The Wagwater Belt is a fault-bounded structural unit in which more than 3000 m of early Tertiary sedimentary and volcanic rocks are exposed. Geochemical analyses of the volcanic rocks show that they comprise a bimodal suite of plateau-type tholeiitic basalts and calcalkaline dacites. The extrusion of these volcanics is associated with the development of an interarc basin, the Wagwater Basin, at the beginning of the Cenozoic Era. The Wagwater Basin formed as a result of the splitting of a mature late Cretaceous volcanic arc into a frontal and third arc represented by the Blue Mountain Massif and the Clarendon Block respectively. This model for Jamaica can be correlated with tectonic events occurring in the NW Caribbean during the early Tertiary. The creation of the Wagwater Basin and the eruption of the basalts is related to the initial opening of the Cayman Trough. The cessation of dacite volcanic activity in Jamaica signified the separation of the Caribbean Plate from the East Pacific Farallon Plate.

Previous radiometric age determinations for the Criffell–Dalbeattie and Cairnsmore of Fleet Newer Granite intrusions are briefly reviewed. Thirteen fission-track dating results are presented for the co-existing accessory minerals sphene, zircon and apatite separated from the two granites. The mean sphene apparent age of 401±10 Ma and single zircon apparent age of 389±26 Ma are interpreted as the age of initial post-intrusion cooling of the granites. Results from apatite are discordant with those of sphene and zircon. Four determinations give a mean Upper Cretaceous apparent age of ∼ 80 Ma which is not readily interpreted. A single apatite determination upon a sample located adjacent to a basaltic dyke yielded a Tertiary age.

Chloritoid and staurolite bearing rocks from the Agnew Lake area in northern Ontario were studied petrographically and with the electron microprobe. A staurolite–chlorite isograd is postulated, above which chloritoid and staurolite coexist in equilibrium, and a Schreinemakers-type petrogenetic grid is constructed to illustrate how the isograd might fit into a paragenetic sequence.

The staurolites from the area are observed to be more ‘siderophile’ than the chloritoids and this suggests that the chlorite participating in the isograd reaction is prograde. This is confirmed in the ‘real’ isograd reaction:

1.559ctd+5.000and+0.009rut+0.058ilm=0.881st+0.039chl+1.366qtz+1.040H2O the coefficients of which are calculated using the mineral analyses of the ideally univariant assemblage staurolite–chloritoid–chlorite–andalusite. Variations in the activity of the unsaturated component ZnO would affect the equilibrium temperature of the reaction and the reaction coefficients.

The Newania carbonatite is mainly ferruginous rauhaugite with subordinate ankeritic carbonatite and dykelets of sovite. In a zone of fenitization the surrounding granite-gneiss country rock has been converted into syenitic fenite, composed mainly of feldspar and ferri-eckermannite with small amounts of albite, anorthoclase and accessory apatite.

The Eller Beck Formation is a thin marine intercalation in a predominantly non-marine Middle Jurassic sequence of coal measures facies. The formation consists of thin transgressive ironstones and siltstones at the base which are overlain by a thicker regressive sequence of shale passing upwards into sandstone. The close association between changes in the local subsidence pattern and the transgression suggest that the incursion resulted from epeirogenic movement rather than from eustatic rise in sea level or a purely sedimentation-controlled change in delta distributary pattern. Facies distribution was greatly affected by local synsedimentary tectonic movement. Water depths were probably very small throughout, and tidal effects on sedimentation minimal.

The Fayûm, one of the largest depressions of the Libyan Desert, is situated some 50 miles south-west of Cairo. It is cut out in rocks of Eocene and Oligocene age, while still younger deposits of Pliocene and Post-Pliocene date are found within the hollow. The depression owes its origin to the action of the ordinary subærial denuding agents, which I have shown in previous papers were capable of producing the oases-depressions of Baharia, Farafra, Dakhla, etc. Faulting, which has played so important a part in the formation of the Nile Valley, appears to have had little or nothing to do with the production of the Fayûm and other depressions of the Libyan Desert.

