Certain small discrepancies in Du Toit's (1937) reconstruction of Gondwanaland are discussed and suggestions made as to its mode of disruption.

The U–Pb geochronology of 687 detrital zircons from the voluminous Upper Neoproterozoic–Ordovician succession in the Wuyishan Fold Belt of South China reveals a common dominant c. 1200–950 Ma group, indicative of an outboard provenance terrane with a Grenville-age province to the southeast during the late Neoproterozoic–Early Palaeozoic. Compared with coeval samples from the Gondwanan and eastern Laurentian margins, our data show a scarcity of distinctive Gondwanan provenances (c. 650–500 Ma) and reveal some Laurentian signatures. These results argue against the peri-Gondwanan setting for South China during the late Neoproterozoic–Ordovician, instead implying a Laurentian affinity.

Ammonites are comparatively common in the Cenomanian or Lower Chalk, become rarer in the Turonian or Middle Chalk, and are very scarce in the Upper Chalk. On a former occasion, when pointing out that while ammonites were unknown from the Micraster cor-testudinarium Chalk of England, they occurred in the same Chalk in the north of France, the writer was inclined to attribute this absence or scarcity to limited horizontal distribution of the ammonites. The possibility, however, of there being gaps in the Chalk succession, for example at the horizon of Actinocamax plena, at the Chalk-Rock, in and above the cor-anguinum zone, etc., cannot be denied. The zone of Micraster cor-anguinum is not quite so barren as the zone below, but the only ammonites hitherto known from it are doubtful examples, probably referable to Parapuzosia. One impression, on an oyster, of part of the ventral area of a large specimen, possibly of P. corbarica Grossouvre sp., was collected by Mr. Dibley in the London-Portland Pit at Northfleet, Kent, and Dr. Rowe recorded probably comparable Parapuzosia (“ammonites of the leptophyllus group”) from Dorset and Yorkshire.

The parabolic surface profiles of the Hormuz and Namakdan salt diapirs in the Persian Gulf suggest that they have been extruding with Newtonian viscous rheologies for the last 104 years. We derive velocity profiles for these diapirs, neglecting gravitational spreading and erosion/dissolution while assuming incompressible Newtonian rheology of the salt. Fitting known rates of extrusion at specific points in its elliptical cross-section, the dynamic viscosity of the salt of the Hormuz diapir is found to range between 1018 and 1021 Pa s. Approximating its sub-circular cross-section to a perfect circle, the range of viscosity of the salt of the Namakdan diapir is obtained as 1017–1021 Pa s. These calculated viscosities fall within the range for naturally flowing salts elsewhere and for other salt diapirs but are broader than those for salts with Newtonian rheology deforming at room temperatures. The salts of the Hormuz and Namakdan diapirs are expected to exhibit a broader range of grain size, which matches the limited existing data.

In the following communication I intend to give a very brief outline of some of the chief results of my investigations among British Graptolites in those departments of inquiry which are more especially connected with consideratious of classification. I shall content myself with offering a concise statement of the main conclusions at which I have arrived, reserving all detail to the future, when I hope to adduce decisive evidence in support of the views here advanced. The special subjects to be noticed in this place are—the development, structure, classification, and geological distribution of that section of the Rhabdo-phora in which the complete polypary can be proved to be composed of one or more polyparies essentially similar to that in the unilateral and uniserial forms to which the name Graptolites (Graptolithus) is commonly applied. Those Rhabdophora supposed to be similar in structure to the genus Retiolites will be considered in conjunction, but no pretension is made to anything like the same certainty in this section.

