In high-grade regionally metamorphosed tectonites three varieties of micro- structures are recognized, namely (1) granoblastic, (2) granoblastic elongate, (3) anastomosing. Relative and absolute grain size, combined with grain boundary shape, provide the basis for their description. This microstructural classification is directly applicable to granulite facies and transitional granulite to amphibolite facies rocks and avoids some of the shortcomings inherent in previous terminologies.

A newly discovered, mainly continental, deformed, Neogene formation – the Raham Conglomerate – records the early existence of the southern part of the Dead Sea Rift. The field relations, the predominance of clasts derived from formations which have been virtually completely eroded, and the presence of pebbles of Precambrian rocks, all attest that a considerable structural relief – possibly exceeding 2 km – already existed in the Middle (?) Miocene. Brackish marine fossils indicate that an ancestral Gulf of Elat (Aqaba) also already existed.

Examination of layered rocks from the Currywongaun-Doughruagh Intrusion, Connemara, Eire, has suggested a possible connexion between adcumulate crystallization and the formation of thin, yet very persistent igneous layering. It is thought that as a result of adcumulate crystallization proceeding under undisturbed conditions near the top of a pile of cumulus crystals, a zone of liquid, supersaturated in those components not required for adcumulate growth, could be generated in the magma just above the cumulate pile. Crystallization from such a supersaturated zone would result in the cumulate phases, inter-directly beneath. The rhythmic deposition is lacking, could by this mechanism build up a sequence of cumulate layers interbedded with fine-scale layers of a non-depositional origin.

Observations on the structure, fabrics, mineral assemblages and distributions of plagioclase compositions from migmatites of the Barousse Massif, Central Pyrenees, are related to the mode of differentiation of leucosome from melanosome. It is concluded that the majority of these migmatites have formed from recrystallization of sedimentary horizons, often accompanied by metamorphic differentiation, although some migmatites appear to have formed from anatexis or magmatic injection.

Basic to intermediate pyroclastic rocks of pre-Albian age are overlain by the Abakaliki shale of Asu River Group in Eastern Nigeria. The shale has been assigned Albian age on the basis of abundant (middle Albian?) ammonites found in it. It was folded (together with the pyroclastics) about a NE–SW trending anticlinal axis during the Santonian time. This new evidence of an early Cretaceous volcanism supports a pre-Albian rifting of the African shield prior to the opening of the Southern Atlantic. The latter event took place (probably in stages) during Albian time (i.e. less than 110 Ma ago), with a widespread marine transgression in West Africa and South America.

Along the length of the Swansea Valley Disturbance, from Clydach (near Swansea) to Hay-on-Wye (Herefordshire), 4 main joint sets are developed. They are NE—SW, NW—SE, N—S and E—W in trend. On the NW and SE sides of the main fault zone only the N—S and E—W sets tend to be developed, whereas within this fault zone only the NE—SW and NW—SE sets are found. It is suggested that the NE—SW and NW—SE sets are shear joints developed at the same time as the main fault zone and the N—S and E—W sets have been developed in response to the release of residual strain energy after the end of the Variscan orogeny.

Dry starch-flour provides a light, suitably cohesive material in which slip structures can be produced. These resemble slickensides and offer some insight into one of the possible processes whereby structures occurring on natural slickensides may be produced. Steps consistently face against the movement direction. They form by the partial disintegration of temporarily coherent lumps dragged along the surface.

Near one of the Younger Granite intrusives of the Jos Plateau is a series of steeply dipping dark and predominantly fine grained rocks. Originally interpreted as argillaceous sediments thermally metamorphosed by the adjacent granite, with development of andalusite, later work established their volcanic origin but did not account for the andalusite. Field relationships and petrography of the rocks suggest they are tuffisites, emplaced by volcanic fluidization processes into part of the fracture system associated with the Younger Granite magmatism. The ‘andalusite’ is topaz, widespread in this province, mainly in the Younger Granite tin veins and greisens, sometimes as an accessory in the granites themselves, but not known from the volcanics — yet abundant in some of these tuffisites. It occurs in well formed crystals, displaying a ‘chiastolite-cross’ arrangement of inclusions, characteristic of andalusite but appearing not to have been previously recorded in topaz. The origin of the topaz must lie either in late-volcanic emanations or in hydrothermal fluids from the mineralizing stage of Younger Granite emplacement.