brown heath and bent, while far below are the green valleys, with their clear winding streams, and their scattered shepherds' hamlets.

INFLUENCE OF MAN UPON THE SCENERY OF THE COUNTRY.

It would lead to too wide a discussion to enter fully here upon the influence of man in bringing the scenery of the country to its present condition. He has uprooted the old forests, drained many of the mosses, and extirpated or thinned many of the wild animals of ancient Caledonia. In place of the woods and bogs, he has planted fields and gardens, and built villages and towns; instead of wild beasts of the chase, he has covered the hills and valleys with flocks of sheep and herds of cattle. The cutting down of the forests and the draining of the mosses has doubtless tended to reduce the rainfall, and generally to lessen the moisture of the atmosphere and improve the climate. Sunlight has been let in upon the waste places of the land, and the latent fertility of the soil has been called forth; so that over the same regions which, in Roman times, were so dark and inhospitable, so steeped in dank mists and vapours, and so infested with beasts of prey, there now stretch the rich champagne of the Lothians, the cultivated plains of Forfar, Perth and Stirling, of Lanark and Ayr, and the mingling fields

and gardens and woodland that fill all the fair valley of the Tweed, from the grey Muirfoots and Lammermuirs far up into the heart of the Cheviots.

In effecting these revolutions, man has introduced an element of change which has extended through both animate and inanimate nature. He has ameliorated the climate, and by so doing has affected the agencies of waste that are wearing down the surface of the land. The rivers are now, probably, a good deal less in size than they were even in the days of the Romans, and there may be fewer runnels and streamlets. The old mosses acted as vast sponges, collecting the rain that fell upon them or soaked into them from the neighbouring slopes, and feeding with a constant supply the brown peaty rivulets that carried their surplus waters to the lower grounds. The evaporation from these wide swampy flats could not but be extensive, and the rain-fall was thus, in all likelihood, proportionately great. But the clearing away of the forests and of the peat-mosses has removed one chief source alike of the rivulets and of the rain. The amount of denudation by the combined influence of rain and streams ought accordingly to be less, on the whole, than it was eighteen hundred years ago. At the same time, it should be borne in mind that the extent to which draining has now been carried all over the country has had the effect of allowing the rain to run off more easily

into the rivers. Hence the latter swell and fall again more rapidly than they used to do. Floods or "spates," though the rainfall may be the same or less, have thus a tendency to be more sudden and violent than formerly, and hence, in the increased amount of erosion performed by the river in flood, there may, perhaps, be an equivalent for the diminution of the stream in its ordinary state.

Among the plants and animals of the country, too, traces of the influence of man's interference are everywhere apparent. He has altered the character of the vegetation over wide districts, driving away plants of one kind, such as the heaths, to put in their stead those of another type, like the cereals. The gradual change of climate must also have affected the distribution of the vegetation of the country: some herbs grow now more abundantly than they did before; or they may now be able to flourish at a higher level than of old. Others, to which the change has been unfavourable, may have been greatly thinned in numbers, and even extirpated altogether. In like manner the coming of man has worked mighty transformations in the animal world. Over and above the extirpation of the beasts of the forest, and the introduction of foreign forms into the country, he has waged incessant war against those which he considers injurious to his interest. He has thus altered the natural proportion of the different

species to each other, and introduced a new element into the universal "struggle for existence." No species, whether of plants or of animals, can notably increase or diminish in number without, of course, thereby exerting an influence upon its neighbours. And here a boundless field of inquiry opens out to us. Man's advent has not been a mere solitary fact, nor have the alterations which he has effected been confined merely to the relations that subsist between himself and nature. He has set in motion a series of changes which have reacted on each other in countless circles, both through the organic and the inorganic world. Nor are they confined to the past; they still go on; and, as years roll away, they must produce new modifications and reactions, the stream of change ever widening, carrying with it man himself, from whom it took its rise, and who is yet in no small degree involved in the very revolutions which he originates.

CHAPTER XIII.

RECAPITULATION AND CONCLUSION.

IN this final chapter let me present the reader with a brief summary of what has been said in the chapters that have gone before. At the outset I tried to show that the common and popular notion which assigns the present inequalities on the earth's surface indiscriminately to the results of early earthquake and upheaval is untenable; that the only principles on which we can advance with confidence in seeking to decipher the history of our hills and valleys are those laid down by Hutton and his illustrator, Playfair; and that by studying the different agencies at work in altering the face of the globe at present, we take the only way open to us of investigating the progress of change in the geological past. In this course we are led to perceive that, although there have been many upheavals, depressions and fractures of the earth's crust, nevertheless the sent inequalities of the land are probably due in the main to the unequal waste of the rocks by rains,

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