The influence of three classes of factors—geological structure, lithologic composition and spatial control over erosion—are examined by trend-surface analysis, followed by stepwise regression, in order to determine their relative importance in explaining the variation observed in the elevation of the Lower Greensand ridge of south-east England. It is concluded that structural controls are dominant, lithological controls very subordinate and the spatial control of very marginal significance.

Twenty-seven specific and subspecific names have been proposed for discocyclines from the Indian region. Only 18 of them are considered to be valid. The morphological features used for distinguishing these forms are listed and their distribution in different parts of this region is described. On the basis of the character of the megalospheric embryonic apparatus, size of the test and the thickness of the equatorial chamber layer they are arranged in three groups. The tentative phylogeny of these three closely related groups of forms is discussed.

Theory based on the sphere as the ideal particle, fails to account satisfactorily for the concentration of solids observed in unconsolidated natural sands, which at the same time display a substantial degree of dimensional ordering of the particles. However, when the prolate spheroid of moderate axial ratio is substituted for the sphere, a theory which is satisfied by observation becomes possible, for the reason that equal spheroids can be regularly packed in both close and open ways. A spheroid assemblage of mixed open and close packings can retain a high degree of dimensional ordering of the constituent solids, yet have a relatively low particle concentration. Observations made on sandstones carefully selected for evidence of rapid cementation seem to bear out the theory as applied to natural sands. Clusters of grains resembling the open packings of equal spheroids are found in these sandstones to be uncommon but not rare, in accordance with the theory as thus far developed.

An early study of part of the Zagros mountains of south-western Iran put forward evidence for extensive overthrusting and nappe formation. A simplified interpretation of the stratigraphy now obviates the necessity for such tectonic complications.

The north-eastern limit of Zagros folding is marked by a long narrow belt of structural deformity and stratigraphic discontinuity known as the Crush Zone, which includes basic intrusive rocks contemporaneous with the late Tertiary foldings.

It is suggested that the Crush Zone is closely related to the Zagros orogeny, and geophysical evidence is used to speculate on a possible explanation. The general concept of the Crush Zone could prove to be of more widespread application.

Ultrabasic lavas of variable picritic-peridotitic composition are found widely distributed in the Upper Pillow Lava member of the Troodos Volcanic Series in Cyprus. Recent work reveals layering of olivine crystals in both lava flows and pillows. An account is given of the field relations of the layered units, their petrography, mineralogy and chemistry.

Splitting, crushing and spalling which occur when boulders move against each other, generate fine material and so give rise to angular large and small sizes. The nature of the rounding process can be deduced from the analysis of moments of the roundness frequency distribution of the size range 4–128 mm. A low standard deviation indicates the dominance of one process—either abrasion or breakdown; a high standard deviation indicates the presence of both. The relationship between mean roundness, standard deviation of roundness, skewness of roundness and mean size allows for an analysis of the size reduction processes at work on the sediment; and for a comparison between the reactions of different rocks. A model, based on actual data, is given for the evolution of roundness of limestone clasts on a beach.

The morphology, origin, and orientation patterns of distinctive types of sedimentary deformation structure are considered. The structures described are laminar folds, load marks and pouches, and convolute and corrugated lamination. A set of criteria obtained from detailed field analysis of the structures is put forward to indicate minor lateral translations of mobilised sediment.

Laminar folds occur in a laminated mudstone/siltstone lithology and are the result of predominantly lateral movements in response to an unstable palaeoslope. Laminar folds are metadepositional or postdepositional in origin. Orientation patterns are characteristically unimodal. Load marks and pouches are preserved in a banded siltstone/sandstone-mudstone lithology, and result from sediment movements which are either vertical, or vertical with some lateral translation. They are syndepositional or metadepositional in origin. Orientation patterns are predominantly unimodal but bimodal and random patterns are also present. Convolute and corrugated laminations are found in thin siltstone/sandstone beds and have developed through sediment movements which were almost exclusively vertical. The convolutions and corrugations are metadepositional in origin. The majority of orientation patterns are unimodal but there is an increase in the number of random patterns.

