A deep seated flow of geoplasma (bathyrheal underflow) subjected crustal blocks to recurring horizontal movements causing north-east trending faults, shearing along anticlines and rotation of the separate crustal blocks. These movements produced extensive faulting and shattering in the South Alligator River area and north of Katherine, providing suitable loci for uranium mineralization. The mineralization occurs as a late phase open fissure filling and two types occur, (i) the nickel–cobalt–native silver type, and (ii) the quartz–pyrite–galena type. These characteristics provide a guide for future prospecting for uranium in Australia.

Boudinage occurs with great regularity in parts of West Cork. The principle break-up of competent beds is into boudins with the separation parallel to the dip of the bedding, but where the exposure permits examination in three dimensions it can be seen that incipient boudinage is developed with separation parallel to the strike of the bedding. The structure is shown to have originated after the main phase of folding by horizontal forces acting on steeply inclined beds. Some unusual features are described.

The major stratigraphic divisions of the Carboniferous rocks of Devon and Cornwall are characterized and new terms suggested to replace those of W. A. E. Ussher. It is shown that there is in South Devon and Cornwall a major unconformity separating an uncleaved group of post-orogenic Carboniferous strata (Ugbrooke Group) from underlying Devonian and Carboniferous with slaty cleavage. It is argued that the Ugbrooke Group is younger than any strata hitherto thought to be present in the Carboniferous of South-West England, and that the major orogeny is either Malvernian or Asturic in age.

The generally accepted interpretation of the structure of the Southern Uplands has been that of an anticlinorium to the north-west flanked by a synclinorium to the south-east. This structure, however, has always been illustrated as one large anticlinorium since the Hawick rocks in the core of the synclinorium have been considered to be older than the Riccarton (Wenlockian) Beds which lie to the south. In Kirkcudbrightshire, a reverse age relationship is demonstrated with the result that the beds could in fact form the southern limb of the synclinorium. When this is shown to be the case doubts are thrown on the validity of the fold and two alternative interpretations are given.

In the Dalradian rocks of Knapdale in south-west Argyll two groups of minor folds have been developed which share the same axial plane; their fold axes lie at right angles to each other within the common axial plane. Field evidence indicates that the two fold groups are strictly contemporaneous. One group of minor folds plunges at 40° to 020° N., and the other group plunges at 45° to 235° N., the common axial plane dipping at 70° to 305° N. Major structures parallel to both sets of minor folds are developed in the area. The fabric diagram of the fold groups shows tetragonal symmetry and this is taken to indicate that the stress field responsible for the deformation had itself tetragonal symmetry. The maximum compressive stress acted almost horizontally in a N.W.–S.E. direction while extension took place equally in all directions in a plane normal to the axis of maximum compression. The relations of contemporaneous fold structures to three basic strain patterns are briefly discussed.

Convolute bedding is described from the Lower Ludlovian in north-eastern Radnorshire in calcareous siltstones probably of the Monograptus tumescenszone. Examples of true slump-structures from the same area are given for comparison. The mode of formation of the convolute bedding is discussed and reference made to such directional information as is available from a study of the sediments.

Thin sills and dykes of pitchstone and felsite and dykes of crinanite, olivine-dolerite, tholeiites of different types, quartz-dolerite, andesite, craignurite-pitchstone, felsite and porphyry are described and the importance of contact and deep-seated hybridization of two magmas of contrasting basic and acid composition in their formation established. Among the dykes, the sequence of intrusion is surmised to be as follows: basic, sub-basic, intermediate, acidic, and, again, basic.

The composite sill of Rudh' an Eireannaich, Skye, is composed of basalt and felsite with narrow hybrid zones between them. The petrography of the rocks is described, accompanied by some chemical and spectrographic data.

Since my account (1937) of the structure of a part of Cornwall and O Devon, I have re-examined in particular the area known as Roseland between the Dodman and Porthallow at the eastern end of the Lizard Boundary. This has led to a re-interpretation of the structure which, though in part concerned with the Gramscatho Beds, applies to a large area of Cornwall and Devon. In the last few years many workers have appeared in the area and I have been frequently asked for my views on the structure and succession. It is evident that my 1937 paper has given rise to some misconception regarding these views, and it is desirable to place on record a brief summary of the main conclusions to which I have been led by my work during the last twenty years (mainly since 1951).