The main deformation of the Carboniferous sediments of north-east Northumberland took place in Armorican times. An analysis of minor structures shows that they occur in three distinct structural environments. These are, (i) as accommodation structures to large folds, (ii) as structures produced by transcurrent movement along lateral shearfaults, and (iii) as minor structures formed in direct response to the regional compression. The detailed interrelation-ships of these minor structures are described for selected areas.

In the neighbourhood of Berwick-on-Tweed a major east-facing monocline has been recognized. It appears that the large-scale folding of the Carboniferous strata was directly controlled by the configuration of the Lower Palæozoic and Lower Old Red Sandstone basement. Major folds have been generated by an east-west compression and are deflected around the Cheviot and Southern Upland masses. A regional fault pattern is interpreted as a conjugate system of strike-slip and oblique-slip shears. The nature and influence of structural control on the emplacement of the Whin Sill suggests that it was intruded during this same tectonic episode.