Low-temperature eclogite-facies rocks from Syros and Tinos (Cyclades, Greece) include meta-igneous blocks of unclear origin (meta-olistostrome or tectonic mélange) with very high trace element concentrations (e.g. Zr up to 4850 ppm; Y up to 475 ppm). The unusual geochemistry is considered to be the result of metasomatic alteration in a subduction-zone environment. Locally, metasomatic exchange with an ultramafic matrix further enhanced compositional anomalies. A concordant U–Pb zircon age of 78±1 Ma recorded for an omphacitite from Syros is interpreted as the time of pre-Eocene high-pressure metamorphism in the Cyclades. Zircon dates of 61 and 63 Ma for a jadeitite from Tinos possibly indicate an additional discrete event (deformation?). These results are a first geochronological indication that high-pressure metamorphism in the Cyclades commenced significantly earlier than indicated by previous white mica chronology which provided ages between c. 50 and 40 Ma.

The Blue Ridge thrust sheet is one of the principal thrust masses of metamorphic rocks in the southern Appalachians. A broad zone of sheared and retrogressively metamorphosed rocks near the sole of the thrust sheet around the Grandfather Mountain window displays numerous small tight or isoclinal folds having axes subparallel to an intense penetrative cataclastic a lineation and axial planes parallel to foliation in the thrust sheet. These folds seem to have formed by tightening, flattening, and passive rotation of earlier more open folds originally formed perpendicular to the direction of transport. The style and orientation of these folds closely resemble those of analogous structures in thrust masses of crystalline rocks in the Caledonian orogenic belt in Scotland and Norway, suggesting that the structures of both regions may have similar origins.

The Tornquist Fan is a northwestward widening splay of late Carboniferous–early Permian fault zones in the region of Denmark emanating from the Teisseyre-Tornquist Zone in northern Poland. The crust–mantle boundary shows an undulating topography which correlates with the main tectonic features of the area. Zones of high average velocity through the consolidated crust coincide with pronounced positive Bouguer gravity anomalies in the deep basins and in the border zone of the shield. Less pronounced, similar correlation to gravity is found for the thickness of the lower crust, whereas the thickness of the upper crust in parts is inversely related to the gravity anomalies. Some magnetic anomalies appear to be related to the gravity anomalies. The positive features are interpreted as magmatic bodies that formed during late Carboniferous to early Permian transtensional movement along the faults of the Tornquist Fan, which explains pull-apart structures in the area and the Ringkøbing-Fyn basement High. The magmatism has strong implications for the subsequent formation of the regional Mesozoic basins. Localized dextral strike-slip movement on the Teisseyre-Tornquist Zone became distributed over the Tornquist Fan, which formed part of the rigid Baltic Shield and was situated at the northwestern end of this major, long-reaching Central European zone. As defined by late Cretaceous–early Tertiary compressional inversion structures, the Sorgenfrei-Tornquist Zone cuts across the Tornquist Fan area.

Lower-Middle Cambrian regional stages of the Iberian Peninsula (Cordubian, Ovetian, Marianian, Bilbilian, Acadoparadoxides and Solenopleuropsidae stages) are now reconsidered in the light of new stratigraphic and palaeontological (trace fossils, trilobites and archaeocyaths) studies. These stages are re-described with selected stratotypes and chronostratigraphic boundaries. The names Leonian and Caesaraugustian are formally proposed to replace the provisional stages of Acadoparadoxides and Solenopleuropsidae, respectively. A correlation chart of the Lower-Middle Cambrian lithostratigraphic units from the Iberian Peninsula is also presented. Two regessive-transgressive cycles are proposed to explain the lithological and palaeontological peculiarities through the Lower-Middle Cambrian sequence in the Iberian Peninsula.

