the atmosphere among the frosts and clouds, which show angular spiry forms, that contrast strongly with the smoothed flowing contours of the lower slopes. These summits are formed of precisely the same rocks as the roots of the hills. Why then should they present contours so different?

As

With these features fresh in his memory, let the observer transport himself in imagination to the west coast of Norway. His first impression there will probably be almost one of doubt whether he really has quitted the Scottish shores, so precisely similar in their essential features, and even in their details, are those of Western Scandinavia. he ascends one of the fjords, he sees around him the same smoothed and polished islets, the same flowing outlines on all the lower hills, and the same craggy crests against the sky. But at the far head of the winding inlet, he will find that, in the northern part of Norway, the sea-filled valley passes inland into a deep glen, down the centre of which a glacier creeps, while snow-fields descend to the very edges of the precipices all around (Fig. 18). He will discover that the smoothed rock-surfaces pass under the glacier, and he may then, as it were, catch the ice in the very act of producing them. A glacier one thousand feet thick—and many modern glaciers attain greater dimensions-exerts on each square foot of its rocky floor a pressure equal to about twenty-five tons. Pressing onward the sand and stones that lie between it and the rocks over which it moves, it is a powerful grinding machine, that wears down, smooths, polishes, and grooves even the hardest rock (see Fig. 84). The rounded polished domes of rock in these Norwegian valleys have all been ground down by the passage of the glaciers across them, and the abundant scratches traced upon them show the direction in which the ice moved as it held in its grip the sand and stones which it pressed steadily upon the rocks

over which it moved. No one can view these scenes without being powerfully impressed with the evidence that the modern Scandinavian glaciers are the mere shrunk remnants of those which once filled up the fjords for hundreds of feet above the present sea-level, buried all the lower hills, and marched boldly out into the Atlantic.

Now, there can be no doubt that Scotland once nourished glaciers in all her larger glens, as Norway still does, for the ice-marks are hardly less distinct than they are among the northern fjords. But there was still an earlier time, when not only were the valleys filled with local glaciers, but when the whole country was swathed in snow and ice. The evidence for this condition of things will be stated in later chapters. To realise what was the condition of this country when the ice-fields that lay upon it were thickest, we must turn still farther north. The present aspect of the northern and eastern parts of Greenland probably presents a close parallel to the condition of Scotland at the height of what is known as the Ice Age or Glacial Period. The interior of that tract of country is deeply buried under one vast sheet of snow and ice, which, constantly augmented by fresh snowfalls, moves steadily downward from the axis of the continent to the eastern and western shores. This vast mer de glace sweeps inland, league after league, in one interminable glacier, broken only here and there by some black hill-top or mountain peak, that rises as an island out of the snow. It covers the face of the country to a depth of hundreds, or even, in some places, thousands of feet, filling up the valleys, mounting over the hills, and pressing with constant resistless force upon all the rocks over which it marches, till it reaches the sea, into which it protrudes a long way from the shore, rising above the waves as a solid glassy wall, sometimes more than three hundred feet high,

which breaks up into huge fragments, that rise and float away as icebergs.

If a single glacier, descending below the snow-line, as in Norway and Switzerland, can grind down, polish, and score the rocks of its channel, it is easy to see how vast and constant must be the erosion carried on by so huge and heavy a mass of ice as that which creeps over the whole of North Greenland from mountain top to sea-shore. Could we strip off this icy mantle, we should find the surface of that country worn into rounded and flowing outlines, its valleys and hills smoothed, often with hollows and deep rock-basins ground out of them, and its rocks covered with ruts and grooves running in long persistent lines, that would mark the direction of the march of the ice. It would, in short, so far as we can tell, bear the closest resemblance to the smoothed and polished aspect of western Scandinavia and the Highlands of Scotland. The ice has so long retired from our mountains and glens that the peculiar contours which it impressed upon them have had time to be in some measure broken up by the disintegrating influence of the weather. But the effects of the glaciation are still so fresh as to afford materials for forming a vivid mental picture of the general aspect of this country when the rigorous climate of the Ice Age was at its height.

We see, then, that one of the most notable of nature's sculpture-tools, land-ice, though no longer at work in Scotland, has left its characteristic marks all over the country. The detailed account of how Scottish scenery has been influenced by ice-action will be given in later chapters. But besides grinding down, smoothing, polishing, and grooving the rocks, glaciers leave other memorials of their presence. In a glacier valley, the frosts, thaws, and rains of every year loosen large quantities of debris, much of which ultimately

comes to rest upon the ice. As the glacier threads its way down the valley, its surface becomes discoloured with the earth, stones, and mud washed from the slopes; piles of rubbish collect along its sides in long lines called moraines. These are slowly borne onward upon the ice, till at last, when the glacier melts, they are thrown down. The confused heaps of earth and stones thus formed are apt to be washed away by the escaping river, as fast as they are deposited. Where, however, they remain, they form along or across the valley a more or less continuous rampart, which is continually growing by the addition of fresh materials as the ice reaches its farthest limit. Should a period of milder temperature come and cause the glacier to retire up the valley, this rampart-like pile of rubbish will be left behind to mark where the ice once reached. Another prolonged halt at a higher part of the valley will give rise to another set of moraine mounds. And thus, by the intermittent recession of the glacier, successive lines of such piles of debris may be thrown down, each line marking a pause in the retreat of the ice, and a sojourn of the glacierend at that place. Now, as will be afterwards pointed out, this characteristic relic of glacier work is to be found in many Scottish valleys. Moraine mounds, singularly fresh, still dam up the drainage from the surrounding slopes as they did when the ice drew back from them (Figs. 61, 70, 71), and huge boulders, once carried on the ice from the higher recesses of the hills, still lie scattered on the heaps of rubbish, or perched on hill and crag where the ice dropped them (Figs. 54, 55, 56, 57).

While land-ice is thus a most powerful geological agent in new-modelling the surface of the earth, its operations are not entirely confined to the dry land. As already stated, it creeps along the sea-bottom for some distance from land,