In three assemblages of widely differing paragenesis, sillirnanite and mullite have been found in apparently stable coexistence. This is interpreted as evidence for the presence of a miscibility gap between the two phases. A fourth occurrence, remini-scent of the early hydrothermal syntheses, is metastable.

New stratigraphic data for the Ordovician ectoproct Diplotrypa cf. D. westoni in the Shan Plateau region of Central Burma indicates correlation with the Trentonian of New York State.

Silurian fossils have been identified from Oscar II Land, western Spitsbergen. They are the first Silurian fossils recorded from Spitsbergen, and throw new light on regional correlations and the dating of Palaeozoic orogenic events in the region.

A collection of basaltic rocks has been dredged from part of the Blackstones igneous centre, a major offshore intrusion situated about 50 km SW of Mull. The basalts are mainly olivine tholeiites and are closely similar to transitional basalts found on the Inner Hebrides. The mean of four concordant K—Ar dates obtained from the lavas indicates an age of 57.1 (± 0.9) Ma. The Blackstones complex thus appears to be coeval with other Tertiary centres of the area.

Within the basal Coal Measures between Ystradgynlais and Abercraf a number of liquefaction layers are seen displaying ball and pillow structures. These layers consist of balled-up, ovoid masses of sandstone some 0.25–0.3 m thick and 0.5–0.7 m across. It is considered that they were formed by loading, resulting from the lique-faction of underlying silts, produced by the passage of earthquake shock waves associated with the main fault zone of the Swansea Valley Disturbance. Elsewhere in South Wales, horizons displaying load and slump structures in rocks of Upper Palaeozoic age may have resulted from seismic shock waves caused by contemporary movements along major Variscan fractures.

The internal variations in the discordance of an inhomogenous zircon population from a bedded quartzite within a c. 2700 Ma old gneiss have been studied. Varying degrees of response to events in a common multi-episodic, post-depositional history are reflected in the uranium and lead isotopic systems of size and magnetic fractions.

A minimum 207Pb/206Pb age for non-magnetic zircons is 2840 Ma with 206Pb/238U and 207Pb/235U data for the three size fractions raising the possibility of an age of at least 3250 Ma. This is interpreted as a minimum age for crustal material that was in existence in the region before the formation of the Lewisian complex. Some of the slightly magnetic zircons also have a pre-2700 Ma radiogenic lead component.

The Carrai Granodiorite is an intrusive magmatic pluton with steeply dipping margins surrounded by a well-developed contact metamorphic aureole. Emplacement of the body was accompanied by little distortion of neighbouring rocks and involved vertical displacement of pre-existing material. Scarcity of country rock blocks, and the presence of numerous dioritic xenoliths indicate that stoping was unimportant, and the pluton was accommodated in the upper crust by vertical uplift of earlier rocks (‘block elevation’). A close relationship existed between faulting and granodiorite emplacement. Deep shears possibly account for the generation of the linear zone of plutons in which the Granodiorite is located.

The formation of a rift valley and its zigzag fault patterns is simulated by a model experiment. A stress analysis of the model shows how the rift valley and its fault pattern are formed on two oppositely inclined boundaries in the stress field.

Quartz nodules and geodes, known as Bristol Diamonds, occur in the Triassic Dolomitic Conglomerate of the Bristol district of England. They are composed of either, megaquartz, milky in the outer part and clear towards the centre, or fibrous quartz, chalcedony and lutecite. Much of the quartz, particularly in the outer parts, is full of anhydrite inclusions which are relics of larger lath-shaped anhydrite crystals. The Bristol Diamonds formed by silica replacement of anhydrite nodules, with replacement proceeding from the outside inwards. In many cases anhydrite solution was faster than silica replacement, so that a central void developed into which grew crystals with fine terminations. The anhydrite formed by precipitation of sulphate from hypersaline sediment-porewaters, probably in a marginal playa situation.

Charges of Fe-tremolite, sulphur and water sealed in gold capsules and run at 600°C and 1 kb confining pressure for one month yielded talc, anhydrite, pyrite and quartz as principal mineral phases. It is concluded that in a S-rich environment talc is stabilized rather than diopside by the strong preference of Ca to form anhydrite.