same forces that carved out the valleys are still busy at their task.

Since the glacial period came to a close, not only have the various powers of waste been ceaselessly at work upon the land, there has likewise been an upheaval of the country to a height of fully forty feet above the level at which it stood when the glaciers crept back from the mouth of Glen Spean. The later stages of this rise will be further alluded to in a subsequent chapter in their relation to the kingdom generally. Forests, too, have sprung up and disappeared. Lakes have given place to bogs and peatmosses. And man, a more rapid agent of change than the elements, has done much to alter the aspect of the Highlands. I think it better, however, to defer the notice of these later changes until the solid framework of the rest of the kingdom has been considered.1

1 It will, of course, be understood that the scope of this volume permits me to treat only of those geological changes of which there are marked proofs in the scenery of the country. Hence I must pass over the evidence of oscillations of level afforded by the sunk forests, and other subjects which, though of great interest, do not specially elucidate the present inquiry.

CHAPTER IX.

THE SOUTHERN UPLANDS.

FROM the iron-bound coast of St. Abb's Head, on the one side of the island, to the cliffs of Portpatrick on the other, there stretches a continuous band of hilly ground, sometimes called the South Highlands, and which for the sake of clearness has been referred to in the foregoing Chapters as the Southern Uplands. This tract corresponds closely to the area occupied by the Lower Silurian formation, and its geology on the large scale is remarkable for simplicity. The whole district from sea to sea consists fundamentally of hard greywackè and shale, with occasional limestone bands, of Lower Silurian age, arranged in highly inclined or vertical strata that strike from south-west to north-east. These rocks, though hardened and even in some places changed into schist, serpentine, felstone, granite and other rocks, have not suffered from the same wide-spread metamorphism which has

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so altered the Lower Silurian rocks of the Highlands. Yet they have been squeezed into endless foldings, as if, to use the oft-quoted simile of Sir James Hall, they had been great piles of carpet, and had been crumpled up by a strong pressure from the north-west on the one side and from the south-east on the other. Hence the folds run from south-west to north-eastthat is, at right angles to the direction of the pressure. And if the student would see the results of the process, let him traverse the rocky shores of Wigton and Kirkcudbright, or the cliffs of Berwickshire. will there find a cross section of the rocks, and see the hard greywackè and shales bent into great arches and troughs, or squeezed into little puckerings, and will be able to trace these plications following each other from top to bottom of the cliffs, mile after mile along the coast. He will thus learn that in a long section of strata that are piled on end there may be endless repetitions of the same beds, very much as the leaves of a bound book are made up of numerous foldings of a comparatively small number of sheets; the top of the arches of the rocks having been cut away by denudation, somewhat as the edges of the leaves have been pared off by the book-binder.1

One result of such a visit to the coast sections of the Silurian uplands is to assure us that, just as in the

1 See this structure shewn in Sections II. and III. along the margin of the accompanying map.

Highlands, so here, the arches of the strata have not given rise to hills, nor have their troughs formed valleys. Indeed, along the crest of the sea-cliffs we see the rocks cut sharply off by the surface of the country, whether they consist of hard greywackè or crumbling shale, whether they are on end or gently inclined, and whether they have been thrown into anticlinal or synclinal axes. It is plain that to whatever origin the present irregularities of the ground are to be assigned, they are not due to the upward and downward folds of the rocks. It will be seen in the sequel, that these uplands, like the Highlands, are a stupendous monument of denudation; that a vast thickness of rock has been ground away from their present surface, and that their hollows and hills have been determined by the same powers of waste that have played a like part in the history of the northern half of the kingdom.

By referring to the map the reader will observe that, in addition to these contorted strata, the Silurian tract of the south of Scotland contains a few outlying patches and strips of the later formations, which run up into the hills from the plains on either side. Thus the Old Red Sandstone lies in bays along the northern edge of the Lammermuirs, caps their summit south of Fala, and ascends from the low grounds of the Tweed up the valley of the Leader. The Carboniferous rocks indent the Silurian belt in a tongue which runs south from Cumnock, and contains the

little coal basin of Sanquhar. The Permian breccias and sandstones likewise mottle the surface of the older rocks of the chain in strips and patches, in the valleys of the Annan and Nith, and even westward on the coasts of Wigton and Ayrshire. Wherever a large enough mass of such later deposits occurs it forms a distinct feature in the landscape.

With these trifling interruptions, the Silurian belt is found to have a well-marked scenery of its own, which is confined with notable strictness between the boundary lines of the Silurian rocks. Its northwestern limit in particular is as well marked as the line that separates the Highlands from the Lowlands between the Clyde and Stonehaven. In East Lothian and Edinburghshire it mounts into the long chain of the Lammermuirs, whose steep bare front seems to project headland after headland into the fertile plains below, as a high river-bank rises out of its alluvial haugh, or as a lofty sea-cliff sweeps upward in promontory and bay above the waves that foam along its base. Across the counties of Peebles and Lanark, the edge of these uplands, though still well defined geologically, is sometimes not so marked in the landscape, owing to the rise of the ground in its front. But in Ayrshire it regains well-nigh all the boldness which marks its course through the eastern counties, and from the head of Nithsdale to the sea at Girvan, it is traceable in