The ostracods described in this paper have all been obtained from the Goniorhynchia boueti bed, as exposed at the little peninsula known as Herbury (“Herbeyleigh” in some of the older geological literature), near Langton Herring, some five miles to the west of Weymouth. The bed is at sea level at the north-west corner of Herbury, and is there about one foot thick. It is from this point (national grid ref. 30/610810) that the samples were taken for the separation of microfossils. Polyzoans, baby brachiopods, foraminifera, “vertebral” ossicles of ophiuroids, radicles of echinoids and minute gastropods, make up as diverse and interesting an assemblage as that formed by their better known macroscopic contemporaries.

Two metabentonite suites occur within the Wenlock limestones and marls of Gotland, one within the Slite Formation (M. belophorus to the C. ellesae biozones) and the other in the Mulde Formation (G. nassa–M. dubius Biozone). Their geochemical characteristics based on rare-earth element (REE) distributions in apatite crystals separated from the metabentonites suggest origins from three separate volcanic sources. One of these sources has an alkaline affinity, reflected in relatively high levels of Th, Nb and Zr, which suggests that it may have lain over thickening continental crust during the waning stages of the closure of the Tornquist Sea, while the other two represent calc-alkaline magmas. The source of the volcanic ash is placed some 400 km to the southwest of Gotland, on the Tornquist–Teysseyre Zone, which is the northernmost expression of the Trans-European Suture Zone. Distinctive differences in REE distribution in apatite from these metabentonites should assist in future correlation studies in Wenlock stratigraphy, both within the Baltic region and further afield.

Cruziana ichnospecies have been repeatedly reported to have biostratigraphic significance. This study presents a re-evaluation of the arthropod ichnotaxa of the Cruziana rugosa Group from bio- and/or lithostratigraphically well-defined Lower to Upper Ordovician siliciclastic sections of southern and central Bolivia. With the exception of Cruziana rouaulti, the ichnofaunas contain all the members of the Cruziana rugosa Group throughout the Ordovician (Arenig to Caradoc) successions in Bolivia. The Bolivian material therefore indicates that these arthropod ichnofossil assemblages are suitable for recognizing Ordovician strata in Bolivia. These findings cast doubt on their use as reliable indicators for a global intra-Ordovician (Arenig to Caradoc) biozonation of Peri-Gondwanan sedimentary successions.

This paper presents quantitative data on the finite strain, quartz crystal fabric, geometry of flow and deformation temperatures in deformed quartzite samples to characterize the ductile deformation along the thrust sheets constituting the Sanandaj–Sirjan Metamorphic Belt within the Zagros Mountains of Iran. The results of this study emphasize the heterogeneous nature of deformation in this belt, showing a spatial variation in strain magnitude and in degree of non-coaxiality. A dominant top-to-the-SE sense of shear is indicated by the asymmetry of microstructures and quartz c-axis fabrics. Quartz c-axis opening angles suggest deformation temperatures range between 435° ± 50°C and 510° ± 50°C, which yield greenschist to amphibolite facies conditions during the ductile deformation. Mean kinematic vorticity number (Wm) measured in the quartzite samples ranges between 0.6 and 0.9 with an average of 0.76, which indicates that extrusion of the metamorphic rocks of the region was facilitated by a significant component of pure shear strain. Traced towards the basal thrust of the Zagros Thrust System from northeast to southwest, the quartz grain fabrics change from asymmetric cross-girdle fabrics in the internal part of the deformation zone to an asymmetric single-girdle fabric at distances close to the basal thrust. This variation may depend on the structural depth and on the geometry of the ductile deformation zone. The observed increase in strain and vorticity within the study area is comparable with patterns recorded within metamorphic rock extrusions within other orogens in the world.

A new structural diagram is proposed that allows simple precise classification of fold orientations. The diagram is also useful for the analysis of the relationship between fold style and orientation.

