Study of the small-scale structures of South-Eastern Cowal provides information about the movement history in an assemblage of grits and slates wherein the original sedimentary structures and textures are discernible. A sequence of folds of both Caledonoid (NE–SW) and cross-fold (NW–SE) axial directions can be recognized, with corresponding successive cleavages or schistosities. In the rocks of higher metamqrphic grade towards the axial region of the Cowal anticline the earlier structures are largely obscured by recrystallization.

A stratigraphical outline of the Hecla Hoek succession summarizing post-war work in Ny Friesland is presented for the first time. This shows a geosynclinal series of sediments reaching down at least 15,000 m. below Cambrian in a more or less continuous succession. It is compared with other Hecla Hoek successions in Svalbard.

The main topographical features of the Gebel Akhdar are described, and attributed to various phases of marine and subaerial erosion. The tectonic structures of the Gebel are also described, and their relations to the erosional features are examined. On this basis an attempt is made to reconstruct the Late Tertiary history of the region in terms of earth-movements and erosional phases; this is a period for which normal stratigraphical evidence is almost non-existent.

Well-preserved examples of spilites show marked affinities with certain tholeiites in texture, chemistry, differentiation trend, and in some aspects of their mineralogy. The presence in them of albite and apparently primary chlorite, in association with unaltered augite, is ascribed to the influence of water as a component of the magma, and the high content of alkali in the basic members to retention of volatile oxides present in tholeiitic magma. Evidence is lacking of large-scale metasomatism by external agencies and the postulate of a special primary magma seems unwarranted. A series may be traced, in rocks of different environments, from “dry tholeiite” to “wet tholeiite” to spilite.

Four new rock analyses and one of chlorite are given.

Data is presented on textural variation, optical properties, and resultant compositions of the olivines from a differentiated teschenite sill. The range in olivine composition is from Fa21 to Fa,60. Both the individual crystals and successive crops of crystals become more fayalitic with progressive differentiation.

An examination of existing definitions of facies and subfacies boundaries in pelitic rocks suggests that some alteration is necessary to emphasize two important reactions:

3 Staurolite + 2 Quartz ⇌ Almandine + 5 Al2SiO5 + 3 Water, and

Muscovite + Quartz ⇌ Potash feldspar + Al2SiO5 + Water A generalized plot shows possible relations between the curves of these two reactions and the inversion, curves of the aluminosilicates within the P-T field of metamorphism. The curves of further reactions commonly used to define facies and subfacies boundaries have been schematically added to this plot, and trends of metamorphism in various areas are indicated thereon. P-T curves of dehydration reactions such as the above will vary according to the chemical potential of the water vapour in each particular case. Observations suggest, however, that the curves are not very differently placed from one regional metamorphic terrain to another. That is, the rate of escape of volatiles is broadly similar in the metamorphism of many of these terrains.

A small body of anorthosite with related gabbroic facies from the Archaean of Southern India is described. The mass is inferred to be a funnel shaped phacolithic pluton, emplaced in the crest of a steeply plunging major anticline of metasedimentary quartzite and quartz schists. The marginal rocks of the mass are gabbroic and foliated, while the core is largely made of massive anortho-sites occasionally showing flow structures. The chemistry and petrography of the rocks of this mass suggest their having resulted from differentiation in place of a gabbroic anorthosite intrusion. This occurrence is thought to be a unique example of the Adirondack type of anorthosite, and supports Buddington's hypothesis of evolution of anorthositic rocks from a gabbroic anorthosite magma.

At two localities near Kanye, in the south-eastern Bechuanaland Protectorate, formations previously assigned to the Waterberg System are now correlated with the Pretoria Series of the Transvaal System. In addition to modifying the palæogeography of the Transvaal period, this correlation may also help to clarify the stratigraphical position of the Matsap Series of the Cape Province.

Herpetopora Lang is considered to be a junior synonym of Pyripora d'Orbigny, from which Rhammatopora Lang is distinguished by possessing apertural spines. A new species of Pyripora is described from the Albian of Texas.

