Phacops turco aff. praecedens Haas, from the Devonian (Eifelian) of Morocco, varies in the type of lens packing in the eye. Cubic close packing in trilobite eyes is described for the first time.

In northern Snowdonia welded ash-flow tuffs, correlated with the Pitt's Head Tuff Formation occur intercalated with Caradoc shallow marine shelf sediments. Within the tuffs there are vent-like structures which have a diapiric form where fiamme are drawn in towards a central core. The cores may have a constrictional linear fabric of streaked out fiamme, or may consist of vitrous tuff surrounded by a zone of buckled planar fiamme. There are associated zones of quartz nodules which are thought to represent quartz filled vesicles. The diapiric structures are believed to be rootless vents. Steam generated by the heat of the flow in contact with shallow water is thought to have caused explosive disruption of the tuffs as consolidation and welding occurred. These structures are thus themselves indicators of deposition of ash-flow tuffs in a shallow water environment.

The Ewarara Intrusion of central Australia contains two vertical fine-banded horizons within a sequence of sub-horizontal ultramafic cumulates. The horizons are arranged in an en échelon pattern adjacent to a steep intrusional contact, and consist of an alternation of two layer types which correspond to the two major lithologies present in the horizontal sequence. The horizons are up to 5 m thick. A number of possible origins, including folding of originally horizontal cumulates, flow differentiation and multiple injection, do not satisfactorily explain the formation of the layering. The most likely origin appears to involve differential viscous flow along the steep contact of an inhomogeneous crystal mush derived from the horizontal layered sequence. This mobilization is related to fresh injections along a feeder zone trending 060µ, the only such zone recognized in the Giles Complex.

The differentiated dyke rocks of Mer Mundwara comprise a subalkaline series which includes basalts and dolerites, and an alkaline series which includes theralites, porphyritic alkali syenites and nepheline syenites. These intrude into the coarse grained Precambrian granites which, in their turn, are subjacent bodies in the Aravalli system of metamorphic complex of archaean age. Absolute age of basic volcanics is 56±8 Ma, thus relating their emplacement to Deccan Trap volcanism in the Cretaceo-Eocene times in Central and Western India. Petrochemical characteristics of the basic rocks exemplify an alkaline character and so indicate that the basaltic magma of Mer Mundwara is tectonically and genetically different from the Deccan basalts which are in the main tholeiitic. The geological setting, petrography and major and minor element chemistry (Na > K and abundance of Nb, Co, Sn and V) relegate the dyke rock suite to the alkaligabbroic formations of Borodin (1974) with their parent magmatic source in the upper mantle. The alkaline igneous rocks of Mer Mundwara strongly suggest a possible occurrence of rare earths, niobium, zirconium and fluorine in industrial concentrations and also thorium and phosphorus.

Previous radiometric age determinations for the Criffell–Dalbeattie and Cairnsmore of Fleet Newer Granite intrusions are briefly reviewed. Thirteen fission-track dating results are presented for the co-existing accessory minerals sphene, zircon and apatite separated from the two granites. The mean sphene apparent age of 401±10 Ma and single zircon apparent age of 389±26 Ma are interpreted as the age of initial post-intrusion cooling of the granites. Results from apatite are discordant with those of sphene and zircon. Four determinations give a mean Upper Cretaceous apparent age of ∼ 80 Ma which is not readily interpreted. A single apatite determination upon a sample located adjacent to a basaltic dyke yielded a Tertiary age.

Igneous layering resulting from variations in intercumulus mineralogy has been observed in the Kalka Intrusion in central Australia. The layering is parallel to cumulus layering, and is outlined by a mottled heteradcumulus ‘clump’ texture in leucogabbros, which occur in a generally adcumulate anorthositic sequence. Such intercumulus layering is thought to originate in slow cooling intrusions at times of slow crystal accumulation and/or relatively high rates of intercumulus crystallization when a zone of melt supersaturation (the cumulus nucleation zone) rises above the intrusion floor leaving the intercumulus melt undersaturated with respect to the settled cumulus phases. Adcumulates are produced when the supersaturated zone is coincident with the top of the crystal pile. The morphological elongation of clump plates parallel to the gross layering is probably controlled by the cumulus plagioclase fabric which tends to be planar laminate.

