In the northern parts of Wales where a group of ancient volcanic rocks has been laid bare by the stupendous denudation of the surface, a small tract of truly highland scenery has been carved out in Cader Idris, Arenig, Snowdon, and the surrounding heights in Caernarvonshire and Merionethshire. Another isolated area of volcanic hills forms the picturesque district of the Lakes. But it is in Scotland that this type is displayed on the largest scale and in the most varied diversity. The Scottish Highlands are built up of the most ancient rocks of the British Islands, and possess a geological structure of extraordinary complexity. They include a vast variety of materials which, rising to the highest elevations in the country, and exposed to the severest climate, have impressed their individual characters upon the landscapes. Thus, in the north-west, where the simplest grouping of rocks is to be seen, masses of horizontal dark-red sandstone have been carved into the huge pyramids that form so singular a feature in the scenery of Ross and Sutherland (p. 71). In the central and south-western counties, gleaming white cones show where the quartzites rise to the surface. In the eastern Grampians, high craggy moors, encircled with stupendous corries and precipices, mark the sites of the bosses of granite. Among the Western Isles, dark splintered crests and pinnacles point out the position of the gabbros. Perhaps the most rugged ground is to be seen among the mica-schists, which combine a wonderful array of pointed peak and notched ridge, with tumultuous masses of craggy declivity. In the eastern Grampians, the mountains include broad tracts of undulating moorland, which, though lying along the summits of the chain, are level enough to be capable of conversion into racecourses. These hills are separated from the sea by a tract of lowland, and lie thus entirely inland. On the west side of the Highlands, however, the ground between the straths and glens mounts upward into narrow ridges, not infrequently sharpened into knife-edged crests, while the whole aspect of the landscape is rugged, rocky, and bare. Land and sea appear there to be inextricably intermingled. Islands, peninsulas, and promontories are penetrated or surrounded by sounds and sea-lochs, in such a curious way that even in what might be thought to be the very heart of the country, the tides of the Atlantic are found to ebb and flow into remote and solitary glens. The mountains plunge abruptly into the salt water, and for the most part only along the valley-bottoms are little strips of level land to be seen.