Various limestones of Middle Jurassic and younger age in the Middle East and Britain, and certain Recent calcareous marine sediments contain pellety debris stained grey or black with finely divided pyrite. The staining appears to involve deposition on pellety debris of limonite, followed by its reaction with bacterially produced hydrogen sulphide to form first ferrous sulphide and subsequently pyrite.

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.

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.

More than 75% of heavy mineral spectra of Rhenohercynian greywackes from the Harz Mountains (Famennian–Visean), the Werra greywacke (Frasnian–Famennian) and the Rhenish Slate Mountains (Frasnian–Visean) contain small amounts of detrital chromian spinels. Similar grains have also been proven in sandstones of the Givetian Stiege beds (East Harz nappe). These sandstones are derived from the area of the Mid German Crystalline Rise, which is commonly interpreted as the source area of the Rhenohercynian greywackes. Microprobe analyses have revealed mainly a picotite composition. Presumable source rocks were chiefly Alpine-type peridotites. Due to the onset of spinel sedimentation in Givetian times, these peridotites must be at least partly of pre-Givetian age, and are assumed to be linked to Cadomian subduction. Potential source rocks are not exposed in the present outcrops of the Mid German Crystalline Rise nor in the Rhenohercynian zone or the Northern Phyllite zone, which implies that the presumed mafic to ultramafic lithologies were completely eroded and/or downfaulted during later stages of the Variscan orogeny.

Contrary to a previously published view, evidence is given to show that the Galway Granite is entirely later than both the quartzandesine migmatization and the potash-felspar migmatization in Connemara, and that the Oughterard Granite is probably earlier than the Galway Granite, not later. There is also strong evidence against regarding the foliated marginal granite of the north and north-east border of the Galway Granite as being different in origin from the marginal granite often found in the southern, western, and north-western borders. These results agree with the radio-chemical date of 365 m.y. determined for part of the Galway Granite.

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.

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.

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.

This paper presents three different age domains, obtained by electron microprobe monazite dating, for granulitic gneisses collected from the Shillong-Meghalaya Gneissic Complex in Sonapahar, NE India, which contain radioactive materials, e.g. thorium (3.32–7.20 wt %), uranium (0.133–1.172 wt %) and lead (0.101–0.513 wt %). The microprobe analyses of monazite grains in the rock samples show that the monazites have three different ages ranging from Mesoproterozoic to Neoproterozoic. The oldest age (1571 ± 22 Ma) represents a peak metamorphic event, the youngest dominant age indicates the Pan-African tectonic event (478 ± 7 Ma) and the intermediate age marks the Grenvillian orogeny (1034 ± 91 Ma) or may be a mixing artefact; these ages are located at the cores, rims and intermediate parts of the monazite grains, respectively. The equilibrium mineral phases calculated for the granulitic gneisses from Sonapahar lie in a P–T range from 5.9 kbar/754 °C to 8.3 kbar/829 °C in the NCKFMASH system. Plotting the P–T conditions of the granulitic gneisses reveals a clockwise P–T path. Two major metamorphic events are observed in Sonapahar. The M1 metamorphic stage is represented by peak mineral assemblages of prograde garnet-forming reactions (8.2 kbar/∼713 °C) during Mesoproterozoic time (1571 ± 22 Ma). The M2 metamorphic stage featured decompression (3.9 kbar/∼701 °C) in which garnet–sillimanite broke down to form cordierite along an isothermal decompression path during the Pan-African tectonic event (478 ± 7 Ma).

John Macculloch, who was the first geologist to describe the Island of Rum, was so perplexed by the geological relations of the lavas of this island, that he wrote— “It is fruitless to accumulate conjectures, but it is not useless to confess ignorance, since it will point out to other travellers the blanks to be filled, and the errors to be corrected; while I may state in the words of St. Augustin my conviction that in this science also ‘Melius est dubitare de occultis quam litigare de incertis’. [It is better to doubt about mysteries than to dispute about uncertainties.]” (Macculloch, 1819, i, 497.) In spite of this self-imposed limitation Macculloch quite correctly compared the “stratified traps” of Rum with those of Skye and Canna, but otherwise he did little towards the description of these rocks.

The well-exposed marine Eocene units from southwestern Patagonia, Argentina, contain useful information for reconstructing regional climate and oceanographic patterns in an area adjacent to the Drake Passage. The aim of this paper is to integrate dinoflagellate cyst data from three sections of the southwestern Austral Basin (Río Turbio Formation) to propose a zonation scheme, which can be applied to other southwestern Atlantic Ocean sites. Assemblages of organic walled dinoflagellate cysts have been analysed in different cropping-out sections and cores, showing the high potential of this fossil group as biostratigraphic markers. Comparison of dinoflagellate cyst events of the upper member of the Río Turbio Formation with calibrated biostratigraphic ranges in the Palaeogene South Pacific Ocean allowed us to date and correlate these sedimentary sections. The resulting zonation consists of four dinoflagellate cyst zones labelled RTF 1 to RTF 4, between the middle Lutetian and late Priabonian. As a final point, we applied dinoflagellate cyst species with importance as palaeoenvironmental markers to assess long-term climatic and oceanographic evolution for the area. This study shows that the endemic–Antarctic dinoflagellate cyst assemblage is dominant during the middle to late Eocene (RTF 1 to RTF 3), while a significant replacement of these taxa by cosmopolitan species characterizes the upper part of the upper member of the Río Turbio Formation (RTF 4). This turnover seems to be a consequence of changes in the ocean circulation patterns forced by deepening of the southern Atlantic gateways (the Drake Passage and the Tasman Gateway).