Evidence is presented that some fibrous veins may be formed by recrystallization of the original rock in place. It is suggested that water in a joint promotes pressure solution of the adjacent wall rock. Redeposition under conditions of tensile strain crystallization causes growth of crystal fibres into the joint and into the wall. The effects of this process are revealed by reference to fibrous veins that are present in the laminated, dolomitic, quartz sediments at Mount Isa Mine.

A method is presented using a nomogram to estimate the size of a random sample from a normal population.

A temporary exposure of the Abbey Shales at Vernons Lane, Nuneaton, yielded a lower Paradoxides davidis fauna. The absence of the upper Paradoxides davidis fauna confirms the southerly overstep of the Abbey Shales by the overlying Mancetter Grits and Shales. Well-preserved fragments of Clarella impar (Hicks) and Tomagnostus gracilis (Illing) are illustrated.

In the Iglesia Irca intrusion early undifferentiated pulses of granitic magma were emplaced at pressures of approximately 1 kb as narrow dykes of vesicular felsite. These dykes are associated with penecontemporaneous burst breccias and gas breccias and are themselves sometimes brecciated. Subsequently a large dyke of granophyre, representing a more fractionated composition, was emplaced by subsidence and stoping along the line of earlier microbreccias, explosion breccias and felsites. The dyke cooled relatively slowly at low structural levels and retained its volatiles while at higher levels more rapid cooling accompanied the greater escape of volatiles. This resulted in marked potassium enrichment of the upper levels of the dyke and the country rocks of the hanging wall. It is argued that the Iglesia Irca intrusion provides an example of the association of gas brecciation with vesiculating and volatile-rich magma which is atypical of the Coastal Batholith as a whole.

Textural and chemical data on altered ‘spinifex’ (i.e. quench texture) ultramafic rocks from Corsair, near Kalgoorlie, Western Australia, have indicated that serpentinisation of contained olivine phenocrysts involved a volume increase of some 60%, due to the addition of both SiO2 and H2O.

In the pre-Anglian Pleistocene of East Anglia and Essex are unfossiliferous gravels with pebbles of flint, quartz, quartzite, chert and volcanic rocks. All appear to belong to the Kesgrave Sands and Gravels of Rose & Allen (1976), which are largely or wholly fluviatile and probably of Beestonian age. Forty-six of the volcanic pebbles, from three different localities, have been examined microscopically. Almost all are fine-grained acid igneous rocks or vitric tuffs, evidently derived from a single suite. Various possible source-areas are considered, of which North Wales, with its Ordovician volcanics, is thought to be the most likely.

Cavities in Cretaceous chalk, Co. Antrim, contain spongy silica. SEM photographs show minute doubly terminated quartz crystals trapped in fibrous mats of amorphous silica. The absence of both opal diffraction lines and a globular structure indicate the prior existence of gelatinous silica which prevented settling of the suspended quartz crystals. Drying and shrinkage of the gel produced the spongy deposit.

A boulder of plutonic igneous rock, petrologically perhaps best termed a trondhjemite, which occurs as an isolated megaclast in slumped mudstones of the Singa Formation (mainly Carboniferous) at Pulau Tepor off NW Malaya, has been dated by the potassium–argon method. Two feldspar fractions, thought to represent alkali feldspar and plagioclase (though both are highly sodic) yield ages of 1029±15 Ma and 575±10 Ma, respectively, while a whole-rock sample yields an age of 264±4 Ma. The highest age is taken to give a minimum age for the rock, and the lower ages to indicate differential argon loss. This is the first radiometrically proved Precambrian rock from the Malay Peninsula, and tends to reinforce earlier inferences of a Precambrian continent as a source area for Palaeozoic sediments in the region.

Evidence is presented for Liassic (Toarcian) faulting at Watton Cliff in coastal W Dorset. This movement is inferred from the abrupt changes in thickness of the Junction Bed and contiguous strata given that the contact with the overlying shale and clay is horizontal. Further evidence for synsedimentary movement is manifested by the presence, in the palaeofault zone, of numerous calcilutite-filled fissures penetrating a coarser, more sandy matrix. These neptunian dykes and sills contain abundant ammonites of the middle to late Toarcian, presumably the time of fault movement. This onshore Jurassic palaeofault broadens the known extent of such features from Sutherland (Brora—Helmsdale Fault) and Yorkshire (Peak Fault) to include southern Britain.