The positioning of deformation units which show internal lateral translation in a broader stratigraphical and geographical context, suggests there may be a regional palaeoslope control on the lateral movement of mobilised sediment.

The origin of eclogite nodules in basalt is reviewed in the light of experimental studies and the conclusion reached that many of them precipitated from basic magma as garnet-pyroxene accumulates at high pressure, although some may represent exsolved clinopyroxenite accumulates.

The Upper Palaeozoic rocks in the Aljustrel area of South Portugal suffered strong Hercynian deformation, including isoclinal overturned shearfolding of two important thrust planes bringing sub-Culm strata over Culm.

Tectonic implications of 32 new potassium-argon age determinations of minerals and rocks of Singhbhum and adjacent regions are discussed along with those of recent structural, stratigraphic and petrologic studies, and some pre-existing geochronologic data. Three distinct orogenic cycles with closing dates at c. 3200, 2700 and 850 m.y. respectively have been recognized. The earliest cycle is represented by the Older Metamorphic Group of metasediments with associated basic intrusives and biotite granodiorite gneiss; they occur mainly as relics within the huge Singhbhum granitic complex. Emplacement of the latter (c. 2700 m.y.) marks the culmination of the Iron Ore orogenic cycle which is characterized by the low-grade metamorphic Iron Ore Group sediments and volcanics and associated basic intrusives. Along the northern and eastern edges of the stabilized Iron Ore orogenic belt, thick sedimentation of the Singhbhum and Gangpur Groups (?2000–1700 m.y.) was followed by large scale basic volcanic activity (1700–1600 m.y.); these rocks were folded and regionally metamorphosed in several phases between c. 1550 and c. 850 m.y. (Singhbhum orogenic cycle); extensive thrusting and granitization occurred in the later part of the cycle.

The lithological and structural characteristics of the metamorphosed Pre-Cambrian rocks of Wales and Leinster are reviewed, and the Dutch Gin Schists are not accepted as a stratigraphical unit. The Bray Series, Cullenstown Group, Ballycogly Group and Bedded Succession of North Wales are regarded as parts of a single Monian System which accumulated in a Caledonoid trough and was involved in a late Pre-Cambrian orogeny. The latter also affected the pre-Monian basement, parts of which (possibly unrelated to one another) are seen in the gneisses of Co. Wexford (Rosslare Complex), Lleyn and Anglesey.

The ‘Maelifell caldera’ is the name given to a separate collapse area situated on the southern margin of the main caldera of the Tertiary Alftafjordur volcano. It is 2 km in diameter and is made up of inward dipping welded tuffs, agglomerate (including patches of welded agglomerate), tuffaceous sediments and rhyolite and andesite lavas. The welded tuffs occur as thin pitchstone sheets and as much thicker felsitic masses: the former contain inclusions of basalt glass and are good examples of the simultaneous eruption of acid and basic magmas. It is suggested that the caldera represents the core of a parasitic volcano, beneath which there was a high level acid magma chamber, the immediate source of the local acid rocks. The magma chamber was intersected by numerous intrusions of basic magma, and these caused explosive eruptions and the emission of acid and basic magma to form thin pitchstone sheets. Decreased pressure in the magma chamber after eruptions caused repeated collapse within the cal

The complex can be divided into three units, here named the Lower, Middle and Upper Layered Series respectively, on the basis of petrochemical data and correction of the dips of the layering for the effects of post-consolidational flexuring. There are no chilled margins, and the contact with the country rock consists of granular basic and ultrabasic rocks, older than the cumulates of the layered series. The intrusive mechanism is considered in the light of field and chemical data.

