Like the highlands, the uplands of Britain contain areas which are not typical. North-east of the Black Mountains lies the Red Marl plain of Herefordshire, recalling much more the Triassic plains of lowland Britain than the uplands to which it belongs, except in the discontinuous ranges of bold hills which cross it in a south-west to north-cast direction. Devon and Cornwall are also exceptional: superficially they are plateau and thus resemble the Pennines, but this plateau surface is an erosion form cut across a variety of rocks and complex structures, for this region was near enough to the main belt of Hercynian folding to be strongly affected and the rocks largely altered to slates. In lithology and structure it resembles highland Britain, but in elevation and surface form it is more like upland Britain. It differs from both in the absence of glaciation and the smaller extent of periglacial activity.
But the most exceptional Hercynian region by far is the Central Lowlands of Scotland, an area shattered by faults into a pavement of blocks of Devonian and Carboniferous rocks. Further, the lithology of the Carboniferous Limestone is abnormal, that bed containing almost more coal than limestone, while the area is characterized by frequent masses of igneous rocks. They cause a great variety of relief from the jointed plug on which Stirling Castle is built to the great fault-line scarp truncating the andesitic Ochils on their southern side. These and other forms, such as exhumed laccoliths, dykes, volcanic necks and plateau basalts around the lower Clyde, ensure a complex pattern of relief different from that found elsewhere in Britain.
In lowland Britain there is simplicity, a predominant dip to the south-cast affecting rocks from the Permo-Trias upwards, a patterned relief of cuestas and vales reflecting the alternating beds of sandstone, limestone and clay, a relief generally below 1,000 ft in maximum elevation, and an area where features of glacial deposition are far more marked than features of glacial erosion.
The oldest beds concerned, the sandstones and marls of the Trias, wrap around the sides of the Pennines and form the great triangular lowland of the Midlands, where diversification of relief is provided principally by the upthrust horsts of Pre-Cambrian and Lower Palaeozoic rocks, such as the Malverns, Charnwood Forest and the Nuneaton ridge. Some of the sharp relief formed on these rocks is in striking contrast to the gentle character of Triassic relief.
The areas of Jurassic and Cretaceous rocks north of London provide considerable contrasts in scenery, because of lithological variations, especially within the Jurassic. In Yorkshire, a great development of sandstone is responsible for the North Yorkshire Moors, a region more akin in lithology, vegetation and elevation to upland Britain than to the rest of the lowlands. Over much of Lincolnshire and the East Midlands the relief is not great as massive limestone beds are lacking in the Jurassic. In Lincolnshire the lowlands are narrow, but, to the south, a general decrease in regional dip is responsible for the great spread of low plateaux through the East Midlands and East Anglia. In the Jurassic rocks of this area limestones are not well developed unlike clays the predominance of which in the Upper Jurassic has facilitated the excavation of the wide plain in which the Fen deposits have been laid down. Both here and in East Anglia a general spread of glacial deposits, mostly boulder clay, has added to the smooth monotony of the relief. Farther south, the main Cotswold and Chiltern section of the lowlands, with Oxford at its centre, forms much more characteristic scarpland, largely because of the strong development of limestone in the Middle Jurassic and the higher relief of the Chalk in the Chilterns, for which there is no obvious lithological cause. This area differs from the lowlands to the north not only in its relief, but also in the far smaller importance of glacial drift in the landscape.