Both low-Al and high-Al adakitic andesites erupted at ∼ 114 Ma in the Sulu collisional belt, eastern China, provide evidence for recycling of continental crust into the mantle more than 100 million years after the Triassic (∼ 240 Ma) collision between the North China and Yangtze blocks. These rocks display similar normalized trace element patterns, with enrichments in large ion lithophile elements (LILE), light rare earth elements (LREE) and depletions in Nb, Ta and Ti, and have highly radiogenic Sr and non-radiogenic Nd isotopic compositions (high-Al: 87Sr/86Sr(i)=0.70645–0.70715 and εNd(t)=−20.1 to −19.1; low-Al: 87Sr/86Sr(i)=0.70593–0.70598 and εNd(t)=−17.1 to −15.8). The high-Al (Al2O3 > 15 %) adakitic andesites are compositionally comparable with experimental slab melts, whereas the low-Al series (Al2O3 ∼ 13 %) have higher MgO, Cr and Ni, and higher Sr/Y ratios, and are compositionally comparable with slab melts hybridized by mantle peridotites. Combined major- and trace-element and Sr–Nd isotope data indicate that the two types of adakitic andesites have been derived from a LILE- and LREE-enriched eclogitic lower continental crust; in the case of the high-Al adakitic andesites, the melts underwent insignificant mantle contamination, whereas the low-Al magmas reacted with peridotites. Generation of the two types of late Mesozoic adakitic andesites favours a model of lithospheric delamination, leading to asthenospheric upwelling and extensive melting of lower continental crust, including a delaminated block, in the Sulu belt.

In previous reconstructions of Gondwanaland the Falkland Islands have been placed in a position intermediate between the Cape Province and Northern Argentina. In the present paper it is suggested on structural, tectonic, and stratigraphical grounds that it would be preferable to position the Falkland Islands due east of the Eastern Province coast, thus completing the truncated Karroo Basin, the missing part of which has until now been suspected to be concealed beneath the ice-capped Queen Maud Land, Antarctica.

Graptoloid evolutionary dynamics show a marked contrast from the Ordovician to the Silurian. Subdued extinction and origination rates during the Ordovician give way, during the late Katian, to rates that were highly volatile and of higher mean value through the Silurian, reflecting the significantly shorter lifespan of Silurian species. These patterns are revealed in high-resolution rate curves derived from the CONOP (constrained optimization) scaled and calibrated global composite sequence of 2094 graptoloid species. The end-Ordovician mass depletion was driven primarily by an elevated extinction rate which lasted for c. 1.2 Ma with two main spikes during the Hirnantian. The early Silurian recovery, although initiated by a peak in origination rate, was maintained by a complex interplay of origination and extinction rates, with both rates rising and falling sharply. The global δ13C curve echoes the graptoloid evolutionary rates pattern; the prominent and well-known positive isotope excursions during the Late Ordovician and Silurian lie on or close to times of sharp decline in graptoloid species richness, commonly associated with extinction rate spikes. The graptoloid and isotope data point to a relatively steady marine environment in the Ordovician with mainly background extinction rates, changing during the Katian to a more volatile climatic regime that prevailed through the Silurian, with several sharp extinction episodes triggered by environmental crises. The correlation of graptoloid species diversity with isotopic ratios was positive in the Ordovician and negative in the Silurian, suggesting different causal linkages. Throughout the history of the graptoloid clade all major depletions in species richness except for one were caused by elevated extinction rate rather than decreased origination rate.

The Upper Jurassic–Lower Cretaceous strato-tectonic belts of the southern Andes and South Georgia, 2000 km apart, can be correlated and explained as the products of an island-arc–back-arc system. From the Pacific Ocean to the Atlantic, these belts, which exhibit structural and metamorphic differences, are: (1) a pyroclastic belt developed on an ensialic volcanic arc; (2) a back-arc flysch sequence underlain in the southern Andes by a basic complex with oceanic affinities; this was intruded into continental crust as a result of sea-floor spreading which created a marginal basin; (3) a slate sequence deposited on a continental shelf. The pyroclastic and marginal basin belts and the adjacent part of the continental shelf were folded and uplifted during the early Upper Cretaceous, whereas the foreland part of the continental shelf assemblage underwent deformation during the early Tertiary.

