Detailed centimetre-scale sampling across two small dolerite dykes (7 and 21 cm wide) of Kestiö Island, SW Finland, has revealed a well-developed internal zonation, with surprisingly systematic compositional variations. From the margins inwards, the dykes exhibit a steady decrease in whole-rock MgO, Mg number (100Mg/(Mg+Fetotal)) and normative Opx (indicating a normal fractionation trend) with simultaneous increase in normative An (100An/(An+Ab)) and decrease in incompatible Zr, Y, TiO2 and P2O5 (indicating a reverse fractionation trend). In addition, marginal rocks of dykes contain normative corundum that is apparently associated with their significant depletion in whole-rock CaO. The extent of margin-to-centre differentiation of dykes in terms of most components is slight to modest, although in some petrochemical parameters it is quite high (e.g. 15 mol. % of normative An). The dykes are almost glassy and uncontaminated by host rocks, suggesting that their compositional profiles are primary and most likely reflect temporal changes in composition of magma filling the dykes. A mechanism responsible for the systematic changes in composition of inflowing magma remains elusive, however, since no known processes are able to force magma to evolve simultaneously along both normal and reverse fractionation trends. The study thus appears to indicate some not yet specified process of magma differentiation.

A new euarthropod from the Emu Bay Shale (Cambrian Series 2, Stage 4) on Kangaroo Island, South Australia, is a rare component of this Konservat-Lagerstätte. The two known specimens of Eozetetes gemmelli gen. et sp. nov., in combination, depict a non-biomineralized euarthropod with a relatively short cephalic shield lacking dorsal eyes and bearing a flagelliform antenna, 18 trunk segments with broad tergopleurae and paired axial nodes/carinae, and an elongate, styliform tailspine. The new species compares most closely with taxa in the putative clade Vicissicaudata, which groups Aglaspidida, Cheloniellida and Xenopoda. A ring-like terminal tergite in E. gemmelli corresponds to the caudal tergite in cheloniellids and xenopodans. Incorporating Eozetetes into recent character sets for Cambrian euarthropods supports close affinities to either Emeraldella or to aglaspidids, but several plesiomorphic character states are inconsistent with membership in Aglaspidida sensu stricto. Eozetetes is among the earliest of various Cambrian taxa informally referred to as ‘aglaspidid-like euarthropods’.

Laser ablation techniques permit the determination of the stable isotopic ratios of finely crystalline calcite cements in chalks for the first time. Modelling of fluid–rock interaction using whole rock and laser ablation stable isotopic data indicates that carbonate mineral diagenesis in the Eldfisk Field consisted largely of the dissolution and reprecipitation of calcite with little associated loss of porosity. Cementation by calcite derived from stylolites apparently occurred throughout the Eldfisk Field chalk, but had only a subsidiary effect on whole rock isotopic ratios. Oxygen isotopic data indicates a pore water temperature of 50–80 °C during the bulk of chalk recrystallization. Increases in whole rock δ13C values with depth are likely the result of bacterial methanogenesis during chalk recrystallization.

The Blattodea (cockroaches sensu lato or roachoids) from the southern coalfields of the UK are reviewed or examined, especially species occurring in more than one coal basin including Mylacris abrupta (Bolton, 1930) comb. nov., and undescribed material from Writhlington (Somerset). It is proposed that a derived mylacrid Mylacris–Sooblatta assemblage is used to extend the latest Westphalian and earliest Stephanian insect zonation from the continent to southern Britain, thus augmenting the European Pennsylvanian scheme.

The town of Dolgelley lies slightly outside the main tract of gold-bearing country of Merionethshire, but it forms a convenient headquarters from which to visit the various gold-mines and auriferous lodes. The Dolgelley Gold-belt lies within the area covered by the quarter-sheets 27 N.E., 27 S.E., 32 S.E., 33 N.W., 33 N.E., 33 S.W., 36 N.W., 36 N.E. of the 6 inch Ordnance Survey maps of Merionethshire. It is on the north side of the estuary of the Mawddach, extending from the sea at Barmouth to the locality of Gwynfynydd on the north-east. The belt forms the south-eastern flank of a range of high ground sloping down to the south and south-east from the mountains of Rhinog, Diphwys, and Garn. It is drained by several tributaries of the Mawddach, of which the principal are the Afons Hirgwm, Cwm-llechen, Cwm-mynach, Wnion, Las, Gamlan, Eden, and Gain.

