The present paper deals with sedimentary structures and palaeocurrents of the Siwaliks exposed between the Yamuna and Gola rivers, U.P., India. Typical sedimentary structures observed in the Lower and Middle Siwalik formations are: cross-bedding, rib-and-furrow structure, parting lineation, plane-laminations and worm burrows. Also the Lower and Middle Siwaliks exhibit a typical, cyclic development of sedimentary bed forms and structures characteristic of flood plain deposits. A study of cross-bedding foreset azimuths indicates south-westerly and southerly paleocurrent directions for the Lower and Middle Siwaliks respectively. Distributions of pebble orientations from the Upper Siwalik have significant preferred orientations along both N–S and E–W directions.

Orthograptus obuti sp.nov. and Orthograptus insectiformis Nicholson are shown to exhibit a complex proximal meshwork developed from a much-divided virgella which closely resembles retiolitid clathrial and lacinial networks. The virgellar meshworks tend to enclose the rhabdosome, at least for the first few thecal pairs, and may support a tenuous periderm. This kind of virgellar complexity is contrasted with a newly discovered form of sicular spinosity represented by the species Glyptograptus (Pseudoglyptograptus) tabukensis sp.nov. and G. (P.) rhayaderensis sp.nov

The pattern of crustal warping in northern Spitsbergen as a result of widespread deglaciation is plotted. This is facilitated by the occurrence on ancient strandlines of pumice fragments at 4 major horizons 14C dated at 6500 (A), 6200 (B), 4100 (C) and 2200 years b.p. (D). Trace element analyses indicate an origin for the pumice in the Jan Mayen area. At least 2 pumice horizons are thought to be contemporaneous with eruptions at 6500 and 4100 years b.p.

Two groups of mafic dikes occur within a terrain of metasomatic granitic rocks and quartzofeldspathic gneiss in the central Bighorn Mountains of Wyoming. The younger group consists of dolerite dikes which possess ophitic, subophitic, hypidio morphic-granular and microporphyritic textures. Mineralogically, the dolerites consist primarily of plagioclase (average An 54), augite (average Ca: Mg: Fe = 41: 43: 16) and uralite. The older dikes are metadolerites which possess granoblastic margins that grade into interiors characterized by relict subophitic and locally, porphyriti texture. Dike margins consist of fresh plagioclase and hornblende primarily. Interiors are principally clouded plagioclase (average An 46), augite (average Ca: Mg: Fe = 39: 54: 7) and uralite and/or hornblende. Textural, mineralogic and chemical data indicate that the meta-dolerites were derived from an earlier generation of mafic dikes comparable to the unmeta-morphosed dolerites in the area. The dikes were metamorphosed under low amphibolite facies conditions during the last regional metamorphic event which affected the country rock. During their metamorphism, minimal amounts of water from the country rock facilitated the total recrystallization of the metadolerite margins and the complete or nearly complete replacement of pyroxene by hornblende in the margins. In general, dike interiors underwent no textural changes other than partial destruction of the original subophitic plagioclase–pyroxene relationship as the pyroxene was replaced peripherally by hornblende. This process was accompanied by diffusion of calcium from the plagioclase to form the hornblende, and by diffusion of iron from the augite to cause the clouding of adjacent plagioclase.

The Vesturhorn Intrusion, exposed over 19 km2 of the south-eastern coast of Iceland, comprises two mafic complexes and a central core of epigranites. The latter can be subdivided into a central area with a flat-lying sheet structure, surrounded and separated from the mafic complexes by a more massive belt called the Transitional Epigranites with variable colour index and containing many rounded-to-angular inclusions and net-veined complexes. The consideration of several lines of evidence suggests that the components were emplaced as magmas in the sequence, first the epigranites with a sheet structure and second the basic complexes. The Transitional Epigranites appear to have originated by the remobilization and local hybridization of the early, sheet-structured epigranites. The relatively large volume of remobilized material and an absence of partially melted zones are considered to result from the early epigranites being still partially molten at the time of emplacement of the mafic complexes, together with a ponding of remobilized material beneath the chamber roof. A final intrusive episode occurred with the emplacement of a body of fayalite—hedenbergite epigranite largely into the Transitional Epigranites, probably after the consolidation of the latter.

