formations, and therefore that the basalt eruptions took place in early Tertiary time. The volcanic episode to which these plateaux owe their origin was one of the most important in the geological history of Britain. It appears to have resembled in its main features those remarkable outpourings of basalt which have deluged so many thousand square miles of the Western Territories of the United States. The eruptions were connected with innumerable fissures in which the basalt rose, and from numerous points on which it flowed out at the surface. These fissures, with the basalt that solidified in them, now form a vast assemblage of dykes which cross Scotland, the north of England, and the north of Ireland, in a prevalent east and west or north-west and south-east direction. That the volcanic period was a prolonged one is proved by the great denudation of the plateaux before the last eruptions took place. This is impressively exemplified in the Isle of Eigg, which will be more specially described in the following Chapter. A remarkable feature in the volcanic phenomena was the subsequent disruption of the basaltic plateaux by large bosses of gabbro and of various granitoid rocks. These intrusive masses now tower into conspicuous groups of hills, -the Coolins and Red Hills in Skye, the mountains of Rum and Mull, and the rugged heights of Ardnamurchan.

Under the Post-tertiary division of geological time come the records of the Ice Age, when Scotland was buried under sheets of ice which ground down, striated, and polished the harder rocks over the whole country, and left behind them the widespread accumulations of clay, gravel, and sand known as glacial deposits. The nature of the evidence and the deductions drawn from it have been already stated in Chapter IV., but a full description of the glaciation of the Highlands will be given in Chapter XI. The youngest

geological formations of the Highlands are the raised beaches, river-terraces, lake-deposits, peat-mosses, and other accumulations, which are related to the present configuration of the country, and contain remains of the plants and animals still living on its surface.

CHAPTER VII

THE TABLE-LAND OF THE HIGHLANDS

If the observer who has mastered the geological details given in the foregoing chapter would grasp at once the leading features of Highland scenery and their relation to geological structure, let him betake himself to some Highland mountain-top that stands a little apart from its neighbours, and looks over them into the wilds beyond. A better height could not be chosen than the summit of Ben Nevis. None other rises more majestically above the surrounding hills, or looks over a wider sweep of mountain and moor, glen and corry, lake and firth, far away to the islands that lie amid the western sea. In no other place is the general and varied character of the Highlands better illustrated. And from none can the geologist, whose eye is open to the changes wrought by sub-aërial waste on the surface of the country, gain a more vivid insight into their reality and magnitude. To this, as a typical and easily accessible locality, I shall have occasion to refer more than once. Let the reader, in the meantime, imagine himself on the highest peak of the British Isles, watching the shadows of an autumnal sky as they steal over the vast sea of mountains that lies spread out, as in a map, around

him. And while no sound falls upon his ear, save now and then a fitful moaning of the wind among the snow rifts of the dark precipice below, let him try to analyse some of the chief elements of the landscape. It is easy to recognise the more marked heights and hollows. To the south, away down Loch Linnhe, he can see the hills of Mull and the Paps of Jura closing in the horizon. Westward, Loch Eil seems to lie at his feet, winding up into the lonely mountains, yet filled twice a day with the tides of the salt sea. Far over the hills, beyond the head of the loch, he looks across Arisaig, and can see the cliffs of the Isle of Eigg and the dark peaks of Rum, with the Atlantic gleaming below them. Farther to the north-west the blue range of the Coolin Hills rises along the sky-line, and then, sweeping over all the intermediate ground, through Arisaig and Knoydart and the Clanranald country, mountain rises beyond mountain, ridge beyond ridge, cut through by dark glens, and varied here and there with the sheen of lake and tarn. Northward runs the mysterious straight line of the Great Glen, with its chain of lochs. Thence to east and south the same billowy sea of mountain-tops stretches out as far as eye can follow it-the hills and glens of Lochaber, the wide green strath of Spean, the grey corries of Glen Treig and Glen Nevis, the distant sweep of the moors and mountains of Brae Lyon and the Perthshire Highlands, the spires of Glen Coe, and thence round again to the blue waters of Loch Linnhe.

In musing over this wide panorama, the observer cannot fail to note that while there are everywhere local peculiarities in the outline of the hills and in the shapes of the sides of the valleys, there is yet a general uniformity of contour over the whole. What seem, at a nearer view, rough craggy peaks and pinnacles, seen from this height are dwarfed into

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And thus over the

mere minor irregularities of surface. whole of the wide landscape, one mountain ridge appears after another, with the same large features, raising their smooth summits from glen to glen, but broken now and again where from some hidden valley a circular corry or craggy cliff lifts itself bare to the sun.

Much has been said and written about the wild tumbled sea of the Highland hills. But, as he sits on his high perch, does it not strike the observer that there is after all a wonderful orderliness, and even monotony, in the waves of that wide sea? And when he has followed their undulations from north to south, all round the horizon, does it not seem to him that these mountain-tops and ridges tend somehow to rise up to a general level, that, in short, there is not only, on the great scale, a marked similarity of contour about them, but a still more definite uniformity of average height? (Figs. 19, 23.) To many who have contented themselves with the bottom of the glen, and have looked with awe at the array of peaks and crags overhead, this statement will doubtless appear incredible. But let any one get fairly up to the summits and look along them, and he will not fail to see that the statement is nevertheless true. From the top of Ben Nevis this feature is impressively seen. Along the sky-line, the wide sweep of summits undulates up to a common level, varied here by a higher cone, and there by the line of some strath or glen, but yet wonderfully persistent round the whole panorama. If, as sometimes happens in these airy regions, a bank of cloud with a level undersurface should descend upon the mountains, it will be seen to touch summit after summit, the long line of the cloud defining, like a great parallel-ruler, the long level line of the ridges below. I have seen this feature brought out with picturesque vividness over the mountains of Knoydart and