It is pointed out, with a few examples, that metamorphic rock compositions can be significantly modified by the stable mineralogy that itself may provoke metasomatic movement, as distinct from externally actuated metasomatism.

Many deep water marine muds, including lower Palaeozoic mudstones from Britain, have thin graded beds in which mud and silt laminae alternate, with the silt becoming finer and less abundant upwards. Of the known deep-sea depositional processes, turbidity currents are the most likely cause of such graded laminated beds. The lamination may be produced by alternating cohesive and granular bed conditions. Much more careful examination of laminated fine grained terrigenous sediment is needed.

A new structural diagram derived from the equal-area net is proposed that helps in conversion of pitch data of folds into amount and direction of plunge, and in precise classification of the fold orientations. A new convention for indexing of folds and the use of subscripts for concise description of inclined folds are suggested.

Glaucophane schists from Oscar II Land in western Spitsbergen are described for the first time. Although lawsonite, aragonite and pumpellyite have not been found, the mineral assemblages correspond generally with glaucophane schist assemblages known from elsewhere. The results of three XRF chemical analyses are presented, and five K/Ar radiometric determinations. The radiometric dating and field evidence both suggest that the glaucophane schists are a result not of the Tertiary orogeny which affected this part of Spitsbergen, but of the earlier Caledonian orogeny.

Values of quartile deviations (QDa) and medians (Mdmm) have been calculated from over 400 grain-size distributions of modern and ancient turbidites. Each QDa–Md pair is plotted on double-log paper to establish any distinctive trends. The QDa–Md analysis of modern turbidites reveals a steep gradient trend derived from the grain-size distributions of submarine canyon and delta fan sediments, and a shallow gradient trend derived from the grain-size distributions of samples from oceanic bottoms and nepheloid water layers. The QDa–Md analysis of ancient turbidites reveals two trends, but these do not coincide with their modern counterparts. The steeper gradient trend is related to distal and proximal turbidites, while the shallow trend is related to fluxoturbidites. The disparity between the ancient and modern QDa–Md analyses is caused by textural modifications of turbidites by diagenetic disintegration of unstable minerals. The alteration products are incorporated subsequently in the matrix. The diagenetic effects on the positions of the QDa–Md plots are demonstrated theoretically by computing the textural alteration of six modern turbidites by assuming that they will lose 20%, and then 40%, of their sand-sized particles to the matrix. By working in reverse the QDa–Md plots of ancient turbidites can be ‘restored’ to their diagenetically unaltered positions. Their restored positions correspond to the QDa–Md trends of modern turbidites.

Quartz–microperthite–hornblende–garnet–plagioclase granulites belonging to the Highland Series of Ceylon are described. The invariable presence of accessory graphite suggests their metasedimentary origin and their chemical composition indicates a possible derivation from feldspathic sandstones. Although the mineral assemblage of these granulites is diagnostic for the upper almandine–amphibolite facies, they are interlayered with orthopyroxene-bearing charnockites of the granulite facies. It is concluded that PHO was initially higher in the sandstones than in the surrounding rocks, and that it remained so during metamorphism under granulite facies conditions, thereby retarding the dehydration reactions that took place elsewhere in the vicinity.

Occurrences of penecontemporaneous folds of varying style and amplitude are described from low-metamorphic flysch sediments from an area in the Central Norwegian Caledonides. A short discussion of the mode of formation of these folds is presented, and from geometrical considerations it is suggested that, in several cases, both foundering and slumping have contributed to the overall deformation. The significance of the presence of these structures in the stratigraphical sequence is outlined, and the inherent danger of their possible misrepresentation as tectonic folds in higher metamorphic areas is briefly discussed.

Potassium–argon ages of a variety of rocks and minerals from the Cheviot Hills, northern England, lie in the range 390 m.y. to 370 m.y. The Cheviot granite, dated at 380 m.y., has an age similar to that of many of the younger members of the British late Caledonian granites.

Tuffs, trachybasalts, aegirine–augite trachytes and aegirine–augite phonolitic trachytes occur on the continental shelf at the southern tip of Africa. They have been radiometrically dated at 58(±2.4) million years (Palaeocene), and together with other alkali-rich basic intrusions onshore form the Alphard Tertiary Igneous Province. Both onshore and offshore sites of intrusion appear to be strongly tectonically controlled.

The average chemical composition of the biotite–gneisses of Rona is very close to that of similar gneisses in the Laxford area, and nearly as close to those of the Torridon area. The biotite–gneisses of Rona are slightly richer in Li, Ba and Zr, slightly lower in Mg and Sr and have a higher Fe2O3/MgO ratio than their mainland counterparts. Biotite mineral ages of 1400 m.y. and hornblende mineral ages of up to 1750 m.y. indicate a similar late-metamorphic history to that of the mainland Laxford assemblage.

The stratigraphy of the early Pleistocene marine deposits erected from a borehole at Ludham, Norfolk, based on pollen and foraminifera, is extended to another borehole at Stradbroke, Suffolk. Pollen analyses from argillaceous parts of the sequence at Stradbroke show a Pre-Ludhamian pollen zone, overlain by the Ludhamian. Foraminiferal evidence indicates that the Pre-Ludhamian is equivalent to part of the Red Crag, thus providing the first direct evidence as to the relative ages of the Red Crag and the Ludhamian. Palaeomagnetic investigations indicate a normal polarity and, by comparison with the Netherlands sequence, an age of at least 1.60 m.y. for the deposition of the Pre-Ludhamian.

