None of the other highland regions is quite like the Highlands of Scotland. In general the relief is smoother, although they have the characteristic of high average elevation in common. The greatest sharpness of relief seems to be provided by a combination of igneous
rocks and severe glacial erosion. Snowdonia provides a good example: a series of lavas and ashes, predominantly rhyolitic in character, and a number of intrusions, mark this region off geologically from much of the rest of Wales. Heavy glaciation has produced on these rocks the corries of the northern side of the Glyders, glacial troughs such as the Nant Ffrancon, and a number of lakes, features which make this region, in spite of its much smaller size, comparable with the Highlands of Scotland. Cader Idris shows similar corried escarpments preserved on doleritic sills, while, in the Lake District, on the andesitic Borrowdale volcanic rocks ice has produced similar glaciated highland. Outside these districts, that is in much of the Southern Uplands, the northern part of the Lake District, and central Wales, the hills are big but rounded. Glacial features occur, but they have not the angularity typical of those of the volcanic outcrops, while the more common occurrence of sheets of drift seems to have softened the landscape.
Although the highlands as described in the preceding section seem to possess certain features in common, notably the absence of a simple structural pattern and its reflexion in a neat relief pattern as well as a general lack of limestones, there is one area which is completely atypical. It is true that the Cambrian Durness Limestone of the far north-west of Scotland introduces karst features on a small scale, but it does not form an area so different from the rest as do the alternating limestones and shales of the upper part of the Silurian in the Welsh borderland. Between and around Wellington and Ludlow the comparatively gentle dips of the Wenlock and Aymestry limestones and interbedded shales have resulted in a pattern of high cuestas, ridges and vales much more characteristic of what will be described below as upland Britain than of true highland Britain. The presence of abundant limestone results in a brightness of landscape not normally found in the highlands and allies this area to the uplands, in spite of the sombre effects introduced by the extensive planting of conifers on the limestones.