This work describes the Wenlock sedimentary sequences south of Killary Harbour where the fullest successions in north-west Galway are exposed; much of the Upper Silurian in the east (Joyces Country) has been removed by erosion.

The Wenlock beds (the Upper Owenduff and Killary Harbour Groups) rest on shallow marine and continental sediments (the Lower Owenduff Group) of Upper Llandovery (C5–6) age. Conglomerates near the base of the Wenlock are followed by 1,500 m of sandstones, which are mostly turbidites and which contain Middle Wenlock graptolites. These basin deposits are succeeded by a transitional sequence of rise, slope and shelf clastics, also of Middle Wenlock age. The youngest Silurian beds exposed are 800 m of red lagoonal deposits with Lingula.

During Wenlock times, the sediment supply to north-west Galway was mainly from the north and north-west. This observation fits well with the regional picture which places Galway near the north-west margin of a Silurian basin which extended eastwards across Ireland.

A lateral cryptic variation is recognized in layered ultramafic rocks of the Hartley Complex, the largest of the four lopoliths that constitute the Great Dyke. Over a lateral distance of some 120 km, the En content of orthopyroxene from thick, continuous bronzitite layers is up to 6% less at the southern extremity of the Complex than in the central area. This is interpreted to be a result of more rapidly falling temperatures in a thinner body of basic magma that gave rise to a condensed sequence in marginal areas of the lopolith compared to the central area.

Following a well-marked period of addition of parental basic magma which appears to have had the incidental effect of linking up the four lopoliths, this compositional relationship in composition is reversed, i.e. the orthopyroxene from the base of an upper bronzitite layer of the southern marginal area of the Hartley Complex is more magnesian than that from the equivalent level in the central area. This is interpreted to arise from the proportion of fresh added magma to previously emplaced and partly crystallized magma being relatively greater in the marginal area than in the central area of the lopolith.

Campanile nigeriense sp. nov. is described and figured from the Palaeocene Ewekoro Formation of Western Nigeria. Its juvenile whorls characteristically have four smooth and broad spiral ribs while adult whorls are completely smooth. Vertical ornamentations are lacking. This second record of Campanile from West African Palaeocene strata suggests that the genus may be a stratigraphically useful index fossil in West Africa.

The negative P-T slope of the wet melting curve of granite sets limits on the degree of upward movement of granitic magma formed at particular partial pressures of water vapour. Wet granite magma cannot rise very far from its place of formation, and only dry granite magma can be erupted as a liquid. This observation leads to a better understanding of the granitic structure of orogenic belts, and explains some of the apparently paradoxical aspects of granites. Other wet magmas would also not be expected to be erupted as liquids.

An area is described in which the main rock type is a variable dioritic rock, thought to have been formed by the expulsion of the residual acidic liquid from a largely crystalline quartz-diorite magma. It contains xenoliths of pyroxenite and appinite. The latter consist largely of hornblende, with some diopside, quartz, orthoclase microperthite and oligoclase. They are considered to be the reaction products of the outer margin of a magma and the adjacent calcareous country rock.

Small trachyte and phonolite bodies are shown as eroded plugs on published geological maps of part of north-eastern Nigeria. Field relationships at two such ‘plugs’ strongly suggest them to be extrusive in origin, formed of an earlier tholoid-building phase, followed by extrusion of a spine (plug dome) of very viscous lava, now forming the central peak at each locality. Petrographic data show that the tholoid and spine-forming lavas are phonolites of contrasted composition. Eruption of salic lavas from scattered centres appears to have occurred intermittently between mid-Tertiary and Pleistocene times.

Jointing in some ‘ironstone’ intraclasts in a sandstone from the Sydney Basin, New South Wales shows that the joints were developed prior to contemporaneous erosion. A number of other features observed in the Sydney Basin sequence support this conclusion and suggest that an anisotropic horizontal stress field developed in the sediments very soon after their deposition.

Non-stratified, poorly-sorted rhyolitic ash deposits previously described as morainic and mudflow deposits are reinterpreted as ignimbrites emplaced in the topographically lower parts of the Santiago basin by pyroclastic flows. These flows probably originated from sources high in the Andes, and swept down the deep Maipo valley to spread out over the sediments filling the basin. An ignimbrite with a zone of dense welding but otherwise of similar character to the non-welded ashes of the basin occurs in one of the Andean valleys; and peculiar ‘pipe’ structures in the ashes of the basin support a pyroclastic flow origin.

Further study of the nature and origin of these rocks may lead to a better understanding of the structural evolution of the area.

A second specimen of Osculocystis confirms that the genus occurs in the Upper Llandovery (Purple Shales) near Buildwas, Shropshire and adds information on morphology. The subvective system consists of a single long brachiole; the stem lacks a root structure. The mouth, gonopore and hydropore are described and the three pectinirhombs B2:IL2, L2:R1 and L4:R3 are confirmed.

Transverse sand bodies of a new type from the continental shelf are commonly 2m high, 500m long and crescentic in plan view. They are believed to be transported at the present day by weak tidal currents (approximately 1 knot peak velocity near the surface) associated with wave induced oscillatory water movements of similar strength, rather than being formed near the shores at times of lower sea level.

Alkaline microgranites and granite, containing aegirine, riebeckite and astrophyllite, from north-west Pakistan, are briefly described, and tentatively correlated with other alkaline rocks in the region.