group of the Cuillin Hills, which now comes into full view. In all the range of the British Isles there is nothing so Alpine in form and so rich in colour as this insular mountain group. Springing from the very level of the sea to heights of more than 3,000 feet, these hills unite in themselves an extraordinary variety of contour. (Plate A.) Their splintered crests surpass for jaggedness any other hills in Western Europe, until we get as far north as the Romsdal and the Lofodden Islands. And as for colour, it is hardly possible to exaggerate the depth of tint which the Cuillins may assume. Their rocks are for the most part dark in hue, and they weather with a surface which seems in some way to drink in the atmospheric tints. When a canopy of cloud just rests on their summits, and casts a shadow over the crags and corries below, their craggy sides put on so deep a hue that we first think of them as black, until, on further reflection, we perceive them to be of the deepest and purest violet. The mountaineer who can spend his holiday in climbing and musing among the corries and crags of the Cuillins is a mortal much to be envied.

A third illustration of the distinctive form and colour of Scottish mountains may be taken from a region still farther north-the western coast of Ross-shire and Sutherland. The hills of Applecross and those around Loch Torridon, and again, the detached groups in the Loch Broom and Assynt districts, stand out from all other features in the landscape around them. (Plate B.) In some respects indeed they are unique in Britain. Their distinguishing characters are that they consist of pyramids, sometimes joined together at the sides as in Applecross, sometimes standing strangely alone as in Assynt, and that these pyramids are built up of a reddish stone in level sheets like courses of masonry. There is something curiously bizarre yet fascinating about these north-western hills. At every turn their odd combination of steep rocky declivity and lines of horizontal terrace suggest gigantic exaggerations of human architecture. warm ruddy hue, too, offers an impressive contrast to the cold blue-grey of the rolling platform of rock from which they rise. Here and there, moreover, a patch of white

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moisture from day to night, and from summer to winterin short, all the atmospheric forces that are ceaselessly at work in wearing down the surface of the land-have combined to carve out the shapes of the hills. But the process of sculpture is not precisely everywhere the same, for here one kind of sculpture-tool and there another is wielded most effectively by Nature; and even if the same tools were everywhere employed in the same way, and with the same amount of vigour, the resulting topography would not always be the same. On the contrary, it would necessarily vary with each change in the character of the material exposed to the great sculptor. We should not look for the same kind of effect to be produced if a statue were carved in granite as if it were carved in chalk. Much more may the results of Nature's operations be expected to vary with the innumerable variations in the character of the resistance offered by rocks to the work of her sculpture-tools.

Bearing this fundamental principle in mind, we carry with us an important clue to the interpretation of mountain forms. We are enabled to understand how each hill or group of hills has come to wear its present topographical features, and why these features change so much as we trace them through the successive mountains and mountain chains of the country.

Consider for a few moments the characteristics of mountains carved out of igneous rocks, and how they are produced. The Arran hills supply us with an admirable illustration. Goatfell and its neighbours are formed of grey granite, which mounts up from the glens partly into steep bare ledges of rock and partly in long screes of débris. The rocky ledges, as they are followed upward, are seen to be built of rudely piled sheets of naked stone, traversed by two sets of irregular divisional planes, one of which cuts the other. The granite is thus divided into large blocks, which, under the influence of the weather, are etched out along. their lines of junction, very much as the joints of ancient masonry are affected by the same cause. The blocks are thus by degrees separated from each other, and becoming detached are launched down the crags and slopes as loose boulders. Meanwhile the crests, being most exposed to the

vicissitudes of our northern climate, are more especially attacked. Their rocks are more splintered and cleft, their forms become more jagged and peaky. Winter after winter the frost drives its wedges of ice farther and farther into the walls of granite, which are thereby rent open. Slices fall away from them. Portions of them are left for a time as outstanding pinnacles, only however to be in turn cut down and hurled in fragments into the corries beneath.

Now in all this process of degradation we shall find, on examination, that tumultuous, capricious, and irregular as it may seem, not a touch is given, not a block is carved out, not a spire is isolated, not a boulder is detached, save in obedience to strict and ascertainable law. And the law is that the destruction of the granite is effected by means of its joints. The rock is traversed by divisional planes, which if we could quarry well into its mass would hardly be visible to the eye, for in the solid unweathered stone the two sides of a joint fit about as closely as the two sides of a crack in a pane of glass. The quarryman knows these lines well, for it is by taking advantage of them that he is enabled to extract the blocks which he furnishes for building purposes. Nature, too, unerringly discovers them. It is along their lines that water most readily percolates, and frost most effectively acts. Hence, where the joints reach the surface the rock is there eaten most away, and begins to gape and split.

The system of joints in granite, as in other rocks, is often extremely complicated. These divisional planes are in great measure fissures of retreat, due to the contraction of the rock as it passed into a solid state from its original molten condition. Two main series of them may commonly be detected, one of which may be vertical, the other horizontal, or they may be inclined to each other at various angles. The intersection of these two sets of joints divides the rock into rudely quadrangular blocks. It is by taking advantage of this double series of lines that Nature severs the blocks from each other. Every mountaineer who has climbed Goatfell will remember the curiously artificial wall - like forms which the granite assumes at various places below the crest. (Plate C.) This Cyclopean architecture is due to the