Misunderstanding exists about the origin of the Himalaya, Indo-Tibetan relationships and the extent and history of Gondwanaland. The Indus Suture Line is a relic of fracture to the mantle but for a period only represented by the faunas of the ‘exotic blocks’ of the Tibetan Himalaya, i.e. Permian—Late Jurassic. Tibet appears originally to have been part of a plate including India, but submerged while India remained continental. Associated with the fracture extending to the mantle represented now by the Indus Suture Line, shallower subparallel fractures developed within which the Gondwana sediments of the Himalaya were preserved. These, together with the salt at the base of the Tethyan marine sequence, facilitated intra-continental orogeny when, much later, India was affected by vigorous sea-floor spreading and plate movement in the NW Indian ocean after it had become attached to Asia.

The northern plate boundary was beyond Tibet, on the N side of the Tarim Basin Block, and along the Tien Shan. The Tien Shan present peculiar features, particularly very deep long intramontane depressions such as Issyk Kul in USSR and Turfan-Hami in China, and their stratigraphy shows persistent mobility. The Tarim Basin Block has moved sinistrally relative to Tibet and in Gondwanaland lay near northern Western Australia. The suggested extent of Gondwanaland explains the present lack of continental crust W of Western Australia, now in Tibet, and the intracontinental origin of the Himalaya is consistent with the absence of recent volcanism in an area of considerable seismicity. The association of Tibet with India in Gondwanaland destroys the effectiveness of arguments against continental drift based upon the extension of Indian stratigraphic sequences across the Himalaya. The hypothesis of an enlarged Gondwanaland is given support by recent Chinese discoveries of terrestrial vertebrate fossils of Gondwanic type near the Tien Shan.

The contents of CaO and Al2O3 in pelites from areas subjected to amphibolite facies metamorphism have been plotted in order to discover the compositional limit of the stability field of the aluminium silicate minerals. Rocks containing kyanite or sillimanite fall within a well-defined field, while rocks plotting outside this field are devoid of aluminium silicate minerals, irrespective of metamorphic grade. With the trace of the curve bounding this field known, the position of the kyanite isograd may be more easily plotted in areas where kyanite or sillimanite are rare.

The history of the study of homological variation in the archaeocyathans is reviewed and some morphological details defined. Homological variability is considered at generic and familial level and a new detailed table of the homological series at generic level is presented.

The mechanical process for producing foliation (banding) in metamorphic rocks, as proposed by Schmidt (1932), is shown to be inadequate. Examples in the literature ascribed to the mechanism are insufficiently supported and the metallurgical analogy for the process is found to be false. A possible restatement of a mechanical process by analogy with particle interaction effects during the laminar flow of suspensions is discussed. Evidence from metamorphic rocks indicates, however, that the modified mechanical process cannot be responsible for common metamorphic layering.

Well-preserved brachiopod faunas collected from four Ordovician horizons range in age from Upper Llanvirn to Lower Caradoc. The generically restricted Upper Llanvirn and Lower Llandeilo assemblages are associated with diagnostic graptolites. In contrast the Upper Llandeilo and Lower Caradoc assemblages are more diverse and correlate well with faunas from the more precisely dated Chrustenice Substage in Bohemia. Two new brachiopod genera Apollonorthis and Cacemia are described.

Glass-breccias and volcanic glass from Marysvale are shown to be welded ash-flow tuffs of rhyolitic composition. They are interpreted as resulting from intermittent volcanic activity.

