It is suggested that Alpine serpentinites are not a characteristic of eugeo-synclinal mountain development, but represent a special case in which the leading edge of a drifting continental mass overrode an oceanic ridge. Serpentinites younger than Caledonian are overwhelmingly of Mesozoic age, and essentially contemporaneous with the latest principal episode of continental drift. Furthermore, they occupy the leading edges of continental blocks which must have been moving during that episode.

Older serpentinite belts of comparable proportions may reflect geosynclinal seaways originally wide enough to accommodate oceanic ridges. The Baltic-Breton and Siberian continents must in that case have drifted westward (with respect to their present alignments) in early Caledonian time, and Australia eastward in early Hercynian. The principal episode of Mesozoic drift is thought to have occurred during Triassic and Jurassic times, and not during Jurassic and Cretaceous.

The alkali syenite assemblage of Kunavaram, Khammam district, Andhra Pradesh in south-eastern India, comprises perthite syenite and nepheline syenite. The massive perthite syenite (locally grading to alaskite) is fringed on either side by foliated nepheline syenite, the latter developing composite gneisses along the contact zones with the country rocks. The syenites are essentially hypersolvus although the alkali feldspar, the dominant constituent of the rocks, shows varying degrees of unmixing and Al/Si order. The mafic constituents (e.g. sodic pyroxene, amphibole and biotite) are appreciably rich in ferrous iron. Mineralogical and chemical data suggest that the primary crystallization characteristics of the syenites were not totally obliterated during the post-magmatic history of the pluton.

Moinian and Dalradian metamorphic rocks occur in the north-east extension of the Ox Mountains. The petrology and migmatization of the Moinian are discussed and Dalradian rocks are described for the first time from this area. Reference is made to the structure and brief comparisons are made with adjacent areas. The status of the so-called ‘eclogites’ in the Moinian is also discussed.

In the Atikwa Lake area biotite tonalite grades into a peripheral zone of hornblende tonalite as the contact with greenstone wallrock is approached. Greenstone inclusions, common within the hornblende tonalite, exhibit varying degrees of digestion and the host becomes more mafic near many such inclusions. The hornblende tonalite is more heterogeneous than the biotite tonalite, particularly near the contact with greenstone where inclusions are abundant. Modal analyses indicate the presence of large amounts of hornblende near the contact. Spectrographic analyses of composite tonalite samples show that silica decreases while alumina, iron oxide, magnesia, lime, titania, nickel, chromium, and vanadium increase toward the contact. As a whole the data support the conclusion that the peripheral hornblende tonalite is a contamination product which resulted from the assimilation of greenstone by intruding biotite tonalite magma.

Whole rock rubidium-strontium age determinations on granitic bodies in S.E. Uganda give ages of 2930 m.y. for the Masaba Granite and 2430 m.y. for the Buteba Granite and granitic gneisses. The former age is considered to represent the upper age limit of the post-Nyanzian orogeny, and 2430 m.y. the upper age limit of the post-Kavirondian orogeny. A second isochron age of 2100 m.y. for the Masaba Granite may reflect a second intrusion, or remobilization of part of the original granite associated with the Buganda–Toro orogeny. Tentative correlations are suggested between these age groups and others within the Tanzanian Shield and beyond.

Rhythmic layering in which the layers grade from coarse base to finer top is described in a plagioclase—pyroxene—olivine gabbro. The medium sizes of the various cumulus minerals at each level have significantly different settling velocities. Variation in the proportions of the cumulus minerals accompanies the size grading. It is shown that these characteristics can reasonably be accounted for if hydrodynamic factors exerted the main control, over-riding any chemical effects.

Rubidium–strontium and potassium–argon measurements on Lewisian intrusive rocks, considered to be late Scourian in age on general geological grounds, have indeed yielded dates in the range 2450–2600 m.y. This demonstrates that rocks of Scourian age that have escaped substantial Laxfordian reworking are preserved in the Eastern Gneisses of Barra. The relevant geological consequences and correlations are briefly discussed. A cross-cutting late pegmatite yields a typical Laxfordian date of 1679 m.y.

A marginal variant of the Mullach nan Coirean granite contains orthoclase microperthite, quartz and plagioclase, with some andalusite, muscovite and iron ore. The stability of andalusite as an igneous mineral is discussed.