The relationships of the Keisley Limestone, an isolated carbonate mudmound in the Cross Fell Inlier of northern England, have long been problematical with respect both to the other upper Ordovician as well as the Silurian strata of the inlier. Bedded limestones, separated by gaps from the Keisley mudmound below and from atavus Biozone graptolite shales above, yielded a prolific shelly fauna to Temple in 1968 which he regarded as being of lower Llandovery age. This age is controversial. To try to establish the precise ages of the rock units, the position of the Ordovician–Silurian boundary, and the detailed nature of the changes which took place at this boundary, a critical section was excavated. Bed by bed lithological and faunal collections reveal from beneath the known atavus outcrop (a) five bentonite bands, unexpected in the context of northern England, (b) graptolites of both acuminatus and persculptus Biozones above the bedded limestones and (c) a similar but distinct assemblage from siltstones associated with these limestones which contains Hirnantia elements. From the palaeontological evidence there is little doubt that the topmost part of the carbonate sequence is of Hirnantian age.

Lower Palaeozoic outcrops near Kemer comprise only Ordovician and Silurian strata in the Upper Antalya Nappes, and are described in detail for the first time. The oldest rocks, Seydişehir Formation (lower Arenig), resemble those of the central Taurides. A disconformity is probable, though unexposed, below the succeeding Şort Tepe Formation (Ashgill), a unit seen elsewhere only in south central and southeastern Turkey; sparse trilobites include Cyclopyge, Cyphoniscus, Panderia, Symphysops, Ulugtella, and one new species Placoparia (Hawleia) marcouxi. Silurian rocks (Sapandere Formation) differ from those further east in the Taurides, and are of Llandovery (Telychian), Wenlock and ?Ludlow age, based on conodonts, graptolites and trilobites (Cerauroides, Otarion (Aulacopleura), Sphaerexochus) the affinities of which lie with the Carnic Alps and western Europe. The Sapandere Formation is unconformably overlain by red sandstones at the base of the Armutlugözlek Formation (Devonian).

Convolute bedding is described from the Lower Ludlovian in north-eastern Radnorshire in calcareous siltstones probably of the Monograptus tumescenszone. Examples of true slump-structures from the same area are given for comparison. The mode of formation of the convolute bedding is discussed and reference made to such directional information as is available from a study of the sediments.

In a recent paper the author attempted to explain something of the mechanism of contamination in acid magmas, but nothing was said about the tendency, of contamination to produce normal rock types. It is to repair this deficiency that the present communication is presented.

Available data from charnockitic rocks (including twenty-eight new pyroxene pairs fromAustralia) suggest that a major cause of variation in optically derived compositional tie-line trends of co-existing pyroxenes is related to the geothermal history of the rocks concerned. It may yet be possible to subdivide the granulite facies, and also to detect mineral instability by critical study of tie-line trends. Recommendations are made whereby mineralogic and structural studies of charnockitic rocks can be integrated to yield more reliable chemical and optical data.

In the southern belt of the Ballantrae serpentine, stretching south-west from Millenderdale, there occur many exposures of altered and more or less recrystallized dolerite and gabbro. Some of these rocks have afforded considerable difficulty to previous observers and they have been variously interpreted. Thus Dr. G. W. Tyrrell, in an interesting paper published twenty-five years ago (Trans. Geol. Soc. Glas., xiii, 283), regarded some of the rocks on Littleton Hill as “relics of an older mass of dolerite or gabbro” that had “become enveloped by the later serpentine”. But this expression of opinion does not appear to have been founded upon conviction, since quite recently Tyrrell states (Proc. Geol. Assoc, xliv, 59) “contact metamorphism presumably by the enveloping serpentine seems to have been developed in rocks on Littleton Hill which may originally have been spilites and diabase porphyrites”. At the time of writing a previous paper (GEOL. MAG., LXIX, 1932, 107) I hadalready inferred that the metamorphic rocks seen on Littleton Hill must have been derived from dolerites and gabbros, but the nature of their association with the serpentine was then merely a matter of surmise. In continuing field work in the province, therefore, I keptin mind the requirement to determine, if possible, the true geological relationships of these rocks, and to that end I have re-investigated carefully the whole southern outcrop of the serpentine and its accompanying metamorphic masses. A short account of the results of the field and laboratory work is given below. Firstly, however, I take leave to acknowledge the very helpful character of Mr. A. G. Macgregor's researches on felspar clouding, “a characteristic effect that is often produced in the fresh plagioclase felspars of igneous rocks by thermal metamorphism” (see Min. Mag., xxii, 524).