Thin undeformed tholeiitic plateau lavas and associated diabase dikes occur intermittently along the western margin of the Appalachian mountain system, and are clearly exposed at its northern extremity in northwestern Newfoundland. In Newfoundland there are consistent chemical differences between the diabase dikes and the plateau lavas which indicate that they were derived from different primary magmas. These differences, along with apparent age discrepancies, could be taken as supporting suggestions of several periods of continental rifting, but such an interpretation is not favoured by the present author.

A method for measuring volume change, which involves combining measurements of the strain ratio with the angle between the surface of no finite longitudinal strain and the principal extension direction in a principal plane, has been used to obtain values for the volume change in two groups of deformed rocks in southern Africa.

The source of far-travelled pebbles in the Pleistocene gravels of the lower Axe is investigated. Reference is made to the possible introduction of far-travelled material by glacial meltwater, flowing into the basin of the Axe through a ‘gap’ in the present watershed at Chard. Gravels of the lower Axe are described and compared with gravels of the upper Axe and of neighbouring streams. Far-travelled material is found in almost all of the gravels examined. The source of the material is identified in early Tertiary gravels which occur within the present basins of the rivers in question. A glacial origin for the far-travelled material is rejected.

Lenticular compositional layering and/or rodding in blastomylonitic rocks, in the simplest situations, can be controlled by (i) the presence of more than one mineral in the parent rock and (ii) relative large grain-size of the parent rock. Deformation and recrystallization during non-cataclastic ductile deformation can produce compositional layering, without chemical segregation.

Mammalian remains are reported from a Pleistocene terrace deposit in the lower Derwent Valley near Derby, which is a correlative of the Beeston Terrace of the nearby River Trent. The faunal assemblage is characteristic of the Ipswichian interglacial and compares favourably with previous finds at other Ipswichian sites in southern Britain. The discovery is significant as it provides the strongest evidence so far for a dating of the Beeston Terrace which is critical to the Pleistocene chronology of the region.

The prevalence of low-variance assemblages, the frequency of the buffered association anthophyllite—cordierite—cummingtonite—plagioclase, and the ubiquity of aluminium-rich clots of diaspore incompatible with the ortho-amphibole of the rock suggest that the cordierite—anthophyllite rocks of the Land's End aureole are not the product of metasomatism, but resulted from the thermal metamorphism of pre-existing rock-compositions. The origin of many kyanite-, amphibole- and cordierite-rich bodies by pre-metamorphic alteration is of economic significance in regions where such curious silicate assemblages accompany sulphide deposits.

Comparison of Old Red Sandstone palaeomagnetism for NW Scotland and Norway lead to the hypothesis of a 200–300 km sinistral movement along the Great Glen Fault. The displacement is thought to be of late Caledonian (late Devonian) age. The new palaeogeographic reconstruction of Northern Britain (prior to late Caledonian times) seems to have interesting geological implications.

Forty-seven new K—Ar analyses are reported from 15 mines in the Lake District. Analyses of clay mineral concentrates from vein gouges and altered wallrock support a hypothesis of at least 3 distinct isotopic events. Caledonian ages (388 Ma) are reported from the Coniston Copper deposits, while the extensive mineralization in and around the Vale of Newlands indicates a metasomatic event occurring at around 360 Ma. The ages of the sporadic mineral localities to the E of the area (i.e. Greenside, Threlkeld, etc.) are grouped around 325 Ma while those of the Caldbeck Fell deposits are close to 230 Ma. An epidosic model may be advanced for the Carrock Fell Tungsten deposits with a range from 197 to 282 Ma. The geochronological significance of these and other previously published results is considered.

Ooids and grapestones from some parts of the Corallian Beds (Oxfordian) contain encrustations of the foraminiferid Nubeculinella. Encrusted layers within ooids clearly reveal lengthy periods when the grains were stationary and not accreting carbonate laminae. It seems likely that during colonisation by the foraminiferids the ooids were immobilised beneath a subtidal algal mat and there are indications that the mats were sufficiently coherent to bind lumps of sediment together during disruption by burrowing organisms.