The Torridonian rocks of Rhum are divided into five sub-divisions on lithological grounds and the succession is found to be closely comparable with that of Skye. On the basis of the comparison, four sub-divisions, totalling 8,500 feet in thickness, are allocated to the Diabaig Group while the 6,000 feet of strata belonging to the fifth and highest sub-division are allocated to the Applecross Group. The sediments of the Diabaig Group are now seen to form a great wedge thickening and coarsening consistently from Gairloch south-south-westwards to Rhum; a phenomenon obscured by the previously held correlation of the Rhum Torridonian with that of Skye and the Mainland.

The known carbonatite eruptive centres in Northern Rhodesia fall within a linear belt trending N.E.-S.W. the most conspicuous elements of which are the colinear troughs of the mid-Zambezi valley and the Luangwa rift. This lineament is an important and longstanding zone of crustal weakness. Its extensions outside Northern Rhodesia are briefly indicated and its ramifications inside the Territory are examined, particularly in reference to the localization of carbonatite activity around rift intersections.

The Cornbrook Sandstone of Titterstone Clee Hill has plants of Westphalian (Middle Coal Measures) age. It is thus probably a correlative of the lower Kinlet Group of the Forest of Wyre. The base is unconformable to the Old Red Sandstone and Carboniferous Limestone while the top is apparently conformable with Productive Coal Measures of the Sweet Coal Group, also of Middle Coal Measures age.

The paper describes an unconformable junction of Upper Llandovery upon Malvernian in the Gullet Quarry of the South Malvern Range and discusses the evidence for and the significance of other comparable junctions in the Malverns. It is considered that Taconic movements are a factor in Malvern tectonics and that the importance of a “ western boundary fault ” to the Malvernian has been overstressed in the past.

Recent studies concerned with the application of rock magnetism to several geological problems serve to illustrate the scope of the methods at present available. Rock magnetism can usefully be applied to determine the age of a rock or to correlate it with some other. It may be used in studying the structural history of a formation or the thermal history of a rock. The examples cited deal with igneous rocks in Britain, but the methods also apply to some sediments, and possibly to metamorphic rocks.

It is stressed that rock magnetism can be applied quite independently of any theory concerning the earth's field. It is necessary only to establish whether the magnetism measured in the laboratory is a true record of that acquired when the rock formed, or at some other known time in its history.

Petrofabric analyses of quartz c-axes have been made at four locations round a fold in a calc-silicate rock. The movement direction during the folding is deduced from the deformation of an older lineation. Two fabrics are present: the earlier, associated with the deformed lineation, is being replaced by a fabric associated with the formation of the fold. It is shown how the symmetry of the later fabric is related not to the axis of the fold but to the direction of the movement that produced the fold; and how the quartz c-axes lie on a conical surface, giving a small circle on a stereogram plot.

Shearing stresses acting on an incompetent layer confined between competent beds during its deformation in the development of folds, differ from those commonly accepted as the cause of a number of minor structures associated with the deformation. It is suggested that the effect of bedding drag is negligible, and that the structures described as slaty cleavage, fracture cleavage, and drag folds can be explained by the laminar flow of the incompetent material whilst accommodating itself to the interspaces determined by the more competent layers.

Published descriptions and new field observations in Ireland and Canada confirm that strain-slip cleavage should not be classified with fracture cleavage. The term crenulation cleavage is proposed to replace the generic one of strain-slip cleavage. Crenulation cleavage differs essentially from slaty and fracture cleavage in that it only develops in laminated rocks and is consequently nearly always a secondary structure. Intense metamorphism converts crenulation cleavage into a new schistosity or cleavage with characteristics similar to slaty cleavage. Two fundamentally different types are recognized and it is suggested that crenulation cleavage is a valuable indicator of metamorphic conditions during the various phases of deformation.

Tie-line data are presented for twelve analysed igneous pyroxene pairs, from which it is demonstrated that a precise point of intersection, at or close to Wo75 En25 in the ternary diagram, does not exist. Eight tie-lines for pyroxene pairs from ultrabasic nodules in basalts are also considered. The tie-lines for metamorphic pyroxenes are compared with the igneous, and are shown to intersect over a similarly wide range, the average (Ca82 Mg18) being the same for both assemblages. It is shown that no conclusions can be drawn as to the genesis of the pyroxene assemblage, from the assumption of a characteristic tie-line intersection point. Optical determinations are considered, and shown to be of little practical value in this particular problem.