Modes in the frequency of distribution of fission track ages obtained from detrital zircon grains may prove characteristic of individual sandstone bodies, supporting the identification of the sources from which a particular flow of sedimentary detritus was derived and thus allowing new inferences to be made concerning palaeogeography. A computer program has been written and used to identify modes in the zircon fission track age distribution within two Lower Cretaceous sandstone samples from the Weald of southern England. Pronounced modes appear in one rock around 119 Ma, 160 Ma, 243 Ma and 309 Ma and in the other around 141 Ma, 175 Ma, 257 to 277 Ma and 394 to 453 Ma. The geological implications of these quite dissimilar zircon age spectra are discussed. It is concluded that they support the palaeogeographical models of Allen (1981) and indicate that the provenance of the first sample, from the Top Ashdown Sandstone member at Dallington in East Sussex, was almost entirely southerly, while that of the second, from the Netherside Sand member at Northchapel in West Sussex, was more varied, but predominantly westerly and northerly.

In the Miocene fluvial system of the Huesca area, in the Ebro Basin, northern Spain, rivers radiated outwards, to the south and west, from a small sector of the northern margin of the basin. The deposits of the system extend about 60 km radially from this sector and then pass into calcareous and gypsiferous deposits.

The magnetostratigraphy of two logged sections, 1 km apart, within this system consists of an upper zone of normal polarity and a lower zone of reversed polarity. The lithostratigraphy and magnetostratigraphy are parallel.

The sands and silts are dominated by angular quartz, intraformational clay lithograins and calcite lithograins. They are mainly pale yellow brown to dusky yellow, and magnetic tests indicate that the magnetization is carried dominantly by ferric oxyhydroxides (haematite and gôethite). The higher temperature Natural Remanent Magnetization is probably due to detrital haematite which would have been partially aligned during fluvial deposition. Post-depositional modification (PDRM) may have occurred during dewatering.

Haematite pseudomorphing pyrite framboids indicates that early reducing conditions were succeeded by a more oxidizing regime which produced secondary magnetizations associated with fine-grained haematite and goethite.

Complete polarity zones are not delineated, but the thicknesses present are not excessive compared with other continental Miocene deposits. The average palaeolatitude of 22° is lower than would be expected for the Miocene of northern Spain, probably due to incomplete averaging of secular variations and other sources of error including possible ‘inclination error’.

Reconnaissance geological mapping (1962–75) followed by detailed geological investigations (1979–80) in the Ellsworth Mountains of west Antarctica have established the existence of extensive Middle and Late Cambrian strata. Forms tentatively referred to Archaeocyatha have been examined by F.D. and A.R., who concluded that, despite the commonly held opinion that the phylum became extinct at the boundary of the Lower and Middle Cambrian, the Ellsworth Mountains' forms represented Irregularian Archaeocyatha which survived in protected niches into the Late Cambrian. The age of the fauna containing the archaeocyaths is firmly dated by abundant trilobites including species of Homagnostus, Pseudagnostus, Kormagnostella, Erixanium and Onchopeltis.

This petrographic and chemical study of the Hercynian granitoids of the Central Palaeozoic Massif of Morocco covers the Zaër, Ment, Oulmès, and Moulay Bouazza plutons. These plutons are formed of biotite or two-mica, quartz-rich granodiorites and monzogranites containing reddish-brown, inclusion-rich biotites as the only essential mafic mineral; zoned plagioclase; and perthitic K-feldspar. The modal contents of micas and K-feldspar are highly variable. The granitoids are generally medium to coarse grained, massive; however foliated varieties are also commonly found, particularly at the contact of the' plutons with sedimentary rocks.

The strongly peraluminous character of the granitoids is shown by high normative corundum and high molar Al2O3/(CaO + Na2O + K2O) ratio, and is reflected by the occasional presence of aluminosilicates.

The mineralogical and chemical characteristics of the granitoids are similar to those of the S-type granites, and were inherited from the crustal source of the granitic magmas which are thought to have been generated by partial equilibrium fusion of the sandy argillaceous sediments of the Massif. The heat source for the fusion might have been provided by intrusion of mantle-derived material.

Biplanispira Umbgrove is closely related to Pellatispira Boussac, from which it probably arose by the subdivision of the median chambers by the rapidly expanding marginal crest and the development of planispirally arranged secondary chambers on both sides of the peripheral flange. The genus appears to be polyphyletic, its species having been derived from different representatives of Pellatispira. Illustrated records of Biplanispira are confined to the region between eastern India and Eua, Tonga, and the genus appears to be restricted to the middle and upper parts of the Upper Eocene. In the Upper Eocene of the Garo Hills, eastern India, it is represented by B. hoffmeisteri (Whipple) and in the Andaman Islands by B. mirabilis (Umbgrove). This is the first record of the genus from mainland India.

