Two Ordovician graptolite assemblages are recognised and described for the first time in the allochthonous siliceous assemblage or succession forming the Guayacan Group of central Sonora in northwestern Mexico. A Middle Ordovician assemblage referable to the Nemagraptus gracilis-Climacograptus wilsoni zonal interval occurs in the upper siliceous shale of unit 1 of the Guayacan Group and an Upper Ordovician assemblage representative of the Dicellograptus ornatus Zone of the Pacific faunal province has been collected from shaly partings in the bedded radiolarian chert constituting unit 2. The stratigraphical make-up of the siliceous assemblage bears a striking similarity to the better known—and correlative—Lower Palaeozoic siliceous succession of central and northern Nevada, giving credence to the hypothesis that the Palaeozoic siliceous assemblage in northwestern Mexico was originally the extension of the Nevadan assemblage into California, which has been transposed to its present position along a left-lateral megashear of the magnitude of at least 1000 km.

A review of the proximal development of the spinose species remaining in the form genus Climacograptus Hall has led to the proposal to restrict the genus to Climacograptus bicornis (Hall), its type species, and to two other septate species of early Middle Ordovician age (Llandeilo-early Caradoc) with a primitive type of proximal-end development. The genus Euclimacograptus, with Climacograptus hastatus T. S. Hall as the type species, is proposed for spinose Upper Ordovician climacograptids with an advanced proximal-end development. The genus Ensigraptus, with Climacograptus caudatus Lapworth as the type species, is also proposed for species homeomorphic with those included in Normalograptus Legrand but with a less advanced proximal-end development. Five species are described.

The stratigraphy, classification and correlation of the marine strata in the Dinantian (Lower Carboniferous) succession of central Scotland are discussed. Correlations of eight principal marine bands in the upper part of the sequence are proposed and four Hosie limestones are recognised in Fife. The marine macrofossils are listed and their vertical and lateral distribution discussed. Biofacies maps of the main marine faunas are presented, which indicate an eastern origin for the marine transgressions and suggest the existence of a river entering the region to the N of Glasgow. Observations are made on the range of host-sediments in which the most commonly occurring genera are found and palaeoecological interpretations are made concerning the main components of the faunas. Some evidence is given to suggest that some elements of the faunas migrated into the region from the E. The palaeogeography is discussed and a correlation is outlined between epifaunal forms at some horizons and areas of less subsidence in the general regional pattern of differential subsidence.

Silurian sediments up to 2500 m thick are exposed in the Pentland Hills, SW of Edinburgh. These sediments, the North Esk Group, are here sub-divided into five well-defined formations: the Reservoir Formation, Deerhope Formation, Cock Rig Formation, Wether Law Linn Formation and Henshaw Formation. The Wether Law Linn Formation is further sub-divided into three members. Based on limited palaeontological evidence, the sediments appear to be late Llandovery (crenulata Biozone) to Wenlock in age. The Silurian sediments represent a regressive sequence, passing from offshore submarine-fan turbidite facies, through shallow marine sediments, with an abundant flora and fauna, possibly a barrier complex, to terrestrial red beds of Old Red Sandstone facies. Changing faunal associations in the shallow marine sediments reflect the availability of different substrates. The regression occurred on the southern margin of the Midland Valley graben.

Air photo interpretation and geochemistry have been used to supplement sparse field data in compiling a reconnaissance geological map of the area around the Lecht. Upper Appin and lower Argyll Group rocks are exposed, the best marker horizons being correlatives of the Appin and Jura Quartzites. Scatter plots, Q mode factor analysis and Pearson correlation coefficients of geochemical data were successfully used in the correlation of the pelite and limestone outcrops. The presence of major recumbent folds is inferred. The area is cut by numerous minor faults which are thought to be related to a major transcurrent fault, the probable north-eastern continuation of the Loch Tay fault, which was active in Lower Old Red Sandstone times.

The Lecht manganiferous ironstone is a seepage-bog ore type deposit derived by weathering of the local Dalradian sequence. Despite intensive leaching, this sequence still shows anomalously high levels of several elements, particularly Mn, Ba and Zn. In addition, stratiform sphalerite and manganiferous garnet are present in Blair Atholl Subgroup limestone and pelite horizons, respectively. Mineralogical and geochemical evidence suggests the presence of Zn–Pb–(Ag)–(?Au) exhalative mineralisation within the upper Appin Group Dalradian of the region, of which the Lecht represents the distal manganiferous expression.

Foliated to massive hornblende and biotite-bearing tonalite, trondhjemite and granodiorite comprise a terrane of batholithic dimensions in southwestern to central Newfoundland. These rocks intrude and include Ordovician ophiolite fragments and metasedimentary rocks of Fleur de Lys type, and are cut by a suite of Silurian gabbro-diorite and norite and Siluro-Devonian (?) granite intrusions.

A U/Pb (zircon, sphene) age of 456 ± 3 Ma (2σ) and a K/Ar (hornblende) age of 455 ± 14 Ma (previously reported) for a representative least-deformed tonalite of the Southwest Brook Complex indicate that it crystallised and cooled in Caradoc time. A less precise U/Pb (zircon) age of 428 ± 41 Ma (2σ) is measured for tonalitic Cape Ray Granite in southern Newfoundland. On discrimination diagrams which use Rb, Nb and Y contents to infer tectonic setting, these rocks fall in the field of volcanic arc granites. The occurrence of zircon cores with average ages of 1430 + 18/–17 and 1541 ± 173 Ma (2σ) also indicate that the magmas formed in part by partial melting of Proterozoic crust, or sediments derived from such crust. It is suggested that the tonalitic magmas were generated during the Taconic Orogeny in an arc: continent collision zone at the ancient margin of eastern North America.

Tonalitic rocks in western Newfoundland broadly correlative in age and chemistry with the batholith include the Burlington Granodiorite and Hungry Mountain Complex, as well as allochthonous slices of foliated tonalite emplaced over Ordovician platform carbonates W of Grand Lake.