Twenty-five new analyses of 10 spilitic pillows from the British Isles offer evidence of considerable variability in distribution of components, notably Si, Na, Mg.Fe2+, Ca, Fe3+, and water. Selvedges of pillows have compositions strongly contrasted with but essentially complementary to those of cores. Redistribution of components is believed to have occurred during devitrification. Geosynclinal spilites are regarded as basalts which have suffered such redistribution under conditions of diagenesis or low-grade metamorphism.

Nigerite occurs in pegmatite as hexagonal crystals enclosed in mica or in association with lithiophilite, apatite and vivianite. Absolute hexagonal parameters are a 5·67 and c 13·88 Å. Powder data are given. Forms and present besides the well-developed {0001}. Density 4·25. Refractive index 1·80, birefringence about 0·005, negative optical character. The chemical composition is studied by means of chemical, X-ray fluorescence and optical spectrography methods.

The Kangerdlugssuaq intrusion (68′ 20′ N. 32′30″ W., roughly circular and 33 km across) is of Tertiary age, like the nearby Skaergaard intrusion. At the present level of erosion the outer part is of nordmarkite and inwards there are successive rings of transitional pulaskite (without quartz or nepheline), main pulaskite and, in the centre, foyaite. The different rock types are due to gradual changes in the amounts of certain of the minerals and there are no sharp junctions such as would be expected to result from successive injections.

Zones of inclusions of basalt, fallen from above, dip inwards at 30 to 60° and, in places, there is a platy parallelism of the tabular alkali feldspars dipping similarly inwards. The three-dimensional form of the intrusion is pictured as resembling a pile of saucers of decreasing size, the sequence of formation being from the outer saucer of nordmarkite to the inner, and smaller saucers of increasingly nepheline-rich syenites. Bottom accumulation of crystals is postulated to explain the disposition of the rock types, but the cause of the succession from quartz-bearing to felspathoidal syenites remains uncertain.

The end-Carboniferous quartz-dolerites form a curious tholeiitic interlude in the alkaline olivine-basalt vulcanicity which characterized central Scotland from the top of the Old Red Sandstone to the Lower Permian. The relationship of the two magma-types is discussed in the light of fresh evidence.

Upper Mesozoic geosynclinal sedimentary rocks, mainly of volcanic (andesitic) derivation, show widespread prehnitization caused by very low grade metamorphism (burial metamorphism). The sediments, which include greywackes, argillites, cherty rocks, and occasional limestone concretions and thin beds, appear little altered in hand specimen and in the field despite the wide extent of recrystalli-zation. Besides prehnite, secondary minerals include quartz, albite, chlorite, sericite, calcite, and sphene. The different modes of occurrence of the prehnite are described and briefly discussed. The alteration of the rocks is compared with similar wide-spread prehnitization recorded in probably correlative rocks on South Georgia.

Six titanomagnetites from a differentiated alkaline intrusion have been studied using microscopie, chemical, and X-ray techniques. The titanomagnetites are homogeneous; with differentiation their FeO and TiO2 contents decrease, and Fe2O3 increases. The titanomagnetite course of crystallization extends from close to the ulvöspinel-magnetite join, near to ulvöspinel, towards magnetite. The recalculated normative compositions of three titanomagnetites indicate that they are essentially Fe3O4-(γ-FeTiO3)-(γ-Fe2O3)solid solutions. The changing chemistry of the titanomagnetites is ascribed primarily to variations in the chemistry of the magma during differentiation.