A rhyolitic breccia-body is emplaced within an indurated mafic tuff which outcrops along the south-western margin of the Beinn na Caillich granophyre mass in the Isle of Skye. The breccia provides evidence of two distinct processes in operation during and prior to emplacement. The tuff which includes felsic rock debris has an intrusive near-vertical junction with the Liassic sediments. It is believed that the tuff was emplaced within a pre-existing volcanic channel. The sequence of post-Liassic eruptive activity in this area ended with the emplacement of the granophyre.

Cynodonts from two localities in Lesotho have been assigned by earlier workers to the Triassic Molteno beds of the upper part of the Karroo (Gondwana) System. These are important inasmuch as they were thought to represent the only evidence of reptilian remains in an otherwise barren sequence and may help to bridge the palaeontological gap in this part of the Karroo succession. Critical examination of both localities during the course of a regional analysis of the Molteno basin showed discrepancies in stratigraphic interpretation. These discrepancies are pointed out and the stratigraphy revised as a result of which the cynodonts can no longer be assigned to the Molteno beds; one is in the underlying Cynognathus zone (confirmed by further finds of typical Cynognathus zone reptiles) and the other is in the Red beds above. At the Tsoaning River locality a pebble conglomerate resting on an eroded surface provides a good local marker for the base of the Molteno. The implications of this with respect to the fossil flora and fauna at these localities are briefly discussed.

Bouldery outcrops of coarse-grained olivine-free lava, containing abundant orthopyroxene and clinopyroxene, mostly in glomerophyric aggregates, occur over a small area among the Tertiary to Recent volcanics of the Jos Plateau, Nigeria. This is the only rock of tholeiitic affinity in an otherwise completely alkaline volcanic province. Petrographically it does not greatly resemble tholeiitic occurrences reported from such provinces elsewhere, but that is believed to be due more to a relatively complex crystallization history than to any fundamentally different process of magma generation. It is not regarded as representing a tholeiitic parent for the alkaline lavas of the Jos Plateau region.

Episodic hydrothermal mineralization has previously been recognized in the northern section of the Pennine orefield. Igneous rocks from the southern section (the Derbyshire orefield) have yielded isotopic ages, some of which are thought to represent ages of hydrothermal metasomatism (deuteric or subsequent). In order to ascertain whether epicyclic hydrothermal events gave rise to the Derbyshire mineral deposits, samples of highly altered doleritic lava and pumice tuff were collected adjacent to areas of mineralization. Clay-mineral concentrates from 34 samples were dated by the potassium–argon method. The conclusions drawn from these analyses support a hypothesis of repeated hydrothermal alteration of the clay minerals, reflecting at least two episodes of mineralization, one about 270 m.y., the other about 235 m.y. The geo-chronological significance of these and other results is considered.

Myrmekite in a two-feldspar migmatite suite has two distinct modes of occurrence: (i) marginally embaying potash feldspar, and (ii) in replacement aggregates after that mineral, the other major constituent of the pseudomorphs being a muscovite-quartz intergrowth. Electron-probe data give quartz proportionalities agreeing with the predictions of existing theories. It is shown that these theories, which refer to either exsolution or small-scale metasomatism, share a common foundation of kinetic impediment to AlSi diffusion. In neither case need one assume the presence of ‘Schwantke's molecule’ as a component of potash feldspar. The two myrmekite occurrences here described are interpreted in terms of essentially simultaneous exsolution and hydrative replacement processes operating as regional metamorphic temperatures began to decline from their climactic values. The existence of exsolution myrmekites of ideal quartz proportionality is not in itself evidence for the existence of ‘Schwantke's molecule’.

A revision of the species of the Upper Cretaceous membranimorph Bryozoa, established by R. M. Brydone between 1906 and 1941, has led to a considerable reduction in the number of species assigned to this group. These species are listed with the writer's opinion as to their more probable taxonomic position.

A description is given of the numerous thin dolomitic sandstone dykes cutting dark marine shales of E1a age in Co. Leitrim. They are almost wholly confined to the Dough–Thur Mountain area, which is cut by the Caledonoid trending Ox Mountain and Belhavel Faults. It is thought probable that movement along one of these faults, possible in E1c times, conferred thixotropic properties to a sand horizon in the marine shales and also produced fractures in the shales up which the sand was intruded.

Although the structures and textures of spilites and keratophyres are comparable to those of fresh lavas, recent work has established that they did not acquire their present mineralogy at the time of extrusion. Furthermore, the compositions of many analyzed samples of spilites and keratophyres are shown to lie outside a ‘spectrum’ of compositions of all comparable fresh igneous rocks. A later metamorphism has therefore been responsible for their formation and has commonly been accompanied by metasomatism. This possibility of later metasomatism must be appreciated before conclusions are drawn that are based upon analysis of rocks of a spilitic or keratophyric mineralogy. This applies to age-dating and to analytically based petrographic and petrogenetic conclusions.

Three subfacies of the granulite facies are recognized: garnet–diopside–quartz subfacies; pyroxene–granulite subfacies; and hornblende–granulite subfacies The erection of a garnet–diopside–quartz subfacies follows De Waard's suggestion (1965) of a garnet–clinopyroxene subfacies. Two major divisions of the hornblende–granulite subfacies are now recognized, (i) garnet–biotite division, (ii) cordierite division. Three sub-divisions of the former are suggested on the basis of critical basic assemblages. Since wollastonite has been found to have a limited areal occurrence within the latter, a two-fold sub-division of the cordierite division is suggested on the basis of the assemblages, (a) calcite–quartz, (b) wollastonite. A seven-fold sub-division of the granulite facies is thus proposed for Ceylon rocks. An attempt is made to trace briefly the major events in the metamorphic history of the rocks supported by available geochronological evidence.