Summary. A distinctive level of bedded, internally laminated, deep-sea cherts in the area west of Città di Castello, central Apennins, has been studied. These cherts form part of the Lower Miocene Monte Santa Maria Tiberina Formation, and belong to the Tuscan sequence, consisting of pelagic and turbidic sediments. The sediment is enriched in diatoms and Radiolaria. The diatoms provided silica as well as barium, now present as submicroscopical baryte concretions. Synsedimentary volcanism could have provided silica as well, through calcitization of volcanic fragments within the sediment. Since the laminations display early diagenetic microdeformations,. it can be concluded that the cherts themselves are an early diagenetic feature.

16 samples of Ordovician basic volcanic rocks of the South Connemara Group, which abut the southern side of the metamorphic rocks of the Connemara massif in western Ireland, have been analysed for both major and trace elements. Although subject to low grade regional metamorphism and subsequently hornfelsed by the Galway Granite (400 Ma), their immobile element contents do not appear to be significantly disturbed. These elements characterise the metabasites of the South Connemara Group as ocean floor basalts having their origins in a marginal basin. The Skird Rocks Fault, separating the South Connemara Group from high grade metamorphic rocks of the Connemara massif, is consequently regarded as the northern margin of the vestiges of the lapetus Ocean which can be traced into, and along, the Southern Uplands Fault.

Ammonites and palynology are described at the Portland-Purbeck junction in the Weald. A major disconformity exists between glaucolithus Zone Portland Beds and the overlying basal Purbeck facies, the basal Purbeck Beds of the Weald are correlated with the Middle Purbeck strata of Dorset. The Cinder Bed of Dorset and Wiltshire is described as one of several marine incursions entering Wessex from further south in the Anglo-Paris basin, not from the Spilsby basin. The use of Cinder Bed as a convenient Jurassic-Cretaceous (Portlandian-Ryazanian) boundary is critically reviewed, as is the placing of the base of the Berriasian Stage in the type Purbeck section. The rival biostratigrahic schemes based on ostracods and palynology are discussed and the discrepancies between the two schemes in southern England are examined.

Summary. The kimberlite pipe at De Beers Mine, Kimberley is a complex, multiple structure. Three concordant argon-40/argon-39 age spectra have been obtained from samples from the 720 m level in the East Peripheral kimberlite. Each spectrum is dominated by a major plateau-feature between 84 and 89 Ma and none shows significant evidence of either excess argon or argon loss discrepancy. The available evidence suggests that the K-Ar age of normal magmatic emplacement-cooling of the East Peripheral kimberlite at De Beers Mine was close to 86 ± 2 Ma.

The Strontian Granodiorite, a ‘Newer Granite’ emplaced late in the Caledonian orogenic cycle, has an aureole which is strongly asymmetrical: the metamorphic zones are broader to the east of the intrusion than to the west. The asymmetry is attributed to a gradient in the background, regional temperatures. The muscovite-out isograd, marking completion of dehydration of muscovite + quartz to sillimanite + K feldspar (estimated temperature 645 °C), lies within 2 km of the contact on the west, whereas the cordierite isograd, due to the onset of dehydration of biotite+sillimanite+quartz (estimated temperature 690 °C) is at least 2.5 km from the contact on the east. This temperature interval of 45 °C, which is rather insensitive to small errors in the estimated pressure (preferred value 4.1 kbar), is used in a simple geometrical treatment to estimate the regional gradient in the plane of present exposure: approximately 5 °C/km in a direction 30° S of E. Because the intrusion does not appear to have been tilted, this result is regarded as an estimate of the horizontal component of the temperature gradient on the west flank of a regional thermal dome, inherited from the regional metamorphic climax and decaying on a timescale which is suggested, by radiometric data in the literature, to be ˜ 10 Ma. A tectonic origin for the perturbed regional temperature distribution (uplift of hot rocks in the east relative to colder rocks further west) is suggested by the metamorphic petrology of the region, and supported by literature data on structural movements, notably of the Sgurr Beag Slide.

Summary. Microsolena thurmanni Koby and M. foliosa Roniewicz (Scleractinia) are important rock-formers in the Upper Oxfordian Stage of Upware and, to a lesser extent, Yorkshire.

Late Precambrian polymict conglomerates are described from Bellsund, western Spitsbergen, where they are intimately associated with authentic glacigenic sediments. They display normal, compound and reverse grading. Spectacular flame, injection and incipient rip-up structures are developed at the base of some beds. The conglomerates were initially deposited either as foreset debris beneath a wet-based glacier, or on the subaqueous part of a glaciomarine outwash delta, and were subsequently redeposited from mass gravity flows initiated by slumping on the unstable glacial detritus slope. An informal stratigraphic nomenclature is proposed for the Kapp Martin area to the north of Bellsund and the Kapp Lyell area to the south.