A microbioherm-bearing hardground within the middle Silurian (Wenlock) Massie Formation near Napoleon, southeastern Indiana, United States is encrusted by the attachment structures of numerous pelmatozoan echinoderms. Among the most common of these holdfasts are multi-plated discoidal structures representing the thecal attachments of diploporite ‘cystoids’. This large population of holdfasts permits the first detailed taphonomic and palaeoecologic study of hardground diploporite attachments, allowing for increased morphological understanding of these rarely studied structures and facilitating identification of holdfasts in deposits where they might have been overlooked or misidentified. The biostratinomic sequence commences with detachment of thecae, followed by weathering of isolated discoidal holdfasts to bring out radiating canal structures and plate sutures, eventually leading to removal of the interior floor to expose the underlying substrate. Continued exposure can result in separation of component holdfast plates, though cementation to the substrate prevents scattering of plates. Diagenetic precipitation of pyrite occurred after burial; the large size of crystals suggests late diagenesis, perhaps seeded by early diagenetic pyrite crystallites produced by decay of ligamentary tissue. Extrinsic taphonomic factors include overgrowth of holdfasts by laminar stenolaemate bryozoans and other echinoderm attachment structures. Diploporite holdfasts are not bored and are absent on microbioherms. Taphonomic data indicate the time-averaged nature of this hardground and its diploporite assemblage and permit prediction of similar occurrences at major flooding surfaces.

The sense and amount of rotation of small garnet porphyroblasts is found to vary from place to place on a fold. By correlating this variation with a proposed mechanism of formation of the fold, a tentative profile for the fold at the time of garnet growth is constructed.

This genus was founded by Mr. Carruthers to include those compound forms of monoprionidian Graptolites in which the polypary is unilateral, growing from the initial point in one direction only. There can be no hesitation in regarding it morphologically as a branching Monograptus; its mode of development, the characters of its hydrothecæ, and its geological distribution, all pointing unmistakably in this direction.

In a recent memoir (Holmes and Harwood, 1937, p. 276) I had occasion to point out that “one of the most remarkable features of the igneous activity of late Cretaceous and early Tertiary times is the geochemical and petrological contrast between the kimberlite and olivine-melilitite which perforated the crust of Southern Africa and the widespread outpourings of olivine-basalt and basalt (often followed by acid rocks) in many other parts of the world”. An essentially similar contrast is found in the more recent and more localized volcanic fields of the Western Rift of Africa. The Toro-Ankole fields of multiple vents, east and south-east of Ruwenzori, are characterized throughout by undersaturated potassic types, free from felspar; whereas in the great lava fields south of Lake Kivu the dominant lavas are olivine-basalts of various types. Between these two strongly contrasted provinces, and in some respects sharing the characters of each, the Birunga field (including Bufumbira) extends across the Rift north of Lake Kivu. Although many of the lavas of this field contain abundant plagioclase and look like basalts, they have been found, with few exceptions, to be potassic types ranging from leucite-basanites to basanitoid trachybasalts. True basalts appear to be absent (Holmes and Harwood, 1937, pp. 16–18), the nearest approach to basalt—geographically as well as petrographically—being certain trachybasalts and limburgites from the south of the field, which differ from the other rocks of Birunga in having more soda than potash.

Mica pegmatites from the Bihar Mica Belt contain three distinct generations of tourmaline. The major-element composition, substitution vectors and trajectories within each group are different, which indicates that the three types of tourmalines are not a part of one evolutionary series. Rather, the differences in their chemistries as well their mutual microtextural relations, can be best explained by growth of tourmaline from pegmatitic melts followed by episodic re-equilibration during discrete geological events. The euhedral, coarse-grained brown type I tourmaline cores have relatively high Ca, Mg (XMgc. 0.37) and Al with correlated variation in Sr, Sc, Ti, Zr, Y, Cr, Pb and Rare Earth elements (REEs). They are inferred to have crystallized from pegmatitic melts. Monazites included within these tourmalines give chemical ages of 1290−1242 Ma interpreted to date the crystallization of the pegmatitic tourmaline. The bluish type II and greyish type III tourmalines with low Ca and Mg contents (XMg = 0.16−0.27) and high Zn, Sn, Nb, Ta and Na, formed by pseudomorphic partial replacement of the pegmatitic tourmaline via fluid-mediated coupled dissolution–reprecipitation, are ascribed to a hydrothermal origin. The ages obtained from monazites included in these tourmalines indicate two alteration events at c. 1100 Ma and c. 950 Ma. The correlated variation of Ca, Mg and Fe and the trace elements Sr, Sn, Sc, Zn and REE within the tourmalines indicates that the trace-element concentrations of tourmaline are controlled not only by the fluid chemistry but also by coupled substitutions with major-element ions.

