sign of infection with Haplosporidium chitonis; a few, however, were slightly parasitised with another Sporozoan. The Californian species Ischnochiton magdalenensis and Cryptochiton stelleri were obtained from Turtox General Biological Supply House, Chicago. Specimens of these species were fixed in formalin, which proved to be a poor fixative for histological work.

Pollen-stratigraphic data, supported by lithological, geochemical and radiocarbon evidence are described from two Late Devensian Lateglacial sites on the Isle of Mull, Inner Hebrides, Scotland. The data suggest that, following the wastage of the Late Devensian ice sheet some time prior to 13,000 BP, an open grass- and sedge-dominated landscape was colonised first by juniper scrub and subsequently by Empetrum heaths. Tree birch development was limited principally, it would seem, by exposure to strong westerly winds, although some scattered birch woodland did become established in more sheltered localities. The thermal maximum of the Lateglacial Interstadial appears to have occurred from c. 13,000 to 12,000 BP after which climate began to deteriorate as the atmospheric Polar Front migrated southwards. The harsh climatic conditions of the Loch Lomond Stadial, the full effects of which were experienced after c. 10,700 BP, led to the break-up of the Interstadial vegetation cover, the development of an ice cap and several smaller cirque and valley glaciers in the hills of south-central Mull, and the establishment of a periglacial regime throughout the island. By c. 10,200 BP, however, climatic amelioration was underway once more, the Loch Lomond Advance glaciers had wasted completely, and a plant succession was initiated which led to the replacement of tundra vegetation communities by Empetrum heath, juniper scrub and eventually hazel-birch woodland within the space of c. 1500 years.

Melt extraction is a process with a length scale that spans many orders of magnitude. Studies of residual migmatites and granulites suggest that melt has migrated from grain boundaries to networks of leucosome-filled structures to steeply inclined cylindrical or tabular granites inferred to have infilled ascent conduits. For example, in anatectic rocks from southern Brittany, France, during decompression-induced biotite-breakdown melting, melt is inferred to have been expressed from foliation-parallel structures analogous to compaction bands to dilation and shear bands, based on location of residual leucosome, and from this network of structures to ascent conduits, preserved as dykes of granite. The leucosome-filled deformation band network is elongated parallel to a sub-horizontal lineation, suggesting that mesoscale melt flow was focused primarily in the plane of the foliation along the lineation to developing dilatant transverse structures. The leucosome network connects with petrographic continuity to granite in dykes; however, the orientation of dykes discordant to fabric anisotropy suggests that their formation was controlled by stress, which indicates that the process is a fracture phenomenon. Blunt fracture tips and zigzag propagation paths indicate that the dykes represent ductile opening-mode fractures; these are postulated to have formed by coalescence of melt pockets. The structures record a transition from accumulation to draining; quantitative volume fluxes are calculated and presented for the generalised extraction process. The anatectic system may have converged to a critical state at some combination of melt fraction and melt distribution that enabled formation of ductile opening-mode fractures, but fractal distribution of inferred mesoscale melt-filled structures has not been demonstrated; this may reflect the inherent anisotropy and/or residual nature of the drained source. Melt extraction has been modelled as a self-organised critical phenomenon, but the mechanism of extraction is not described and the relationship between these models and the spatial and temporal granularity of lower continental crust is not addressed. Self-organised critical phenomena are driven systems involving ‘avalanches’ with a fractal frequency-size distribution; thus, the distribution of melt batch sizes might be expected to be fractal, but this has not yet been demonstrated in nature.