The paper deals with regional variations in the contact–effects of Caledonian granites and in the characters of certain associated minor intrusions in the metamorphic Caledonides. It is suggested that these variations are related to the thermal structure of the fold–belt at the time of emplacement.

It is established that the Dawros peridotite of north Connemara contains basic plagioclase mainly in a gabbroic layer in the peridotite but occasionally as rare crystals in the peridotite itself. Carlsbadalbite twin extinction angles indicate that the composition of this feldspar is similar to that in the adjoining Currywongaun-Doughruagh intrusion and that in the ultrabasic rocks of the Cashel-Lough Wheelaun intrusion and the Roundstone intrusion of south Connemara. As all these feldspars are extremely heavily saussuritized because of metamorphism it is difficult to determine their precise composition and so an exceptionally fresh plagioclase from an anorthosite in the Currywongaun-Doughruagh intrusion has been chemically analysed. It is An91·5Ab6·8Or1·7. This is in close agreement with the composition given by measuring 2θ(131)–2θ(131), the refractive indices and 2V while the extinction angles of Carlsbadalbite twins give only a slightly too anorthitic result (An95). The particularly calcic nature of the plagioclase is strong evidence that all the ultrabasic bodies in Connemara are genetically related. Some new structural ideas on the Dawros body are suggested which integrate the structure, petrography and cryptic variation.

The technique of vacuum shadowing small objects and the advantages of this method in light photography are detailed. The ultra-thin metal-carbon films thus prepared show greater contrast and resoultion than acetate peel replicas.

The Marumbe complex is a small ring-intrusion consisting essentially of a plug of nordmarkite separated from the basalt country rocks by a later ring-dyke and roof-sheet of granite. The lower and upper surfaces of a screen of basalt, which lies between the top of the nordmarkite body and the base of the granite roof-sheet, correspond to successive horizontal fractures which permitted blocks limited by ring-fractures to subside as the nordmarkite and granite magmas were intruded. A series of sheets of granite are developed locally in the hanging-wall of the above-mentioned ring-dyke, and further granite ring-dykes cut the nordmarkite and the country rocks.

During the Laxfordian orogenic period dolerite intrusions crosscut and were chilled against vertical bands of hornblende schist that trend N.W.–S.E. Subsequent metamorphism affected both the regional hornblende schists and the dolerites, and narrow bands of hornblende schist were formed in places at the expense of doleritic chilled margins. Previous interpretations of Lewisian geochronology, tectonics and metamorphic history made on the basis of a unique pre-Laxfordian basic dyke phase, cannot be applied to the rocks south of Gairloch.

Most of the cross-bedding in the Central Pennine Millstone Grit occurs in the coarse sandstones and indicates that they are probably fluvial in origin. The cross-bedding often occurs within sheets of sandstone, and it is suggested that each sheet was deposited during one episode of flooding. Medium-grained arenaceous rocks show other varieties of cross-bedding that could have been formed on tidal flats, but this evidence is inconclusive.

Chemical and modal analyses have been made for a series of ten homogeneous specimens of meta-sediments, with identical metamorphic histories, from the aureôle of the Ardara pluton. Results showed that total amount of garnet was determined by the quanity of “free ferrous oxide” (assuming that the reaction: FeO + Fe2O3→ Fe3O4, has gone to completion) in the rock. Size distribution curves showed that each specimen contained crystals with a preferred radius and throughout the series a quantitative relation between the preferred radius and the frequency distribution about this value was observed.

Measurement of the number of crystals per unit volume showed that this gave trends with functions of the chemical composition of the rock. A discussion of the mechanism of garnet formation in terms of chemical laws of nucleation and growth is given.

The “Beach-Beds” at Castleton, Derbyshire, are shown to be detrital deposits containing numerous water-worn and broken brachiopod shell fragments set in a matrix of finely comminuted shell and crinoid debris. They occur at the junction of the fore-reef and basin facies of the Carboniferous Limestone. Previous interpretations of the “Beach-Beds” as cliff-foot screes or as beds lying above an unconformity are not supported, and it would appear that they are composed largely of debris transported down a submarine channel (the approximate position of which is now the dry valley of the Winnats) rather than in shallow water on a sea-beach, being deposited at the foot of the channel contemporaneously with the adjacent fore-reef beds.

The stratigraphy of the Lower and Middle Jurassic rocks of the Hebrides is briefly summarized, and the lithostratigraphical nomenclature reviewed. To replace the inappropriate name “Inferior Oolite” for the lower marine part of the Middle Jurassic a new name, Bearreraig Sandstone Series, is proposed. This series is defined, and the succession at the type section is summarized.

The similarity between the “whole-rock” ages of the Nchanga and Lusaka granites, 755 m.y. and 725 m.y. respectively, is misleading. The field evidence indicates that the Lusaka granite, although syntectonic, intrudes Katanga metasediments, whereas the Nchanga granite is overlain unconformably by basal Katanga conglomerate and arkose. The age of the Lusaka granite thus sets a younger limit to the age of the Katanga metasediments of the Central Province and dates the waning phases of the Lufilian orogeny. The radiometric age of the Nchanga red granite is too young for a pre-Katanga intrusive, and it is suggested that it has been modified by subsequent metasomatism.

X-ray analyses of Kimmeridgian clays recovered from the Warlingham Number 1 Borehole indicate that illite and kaolinite are the dominant clay minerals present. Illite, chlorite, and kaolinite, are present in the Devonian clays recovered from the Willesden Number 1 Borehole. The relationships between the clay minerals of the Kimmeridgian and Devonian clays and the clay mineral assemblage of the English Wealden is discussed.

In current direction studies, when unfolding strata to their original horizontal attitude, plunge is usually allowed for on the assumption that it was acquired by rotation about horizontal axis at right-angles to the fold axis. Errors resulting from plunge correction on this assumption, if mistaken, are examined