A newly measured and sampled section in the upper part of the early Neoproterozoic Visingsö Group, south central Sweden, has been investigated for its stable carbon and oxygen isotope geochemistry. The 30 m-thick succession crops out on the southeastern shore of Lake Vättern, close to the village of Boeryd, and consists mainly of black mudstones with carbonate lenses, some of which have been dolomitized. High H/C ratios of the kerogen preserved in the investigated succession indicate that organic carbon generally is well preserved. The observed δ13Corg values are comparable to previously observed Neoproterozoic organic carbon values, with the exception of a few exceptionally 13C-depleted kerogens, with δ13Corg[ges ]−41.1 ‰. The latter are interpreted to be the result of fermentative bacterial reworking of sedimentary organic matter. The Boeryd carbonates display an unusual array of heavy δ18O values (with δ18O[les ]+3.3 ‰) that are interpreted as reflecting deposition in an arid climate. Geochemical data indicate that the carbonates have been diagenetically altered, but only to a limited extent, and a range of δ13Ccarb values from +2.4 to +4.7 ‰ appears to be representative of the primary seawater composition for the time of deposition of the upper Visingsö unit. Positive carbonate isotope values are typical for lower Neoproterozoic, pre-Varangerian successions elsewhere. The C isotope values obtained from the Boeryd section, although not conclusive by themselves, are consistent with the formerly biostratigraphically and radiometrically inferred early Neoproterozoic age for the upper Visingsö Group.

The detailed studies on rocks of the prasinite-green schist facies published during the last decade have thrown a flood of light on the genetic relations of the various members of this facies group. References may be made to the work of Vogt at Sulitelma (l),1 Fischer in the Wippra metamorphic zone (2), Weg's studies in the Saxon Zwischengebirge (3), Turner's contributions on the Otago schists (4), and finally in this country to Wiseman's study of the progressive metamorphism of the Dalradian epidiorites (5).

Evidence for the growth of andalusite and staurolite porphyroblasts prior to the first penetrative movements in the rocks of the Mt. Lofty Ranges is presented. The implications of this unusual observation are discussed.

X-ray analyses of selected samples from the argillaceous subdivisions of the English Wealden indicate that illite, kaolinite, and mixed-layer structures are present in variable amounts. The clay mineral assemblage is thought to reflect parent material, weathering conditions in the source area, and possibly some degrading of the illite structure by the action of active waters in the depositional environment. The specific clay minerals are tentatively correlated with the palaeogeographical framework proposed by Allen (1954). It is suggested that the kaolinite was derived mainly from the Palaeozoic uplands, and the bulk of the illite and mixed-layer structures from the marginal Jurassic lowland.

The oil regions of India lie in the north-west and in the east, within broad strips of Tertiary rocks stretching in a general southerly or south-westerly direction from the Himalayas to the sea. On the eastern side of India the main Tertiary outcrop runs from the head of the Assam Valley south-westwards through part of the Central Assam Range into the Surma Valley and thence southwards to the Bay of Bengal at Chittagong, whence the Tertiary beds continue along the Arakan Coast of Burma. This strip forms one geological province, distinct both from the better-known Tertiary development of western India and from the Tertiaries of the Chindwin–Irrawaddy Valley of Burma. This Assam–Arakan region includes parts of the provinces of Assam and Bengal and part of the western coast of Burma: although Burma is now separated from India, it is convenient to consider the Assam–Arakan oil-belt as a whole, without regard to political divisions.

Integrated graptolite and chitinozoan biostratigraphical data are presented from the upper Telychian (Oktavites spiralis and Cyrtograptus lapworthi graptolite biozones) of the Ventspils D-3 core, Latvia. The base of the Angochitina longicollis chitinozoan Biozone is approximately coincident with that of the spiralis graptolite Biozone, as it is elsewhere in the East Baltic, although in Wales it lies within the upper spiralis graptolite Biozone. Conochitina proboscifera appears in the upper spiralis graptolite Biozone in the Ventspils D-3 core, but at lower and higher horizons elsewhere, presumably reflecting its patchy distribution during the lower part of its stratigraphical range. Ramochitina ruhnuensis appears to be a stratigraphically useful, although geographically restricted, species, appearing at a level close to the base of the lapworthi graptolite Biozone. The most remarkable feature of the Ventspils D-3 chitinozoan record is the very early occurrence, in the upper spiralis graptolite Biozone, of two chitinozoan biozonal index species: Margachitina banwyensis and M. margaritana. Previously, these two taxa were considered unequivocal indicators of the uppermost Telychian to Sheinwoodian or Homerian, respectively.