The surface geologic map of the Wadi El Rayan area, based on the study of aerial photographs and field observations, is correlated with seismic structural two-way time maps for the basement, the top of Cenomanian and the base of Tertiary horizons. Major structural features comprise a northeasterly faulted plunging anticlinal stretch traversing the NW-SE Wadi El Rayan depression. Three sets (ENE-WSW, NW-SE and NE-SW) of faults dissect the area. Folding movement was still active at least to the end of Middle Eocene epoch. ENE-WSW faults affecting the basement, and traced in higher levels, have the same trend as the fold axes. It is thus possible that compressional features appearing on the surface and subsurface horizons are in part due to thrusting in deeper levels that took place parallel to folding.

Summary. A m´lange on Fredriksen Island, South Orkney Islands, is part of a Mesozoic subduction- accretion complex which formed along the western, Pacific side of Gondwana. It consists of a chaotic arrangement of irregular sized blocks, up to 8 m across, of basic pillow lava, chert, felsite and epiclastic sandstone in a pervasively sheared cataclastic matrix. Inclusions are typically lozenge-shaped and are characteristic of a tectonic m´lange. As the m´lange incorporates both possible ocean floor material that was accreted on to the continental margin and inner slope basin sediments it probably formed beneath the trench-slope basin along a shear zone at a high level in the subduction complex.

Comparison is made between the semipelitic and psammitic schists of the Morar and Glenfinnan Division in their type areas and the succession in the Fannich district of Northern Ross-shire. The tentative lithological correlation of the Morar Pelite with the Sgurr Mor Pelite is confirmed, while the Meall an t-Sithe Pelite and the semipelites of the Glenfinnan Division likewise have a similar geochemistry. In establishing these similarities, ratios involving Sr, Nb, Y, Zr and P2O5 have been found to be most useful, particularly Sr/Y. Other ratios (Ca/Y, K/Rb, K2O/(Na2O+CaO) and K/Ba) can also yield useful information regarding correlation and sedimentary history. Sr/Y decreases stratigraphically upwards in these successions and also towards the north east, suggesting a palaeogeography for the Morar Division involving increasing remoteness from the source area with time and in a northeasterly direction.

Summary. The large number of species assigned to Triarthrus Green are here allocated to three genera - ten species to a revised Triarthrus Green (late Caradoc-Ashgill), thirteen species to a revised Porterfieldia Cooper (Arenig-Llandeilo), and five species to Bienvillia Clark (Tremadoc-Arenig). Triarthrus lacks an anterior border furrow on the cranidium; this furrow is confined to the yoked cheeks. Both Porterfieldia and Bienvillia have an anterior border furrow on the cranidium; these genera are distinguished primarily on the length of the preglabellar field.

Summary. The available data on radiometric dating of Riphean and Vendian deposits in the European part of the U.S.S.R. enabled us to establish the age of geochronological boundaries. The Riphean lower boundary was adopted as 1650 ± 50 Ma, the Vendian lower boundary as 650 ± 10 Ma, and the Cambrian lower boundary as 590 ± 10 Ma, making the total length of the Riphean about 1000 Ma and that of the Vendian about 60 Ma. This paper suggests a draft of the geochronological scale of the Late Precambrian.

Sedimentary and volcanic rocks, now unrepresented in surface exposure, occur as xenoliths in the kimberlite of the Koidu District of eastern Sierra Leone. The sedimentary rocks prove, on micropalaeontological evidence, to have Lower Palaeozoic stratigraphic age. An eastern extension of the Ordovician/Silurian marine transgression on to the Leo Uplift of the West African Craton of some 200 km is indicated. The volcanic rocks may belong to the same cycle of surface rock generation or relate to the younger, widespread, Triassic magmatic event.

This work proposes a mechanism for the formation of the characteristic ‘double cone’ cracking and ‘bulb of percussion with bulbar scar’ cracking caused by the artificial fracture of flint. The double cone fracture is observed as a large, small apex angle, cone that is truncated by a smaller cone of increased apex angle. The author considers that the large narrow apex angle truncated cone of the fracture is caused by Hertzian loading of the flint on impact and the upper complete cone is formed as a result of the unloading of the stressed flint. This mechanism has been deduced from work carried out in the fractography of glass by others and from some restricted laboratory experiments.

Summary. The Alas Formation (shelf limestones) of Sumatra is reinterpreted to be of late Visean age, on the basis of conodonts and brachiopods, rather than of Permian age as previously thought. It is, therefore, the oldest dated formation in Sumatra. The Alas Formation probably underlies or is equivalent to the lower part of the Kluet Formation within the Tapanuli Group.