Tear faults cutting the Barnesmore Granite in County Donegal are described. The Lough Belshade fault trends N.E.–S.W., and there has been a lateral movement along it in a left-handed or sinistral sense of 2·2 miles; it is believed to be of the same age as the Great Glen Fault. The Barnes Lough Fault crosses and displaces the Lough Belshade fracture, and may be, in part at least, Tertiary. Although the movement along it is much smaller, it has taken place in the opposite sense.

Alkaline syenites from the Ruri Hills in Western Kenya are described, and the hypothesis advanced that their present constitutions have been developed partly by replacement. The syenites occur as dykes and small plugs associated with ring complexes of carbonatites which, together with agglomerates, largely form the hills, and are presumed to be congeneric with an ijolite mass at Usaki.

Compact “streaky” rocks, from the Borrowdale Volcanic Series, English Lake District, are diagnosed in part as welded tuffs. Original glass is completely replaced, but similarity to welded tuffs elsewhere is shown by the dacitic-rhyodacitic composition, lack of bedding, and development of columnar jointing. The deposition of welded tuffs, as nuée ardentes, or incandescent tuff flows, is discussed.

The marine Johnstone Shell Bed, an important index horizon in the Limestone Coal Group of the Carboniferous of Scotland, is succeeded in North Ayrshire by a bed containing Lingula squamiformis Phillips, and many small shells here referred to a new species of the genus Carbonicola. This Carbonicola community has been examined in detail, and graphical representation of the great variability has been employed.

Previous descriptions of the plastron of Somaliaster Hawkins have been conflicting and, in consequence, there has been some doubt regarding the systematic position of this genus. The type-material has been re-examined and the plastron found to be meridosternous. Somaliaster is here referred to the family Stenonasteridae, where it has close affinities with Iraniaster Cotteau and Gauthier.

The brickearth of Pegwell Bay in Kent is identified as a true loess. It rests on solifluction deposits and frost-shattered rocks.

A record has been made of the outliers of Basal Grit occurring on the Limestone of the North Crop of the South Wales Coalfield, some of which have not previously been located. The solution subsidence theory to account for their present anomalous levels when compared with the parent Grit outcrop to the south has been enlarged upon, and an attempt has been made to determine the mechanism of this subsidence which ranges in vertical extent up to a maximum of approximately 600 feet. The outliers are of economic importance since their predominant crumbly quartzose sandstones are a source of almost pure silica sand.

It is demonstrated that a deficient mass reaching within 10 km. of the surface is responsible for the central belt of negative gravity anomalies in the Eastern Alps. Hypotheses for explanation of the deficient mass are discussed and it is concluded that the presence of unexposed granite in addition to crustal downwarp is the most satisfactory of these. The position of part of the mass deficiency is irreconcilable with existing isostatic hypotheses and an alternative hypothesis is proposed. The development of the granite mass deficiency is briefly discussed.

It is possible, from study of twinned calcite grains in a thin section of marble, to locate the most probable positions of the applied stresses likely to have caused the twinning. By this means inferences may be drawn as to the stress system operative during the late stage deformation of the marble.

Marble outcrops over an area of about 5 square miles, in the Tomintoul region of the Scottish Highlands, have been investigated. It has been found that a consistent stress pattern exists for the area as a whole. The calcite twinning can best be explained by a N.E.–S.W. compression applied normal to the trend of the regional fold axis, followed by a mild N.–S. squeeze.

The hypostome of a specimen of Encrinurus variolaris (Brongniart) from the Wenlock Limestone (Silurian) is described with particular reference to the intricate shape of the lateral wing. This lies very closely underneath the axial furrow of the cephalon in the region of the anterior pit, but it is unlikely that there was a direct articulation of the wing with the pit or the furrow during life.

Some variations in the apertures of Cribrohantkenina are arranged in morphological series. The development of the “cribrate” aperture and its relation to other biocharacters, such as the shape of the chambers, development of spines, and globosity of the chambers, is discussed, as also the status of the subgenera of the genus Hantkenina.