Siberia contains several key reference sections for studies of biological and environmental evolution across the Proterozoic–Phanerozoic transition. The Platonovskaya Formation, exposed in the Turukhansk region of western Siberia, is an uppermost Proterozoic to Cambrian succession whose trace and body fossils place broad limits on the age of deposition, but do not permit detailed correlation with boundary successions elsewhere. In contrast, a striking negative carbon isotopic excursion in the lower part of the Platonovskaya Formation permits precise chemostratigraphic correlation with uppermost Yudomian successions in Siberia, and possibly worldwide. In addition to providing a tool for correlation, the isotopic excursion preserved in the Platonovskaya and contemporaneous successions documents a major biogeochemical event, likely involving the world ocean. The excursion coincides with the palaeontological breakpoint between Ediacaran- and Cambrian-style assemblages, suggesting a role for biogeochemical change in evolutionary events near the Proterozoic–Cambrian boundary.

The U-Pb isotope ages and Nd isotope characteristics of asuite of igneous rocks from the basement of eastern England show that Ordovician calc-alkaline igneous rocks are tectonically interleaved with late Precambrian volcanic rocks distinct from Precambrian rocks exposed in southern Britain. New U-Pb ages for the North Creake tuff (zircon, 449±13 Ma), Moorby Microgranite (zircon, 457 ± 20 Ma), and the Nuneaton lamprophyre (zircon and baddeleyite, 442 ± 3 Ma) confirm the presence ofan Ordovician magmatic arc. Tectonically interleaved Precambrian volcanic rocks within this arc are verified by new U-Pb zircon ages for tuffs at Glinton (612 ± 21 Ma) and Orton (616 ± 6 Ma). Initial εNd values for these basement rocks range from +4 to - 6, consistent with generation of both c. 615 Ma and c. 450 Ma groups of rocksin continental arc settings. The U-Pb and Sm-Nd isotope data support arguments for an Ordovician fold/thrust belt extending from England to Belgium, and that the Ordovician calc-alkaline rocks formed in response to subductionof Tornquist Sea oceanic crust beneath Avalonia.

Western Turkey is an area which has experienced large-scale extension of continental crust. Here we report precise crystallization ages of two intrusions in the central Menderes Massif, the Turgutlu and Salihli granodiorites, using U–Pb dating. Both intrusions occur in the southern footwall of the seismically active Alaşehir graben and were emplaced syntectonically in an extensional top-to-the-NNE shear zone which was active at retrograde greenschist-facies conditions. The U–Pb ages of 16.1 ± 0.2 Ma (monazite, Turgutlu granodiorite) and 15.0 ± 0.3 Ma (allanite, Salihli granodiorite) document that tectonic exhumation of middle-crustal rocks in the central Menderes Massif was already underway at the Early to Middle Miocene transition. Combined with published geochronological, structural and sedimentological data, the new U–Pb ages point to a continued extension since at least 16 Ma. There is no convincing evidence for a late Miocene/Pliocene phase of tectonic shortening.

The calc-alkaline, gneissic El Shalul granite is the westernmost gneiss dome or core complex within the Arabian–Nubian Shield. Previous studies have indicated that it represents either a window into the underlying pre-Neoproterozoic Sahara metacraton or a melt derived from the metacraton. U–Pb LA-ICP-MS dating of magmatic zircons from two samples of the variably foliated El Shalul pluton gives ages of 637 ± 5 Ma and 630 ± 6 Ma, excluding it from representing exhumed cratonic rocks. The ages are, however, indistinguishable from the age of the Um Ba'anib pluton, constituting the core of the Meatiq Gneiss Dome, as well as several other plutons in the Eastern Desert, indicating an important magmatic pulse in the Arabian–Nubian Shield in Late Cryogenian time. Major and trace element data indicate a within-plate setting. Bulk rock Nd-isotope and Hf-isotope data on zircons from the El Shalul pluton indicate derivation of the primary melt from a relatively juvenile source, either the lower crust of a mid-Neoproterozoic volcanic arc or as a result of fractionation of a mantle-derived mafic melt. Sm–Nd bulk rock isotopic data indicate a model age of c. 720 Ma for the protolith from which the melt was derived. Time-corrected Hf-isotope data obtained on the magmatic zircons indicate that the bulk of the source rock was extracted from the mantle around 810 Ma.