Systematic descriptions of specimens collected from Pachchham ‘Island’, Kachchh, Western India, belonging to the genera Micromphalites Buckman and Gracilisphinctes Buckman are given. Their affinities with the different forms belonging to the above genera are discussed and described as Micromphalites aff. hourcqui Collignon and Gracilisphinctes cf. arkelli Collignon respectively. The distribution of these two genera in other regions is also briefly discussed.

Assemblages with muscovite + quartz show a regular increase in grade from the Chlorite Zone at the base of the Lycian Nappe Complex to the Garnet Zone within the structurally underlying Menderes Massif. Biotite enters before garnet, which precedes oligoclase. Garnet-bearing assemblages in pelites are compared with those in re-equilibrated quartzofeldspathic gneisses, where garnet is unusually calcic (in one case approaching Gross50 Alm50). Local retrograde effects are noted but no evidence is found for a polymetamorphic record in the mineral compositions. Garnet zoning, with Mn decreasing outwards, is interpreted as growth zoning; Ca decreases outwards in pelite garnets but shows the reverse effect in the gneisses. Chloritoid is common but rarely coexists with biotite, and garnet + chlorite + paragonite is found rather than chloritoid + albite. Garnet-biotite geothermometry, corrected for the effect of Ca in garnets with up to 29 mole % grossular, indicates temperatures of 530±5O°C near the garnet isograd. As in other areas, an attempt at muscovite-paragonite geothermometry gives an anomalous result. Metamorphic pressure isconsidered in the light of (i) Mn/Fe partition between garnet and biotite, (ii) Ca content of garnet coexisting with plagioclase + muscovite + biotite, (iii) Na in actinolite coexisting with albite + chlorite + magnetite, and (iv) celadonite content of muscovite which, however, shows variation due to disequilibrium within a specimen and does not provide an accurate geobarometer. Comparisons with published studies indicate a strong similarity to the Barrovian Dalradian of Scotland and lead to a tentative pressure estimate of approximately 5 kbar.

An understanding of the response of migmatites to deformation is crucial to an interpretation of their structures, and in anatectic and intrusive migmatite terrains due consideration must be given to the modification of deformation processes imposed by melts. In partially molten systems containing more than 30% melt the classical theories of fold formation are inapplicable; the folds produced are of the ‘viscous fold’ type. Their geometry is unpredictable and may mimic structures due to refolding; this is particularly true at very high degrees of melting where flow of melt carrying rafts of solids begins. Failure to distinguish ‘viscous folds’ from the products of refolding will lead to errors in interpreting the structural and metamorphic history of an area, and to consequent misinterpretation of the true structural relations between geometrically complex high-grade and more regularly deformed low-grade areas.

The colours of conodont elements recovered from Silurian limestones in the Oslo region, Norway, range from brown to grey. Samples from the south of the region contain black and grey conodonts, indicative of high palaeotemperatures. There is a general decrease in thermal metamorphism towards the north, with the lowest palaeotemperatures recorded from Toten, Ringsaker and parts of the Ringerike district. There is a close correlation between thermal metamorphism and the proximity of Permian intrusions.

Upward-thinning stellate and polygonal carbonate structures are described and compared to modern and ancient stromatolites. Although tufted microbial mats are common in modern settings they have rarely been described from ancient rocks owing to their poor preservation potential. The preservation of these from the Stoer Group is due to early replacement by calcite before their original tufted relief could be obliterated by compaction. Associated limestones with some similar features are interpreted as flat to mamillated microbial mats.

Two new graptolite species from the Ordovician of Bolivia are described. These species, Maeandrograptus bolivianus n.sp. and Gymnograptus floweri n.sp., were probably contemporaneous with congeners from the Didymograptus hirundo Zone (Lower Ordovician) of Sweden and the lower half of the Glyptograptus teretiusculus Zone (Middle Ordovician) of Baltoscandia, respectively. This is the first report of these genera in the Western Hemisphere.

The assignment of a new species to Maeandrograptus necessitated a review and revision of that genus. As revised, it consists of M. schmalenseei Moberg, Didymograptus mobergi Törnquist, and M. bolivianus n.sp. Cymatograptus undulatus is a possible ancestor for this group of species, and an assignment of Maeandrograptus to the Sinograptidae is favoured.