A small brachiopod fauna of early Permian age is recorded from pebbly mudstones and sandstones of the Phuket (Kaeng Krachan) Group at the Thai islands of Ko Muk, and Ko Phi Phi in the Andaman Sea. Most species belong to genera found in temperate to high Permian palaeolatitudes, whereas other Permian faunas from Thailand are strong in tropical affinities, suggesting that the pebbly mudstones are cool water deposits, contemporaneous with the late Asselian glacial deposits of Gondwana. New taxa are Arctitreta percostata sp.nov., Komukia solita gen.nov., sp.nov. (Rugosochonetidae), Cancrinelloides monticulus sp.nov., Rhynchopora culta sp.nov., Arionthia sapa sp.nov. and Elasmata retusus gen.nov., sp.nov. (Heterelasminidae).

A reinterpretation is attempted of the 25 years of graptolite ultrastructural work based upon the present state of knowledge. It is emphasized that studies need to embrace many more species of graptolites, particularly in the dichograptid groups, and with different growth stages, before the gross evolution of ultrastructural elements can be satisfactorily appraised. The factual (morphological, ultrastructural) data are themselves reappraised, summarized, and very tentatively related to Bulman's anagenetic grades of graptolite development.

From a study of silicified fossils, and in particular the microstructure of brachiopods, from the Wilmington Sands (Upper Cretaceous) of Devon, a model of skeletal silicification is proposed. Three distinct morphologies of silica were formed, controlled by the relative rates of silica supply and carbonate dissolution: (a) a fine-scale replacement of the original shell microstructure where silica was abundant; (b) a concentric ring morphology called ‘beekite’ where silica supply was limited, and (c) a granular white crust formed where carbonate dissolution was restricted. Silicification occurred during early diagenesis as a result of bacterial decay of organic matter intimately associated with skeletal fragments, within a sediment of restricted permeability. A build-up of CO2 probably caused dissolution of skeletal carbonate, and bicarbonate released from this caused local precipitation of silica. The proposed mechanism is belived to be of general applicability to micrite-rich carbonate sediments.

Boreholes penetrating the inverted limb of a major fold in an allochthonous thrust sheet at Chillaton, West Devon, revealed highly fossiliferous strata spanning the Devonian–Carboniferous boundary in continuous succession. Details of the fauna, which includes conodonts, trilobites and ostracods, are given. Abundant siphonodellid conodonts allow the boundary to be determined according to the recommendations of the working group on the Devonian–Carboniferous boundary of the IUGS Commission on Stratigraphy. The nature of the imbricate zone beneath the Main Thrust, in which the succession is situated, is described. In addition, the fabrics associated with thrusts which cut the olistostromic succession lower in the tectonic unit are discussed.

Authigenic albite occurring as euhedral overgrowths up to 400 μm in size is a characteristic feature of the Pendleside Limestone in the Craven Basin of northern England. The albite is very pure, low-albite in keeping with other authigenic albites in carbonate rocks. The detrital cores of the albites are angular plagioclase grains of approximately An20 composition which are sometimes altered to kaolinite. The albite crystals with their detrital cores are frequently concentrated in discrete laminae, suggesting that the plagioclase cores may have been supplied by a basic volcanogenic source. This view is supported by geochemical studies of limestones which reveal significant correlation between K–Na, Na–Al and K–Al.

Interstitial alteration of detrital components, in particular the reaction intermediate plagioclase → kaolinite + albite, was primarily responsible for albite authigenesis. The initial products of this reaction probably included smectite which fixed Mg2+ in the decomposing volcanic grains. Subsequent alteration of the smectite resulted in the formation of small microdolomite inclusions which are commonly seen in the authigenic albites. An equilibrium model in terms of Na+/H4 ratios and H4SiO4 activity is proposed for the silicate assemblages in the Pendleside Formation.

Extremely fine-grained granular rocks are found interleaved with cumulates in some layered differentiated intrusions. The question arises as to whether these can be interpreted as chilled magmas. If this were so it would allow the liquid line of descent to be determined directly. A study of extremely fine-grained granular rocks in the differentiated, layered basic Fongen–Hyllingen complex, Norway, however, showed rocks of this type to be cumulates. Fluctuations in volatile pressure due to crystallization of a hydrous phase may give rise to modal and grain-size variation in layered intrusions.

Granophyre patches on the sites of former sedimentary feldspars in the feldspathic Appin Quartzite show that partial melting took place in the inner parts of the aureoles of late Caledonian minor intrusions. Mobilization of the melt and refractory quartz residue as a thixotropic suspension is shown to result in the formation of veins and breccias. Textures are related to the wetting of quartz/quartz grain bounderies by the eutectic melt and the later growth of crystals during cooling. From the presence of high (β) quartz coexisting with melt, minimum contact temperatures are estimated as 780°C, showing that some convective circulation of magma took place.