But if we need further confirmation of the fact that these accumulations on either side of this and other Swiss lakes are ancient lateral moraines, we have it in their connection with walls of a like nature at their lower end, where we find again transverse moraines barring their outlet, and also in the continuity of long trains of fragments of similar rocks extending side by side across wide plains for great distances without mixture. From the beginning of my investigations upon the glaciers, I have urged these two points as most directly proving their greater extension in former times, and more recent researches constantly recur to this kind of evidence. All our lakes would be filled with loose materials, had their basins not been sheltered by ice against the encroachments of river-deposits during the transportation of the erratic boulders to the farthest limits of their respective areas; and all the continuous trails of rocks derived from the same locality would have been scattered over wide areas, had they not been carried along, in unyielding tracks, like moraines. On a small scale the waters of the Rhone and of the Arve recall to this day such a picture. There are few travellers in Switzerland who have not seen these two rivers, where they flow side by side, meeting, but not mingling, at the southern extremity of the lake, the different color of their water marking the two parallel currents. In old times, when the glaciers filled all the valleys at the base of Mont Blanc, and to the east of it, uniting in the valley through which now runs the River Rhone, the glacier of the Arve came down to meet the ice from the valley of the Rhone, in the same manner as the River Arve now comes to meet the waters of the Rhone where they rush out from the southern end of the lake.
This would be the proper place to consider the formation of the lakes of Switzerland, as well as their preservation by the agency of glaciers. But this subject is so intricate, and has already given rise to so many controversies which could not be overlooked in this connection, that I prefer to pass it over altogether in silence. Suffice it to say that not only are most of the lakes of Switzerland hemmed in by transverse moraines at their lower extremity, but the lakes of Upper Italy, at the foot of the Alps, are barred in the same way, as are also the lakes of Norway and Sweden, and some of our own ponds and lakes. Strange as it may seem to the traveller who sails under an Italian sky over the lovely waters of Como, Maggiore, and Lugano, it is, nevertheless, true, that these depressions were once filled by solid masses of ice, and that the walls built by the old glaciers still block their southern outlets. Indeed, were it not for these moraines, there would be comparatively few lakes either in Northern Italy or in Switzerland. The greater part of them have such a wall built across one end; and but for this masonry of the glacier, there would have been nothing to prevent their waters from flowing out into the plain at the breaking up of the ice-period. We should then have had open valleys in place of all these sheets of water which give such diversity and beauty to the scenery of Northern Italy and Switzerland, or, at least, the lakes would be much fewer and occupy only the deeper depressions in the hard rocks.
Such being the evidences of the former extent of the glaciers in the plains, what do the mountain-summits tell us of their height and depth? for here, also, they have left their handwriting on the wall. Every mountain-side in the Alps is inscribed with these ancient characters, recording the level of the ice in past times. Here and there a ledge or terrace on the wall of the valley has afforded support for the lateral moraines, and wherever such an accumulation is left, it marks the limit of the ice at some former period. These indications are, however, uncertain and fragmentary, depending upon projections of the rocky walls. But thousands of feet above the present level of the glacier, far up toward their summits, we find the sides of the mountains furrowed, scratched, and polished in exactly the same manner as the surfaces over which the glaciers pass at present. These marks are as legible and clear to one who is familiar with glacial traces as are hieroglyphics to the Egyptian scholar; indeed, more so,—for he not only recognizes their presence, but reads their meaning at a glance. Above the line at which these indications cease, the edges of the rocks are sharp and angular, the surface of the mountain rough, unpolished, and absolutely devoid of all those marks resulting from glacial action. On the Alps these traces are visible to a height of nine thousand feet, and across the whole plain of Switzerland, as I have stated, one may trace the glaciers by their moraines, by the masses of rock they have let fall here and there, by the drift they have deposited, to the very foot of the opposite chain, where they have dropped their boulders along the base of the Jura. Ascending that chain, one finds the grooved, polished, and scratched surfaces to its summit, on the very crest of which boulders entirely foreign to the locality are perched. Follow the range down upon the other side and you find the same indications extending into the plains of Burgundy and France beyond.
With a chain of evidence so complete, it seems to me impossible to deny that the whole space between the opposite chains of the Alps and the Jura was once filled with ice; that this mass of ice completely covered the Jura, with the exception of a few high crests, perhaps, rising island-like above it, and mounted to a height of some nine thousand feet upon the Alps, while it extended on the one side into the northern plain of Italy, filling all its depressions, and on the other down to the plains of Central Europe. The only natural inference from these facts is, that the climatic conditions leading to their existence could not have been local; they must have been cosmic. When Switzerland was bridged across from range to range by a mass of ice stretching southward into Lombardy and Tuscany, northward into France and Burgundy, the rest of Europe could not have remained unaffected by the causes which induced this state of things.
It was this conviction which led me to seek for the traces of glaciers in Great Britain. I had never been in the regions I intended to visit, but I knew the forms of the valleys in the lake-country of England, in the Highlands of Scotland, and in the mountains of Wales and Ireland, and I was as confident that I should find them crossed by terminal moraines and bordered by lateral ones, as if I had already seen them.
The reader must not suppose, when I describe these walls, formed of the débris of the glacier, as consisting of boulders, stones, pebbles, sand, and gravel, a rough accumulation of loose materials indiscriminately thrown together, that we find the ancient moraines presenting any such appearance. Time, which mellows and softens all the wrecks of the past, has clothed them with turf, grassed them over, planted them with trees, sown his seed and gathered in his harvests upon them, until at last they make a part of the undulating surface of the country. Were it not for anticipating my story, I could point out many a green billow, rising out of the fields and meadows immediately about us, that had its origin in the old ice-time. Thus disguised, they are not so evident to the casual observer; but, nevertheless, when once familiar with the peculiar form, character, and position of these rounded ridges scattered over the face of the country, they are easily recognized.
Of course, the ancient glaciers of Great Britain were far more difficult to trace than those of Switzerland, where the present glaciers are guides to the old ones. But, nevertheless, my expectations were more than answered. The first valley I entered in the glacial regions of Scotland was barred by a terminal moraine; and throughout the North of England, as well as in Scotland and Ireland, I found the hill-sides covered with traces of glacial action, as distinct and unmistakable as those I had left in my native land. And not only was the surface of the country polished, grooved, and scratched, as in the region of existing glaciers, and presenting an appearance corresponding exactly to that described elsewhere, but we could track the path of the boulders where they had come down from the hills above and been carried from the mouth of each valley far down into the plains below. In Scotland and Ireland the phenomena were especially interesting. I had intended to give in this article some account of the "parallel roads" of Glenroy, marking the ancient levels of glacier-lakes, so much discussed in this connection. But the reminiscences of old friends, and the many associations revived in my mind by recurring to a subject which I have long looked upon as a closed chapter, so far as my own researches are concerned, have constantly led me beyond the limits I had prescribed to myself in these papers upon glaciers; and as the story of Glenroy and the phenomena connected with it is a long one, I shall reserve it for a subsequent number.