The granitic sheets of Tremearne are believed to have originated from the roof of the Tregonning granite and to have undergone lateral differentiation from leucogranite to aplite with associated pegmatite in a direction away from this granite. Several types of banding are described from the pegmatite-rich region at the Megiliggar Rocks. Some decimetre-scale banding is the result of intrusion of “magmatic” aplitic material, but coarse pegmatite bands are believed to have grown in solid aplite. A close examination of centimetre-scale banding and fine-banding in aplite (line rock) indicates that this is related to pegmatite development and is metasomatic. The mobility of alkalies and the concentration of potash in pegmatite relative to aplite is discussed.

The Blue Ridge thrust sheet is one of the principal thrust masses of metamorphic rocks in the southern Appalachians. A broad zone of sheared and retrogressively metamorphosed rocks near the sole of the thrust sheet around the Grandfather Mountain window displays numerous small tight or isoclinal folds having axes subparallel to an intense penetrative cataclastic a lineation and axial planes parallel to foliation in the thrust sheet. These folds seem to have formed by tightening, flattening, and passive rotation of earlier more open folds originally formed perpendicular to the direction of transport. The style and orientation of these folds closely resemble those of analogous structures in thrust masses of crystalline rocks in the Caledonian orogenic belt in Scotland and Norway, suggesting that the structures of both regions may have similar origins.

In the Clackmannan Syncline and the north-eastern part of the Central Coalfield the Passage Group succession between No. 2 Marine Band (?Arnsbergian, E2) and the Netherwood Coal (Kinderscoutian, R1) represents a period when meandering rivers with gently sloping floodplains replaced deltas. The succession consists of upward-fining cycles in which crossstratified sandstones with disconformable bases grade up into unstratified rooty siltstones and mudstones. The thicker sandstones probably represent meander belt deposits, the thinner sandstones the infillings of single channels and the mudstones and siltstones overbank (floodbasin) deposits. Desiccation cracks and partial oxidation phenomena indicate periods of low water table.

Field, petrographic and chemical studies on the Silurian volcanic rocks of the Mendip Hills show that there are probably 15 or more rock units in the series including andesite and rhyodacite lavas, rhyodacite tuffs, agglomerates, and a dolerite dyke. The predominant rock type is rhyodacite which may be as much as 80 percent of the volcanics. Volcanics of Silurian age from the Tortworth area, Gloucestershire, are of latite-andesite composition.

The Mendip rocks have been deuterically altered. Calcite-quartz-laumontite veins are common in fractures in these rocks. The agglomerates are particularly susceptible to weathering and some bombs are extensively altered to clays. Twelve rocks were chemically analysed for 36 elements each. No anomalous base metal concentrations were found in the volcanics although Pb, Zn, and Cu mineralisation is known in the area. K/Rb varies from 202 to 909 in these calc-alkaline rocks.

A dolerite intrusion on Long Island, Seychelles contains exceptionally large plagioclase (labradorite) phenocrysts essentially unzoned, set in a doleritic groundmass. Many of the mega-phenocrysts have a dark redbrown interior.

In the groundmass, zoned plagioclase is in a doleritic texture with a slightly titaniferous ferro-augite that has been almost completely replaced by an actinolite uralite.

The mega-phenocrysts are considered to have crystallized slowly at depth and concentrated locally in a chamber of basaltic magma. The portion of magma containing these plagioclase crystals was later injected to higher levels as dykes. Although emplaced in a granitic (continental) environment, the intrusion has oceanic basalt affinities, and in chemical composition resembles high alumina basalts.

Inclusion textures within garnets are often used to demonstrate the relationship in time between garnet growth and deformation. The evidence for syntectonic growth is discussed, and it is shown that several thin sections are required before an accurate interpretation can be made. The patterns predicted by Powell & Treagus (1967) are matched with natural examples, and a mechanism for the aevelopment of these fabrics is suggested.

Some graphite-sillimanite-schists and -gneisses, containing natrojarosite and ‘collophane’, from north-east Tanzania, are described, with an analysis, and their sedimentary origin briefly discussed.