Perim Island is an eroded fragment of the southwest flank of a late Miocene (10.5 ± 1.0 Ma) volcano whose centre lay on the southwesternmost tip of Arabia. The volcano is the westernmost of the E–W line of six central vent volcanoes (the Aden Line) that extends 200 km along the south coast of Arabia from Perim to Aden. Major oxide and trace element abundances are given for 35 Perim specimens and these show that the volcano has within-plate trace element characteristics and consists of a petrographically and geochemically simple suite of alumina-poor olivine basalts, andesites, and transitional andesite–trachyandesites. Six specimens, however, are markedly enriched in Al2O3 and CaO, and contain abundant (20–30 mode %) highly calcic (An77–83) plagioclase phenocrysts. Geochemical modelling suggests that the main Perim volcanic sequence was produced by the fractional crystallization (o1 + cpx + Ti-mt + plag) of a silica saturated (SiO2 c. 45%) basic melt. The high A1, high Ca, magmas appear to be mixing products of plagioclase-enriched basic magmas with more evolved melts. Perim is the oldest volcano of the Aden line, which becomes increasingly younger and alkalic eastward. It is suggested that the volcanism is related to an eastwards-propagating rift produced before the most recent stage of sea-floor spreading in the Gulf of Aden (4.5 Ma–present).

Having devoted several weeks to the study of the magnificent collection of the remains of Ichthyopterygians preserved in the British Museum (Natural History), I purpose on this occasion to give a brief notice of some of the conclusions at which I have arrived, since a considerable interval will elapse before the publication of that part of the Museum “Catalogue of Fossil Eeptilia” in which my observations will be more fully recorded.

Some thousands of Australian coal samples have been studied at the Division of Coal Research, C.S.I.R.O. On the basis of these studies, the present usage of the term “sclerotinite” is considered and possible justifications for the retention of this maceral category are outlined and discussed. No characteristic differences in physical properties, form, or utilization behaviour have been found whereby sclerotinite may be distinguished from the other macerals of the inertinite group. Most of the material which has been referred to as sclerotinite is probably not fossil fungus. The “discrete body” category of sclerotinite may well represent fusinized resin bodies, while the more extensive material represents degraded plant tissue. There would appear to be no case for the retention of the maceral category sclerotinite, and alternative means are suggested of classifying for petrographic analysis material which has hitherto been regarded as coming within this category.

Some time since Prof. T. Rupert Jones directed my attention to a curious fossil in the British Museum, obtained by Mr. Bain from Styl Krantz, Sniewe Berg, South Africa. The matrix is of the same nature as that in which the Dicynodonts are so commonly found, and exhibits the greater part of the skeleton, but unfortunately not the skull, of a Lacertilian reptile, not more than seven or eight inches in length. It is represented of the natural size in Plate XI., Fig. 1. The trunk is about two and a half inches long, and appears to have attained hardly more than one-third the length of the tail, which is bent round into three-quarters of a circle, and consists of vertebræ, which are very stout near its root, but become attenuated at its termination (a). The centra of these vertebræ appear to have been slightly constricted in the middle, and are about one-tenth of an inch in length. The anterior caudal vertebræ present strong and long transverse processes. The dorsal vertebræ can hardly have been fewer than eighteen or twenty, and seem also to have possessed hour-glass shaped centre. They are for the most part provided with long curved ribs, the hindermost four or five pair of which become gradually shorter. One of two vertebræ in front of the sacrum may have been devoid of ribs.

The diversity of orbicule types exposed within granitoids of the Bonney Pluton in southern Victoria Land attests to the dynamic and complex interplay of magmatic processes that were responsible for their formation. Orbicules formed in small pockets of H2O-rich silicate melt that was extracted from the crystallizing and fractionating Bonney Pluton magma and concentrated along the pluton margins. These pockets of melt experienced a superheating event that destroyed almost all pre-existing nuclei and a subsequent delay in crystallization, which led to undercooling conditions that promoted rapid dendritic crystal growth. Superheating was induced by the injection of hot mafic magmas, evidenced by elevated plagioclase XAn, and Mg-Al-Ti-contents in hornblende that point to a higher temperature and a more mafic composition in the melt that the orbicule shells crystallized from. Variation in the type and structure of orbicules (hornblende-rich versus plagioclase-rich shells) were likely due to repeated changes in the composition, H2O-content, temperature and PH2O at the crystallizing orbicule boundary layer in response to pulses in the movement of magma, competition between crystallizing phases, episodic vesiculation, degassing and/or second boiling which dictated the composition, texture and size of individual orbicule shells. Brittle fragmentation of orbicules occurred in response to vesiculation and fragmented orbicules are often found as cores within intact orbicules, indicating that multiple phases of orbicule formation were common. The alignment and compaction of orbicules in ‘pods’ indicates movement of orbicules within the melt-rich pockets occurred, prior to resumption of near-equilibrium crystallization in the host granite.

