Textural differences in the occurrence of microcline define augen gneisses, subhedral porphyroblastic gneisses and euhedral porphyroblastic gneisses within the Bartica Assemblage, British Guiana. The introduction of microcline is metasomatic and the nature of the porphyroblasts appears to be a reflection of tectonic control during their development.

The late-formed joint sets in the Armorican belt of south Pembrokeshire are younger than both the folds and wrench faults of the region. On fold limbs these joint sets are oriented normal to bedding surface and symmetrically about axial-traces. Lens-belts and joint-drags parallel to the joint sets indicate a shearing pattern parallel to stratification planes. The orientations of fractures in collapsed blocks of Carboniferous Limestone, in Triassic breccias, show that the late joints were formed before the end of the Triassic. The term kathetal-joints is used for those which always remain normal to bedding surfaces.

Basalt groundmass textural nomenclature is reviewed and revised. The intergranular and ophitic extures are seen as end members of a series with steadily increasing grain-size, the international representative of which is here termed the “isogranular” texture. Undere intrusive conditions the series may be extended to include the poikilitic texture. Ophitic texture is regarded as an intergrowth;the term “sub-ophitic”s not suitable for basalts but may be retained for texturally isotropic rocks. When basalts cool hurriedly they will tend to develop an intergranular texture whereas extension of the crystallization period permits the formation of an ophitic texture. Cooling conditions will be determined by a combination of the effects of the volatile concentration and the flow characteristics, the latter partly depending on topography.

The nepheline syenites of Koraput, Orissa, in eastern India, are described for the first time with mineralogical details. The major rock type is a hypersolvus nepheline syenite. The mafic minerals are iron-rich biotite and subordinate alkali ferrohastingsite, the latter coexisting with titanomagnetite. The crystallization history of the magma has been interpreted in the light of chemical data on the rock and coexisting nepheline and alkali feldspar.