Three large collapse structures, two bounded by straight, vertical escarpments and curved head regions, are described from Tenerife. Similar structures appear to exist on Hierro and La Palma. Their size precludes landsliding as the dominant force in their formation, although it may have played a minor role in modifying the bounding walls. It is suggested that these structures are true volcanic collapse features developed by a ‘trap-door’ type of mechanism. The lack of classical caldera shapes appears to be a reflection of a lack of well-defined central volcanism on any of the islands, the collapses probably resulting from migration of magma away from the central rift-zones towards the flanks of the islands.

Recent coastal erosion has revealed another chalky till above the Lowestoft Till and separated from it by bedded clays and sands. These have shown no evidence of contemporary life and, together with the newly discovered till, are assigned to the Lowestoft Stadial at this the type-section of the Anglian (Lowestoftian) Glacial Stage.

The olivine minette described by Tidmarsh from the Holmead Farm, Lox-beare, contains analcite microphenocrysts in addition to olivine, biotite, clinopyroxene and alkali-feldspar. A new chemical analysis shows that the rock is undersaturated with respect to silica. This is still another example of analcite occurring in a potash-rich rock.

The genotype of Bryograptus, B. kjerulfi Lapworth, is figured and redescribed together with B. ramosus Brøgger, B. bröggeri Monsen and Pseudobryograptus cumbrensis (Elles).

Two incomplete graptolite rhabdosomes in the Hugh Miller Collection (Royal Scottish Museum) are referable to Monograptus priodon (Bronn). The specimens were obtained from the Macduff Group, the youngest member of the Upper Dalradian succession in Banffshire (Read, 1923). This occurrence extends the upper stratigraphical range of the Dalradian Series into, at least, the Lower Silurian and possibly into the lowermost part of the Upper Silurian.

Chloritoid and staurolite bearing rocks from the Agnew Lake area in northern Ontario were studied petrographically and with the electron microprobe. A staurolite–chlorite isograd is postulated, above which chloritoid and staurolite coexist in equilibrium, and a Schreinemakers-type petrogenetic grid is constructed to illustrate how the isograd might fit into a paragenetic sequence.

The staurolites from the area are observed to be more ‘siderophile’ than the chloritoids and this suggests that the chlorite participating in the isograd reaction is prograde. This is confirmed in the ‘real’ isograd reaction:

1.559ctd+5.000and+0.009rut+0.058ilm=0.881st+0.039chl+1.366qtz+1.040H2O the coefficients of which are calculated using the mineral analyses of the ideally univariant assemblage staurolite–chloritoid–chlorite–andalusite. Variations in the activity of the unsaturated component ZnO would affect the equilibrium temperature of the reaction and the reaction coefficients.

A new structural diagram is proposed that allows simple precise classification of fold orientations. The diagram is also useful for the analysis of the relationship between fold style and orientation.

By the study of dilation associated with cone-sheet emplacement and the deformation of the basal Carboniferous unconformity at the Irish Tertiary igneous centre of Carlingford, it is shown that cone-sheets are capable of producing considerable uplift. This process is also the cause of the steep-sided domes which occur at some carbonatitic centres in Kenya.

It is demonstrated that the Kvamshesten area of continental Devonian rocks has been thrust over an older basement. The movements are correlated with the Svalbardian phase.

Zonal arrangements in ancient ignimbrites have usually been interpreted as a reflection of variations in welding. Detailed study of two Lower Palaeozoic ignimbrites from Newfoundland demonstrates that crystallization zones can also be recognized and that in some cases it is these zones which are responsible for the gross features of the cooling unit.

The sense and amount of rotation of small garnet porphyroblasts is found to vary from place to place on a fold. By correlating this variation with a proposed mechanism of formation of the fold, a tentative profile for the fold at the time of garnet growth is constructed.

A recent hypothesis concerning the age of orogenic deformation of the Skiddaw Slates in the English Lake District has proposed that the main slaty cleavage (S1) and superimposed subhorizontal crenulation-cleavage (S2) are of intra-Ordovician age. A study of the fabric of the aureole of the (end-Silurian) Skiddaw granite shows that the granite was emplaced towards the end of the D1 deformation phase, but before the formation of S2. These structures are therefore of broadly end-Silurian age, and evidence of an intra-Ordovician orogeny in this area is lacking.