New zircon U–Pb ages and whole-rock chemical data from four adakitic and two non-adakitic igneous rocks as tectonic blocks in the southern West Junggar accretionary complexes, northwestern China and one gabbro enclave in adakitic block provide further constraints on the initial subduction and following rollback process of the Junggar Ocean as part of southern Palaeo-Asian Ocean. The oldest adakitic monzonite in Tangbale is intruded by the non-adakitic quartz monzonite at 549 Ma, and the youngest adakitic diorite in Tierekehuola formed at 520 Ma. The Ediacaran–Cambrian magmatism show a N-wards younger trend. The high-SiO2 adakitic rocks have high Sr (300–663 ppm) and low Y (6.68–12.2 ppm), with Sr/Y = 40–84 and Mg no. = 46–60, whereas the non-adakitic rocks have high Y (13.2–22.7 ppm) and Yb (2.32–2.92 ppm), with Mg no. = 36–40. The gabbro has high MgO (14.81–15.11 wt%), Co (45–48 ppm), Cr (1120–1360 ppm) and Ni (231–288 ppm), with Mg no. = 72–73. All the samples show similar large-ion lithophile element (LILE) and light rare earth element (LREE) enrichment and Nb, Ta, Ti and varying Zr and Hf depletion, suggesting that they were formed in a subduction-related setting. The adakitic rocks were produced by partial melting of subducted oceanic slab, but the melts were modified by mantle wedge and slab-derived fluids; the non-adakitic rocks were likely derived from partial melts of the middle-lower arc crust; and the gabbro originated from the mantle wedge modified by slab-derived fluids. The magmatism could have been generated during the Ediacaran initial subduction and Cambrian slab rollback of the Junggar Ocean.

The metamorphic P–T conditions and associated relationships of the Barrovian zones near Glen Muick were re-examined by focusing on the petrology and thermodynamics of rocks at Cairn Leuchan, where garnetite lenses and layers occur in surrounding garnet amphibolite in the highest-grade sillimanite zone. The representative mineral assemblages in the garnet-rich lenses and garnet amphibolite are garnet + quartz + clinopyroxene + plagioclase + amphibole ± epidote, and garnet + amphibole + quartz + plagioclase ± clinopyroxene ± epidote, respectively. The chemical compositions of constituent minerals are the same in both garnetite and garnet amphibolite. The metamorphic P–T conditions of these rocks were estimated by thermodynamic calculations. The results show that the rocks underwent high-pressure granulite facies metamorphism at P = c. 1.2–1.4 GPa and T = c. 770–800°C followed by amphibolite facies metamorphism at P = c. 0.5–0.8 GPa and T = c. 580–700°C. Integration of our new results with previously published data suggests that the retrograde P–T trajectory of the highest-grade Barrovian metamorphic rocks marks a temperature decrease during decompression from a crustal depth of the high-pressure granulite facies, which is much deeper than previously considered.

Barrettia, the most abnormal of the Rudistæ, and among the strangest of all the mollusca, was first found in Jamaica by Lucas Barrett, F.G.S., in the year 1861. The specimens were ably described by S. P. Woodward, F.G.S., in 1862. The original specimens, now in the British Museum of Natural History, consist of polished transverse and longitudinal sections of the upper part of the shell, the latter showing the junction of the upper and lower valves, and a cross section of the young shell near the apex of the lower valve. They were called Barrettia monilifera in honour of the discoverer. The locality where they were found was on the banks of the Back River, a tributary of the Rio Grande, about 15 miles from the coast in Portland Parish in the north-east of the island. The rock is described as a hard, grey limestone which occurs in bands of a few inches to a yard in thickness, subordinate to many hundreds of feet of shale which graduate up into other grey shales of the Eocene, followed by white limestones of Miocene age.