Available data from charnockitic rocks (including twenty-eight new pyroxene pairs fromAustralia) suggest that a major cause of variation in optically derived compositional tie-line trends of co-existing pyroxenes is related to the geothermal history of the rocks concerned. It may yet be possible to subdivide the granulite facies, and also to detect mineral instability by critical study of tie-line trends. Recommendations are made whereby mineralogic and structural studies of charnockitic rocks can be integrated to yield more reliable chemical and optical data.

The Lower Old Red Sandstone deposits of Ekmanfjorden belong mainly to the Lykta Division, but pale sandstones with Giganthaspis representingthe Kapp Kjeldsen Division also occur in the core of what is probably a N.-S. striking anticline. The lower beds of the Lykta Division are soft, dull and silty and not very fossiliferous; above them are some 1,100 feet of sandstones and conglomeratic beds alternatingwith shales or marls. Locally abundant vertebrate remains include the guide fossil Doryaspis. Various sedimentary structures suggest rapid deposition on a broad shallow delta front.

The English Bathonian contains a rich foraminiferal fauna composed largely of Lagenidae. The succession of foraminifera is as yet only partially revealed, but some faunal changes between the Lias and Bathonian are apparent, and four faunules have been distinguished in the Bathonian. In Dorset and the vicinity of Bath the faunules occur in the same order of superposition. In comparing the English Bathonian foraminifera with those in the German section the present data suggest that a number of species range higher in England than in Germany.

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.

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.

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

The two-dimensional theory of two simple generalizations of the Coulomb-Navier criterion for shear failure is developed. The first of these refers to a material with a single plane of weakness which has a different shear strength and coefficient of internal friction from the remainder of the material. In this case it is shown that failure may take place, according to circumstances, either in the plane of weakness or in planes cutting across it. The second criterion refers to a layered material whose shear strength varies continuously from a maximum in one direction to a minimum in the perpendicular direction. In this case it appears that, instead of the two directions of failure possible for an isotropic material, there is only one possible plane of failure which lies between the plane of minimum shear strength and the nearest to it of the two Coulomb-Navier planes. Numerical results are given for the case of uniaxial compression and experimental results are shown to be in reasonable agreement with them.

Petrofabric analysis has been carried out on Carboniferous rocks involved in thrust masses of the Benton system in Pembrokeshire. Evidence is contributed, which indicates stages of fracturing and crystallographic control in the deformation of individual quarts grains.