Ultrabasic lavas of variable picritic-peridotitic composition are found widely distributed in the Upper Pillow Lava member of the Troodos Volcanic Series in Cyprus. Recent work reveals layering of olivine crystals in both lava flows and pillows. An account is given of the field relations of the layered units, their petrography, mineralogy and chemistry.

The ‘Maelifell caldera’ is the name given to a separate collapse area situated on the southern margin of the main caldera of the Tertiary Alftafjordur volcano. It is 2 km in diameter and is made up of inward dipping welded tuffs, agglomerate (including patches of welded agglomerate), tuffaceous sediments and rhyolite and andesite lavas. The welded tuffs occur as thin pitchstone sheets and as much thicker felsitic masses: the former contain inclusions of basalt glass and are good examples of the simultaneous eruption of acid and basic magmas. It is suggested that the caldera represents the core of a parasitic volcano, beneath which there was a high level acid magma chamber, the immediate source of the local acid rocks. The magma chamber was intersected by numerous intrusions of basic magma, and these caused explosive eruptions and the emission of acid and basic magma to form thin pitchstone sheets. Decreased pressure in the magma chamber after eruptions caused repeated collapse within the cal

Field, petrographic and chemical studies on the Silurian volcanic rocks of the Mendip Hills show that there are probably 15 or more rock units in the series including andesite and rhyodacite lavas, rhyodacite tuffs, agglomerates, and a dolerite dyke. The predominant rock type is rhyodacite which may be as much as 80 percent of the volcanics. Volcanics of Silurian age from the Tortworth area, Gloucestershire, are of latite-andesite composition.

The Mendip rocks have been deuterically altered. Calcite-quartz-laumontite veins are common in fractures in these rocks. The agglomerates are particularly susceptible to weathering and some bombs are extensively altered to clays. Twelve rocks were chemically analysed for 36 elements each. No anomalous base metal concentrations were found in the volcanics although Pb, Zn, and Cu mineralisation is known in the area. K/Rb varies from 202 to 909 in these calc-alkaline rocks.

A recent excavation at Newtown Unthank, 9 km west of Leicester, has permitted study of the sub-alluvial gravels of the Rothley Brook valley. The junction of the gravels with the underlying Keuper Marl is sharply contorted, with an upward progression from undisturbed bedrock, through displaced marl and siltstone layers into masses of marl which have apparently been thrust up into the overlying gravel and incorporate many foreign stones. Possible causes of the structures are outlined, and reasons adduced for believing them to be of periglacial origin and of Weichselian age. Comparable occurrences have been recorded from elsewhere in the Soar basin, and also from other parts of the Midlands, and these are briefly discussed.

Study of arenite—rudite bodies within the traditional Welsh basin reveals two contrasted modes of situation, here termed concordant and discordant It is inferred that the former represent submarine fans developed on relatively level topography and the latter represent submarine channels adjacent to (and incising) major breaks in palaeoslope. The size and disposition of these palaeoslopes makes their control by deep fractures very probable.

The calcite of brachiopod, lamellibranch and echinoid shells from the Upper and Middle Chalk of Hertfordshire and Bedfordshire is partly replaced by chalcedonic silica. The crystallographic forms of the silica are described, and its diagenetic emplacement inferred from thin section studies.

The rocks of the Skiddaw Group of the Black Combe inlier were subjected to low grade regional metamorphism during the D1 movementphase of an intra-Lower Ordovician orogenic episode. Mimetic recrystallisation of clay minerals parallel to the bedding was ubiquitous. Later, axial-plane cleavages were superimposed on this fabric. The nature of the cleavages and possible mechanism of their formation is discussed.

Silica has been mobilised on at least three occasions during the tectonic history of the inlier. In no case was this due to metasomatism but simply to metamorphic differentiation. The D1 veins are of either quartz, or quartz and chlorite whereas veins of later generations are of quartz alone.