The mylonitic character of the peridotites of St. Paul's Rocks on the Mid-Atlantic Ridge was reported in a contribution by the writer (Tilley, 1947), these ultrabasics then being referred to as dunite or peridotite mylonites. The available chemical analytical data were assembled in that paper and a new analysis provided of a two-pyroxene representative. The type carrying porphyroclastic amphibole was represented by an analysis by Washington (1930) but it was shown that this analysis erred in its alkali determination, and that the reported occurrence of jadeite could not be confirmed.

The Dictyonema species currently named flabelliforme (Eichwald) (as distinct from D. norvegicum Kjerulf) from the Tremadocian of Estonia is described and compared with the lectotype of Kjerulf's D. graptolithinum from Norway, and their synonymy is confirmed.

Investigations of the sedimentary rocks of the Umkondo System have enabled six zones of eastwardly increasing metamorphic grade to be delineated on the basis of index mineral assemblages in pelite horizons.

Chlorite, garnet (almandine), staurolite, kyanite, and sillimanite isograds have been recognized over a distance of 500 km. along the eastern border of Southern Rhodesia and are plotted on a map. More detailed reconnaissance work has been confined to the Barué highlands north-east of Inyanga. In addition, a “zone of intermediate isotopic age measurements” is proposed to the west of the lowermost chlorite zone. The isograds lie parallel to the structural edge of the north-south trending Mozambique orogenic belt and can be joined with those of similar metamorphic rocks in the east-west trending Zambesi orogenic belt, suggesting contemporaneity of the c. 500 m.y. regional tectono-thermal event in these two belts.

The character, horizon, and extent of ten kaolin tonsteins occurring in the Westphalian strata of the North Staffordshire Coalfield are described, and four additional horizons considered worthy of further study, when this is possible, are noted. The value of these kaolin tonsteins in correlation, and the possibility that they may fall into two groups having different origins, is briefly discussed.

The Caledonian dykes fall into two age groups, one older than the Newry complex and the other younger, and these have been compared with the Older and Younger Series of Caledonian dykes from the Ards Peninsula (Reynolds, 1931), which are older and younger respectively than the cleavage movements affecting the Silurian sediments. The suggestion is therefore made that the emplacement of the Newry complex and the cleavage movements in the Ards Peninsula were temporally associated events.

The Caledonian dykes are older than the joints in both the complex and the sediments, while the Tertiary dykes are younger.

Certain amygdaloid textural features have been observed in a diopside-potash felspar rock within the Lewisian of the Island of Tiree; so far as the writer is aware, such features have not previously been noted in Lewisian rocks.

Evidence as to the genesis of these textures is sparse but they appear to have attained their present nature after the principal metamorphic events which have affected the enclosing rocks.

Six serpentinites occur in the Moinian granulites of the North-East Ox Mountains. Four have been known for some time and have been previously described. Additional information on these and the associated vermiculite deposits is provided. The remaining two serpentinites are described for the first time. A pyroxenite vein associated with one of these may have been produced by meta-morphic regeneration.

The relationship of some of these serpentinites to the probable position of the Highland Boundary Fracture-zone in Eire is also discussed. Brief comparison is made with serpentinites occurring in the Scottish Moinian.

Diagnostic analcime-, heulandite-, and laumontite-bearing mineral assemblages from four areas in the Upper Carboniferous and the Permian of New South Wales have been correlated with the rank of the associated coals, represented by the carbon content of vitrinite. The coals are high-volatile bituminous to semi-anthracitic; their vitrinites contain from about 82 per cent up to an estimated 91 per cent carbon. Analcime-quartz is found associated with the lower-rank, the laumontite-rich assemblages with the higher-rank coals. Comparison with a similar correlation in Northern Yakutia (U.S.S.R.) indicates that diagnostic zeolites are not necessarily associated with coals of the same range of rank in different areas. Unlike the occurrence and stability range of burial metamorphic zeolitic assemblages, degree of coalification is probably independent of partial pressures of H2O and CO2: it is controlled mainly by maximum depth of burial, its duration, and the geothermal gradient.

Eighteen potash felspars from the potash felspar gneisses of the Connemara migmatite belt have been partially analysed and the associated plagioclase optically determined. Comparisons have been made with seventeen similar felspar pairs from the Galway Granite. Albite components are expressed graphically in an attempt to illustrate sodium distribution between associated felspar phases. On such a plot it is possible to contrast the “magmatic” felspars of the Galway Granite with those of the migmatitic gneisses; the separation of the two fields being a function of total rock chemistry. Crystallization temperatures have been determined by the two felspar method and the range 460 to 480° C. is thought to represent retrograde amphibolite conditions in the migmatitic gneisses, while petrographic evidence supports 550° C. as the temperature of amphibolite facies metamorphism in these rocks. Triclinicity measurements have also been made on the analysed potash felspars.