Trepostome bryozoan Dianulites borealis Astrova, 1965, the earliest known member of this genus, has been identified from the Early Ordovician of Severnaya Zemlya, Arctic Russia. This species developed hemispherical colonies which indicate that it lived on a relatively soft substrate with moderately low rates of sedimentation and erosion. The new record from Severnaya Zemlya expands the palaeogeographical distribution of Dianulites, known before from the Early Ordovician of Novaya Zemlya, Arctic Russia.

Geometry of the boundary of the serpentine in the south-east Lizard indicates that it is a sheet. The serpentine sheet rests on hornblendic gneisses and their migmatized equivalents; the upper part of this basement represents a thrust-sole in which bodies torn from the base of the serpentine are enclosed. Coastal erosion of rocks beneath the serpentine tends to marginal collapse of the unsupported sheet, so that slipped masses may conceal its base.

Conventional K—Ar age determinations are frequently discrepant. A major factor is the failure of rocks to conform to the basic simplifying assumptions made in the total fusion method. Many rocks incorporate initial argon with an isotopic composition different from the present atmosphere and others have not remained closed systems.By careful sampling and the application of isochron geochronometry more reliable and geologically acceptable K-Ar ages can be obtained. K-Ar step heating isochrons from Kenyan Miocene volcanic sanidines are used to illustrate the accumulating evidence for the presence in ancient rocks of initial argon with an isotope ratio unlike that of the modern atmosphere. Single whole rock total fusion K-Ar isochrons from the Olduvai basalt, Tanzania and the Upper basalts of Antrim are presented to illustrate a new version of the K-Ar isochron technique. Special circumstance multiple rock K-Ar isochrons from the Belfast section of the Antrim basalts and from an ignimbrite-ash flow unit in Bed I, Olduvai Gorge, are used in a further discussion of the general applicability and usefulness of K-Ar isochrons.

This preliminary note records two discoveries in the Ross of Mull. Kyanite is considerably more widespread in the Moine rocks than previous investigations have indicated. Where the kyanite-gneiss enters the thermal aureole of the granite, large andalusite paramorphs are formed from kyanite.

Local magnetic anomalies of large magnitude are found over the marginal ultrabasic rocks of the Loch Ailsh intrusion. An intrepretation of these anomalies based on the measured magnetic properties of the pyroxenites shows that they are not reconcilable with a low-angle structure as required by the hypothesis that the intrusion is a stratified laccolite, and suggests that they form a steeply dipping sheet at the syenite-limestone contact. Similar anomalies occur along the southern margin of the Loch Borralan complex, suggesting steeply dipping marginal ultrabasic rocks.

The lower Williamson Shale at Tryon Park, Rochester, New York State is unique in the co-occurrence of Stimulograptus clintonensis (Hall), previously recorded only from the middle Telychian, and Pterospathodus amorphognathoides amorphognathoides Walliser, previously recorded only from the upper Telychian (Cyrtograptus lapworthi Biozone and higher). These two co-occurring fossils are clearly providing contradictory ages for the lower Williamson Shale. The incorporation of chitinozoan data from both the Williamson and Willowvale shales does not support unequivocally either the graptolite- or conodont-derived biostratigraphy and thus the age of the lower Williamson Shale remains problematical.

Mr. Damon of Weymouth having recently received a third consignment of fossil fishes and Fish-remains from the Devonian Rocks of Canada, an interesting selection has been made for the Edinburgh Museum, and I am thus enabled to contribute some additional notes regarding the palæozoic ichthyology of this region. The specimens were, as before, collected by Mr. Jex.

Lower Palaeozoic rocks in the Langkawi Islands have been subject to three generations of deformation. In the slightly dynamo-meta-morph slates in the south-east two generations of cleavage folding have been developed with a N.N.W. trend. The first resulted in a recumbent folding with a subhorizontal slaty cleavage, whereas during the second generation the slaty cleavage was deformed in open folds and a crenulation cleavage developed in the steep limbs. The two deformations were probably not formed at exactly the same time, but seem to be related with each other. Boudinage of granite sills was contemporaneous with the development of the slaty cleavage.

In the unmetamorphosed northern part of the area cross-folding is found. Flexure folds with a N.W. trend are superimposed on folds with a N.N.E. trend. In the Upper Palaeozoic sediments such deformations are missing. The Permian and Carboniferous strata show only a slight warping around the granite batholith which was intruded during Jurassic time (Pacific orogeny). A similar warping is found in the large low-angle overthrust, in which Silurian was thrust over Permo-Carboniferous. Consequently this thrust plane is dated as pre-granitic and post Permo-Carboniferous. Contact metamorphism by the granite intrusion has resulted in hornfelses in the Permo-Carboniferous sequence and in the development of oriented minerals, mainly clinozoisite, in the Ordovician-Silurian slates. Knick zones and intense jointing parallel with the mineral orientation (third generation structures) are also a result of the granite intrusion.

The first two generations of folding, which are not present in the Upper Palaeozoic beds, are products of an erogenic phase, “the Langkawi folding phase,” during late Silurian-Devonian time. The lack of Devonian strata in Thailand and the incompleteness of the Devonian sequence in Malaya (recently a few outcrops of probably Middle-Upper Devonian strata are found along the west coast of Malaya) can be an indication that the Langkawi folding phase is not restricted to the Langkawi Islands.