Chromite-marbles from India and Finland are compared.

The occurrence of large blocks of fossiliferous Cretaceous limestone among the Lower Cretaceous shales of the Central Range area of Trinidad, B.W.I., has been known for many years, and several different modes of origin have been advanced. A critical exposure which shows the field relationships between the shales and limestone blocks is described, from which it is concluded that the limestone blocks were derived from the contemporaneous breaking up of limestone reefs, and the inclusion of such blocks, together with fore-reef breccia, in the adjacent shale deposits.

Detailed mapping of a small area has shown that the Eilde Schist undergoes marked variations of facies when traced southwards from Loch Leven. Through the appearance of interbedded quartzite the normal schist of the western outcrop passes into a banded facies, while much of the banded facies of the eastern outcrop is believed to pass into massive quartzite mapped as Elide Quartzite. This sedimentary transition, rather than tectonic causes, probably accounts for the rapid variations in thickness of the two stratigraphical units. An additional factor controlling the thickness of the Elide Schist belonging to the eastern outcrop is the existence of an erosional surface at the base of the succeeding Binnenian Quartzite. The possible significance of these factors in the geology of the country north of Loch Leven is discussed briefly with special reference to some of the minor slides.

The use of the term mugearite as a synonym for oligoclase-basalt is discussed. It is shown that the two rock-types, though often agreeing closely in chemical composition, may differ appreciably in their fabric and mineralogy.

An unusual appinitic sill intrudes and thermally alters regionally metamorphosed Dalradian sediments near Killin, Perthshire. The sill is composed of ultrabasic, basic, dioritic, and acid varieties, the last two being present only in minor quantity. The dioritic intrudes, and is chilled against the ultrabasic type. The appinitic varieties and contact Dalradian rocks are described together with their field relationships.

The Malvern ridge consists of a series of Pre-Cambrian fault-blocks, which have been thrust upwards into their present positions through an overlying cover of Cambrian, Silurian, and Lower Old Red Sandstone sediments. The formation of the narrow. localized belt of folds which lie immediately to the west of the Malverns is the result of the displacement of the Pre-Cambrian basement blocks.

A possible cause of the lineation developed in the Scottish Highlands and elsewhere may consist in the presence of sub-crustal convection currents. While it is recognized that these are, to some extent, conjectural, the probable results of the conjecture are compared with the directions of lineation, in areas where this structure has been investigated.

This paper provides field and petrographic evidence believed by the authors to indicate that the Great Glen, over a lateral distance of some 40 miles between Fort William and Foyers, is flanked on the south-east by a broad crush-belt characterized by intense cataclasis and localized mylonitization. Most of the detailed evidence has not previously been published.

The carbonatite plugs of Eastern Uganda represent the final phase of Elgon type volcanoes. The types of structure observed in the carbonatites are discussed and a general description of the structural components of the Tororo Hills is given. It is suggested that the ring features originated through the congealing in the conduit of the central portion of the carbonate mass.

There are two alternative hypotheses regarding the relationship of the goniatite-bearing reef limestones to the coral-bearing “massif” limestones. One claims an unconformity between the reefs and bedded limestones, the other a lateral passage from a “massif facies” to “marginal facies”. Surface exposures are such that it is difficult to be convinced of either hypothesis. Details of underground exposures in natural cave systems and associated mine-workings show a clear transition between facies and no trace of unconformity.

The following note provides the first detailed description of an inlier of metamorphic rocks occurring in the core of an anticline of Carboniferous Limestone at Rosses Point, three miles north-west of Sligo.

The metamorphic rocks are shown to belong to the kyanite zone; comparison with the Lough Derg area suggests a Moinian Age.

An attempt is made to correlate the concept of the fossil lineage with our knowledge of polytypic species. The influence of changing environmental conditions in the geological succession and the relationship between geographical and chronological sub-species is analysed on a theoretical basis. The fossil lineage is considered to be the resultant of combined evolutionary and environmental change. Phenotypic modifications in response to environmental conditions are discussed in relation to the study of variation in fossil communities.

Thin bands of fibrous calcite occur in the Carboniferous reef limestones of northern England and have been regarded as bands of primary tufa within a marine limestone series. A study of these fibrous bands has been carried out and the results show conclusively that they are in fact secondary recrystallization structures.

Description of ash which fell on a trawler, fishing off Iceland, during the first hours of the 1947 Hekla eruption. Discussion of the probable track of the ash from the volcano to the ship and the factors affecting sorting involving upper wind velocities, terminal velocities of the various sizes of pumice and mineral fragments which constitute the ash, and weather conditions.

A preliminary report is presented on the paragenesis of the Varuträsk pegmatite, situated about 10 km. from Skellefteå, in Sweden. Three main stages can be distinguished (a) An epimagmatic-pegmatitoid stage during which the primary zonal development of the pegmatite body into border zone, wall zone, intermediate zones, and core was accomplished; (b) a hydrothermal replacement stage, divisible into a high temperature phase with a Li-replacement unit and a Cs-replacement unit, and a lower temperature phase with a cleavelandite replacement unit and a feebly developed fluorite unit (c) a final stage of supergene alteration. The age of the pegmatite lies between 1650 and 1800 million years.

A group of eruptive rocks (weilburgites), widespread in the Lahn-region, is discussed in respect to its genesis. Their close relation to the keratophyres suggests a later mobilization of the keratophyric magma through the volatiles originating from the ascending diabasic magma (allopegmagenesis). In accordance with the character of the weilburgitic magma its ascent was accomplished by adaptation to the orogenic process (gradational ascent).

Conditions of this kind might influence the magmatic evolution in several respects. They are intimately related to geological conditions. To them are referred the favouring of allopegmagenetic or even allomagmagenic rocks in Palaeozoic time, the possible difference in age between the beginning of ascent and the emplacement, the lack of correspondence in composition of some rocks with the composition of the originating magma. Thus, the question arises as to how far correlations may exist generally between the mode of magmatic evolution in space and time, the composition of the rocks and the geological age.

The discovery of a glacial erratic boulder of Shap Granite in South Northumberland is recorded. Erratics of this rock have not previously been reported north of the Penrith area. It is suggested that the boulder was carried into Northumberland by ice flowing eastwards over the Tyne Gap.