Quantitative modelling of potential field data has been used to test and extend geological sections constructed for the new British Geological Survey Tectonic Map of Britain and Ireland. Three of the profiles cross part of the Anglo-Brabant Massif and provide new information on the nature of the pre-Mesozoic basement. A profile across southern England (passing just to the west of London) suggests that a significant contribution to observed gravity variations in the region results from changes in the thickness of relatively low density Lower Palaeozoic rocks. It also identifies a major deep-seated body with relatively high magnetic susceptibility and low density which is interpreted as a Precambrian cratonic core underlying the southeastern part of the Midlands Microcraton. Profiles across central and eastern England reveal major boundaries within the Precambrian basement, some of which coincide with structures mapped at surface. A number of intrusions of probable Caledonian age have been recognized, including bodies beneath the Widmerpool Gulf and The Wash. Those beneath The Wash appear to lie in a discrete basement region which separates belts of more magnetic basement lying to the northwest and southeast.

Laboratory measurements of the effect of a confining pressure on the strength and stress-strain characteristics of a metallurgical coking coal are described. Several-fold increases in the strength, the Young's modulus and the elastic strain at failure were found as the confining pressure was increased to 5,000 lb./n.2. The results are discussed in relation to various criteria of failure. It was found that failure was represented by Coulomb's equation relating shear stress and normal stress, provided the observed angles of fracture were not influenced by local edge stress concentrations.

This year, the 150th anniversary of Hutton's death, we are particularly reminded of the lively struggle of the eighteenth century between Vulcanists and Neptunists; the more so since that struggle finds its counterpart to-day in the divergence of opinion between two schools of petrology whose respective members might aptly be called Magmatists and Transformists. Much of the disagreement between the modern opponents arises from a belief on the part of the Magmatists that Hutton proved the magmatic origin of granite, and, in addition, the disagreement is probably strengthened by a misunderstanding of the views held by Transformists, and by lack of knowledge or experience of the evidence on which they base their conclusions. Indeed, Transformists might be tempted to preface their writings with the following very apposite quotation from Werner (1781):—

“I must here present a request to all who would judge of this theory, or communicate their sentiments on it to the public, viz. to begin by reading through the whole treatise, and then to peruse it a second time, with attention. Such a request will not only appear strange to many persons, but even superfluous ; I find myself, however, under the necessity of making it from the manner followed by some individuals with my book on the external characters of fossils. They have often represented me as saying quite the contrary of what I have expressly written. This may have been done by some, through design, but in by far the greater number of instances, it has happened from that work not having been read through ; and in this manner the public has frequently been led into an error, at least for some time.”

More than forty years ago the detached teeth of Hybodont Sharks were recognized by Reuss in the Cretaceous rocks of Bohemia, and these were referred to the genus Hybodus under no less than eight specific names. About twenty years later, evidence of a somewhat similar Selachian was discovered by Mr. William Davies and Mr. S. J. Mackie, in the Lower Chalk of Kent; and the cartilages of the jaw, with a few teeth, were briefly described by the last-named geologist under the name of Hybodus dubrisiensis. In 1886, the present writer pointed out, from more recently discovered specimens, that the English Cretaceous species was more specialized in every respect than any of the typical forms of Hybodus; and quite lately it has been proposed to regard this fossil as generically distinct, with the new name of Synechodus.

The Caledonides of the west of Ireland provide a well-exposed and well-mapped example of an oblique collision zone. The east-northeast trending Deer Park and Achill Beg Fault system is a crustal scale ductile sinistral strike-slip duplex of late Ordovician age, imbricating late Precambrian granulite facies lower crustal rocks, near eclogite facies supracrustal rocks, up to amphibolite facies Dalradian metasedimentary rocks and greenschist facies Cambro-Ordovician rocks. This fault system is correlated with a pre-Devonian component of the Highland Boundary Fault system in southern Scotland. In the Clew Bay area, the high pressure-low temperature facies metamorphic rocks, in tectonic contact with greenschist facies Cambro-Ordovician rocks, are together interpreted as an accretionary prism complex related to northwestward directed subduction. Both of these are allocthonous terrains with respect to the Dalradian terrane to the north (North West Mayo). To the south, the Cambro-Ordovician rocks docked with a probable Dalradian block containing ultramafic intrusives (Deer Park Complex) during the late Ordovician. The Deer Park Complex and South Mayo Trough linked earlier, during the Arenig.