Certain lamprophyres in Moidart exhibit at least three sets of minor structures (cleavages, lineations and small-scale folds). During the formation of the first set the lamprophyres acquired a schistose fabric: hornblende and biotite laths crystallized along the axial surfaces of tightly compressed folds. The deformation episodes recognized in the lamprophyre sheets post-date the main episodes of major and minor folding (F1-F3) that affected the surrounding Moine gneisses. The existence of a metamorphic fabric in these lamprophyres raises interesting problems—was the thermal energy required to “metamorphose” the lamprophyres derived from deformational heat, or by a heat flow from the Moine country rocks, or were the lamprophyres deformed during cooling and consolidation from the magmatic state (autothermal metamorphism) ?

Various limestones of Middle Jurassic and younger age in the Middle East and Britain, and certain Recent calcareous marine sediments contain pellety debris stained grey or black with finely divided pyrite. The staining appears to involve deposition on pellety debris of limonite, followed by its reaction with bacterially produced hydrogen sulphide to form first ferrous sulphide and subsequently pyrite.

Basal and perhaps higher Coal Measures are overthrust by earlier rocks at the front of the Hercynian arc of southern Ireland. The marine bands, lacking cephalopod phases, are faunally poor and in respect are unlike the marine bands of the other Coal Measure outliers of the South. The coal seams are crushed and in part pulverized and appear to have developed a “pinch and swell” structure.

Unusual single kink-band sets in calcareous slates are described and their mechanism of formation discussed. Regional inferences are drawn concerning Armorican strike-slip movements.

A number of coarse-grained blocks, consisting of forsteritic olivine, chrome-diopside, calcic plagioclase, and chromite in varying proportions, were found in an ankaramitic basalt on Faial. With one exception, the blocks show remarkably little alteration. There is no evidence of zoning in any of the minerals. Indications of strain are frequent. Dark scoriaceous material is often present along intercrystal boundaries and fractures. The textures and gradations in composition suggest that these blocks were formed by crystal accumulation.

As a result of magnetic, seismic, and gravitational studies it has been possible to describe the nature of the boundaries of the Mountsorrel granite massif in more detail. Confirmation has been found of faulting postulated on other grounds; and also it is shown that there is no substantial underground extension of the granite beneath the surrounding Triassic countryside to the west of the outcrop.

The nature and origin of some soda-granites from the western part of the Singhbhum shear zone, Bihar, India, are discussed. These soda-granites are responsible for copper sulphide, apatite-magnetite, and uraniferous mineralization within the shear zone. Earlier workers regarded these rocks as sheared materials representing a portion of the high sodic residual liquid from the neighbouring Singhbhum granite magma. The present work indicates that these rocks are migmatitic in nature and are the products of progressive replacement of pre-existing pelitic and semi-pelitic schists by felspathic materials. Migmatization is essentially post-shearing in age while the Singhbhum granite is pre-shearing in age. The migmatitic materials appear to have been derived by the partial melting of the Singhbhum granite during shearing, particularly in depth, as a result of sudden release of confining pressure consequent upon shearing and generation of heat caused by friction at the base of the shear zone. The resulting liquids, which were albite rich, found easy passage through the shear zone and brought about migmatization and mineralization in its wake.

One of the internal contacts of a doleritic intrusion, Co. Donegal, is lined with large augite dendrites. The habit is revealed by parting on a median zone of chlorite which is regarded as an altered exsolution feature. It is suggested that an initial platy dendrite grew, in response to undercooling, as a metastable phase with the composition and structure of a high-calcic pigeonite. A later overgrowth of augite preserved the delicate crystal against destruction.

A new correlation of the Precambrian Torridonian sediments of Rhum and Skye is suggested which equates the Bagh na h-Uamha Shale of Rhum with the upper part of the Kinloch Formation in Skye and with the Diabaig Formation on the mainland. The Rudha na Roinne Grit, Loch nan Eala Arkose, and Guirdil Arkose of Rhum are correlated with the Applecross Formation. The occurrence of sedimentary cycles at the base of the Applecross in Rhum and Skye is noted. The strata beneath the Kinloch Formation in Skye are not represented either in Rhum or elsewhere on the foreland and do not belong to the Diabaig.

The Lower Cretaceous Palaeogeography of the British Isles and surrounding areas is postulated from micropalaeontological and stratigraphical evidence and its implications discussed.

In an attempt to obtain information about garnet nucleation a series of eleven apparently homogeneous metamorphic rocks, from a small area near Mallaig, Inverness, Scotland, have been analysed to determine bulk chemical and modal compositions, garnet grain size and number of garnet crystals occurring in unit volume of rock (N). No correlation of N with any function of chemical and modal compositions could be found, and it is therefore concluded that, if the influence of trace components can be neglected, externally imposed factors (for example, time-temperature variation) or internal physical factors (for example, the surface area of the rock just prior to garnet formation) must exert a controlling influence on garnet nucleation. It was found, however, that in each specimen, there was a preferred crystal radius and the relative frequency of occurrence about this preferred value was constant for all samples studied. Preliminary comparison with other systems, investigated by the authors, suggested that the nature of this relationship may provide evidence of the conditions under which these rocks recrystallized.