Since writing the first report on the arthropods of the Rhynie Chert beds (see Ann. Mag. Nat. Hist. (9), xii, pp. 455–74, 5 pls., and 13 text-figs.) some additional specimens of Palaeocharinus have been collected. A few examples are fairly complete and well preserved, showing a considerable amount of structural detail, such as the chaetotaxy, claws of the legs, ornamentation of the chitin, eyes, etc. An account of the lateral eyes is given below. We also include notes on a supposed insect and another fossil arthropod which we refer with doubt to the aquatic Merostoma. All the illustrations in this little paper have been drawn by Miss Violet Borrow, A.R.C.A., with the aid of a camera lucida under our personal supervision.

Lower Palaeozoic rocks in the Karadere-Zirze area, east of Safranbolu (Pontides, northern Turkey), range from Early Ordovician to Silurian. Overlying the probably Tremadoc Bakacak Formation are Aydos Formation quartzites, followed conformably by the Karadere Formation, dated as Early Arenig to Early Llanvirn by means of graptolites which are assigned to seventeen genera and include three new forms: Eoglyptograptus bouceki, Prolasiograptus haplus praecursor and Undulograptus? mui. Late Arenig trilobites from the Karadere Formation include Bergamia, Cyclopyge, Dionidella?, Leioshumardia and Seleneceme. In the Limestone Member of the overlying Ketencikdere Formation, uncommon trilobites suggest only a mid- to late Ordovician age, but conodonts with Colour Alteration Index 5–6 indicate the Amorphognathus tvaerensis Biozone (early Caradoc). Macrofossils are rare in the Siltstone Member, but conodonts from the middle of the unit suggest the highest subzone of the A. tvaerensis Biozone; the youngest visible strata are, on acritarch evidence, at least as high as Caradoc, but the Ashgill is not confirmed and the contact with overlying Silurian rocks is unexposed. The Findikli Formation comprises: a Lower Member, black argillites with Llandovery graptolites and acritarchs; and an Upper Member, grey shales with late Wenlock graptolites, overlain unconformably by Devonian rocks. The succession differs significantly from contemporaneous deposits in southern Turkey and its affinities lie with western Europe, including the Welsh Basin.

General agreement exists that the position of the base of the Cambrian (Precambrian–Cambrian boundary) should coincide with a biostratigraphic marker that can be widely traced and is linked to the evolution of the small shelly fauna. On the Siberian platform the presence of distinct facies during the Vendian–Cambrian interval has made biostratigraphic correlation based on palaeontological data highly contentious. A solution to this problem appears to exist with the recognition of an almost uninterrupted profile in the Aldan–Uchur watershed where key sections expose the eastern and transitional facial region. On this basis we present a general biostratigraphic scheme for the Vendian–Cambrian across the southern Siberian platform that connects separate facies. Further correlation with key sections in northern Siberia leads to the recognition of three biostratigraphic zones for the Vendian–Cambrian interval. These are: Anabarites trisulcatus Zone; Purella antiqua Zone; Aldanocyathus sunnaginicus Zone. The abundance of Chinese-type small shelly fossils in the region of the eastern facies suggest correlation of the A. sunnaginicus Zone with the Siphogonuchites–Paragloborilus Zone of China, and the P. antiqua Zone with the Circotheca–Anabarites–Protohertzina Zone. In places, at the base of the Circotheca–Anabarites–Protohertzina Zone in China, analogies to the A. trisulcatus Zone can be identified. It is proposed that in Siberia the base of the A. sunnaginicus Zone (= base of Tommotian Stage) be taken as the base of the Cambrian. This would correspond with Marker B of the Meishucunian in China