Metamorphosed limestones carrying tilleyite are described from the northern slopes of Glen Dibidil, Isle of Rhum.

This note records the presence of Eocene limestones in situ on the bed of the English Channel along an east-west line to the west of the island of Jersey. The microfauna of samples of these limestones is compared with those of some other beds of similar age. There are comments on the relevance of the above discoveries to the structural history of the area.

Air-heave structures have previously been described from marine lagoonal deposits, both from present day and ancient sediments. This paper records the find of such structures in playa sediments from the Scottish Old Red—perhaps the first record of such structures from non-marine sediments in the geological column. It is suggested that the structures were formed on the beaches of “Lake Caledonia”, “during a storm, seich, or a heavy rainfall”.

Two dissimilar rocks have been confused under the title “cornstone”: one is a concretionary limestone, the other a calcareous conglomerate. A return to the names “concretionary cornstone” and “conglomeratic cornstone” is advocated since the rocks differ in their significance. Conglomeratic cornstones, intra-formational in character, point to sudden increases in current activity. Concretionary cornstones suggest declines in the supplies of clastic detritus.

Idiomorphic, pale blue corundum crystals (S.G. =4·02, n0=1·770 ± 0·002) up to one inch long occur as porphyroblasts in a finegrained biotite-sillimanite gneiss cut by pegmatite veins at Gangoda, 5½ miles south of Polgahawela. The field relations and petrography of the corundum-bearing rocks are described briefly. The corundum is thought to have crystallized by metamorphic differentiation in alumina-rich silica-poor bands in a semipelitic gneiss.

From assemblages of Upper Jurassic organic-shelled microplankton from Dorset are described five new species of hystrichospheres. Of these, two are attributed to a new genus, Polystephanosphaera; one new species of the genus Hystrichosphaeridium, and two of the genus Baltisphaeridium are also described.

The well-known Carboniferous cyclothems of North America and Europe are discussed as examples to illustrate the great extent and lateral variation of sedimentary cycles. Very many other instances of cyclic sedimentation, in rocks of most ages, in many parts of the world, are also characterized by a more or less regular lateral migration of simultaneously existing depositional environments, caused by repeated transgressions and regressions of the sea over an epicontinental platform. Theories of varying complexity which have sought to explain cyclic sedimentation are briefly summarized, and it is suggested that the two basic requirements are a slowly subsiding sedimentary basin and more or less regular eustatic changes of sea level. The former will decide the geographical location. The latter could be a natural, periodic and world-wide consequence of the combination of the continuous effects of sedimentation and sostatic or orogenic movements of the sea floor.

Ignimbrite steeply intrusive into the basaltic agglomerate of the Kilchrist vent is described. Like the intrusive ignimbrite near Kilchoan, Ardnarnurchan, it shows flow structure parallel to the walls, flow being similarly expressed by the elongation and alignment of the constituent shreds of devitrified glass and pumice lapilli. Fragments of basalt, derived from the vent agglomerate, are sometimes also drawn out in the direction of flow.

The lower part of the limestone succession of the Hagab Monocline in the Oman Peninsula, Arabia, is divided into the Bih Dolomite (Permian, 650 m.), Hagil Limestone (Permian, 260 m.), Ghail Limestone (Trias, 600 m.) and the Elphinstone Beds (Noric, 431 m.). The latter consists of five formations, two of which are very fossiliferous. The succession also occurs to the south in borings in the forelands of the Oman Mountains and is similar to that of the foreland of the Zagros Range of Iran.

An outcrop of obsidian pebbles in a grey volcanic rock was investigated in the field and subsequently examined in the laboratory by means of optical, X-ray, and D.T.A. methods. The results show that the grey rock arose from obsidian through a micro-cracking, causing a formation of marekanite balls (massive obsidian) surrounded by a very brittle grey rock (micro-cracked but completely unaltered volcanic glass).