The Variscides of southeast England are buried beneath post-Carboniferous cover. Interpretations of the basement are based mainly on deep boreholes. Geophysical signatures from the basement are contained within the regional gravity and magnetic data. A gravity stripping exercise has been undertaken to remove the gravitational effect of the post-Variscan cover to generate a residual gravity map. This map is interpreted along with integrated potential field modelling along four long interconnected profiles and compared with a revised pre-Permian subcrop map. The magnetic evidence suggests that Precambrian magnetic basement of the Midlands Microcraton has been buried southwards by north-vergent Variscan thusting over the foreland. North of the Variscan Front, short-wavelength anomalies superimposed upon this deep Precambrian source are due to shallower Silurian and Carboniferous volcanic rocks. Many residual gravity lows within the Rhenohercynian zone may be related to thick, low-density Devonian basins. In the English Channel a change in geophysical signature occurs north of the Portland–Wight Fault, coinciding with phyllites in the basement. Models are presented in which the English Channel magnetic anomalies originate within the pre-Permian basement. Comparisons with anomalies in the Southwestern Approaches suggest that the Portland–Wight Thrust is a terrane boundary, possibly a subduction-related suture, implying southerly directed Variscan subduction.

The late Carboniferous to Triassic Karoo Supergroup of Madagascar is a sequence of predominantly continental clastic sediments deposited during a long period of regional crustal extension. In the Morondava Basin of western Madagascar the lower two divisions of the Karoo sediments – the Sakoa and the Sakamena – are deposits of fluvial and lacustrine sedimentation systems supplied from the Precambrian metamorphic basement terrain to the east. East–west crustal extension produced a series of graben and half-graben structures after the Sakoa period which were reactivated after the Sakamena. The position and orientation of these half graben, which were marginal to a larger rift system to the west, were partly controlled by the steep NNE–SSW mylonitic fabric in the metamorphic basement. Palaeocurrents in the braided river deposits of the Sakoa and Lower Sakamena indicate flow to the southwest and west in both sequences. The rivers followed a regional palaeoslope to the southwest/west and were apparently not significantly influenced by the local structural trends which were oriented perpendicular to this slope. The absence of local structural control is attributed to extensive erosional events which followed each tectonic episode and preceded the onset of further sedimentation which took place on an essentially peneplained surface. The tectonic episodes brought about changes in base level which caused this part of the basin to fluctuate between erosion and deposition.

FOR the past two winters it has been the author’s good fortune to undertake the geological work for Miss Caton-Thompson’s investigations into the prehistory of Kharga Oasis. This necessarily involved a close consideration of the water supply in Pleistocene times, the results of which disclosed some interesting new facts and raised climatic questions of more than local interest.

The classification of the Palæozoic starfishes has long been in chaos. The earlier palæontologists, who founded most of the known genera, made no attempt at a general classification or to indicate the relations between the Palæozoic and existing representatives of the Asteroidea. The first step towards progress was Bronn's division of the extinct genera into three groups—the Ophiurasteriæ (which may be left out of account as Ophiuroidea), the Encrinasteriæ, and the Asterias veræ.

Sm–Nd and K–Ar isotopic determinations on an amphibolite from the Highland Border Complex yield Cambrian ages. Collisional events which might have generated the amphibolite appear incompatible with the passive margin character of Laurentia at that time. A possible explanation is that the part of the Highland Border Complex containing the amphibolite and associated rock units was generated outside Laurentia.