The paper records the results of petrofabric analyses of four specimens of marble from the South-West Highlands of Scotland. The marble fabric has a high degree of homogeneity. Calcite grains are flattened in the foliation plane and are elongate in a direction normal to the fold axis. The c crystal axes lie in a distinct girdle about b, with a maximum near the pole of the foliation; the a crystal axes tend to occupy three maxima, one of which is close to b. Late twinning has occurred on {011¯12} apparently in response to a simple stress system, operating in the ac plane. The symmetry of the general calcite fabric, the twinning and the megascopic structures coincide.

Optical examination of the potash feldspars in the granitic gneisses of the Carn Chuinneag-Inchbae complex suggests that both ortho-clase and microcline occur together—not infrequently in the same crystal. Optic axial and extinction angles, intermediate in value between those characteristic of the two polymorphs, have been recorded and plotted graphically. X-ray powder diffraction patterns confirm that both orthoclase and microcline are present together in these rocks. It is believed that most of the microcline developed from orthoclase during the regional metamorphism of the area, which permitted recrystallization at a lower temperature than that at which the orthoclase was formed.

The oldest formation exposed in the Gorsley area is a hard limestone considered by previous authors to be equivalent to the Aymestry Limestone. All the available evidence, however, supports a correlation with the Wenlock Limestone. The succeeding strata comprise 4½ feet of Dayia Beds and 7 feet of Upper Ludlow Beds, so that the total thickness of Ludlovian strata is only 11½ feet. AH the Lower Ludlow Shales and the Aymestry Limestone are cut out by the unconformity below the Dayia Beds. This remarkably thin development is attributed to movement at various times during the Ludlovian epoch along an axis passing through the Gorsley region. The main movements probably took place in middle Ludlow times.

The coarse porphyritic Aswan Granite used in many ancient Egyptian monuments has been held to intrude a tract of gneisses and schists. It is suggested in this paper that the granitic body was formed during a phase of granitization which followed the folding and metamorphism responsible for producing the gneisses and schists. A part of the granite retains mimetic structures inherited from the pre-existing rocks, but the southern part became mobile and developed a new structure. The intrusion of a magmatic granite in dykes and sheets followed the phase of granitization.

The inversion temperatures of the quartz from twenty-five specimens of the Beinn an Dubhaich granite have been measured and found to correspond to the inversion temperatures of quartz from rhyolites previously studied. Optical and X-ray studies of the alkali and plagioclase feldspars indicate high temperature modifications. The Beinn an Dubhaich granite has the textural and compositional features of a granite together with mineralogical features normally associated with rhyolitic rocks. The results serve to emphasize that methods are now available which make it possible in some cases to determine whether a particular granite was formed by metamorphism of sediments or by crystallization of a magma. It is concluded that the older granites and those which crystallized at greater depths probably have undergone considerable rearrangement of their mineralogical and textural features subsequent to primary crystallization.

Peridotite, troctolite, and olivine-gabbro are exposed in the Bourtie area at the eastern end of the Insch igneous mass. The distribution of outcrops suggests that the rocks are disposed in bands running north and south and a smaller-scale north-south banding can be seen in some exposures. The earlier view that the ultrabasic rocks form an east-west lens on the floor of a northerly-dipping gabbro sheet is therefore abandoned and both the northern and southern contacts are believed to be part of the roof of the igneous body.

Cyrtograptus hamatus, first described from Ireland by Baily in 1862, is now described more fully from fresh material which can be assigned to the zone of C. lundgreni. The proximal part of C. lundgreni is also described. Three species of Retiolitids occur with the Cyrtograptids, one of which, Paraplectograptus eiseli Manck, has not previously been recorded in the British Isles.

This paper describes a revised method of plotting analyses of igneous rock suites using the Mafic and Felsic Indices as defined. A composite M–F diagram has certain advantages over the triangular iron-magnesia-alkalis diagram and enables a genetic distinction to be made between the tholeiitic and calc-alkaline series.