The orientation of the optical indicatrix in synthetic and volcanic plagioclases differs from that in plutonic and metamorphic plagioclases, the former “optics” being commonly known as “high-temperature”, and the latter as “low-temperature”. The difference between the two series is most marked at the sodic end and decreases towards An70. The conclusion that the difference, though small, still persists in the range An70 to An100 is shown to be unwarranted on the evidence available. Grave doubt is thrown on the supposition that temperature is the controlling factor in determining the type of optics by Tuttle and Bowen's failure to synthesize low-temperature albite, even at low temperatures. It is known, however, that some low-temperature plagioclases (e.g. in albite-schists) have grown without the intervention of melt. The real antithesis may therefore be between plagioclases crystallized from melts, and those developed during the metamorphic reconstitution of rocks.

From the fact that the plagioclase, quartz, and alkali feldspar of undoubted magmatic rocks such as quartz-porphyry and rhyolite are respectively systematically different from those of granite it is concluded that the latter is a metamorphic rock

The ontogeny of Dalmanitina olini Temple (Upper Ordovician) is described on the basis of specimens from Scania and North Wales. The development is similar to that of D. socialis (Barrande), but good preservation has enabled some detailed changes in the cephalon to be followed. The protaspid and early post-protaspid stages bear an anterior pit in each axial furrow opposite the frontal lobe. The protaspid anterior glabellar furrow becomes joined to this pit by an oblique furrow, and forms with the latter a composite oblique furrow which develops into the adult anterior-glabellar furrow. This mode of development is considered probably to be common to all Phacopids: the significance of the anterior pits in this family is discussed. Preliminary observations are made on the growth-rates of various parts of the glabella, and the frontal lobe is found to grow in length (sag.) at a rate approximately equal to that of the rest of the glabella.

The history of this block of low-grade metamorphic sediments begins with sedimentation, followed by strong deformation. Intrusion of spessartite dykes then took place, after which movement was resumed with deformation of the spessartites. Next followed jointing and the production of peculiar structures here called joint-drags. The final episode was one of block faulting, to which the formation of the Muness Phyllite Block itself as a graben is due.

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 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.

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.