Certain microtonalite dykes cut across the flow banding of the Main Donegal Granite in the direction of an important cross-joint, yet they and their granite host are shown to have crystallized together and in the same manner as both the darker flow bands in the granite and the pelitic xenoliths within it. It appears that an embryonic joint system existed in the Donegal Granite before consolidation and crystallization were complete. It is suggested that the early dykes represent metasomatized pelitic enclave material and are not differentation products of granitic magma. Comparison is made with the basic analogue provided by the beerbachite enclaves and dykes of the hypersthene-gabbro of Ardnamurchan.

An area of high, north-eastward plunge of b-axes has been mapped in Silurian greywackes around the mouth of Strangford Lough, N. Ireland. Reconnaisance over a wider area to the south-west is consistent with the hypothesis that this steep plunge is due to the upward push exerted during the emplacement of the Newry Granodiorite. A near surface extension of the intrusion towards the east-north-east is inferred.

A garnet-hornblende-two pyroxene rock from Glenelg is described. It is assigned to the eclogite facies by virture of its density, mineral composition, and associations. Its chemical composition is that of a picrite-basalt. Comparison with other garnet-pyroxene assemblages suggests that there are no clear differences between the partition of major and minor elements in these minerals at the eclogite and granulite facies of metamorphism. A diagram to represent parageneses in basic and ultrabasic rocks of the eclogite facies is presented, and points of interest discussed.

Two basic xenoliths were taken from the Shap adamellite and two from the Glen Fyne porphyritic granodiorite. Each specimen was divided into the three parts; margin and core of the xenolith and the surrounding host rock. Porphyritic alkali feldspar and sphene were separated from each part and the rocks and minerals were analysed for trace elements and for Na and K. Four specimens of the assumed parent rocks of the xenoliths were also analysed. The results indicate that the two host rocks are similar in trace element content, that equilibrium between minerals in host rock and xenoliths extends to their trace element content and that late stage magmatic fractions may have played a part in the alteration of the xenoliths.

Crop markings reveal a polygonal network resembling that of “patterned ground” in arctic Alaska. From this the former presence of perennially frozen ground is inferred, with the implication that the mean annual isotherm of this part of Worcestershire was at least 13½° C. lower than it is at present. It is argued that this condition obtained at the period of the Irish Sea Glaciation maximum.

A new instrument for the use of field geologists in orientation studies is described; the method of use is outlined and briefly appraised in comparison with common practice.

Comparison of streaked-out “ripples” formed by the drag effects of a current passing over a watery, yet cohesive sediment bottom with convoluted laminae formed within beds of fine-grained sandstone suggests a common origin. Application of Bagnold's recent discoveries on the behaviour of cohesionless sediment in flowing fluids to the problem results in a modification of Kuenen's hypothesis of origin of the convolutions. According to the new interpretation, convolutions arise when formerly cohesionless sand grains become cohesive after deposition and respond to increased shearing due to higher current velocity by a décollementtype of adjustment with the plane or planes of adjustment located within, or in some cases at or below the base of the growing sandstone bed. Convolute “anticlines” in cohesive sand are thought to serve the same function as that played by current ripple-marks in cohesionless sand, i.e., they create additional bottom relief in order to increase the drag and restore equilibrium to the added shearing stress imposed by the current that cannot be counterbalanced by grain-to-grain encounters.

Allogenic biotite flakes, together with fish and conodont remains, are concentrated into bands at particular horizons within Upper Ludlovian rocks of Woolhope and other Welsh Borderland areas; and are present but more scattered within the Aymestry Limestone and Dayia Beds. Metamorphic rocks of Malvernian type appear to have provided the source of the biotite.

Mugearite is described for the first time from the Tertiary lava series of Antrim, Ireland.

Eight nomenclatural problems connected with Mesozoic brachio-pods of the suborder Rhynchonelloidea are discussed and solutions suggested. A new genus is proposed related to Halorella and a new name is given to a species of Norella