Zircon U–Pb ages, major and trace element geochemistry and Sr, Nd and Pb isotope compositions of diorite and diorite porphyry dykes from the Jinchanggouliang (JCGL) gold ore field on the northern margin of the North China craton (NCC) were studied to investigate their sources, petrogenesis and geodynamic significance. LA-ICP-MS zircon U–Pb dating reveals three major age groups of 2500 Ma (n = 2), 253 ± 7 Ma (n = 5) and 227 ± 1 Ma (n = 9). The inherited ages of 2500 Ma, contemporary with the Archaean NCC continental growth, imply that crustal material was involved in the magma source. The igneous zircons with a concordia age of 227 ± 1 Ma may record the emplacement age of the JCGL dykes. Both diorite and diorite porphyry exhibit a wide range of SiO2 and MgO contents and are characterized by high concentrations of Na2O+K2O and Al2O3, and low abundances of P2O5 and TiO2. They are enriched in large ion lithophile elements and light rare earth elements without significant Eu anomalies, and depleted in high-field-strength elements; all are categorized as shoshonitic rocks. All samples show a narrow range of Sr isotope compositions with initial 87Sr/86Sr ratios from 0.70394 to 0.70592, variable εNd(t) values (1.1 to −12.0) and TDM2 ages of 913–1972 Ma. Their Pb isotope compositions form continuous variation trends and plot in the fields between enriched mantle 1 (EM1) and lower continental crust (LCC). The above results suggest that the JCGL dykes studied could have been derived from mixing of lower crust, lithospheric mantle of the NCC and ascending asthenospheric melt in a post-orogenic extensional geodynamic setting. These shoshonitic dykes, together with the geochronological data of regional ENE-trending retrograded eclogites, ophiolites, continental arc magmatic belt, A-type granite, alkaline intrusions and metamorphic core complex from the northern NCC and Central Asian Orogenic Belt (CAOB) suggest that closure of the Palaeo-Asian Ocean (i.e. stage of pre-collision to collision) had completed during latest Permian to earliest Triassic time, and that the CAOB was subsequently tectonically dominated by post-orogenic extensional regimes. The involvement of asthenospheric melt in the magma source implies that the sub-continental lithospheric mantle (SCLM) of the NCC had been modified, and the onset of lithospheric destruction and thinning beneath the northern NCC may have occurred in Middle–Late Triassic time as a result of post-orogenic subducting slab detachment and lithospheric delamination.

South of Clew Bay, Co. Mayo, Wenlock strata, cut off to the north by a belt of serpentine marking the Highland Boundary, are divisible into three stratigraphical groups. The succession is repeated by a syncline overturned towards the south, which is modified by north-west cross-folds. The Wenlock strata have undergone low-grade “regional” metamorphism, in spite of which fossils have been preserved at a few localities.

The first conclusive evidence for Silurian rocks in the Paraná Basin, Brazil, was reported in 1985. This evidence was based on organic-walled microfossils, principally spore tetrads, and associated phytoplankton (‘acritarchs’ and prasinophytes), the first recovered from the Vila Maria Formation on the northeastern rim of the Basin. The spore assemblage was typical of Gray's Microfossil Assemblage Zone I; size-frequency data for the tetrads suggested an early Silurian (early Llandovery; Rhuddanian) age. We now document a new MA Zone I occurrence of spore tetrads together with a few single trilete spores, from the southwestern rim of the Paraná Basin, Paraguay. The single spores are among the earliest known to have normally dissociated from a tetrahedral tetrad. Size-frequency data for the tetrads suggest a late Llandovery, pre-C5 (mid-Telychian) age. These spores, together with phytoplankton and chitinozoans, were recovered from beds laterally equivalent to the Vargas Peña Shale at the type locality from which Llandovery diplograptids and monograptids are known. Llandovery age rocks on the southwestern and northeastern borders of the Paraná Basin, c. 1400 km apart, suggest that early Silurian rocks were extensively distributed throughout southern Brazil and adjacent Paraguay. Close conformity between the age reference obtained with graptolites and spore tetrads again demonstrates the stratigraphic utility of early Silurian spores in providing reliable age determinations for otherwise unfossiliferous rocks. Spore tetrad assemblages available from the Malvinokaifric Realm (South America, Africa, Arabia) represent a distinct phytogeographic unit contrasted with spore tetrad assemblages from the North Silurian Realm of North America and parts of Europe.