that runs round the northern margin of the Highlands from the coast of Banffshire to the far headlands of Caithness. Though now mostly stripped off from the continuation of the same low grounds eastward into Aberdeenshire, the Old Red Sandstone is left in many little patches, and not improbably at one time covered most or all of these plains, even as far south as Aberdeen, if not quite to the broad tract of the same formation in Kincardineshire. On the west side of the Highlands, lies the broken chain of the Inner Hebrides with its green terraced hills of Tertiary lavas. Considered broadly, therefore, the area of the Highlands may be looked upon as a kind of island of ancient crystalline masses set in a sea of younger formations. I shall now proceed to describe its component rocks and their distinctive outer features, beginning with the oldest, and will then give an account of the manner in which they have been arranged.

The oldest rock of the Highlands is a massive gneiss, representative of that ancient series which is grouped under the name of Archæan. It varies considerably in texture and colour. Some portions are structureless like a granite, others are finely schistose, and between these two extremes every gradation may be found. It contains also many veins of pegmatite and dykes of diabase, as well as seams of dark hornblende and hornblendic gneiss, which doubtless represent what were once intruded veins. Almost everywhere it is marked by great toughness and durability. There could have been no fitter material for the foundation- stone on which the geological structure of Britain should be built up.

The areas occupied by this rock are readily recognisable even at some distance by their singularity of contour. They do not occupy much space in the general area of the Highlands, being, indeed, confined to the north-western

margin. The old gneiss forms the long chain of the Outer Hebrides. On the mainland, it runs as a broken fringe from Cape Wrath to the island of Raasay, coming out boldly to the Atlantic in the northern half of its course, but throughout the southern portion retiring towards the heads of the bays and sea-lochs, and even stretching inland to the upper end of Loch Maree. Whether the traveller approaches a tract of the gneiss from the sea or from the land, he can hardly fail to remark its curious peculiarities of outline. If he looks at it from the western or Atlantic side, as, for instance, in sailing up Loch Torridon, or coasting along the western sea-board of Sutherland, he sees the land rising out of the water in bare rounded domes of rock, crowded behind and above each other as far as the eye can follow them. Not a tree nor a bush casts a shadow over these wastes of barren rock. It might at first be supposed that even heather had been unable to find a foothold on them. Grey, rugged, and verdureless, they look as if they had but recently been thrust up from beneath the waves, and as if the kindly hand of nature had not yet had time to clothe them with her livery of green. Strange, however, as this scenery appears when viewed from a dis tance, it becomes even stranger when we enter into it, and more especially when we climb one of its more prominent heights and look down upon many square miles of its extent. The whole landscape is one wide expanse of smoothed and rounded bosses and ridges of bare rock, which, uniting and then separating, enclose innumerable little tarns. There are no definite lines of hill and valley; the country consists, in fact, of a seemingly inextricable labyrinth of hills and valleys which, on the whole, do not rise much above nor sink much below a general average level. Over this region of naked rock, with all its bareness

and sterility, there is a singular absence of peaks or crags of any kind. The domes and ridges present everywhere a rounded flowing outline, which has only here and there been partially defaced by the action of the weather.

These contours, however, though now so characteristic of the old gneiss in the north-west of Scotland, are not the natural forms which the rock would have assumed if left to mere ordinary atmospheric disintegration. They bear emphatic testimony to the work of land-ice. The whole surface of the country has been ground smooth by ice. The polished, striated, and grooved surfaces left by the ice are still everywhere to be seen, and huge blocks of rock scattered all over the ground, and sometimes poised on the very summits of the rounded rock-domes, remain to complete the proofs of former glacial action (Figs. 56, 57). It is only here and there, where the ice-worn surface has been broken up that we can see how the gneiss yields to the process of weathering. One of the best localities for observing its aspect under these conditions is along the range of cliffs to the south of Cape Wrath. Bearing there the full brunt of every storm that sweeps across the Atlantic, it is peculiarly exposed to disintegration. Every weak part of its framework, discovered by the furious winds, fierce rains, and surging breakers of that desolate and iron-bound coast, is hollowed out into cleft and gulley, tunnel and cave, while the harder parts protrude in massive buttresses, or tower aloft in fantastic columns. Its huge veins of pink pegmatite seem to writhe up the face of the dark cliffs like the sinews of some antique statue (Fig. 15).

Above this venerable rock the next member of the series of geological formations represents a much less ancient period. It consists of dark-reddish and purplish-brown sandstone and conglomerate (Torridon sandstone), in which as yet no dis

tinctive fossils have been found. These stratified rocks were called Cambrian by Murchison, being regarded by him as probably equivalents of the oldest sedimentary formations. of Wales. But we are still without satisfactory evidence as to their true place in the geological scale. All that can be said is that, if they are not Cambrian, they must belong to some still earlier epoch in the world's history, perhaps to that of the Huronian rocks of North America. The wide interval that separated them from the time of the old gneiss is shown by the fact that they lie upon an eroded surface of the latter rock, and contain pebbles of it. The gneiss was in truth just as gnarled and venerable-looking a rock when these sandstones were laid down upon it as it is now.

Between the aspect of the tracts occupied by these sandstones and that of the ancient gneiss there is a contrast more abrupt and impressive than almost any other in Highland landscape. So sharp is the line of demarcation between the two rocks, that their respective areas can be accurately followed by the eye even at a distance of several miles. The tumbled sea of bare gneiss rolls, as it were, under the red sandstones, which in nearly horizontal beds rise into isolated and strangely-shaped mountains, sometimes to a height of 3400 feet above the sea (Figs. 20, 43). As the ground mounts into these eminences, the covering of herbage grows more and more scant, but the same terraced bars of rock which begin where the sandstone first appears continue to stand out more and more clearly until they form naked precipices, where there does not seem to be room even for a tuft of heather or an alpine plant. The parallel bars that mark the successive strata can be traced with the eye to the far summits, and from crest and to crest of these vast solitary cones which, standing alone on their platform of gneiss, remind one rather of rude colossal pyramids than of