Silurian and Lower-Middle Devonian redbed successions sit unconformably on the metamorphic rocks. Deposition and deformation of these cover rocks was controlled by oblique strike-slip movements on the Leek Fault whose strike swings from west-northwest to north-northeast, following earlier basement trends, as it is traced eastwards from Clew Bay. The Leek Fault System may be correlated with the Leannan Fault of northwest Donegal, a splay of the Great Glen Fault system of central Scotland. East of Clew Bay, this sinistral shear generated local dilation on the more northerly trending bend of the Leek Fault. Lower and Middle Old Red Sandstone redbeds were developed here. The west-northwest trend of the Leek Fault in Clew Bay acted as a compressional bend during these sinistral movements and transpressional southwest directed thrusting developed in Silurian rocks. Post-Middle Old Red Sandstone pre-late Tournaisian dextral displacement on the Leek Fault reversed this pattern with transtension in Clew Bay allowing intrusion of small carbonated peridotite bodies into Silurian rocks and easterly directed thrusting of Middle Old Red Sandstone rocks east of the Bay on the transpressional north-south bend.

A tectonic model for the region is presented here. This model involves a northwestward directed subduction system, 150 to 750 km of Arenig sinistral strike slip movement, and eastwards insertion of the Connemara block with formation of the Ordovician South Mayo Trough as a pull-apart basin. Subsequently, a further 130 to 650 km eastward displacement of rocks took place south of the Deer Park Fault in later Ordovician times. The magnitudes of these estimates are directly proportional to an assumed maximum wavelength of 1500 km for promontories on the original Laurentian margin, and using the current juxtaposition of terranes, a minimum wavelength of 300 km is inferred.

Mafic dykes from the Øksfjord-Langfjord area were intruded at different stages during the prolonged tectonomagmatic evolution of the Seiland Igneous Province. Field relations, petrography and geochemistry indicate the presence of four dyke generations with alkali basalt composition and one generation of alkaline lamprophyres. The entire dyke suite has geochemical signatures consistent with formation in a within-plate geotectonic environment. Trace elements indicate that the alkali basalt dykes have OIB (ocean island basalt) affinities and we suggest a sublithospheric mantle source. The data support a rift-related origin for the Seiland Igneous Province. Longevity of magmatism in the Seiland Igneous Province (300 m.y.) is difficult to explain within a conventional mantle plume framework. Instead, it is proposed that the intermittent magmatism in the province was predominantly permissive and controlled by lithosphere structure.

Isotopic and geochemical data indicate that intrusions in the eastern Creignish Hills of central Cape Breton Island, Canada represent the roots of arcs active at ∼ 540–585 Ma and ∼ 440 Ma. Times of intrusion are closely dated by (1) a nearly concordant U–Pb zircon age of 553±2 Ma in diorites of the Creignish Hills pluton; (2) a lower intercept U–Pb zircon age of 540±3 Ma that is within analytical error of 40Ar/39 Ar hornblende plateau isotope-correlation ages of 545 and 550±7 Ma in the River Denys diorite; and (3) an upper intercept U–Pb zircon age of 586±2 Ma in the Melford granitic stock. On the other hand, ∼ 441–455 Ma 40Ar/39 Ar muscovite plateau ages in the host rock adjacent to the Skye Mountain granite provide the best estimate of the time of intrusion, and are consistent with the presence of granitic dykes cutting the Skye Mountain gabbro–diorite previously dated at 438±2 Ma. All the intrusions are calc-alkaline; the Skye Mountain granite is peraluminous. Trace element abundances and Nb and Ti depletions of the intrusive rocks are characteristic of subduction-related rocks. The ∼ 540–585 Ma intrusions form part of an extensive belt running across central Cape Breton Island, and represent the youngest Neoproterozoic arc magmas in this part of Avalonia. Nearby, they are overlain by Middle Cambrian units containing rift-related volcanic rocks, which bracket the transition from convergence to extension between ∼ 540 and 505/520 Ma. This transition varies along the Avalon arc: 590 Ma in southern New England, 560–538 Ma in southern New Brunswick, and 570 Ma in eastern Newfoundland. The bi-directional diachronism in this transition is attributed to northwestward subduction of two mid-ocean ridges bordering an oceanic plate, and the migration of two ridge–trench–transform triple points. Following complete subduction of the ridges, remnant mantle upwelling along the subducted ridges produced uplift, gravitational collapse and the high-temperature/low-pressure metamorphism in the arc in both southern New Brunswick and central Cape Breton Island. The ∼ 440 Ma arc magmatism in the Creignish Hills extends through the Cape Breton Highlands and into southern Newfoundland, and has recently been attributed to northwesterly subduction along the northern margin of the Rheic Ocean.

The fossils described below were collected by Messrs. B. K. N. Wyllie, Keir A. Campbell, and G. M. Lees, working on behalf of the Turkish Petroleum Company, who have kindly made arrangements for me to investigate their collection, which proves to be of some interest.