A new genus and species of the Lepidocentridae is described from the Lower Carboniferous at Hook Head, Ireland.

Some essential features of the general tectonic description of a region are outlined under the above heads. Tectonic style is the product of facies and orientation in their distinctive sequence, and is assumed to be independent of date. A type of tectonic sequence is outlined from Ny Friesland, Spitsbergen, with a distinct late stage elongation along the fold axes.

Consideration of the field occurrence of certain post-Palaeozoic brachioppds, and of published experimental work on the transport of brachiopod shells by water, leads to the conclusion that these fossils are often deceptive as evidence of former conditions at the places where they now occur fossil, due to shell-transport by marine currents after death.

Structures including folds, cleavages, faults, joints, and lineations are described. Three periods of folding are distinguished to which three cleavages are related. In order of decreasing age the cleavages are flow-cleavage, fracture cleavage, latest fracture cleavage. The main fault systems trend north-north—east, approximately east—west, and north-west. Joints follow two principal directions. These are north-west—south-east, and north-east—south-west. The dominant lineation is north-east—south-west. At right angles to this is a north-west—south-east lineation which affects all visible foliation. It is confined to a faint crinkling.

The transformation of tillite to granite and gneiss by granitization has recently been postulated for rocks of the Mount Fitton area of South Australia. After examining the relationships in the field we have concluded that another interpretation is possible; the granites could be regarded as an older basement upon the eroded surface of which the tillites have been laid. The zone of feldspar rich rocks between the two could represent a basal arkose resting directly on the old granitic surface.

A preliminary analysis of slope forms in Buganda has indicated an erosional cycle characterized by both parallel scarp retreat and summit lowering, of which the latter process predominates in the later stages of the cycle. The recognition of characteristic stages in the erosional development of the landscape may provide a means of distinguishing a warped erosion surface occurring at differing altitudes from the products of separate erosion cycles.

The contact aureole on the northern side of the Ardara granitic pluton is made up of an outer part where contact effects are slight, and an inner part in which a broad zone of andalusite hornfelses is succeeded towards the contact by a narrower zone of sillimanite hornfelses. The textures of the hornfelses indicate that several phases of recrystallization, some of them associated with phases of movement, took place during contact metamorphism. Certain phases can be correlated with particular episodes in the evolution of the pluton itself.

General considerations relating to the use of analyses for determining depth-volatile relations in coalfields are discussed. New evidence from New Zealand is presented and British evidence reviewed. A maximum rate of downward decrease of volatiles is inferred at 23 per cent volatiles, and a depth-volatile band from 42 to 5 per cent volatiles is presented. British coalfield sequences fit the band, rendering unnecessary the complex geological explanations for differing rates of downward decrease of volatiles given by previous authors. Tectonic pressure is rejected in favour of depth of burial as a cause of rank differences.

Almandine-rich garnets occur as euhedral crystals in extrusive and intrusive rocks which range in composition from 59 per cent, to 70 per cent. SiO2. Eight complete garnet analyses (major and trace elements) indicate a small variation in composition which, together with corresponding variation of physical properties, appear to correlate with the mineralogical composition of the containing rock. Field, microscopic and chemical evidence suggests, on balance, that the garnets are pyrogenetic. Magmatic conditions suitable for the crystallisation of almandine-rich garnet are discussed.

The origin of precious corundum found in the gem-bearing gravels of Ceylon has long been unknown. An occurrence of sapphire is described from a contact zone where syenite has been intruded into, and desilicated by, crystalline limestone. The process of desilication in such contact zones is considered capable of accounting for much of the gem-quality corundum of the island.

Some sedimentary structures commonly found at the base of beds of greywacke have been given a variety of names. It is suggested that the name flute-cast be used for scour-and-fill structures, which are shown to be oriented parallel to the direction of sediment movement. Superficially similar structures, described as flow-casts, are formed by movement of the greywacke during and after its deposition; study of their internal structure and their relations to ripple-direction shows them to be oriented at right angles to the current direction.