In 1740, Kapeler, a physician of Lucerne, undertook a journey to the mountains of the Aar, to visit certain crystal grottos, now well known, but then recently discovered. He prepared a map of these grottos and their vicinity, in which they are represented as being situated at some distance from the extremity of the glacier, the lower end of which is now considerably beyond them.[50]
But to return to the glacier of the Rhone. We can detect the sequence and relative age of its ancient moraines, not only by their position with reference to each other and to the present glacier, but also by their vegetation. The older ones have a mature vegetation; indeed, some of the largest trees of the valley stand upon the lower moraines, while those higher up, nearer the glacier, have only comparatively small trees, and the more recent ones are almost bare of vegetation. Moreover, we do not lose the track of the great glacier of the Rhone even when we have followed its ancient boundaries to the shores of the Lake of Geneva; for along its northern and southern shores we can follow the lateral moraines marking the limits of the glacier which once occupied that crescent-shaped depression now filled by the blue waters of the lake.
M. de Charpentier was the first geologist who attempted to draw the outlines of the glacier of the Rhone during its greatest extension, when it not only filled the basin of the Lake of Geneva, but stretched across the hilly plain to the north, reached the foot of the Jura, and even rose to a considerable height along the southern slope of that chain of mountains. At that time the colossal glacier spread at its extremity like a fan, extending westward in the direction of Geneva and eastward towards Soleure.[51] The very minute and extensive investigations of Professor A. Guyot upon the erratic boulders of Switzerland have not only confirmed the statements of M. de Charpentier, but even shown that the northeastern boundary of the ancient glacier of the Rhone was more extensive than was at first supposed. Other researches upon the ancient moraines along the shores of the Lake of Geneva, and in other parts of Switzerland, in which most geologists of the day took an active part, have made us as fully conversant with the successive outlines and varying extent of the principal glaciers ranging from the Alpine summits to the surrounding lowlands as we are with the glaciers in their present circumscription. But no one has done as much as Professor Guyot to add precision to these investigations. The number of localities, the level of which he has determined barometrically, with the view of fixing the ancient levels of all these vanished glaciers, is almost incredible. The result of all these surveys has been a distinct recognition of not less than seven gigantic glaciers descending from the northern and western slopes of the Alps to the adjoining hilly plains of Switzerland and France. It is most interesting to trace their outlines upon a recent map of those countries, but it requires that kind of intellectual effort of the imagination without which the most brilliant results of modern science remain an unmeaning record to us. Let us, nevertheless, try to follow.
The glacier of the Rhone, occupying the whole space between the Bernese and Valesian Alps, filled to overflowing the valley of the Rhone; at Martigny it was met by a large tributary from Mont Blanc, by the side of which it advanced into the plain beyond, filling the whole Lake of Geneva, and covering the beautiful Canton de Vaud and parts of Fribourg, Neuchâtel, Berne, and Soleure, rising to the crest of the Jura, and in many points penetrating even beyond its outer range.
To the east of this, the largest of all the ancient glaciers of Switzerland, we find the ancient glacier of the Aar, descending from the northern slope of the whole range of the Bernese Oberland. The glaciers that once filled the valley of Hasli, from the Grimsel to Meyringen, and those that came down from the Wetterhörner, the Schreckhörner, the Finster-Aarhorn, and the Jungfrau, through the valleys of Grindelwald and Lauterbrunnen, united in a common bed, the bottom of which was the present basin of the Lakes of Brientz and Thun. These were joined by the glaciers emptying their burden through the valley of the Kander. To these combined glaciers the formation of the terminal moraine of Thun must be ascribed. But before this had been formed, the glacier of the Aar, in its amplest extension, had also reached the foot of the Jura, without, however, spreading so widely as the glacier of the Rhone. Farther to the east Professor Guyot has traced the boundaries of three other colossal glaciers, one of which derived its chief supplies from the Alps of Uri, bringing with it all the tributaries which the main glacier coming down from the St. Gothard received right and left, in its course through the valley of the Reuss and the basins of the Lakes of Lucerne and Zug. The second, born in the Canton of Glaris, followed mainly the present course of the Linth and the basin of the Lake of Zurich. Professor Escher von der Linth has shown that the lovely city of Zurich is built upon a moraine, like Berne. The imagination shrinks from the thought that all the beautiful scenery of those countries should once have been hidden under masses of ice, like those now covering Greenland. The easternmost ancient glacier of Switzerland is that of the Rhine, arising from all the valleys from which now descend the many tributaries of that stream, spreading over the northeastern Cantons, filling the Lake of Constance, and terminating at the foot of the Suabian Alp. Next to the glacier of the Rhone, this was once the largest of those descending from the range of the Alps.
West of Mont Blanc Professor Guyot has traced the boundaries of two other distinct ancient glaciers; one of which, the glacier of the Arve, followed chiefly the course of the Arve, and, though discharging the icy accumulations from the western slope of Mont Blanc, was, as it were, only a lateral affluent of the great glacier of the Rhone. The other, the glacier of the Isère, occupied, to the south and west of the preceding, the large triangular space intervening between the Alps and the Jura, in that part of Savoy where the two mountain-chains converge and become united.
It would lead me too far, were I to describe also the course of the great ancient glaciers which descended from the southern slopes of the Alps into the plain of Northern Italy. Moreover, these boundaries are not yet ascertained with the same degree of accuracy as those of the northern and western slopes; though very accurate descriptions of some of them have been published, with illustrations on a large scale, by MM. Martins and Gastaldi, and of others by Professor Ramsey. I have myself examined only the upper part of that of the valley of Aosta.
The evidence concerning the ancient glaciers of the Alps, especially within the limits of Switzerland, is already so full that it affords ample means for a comprehensive general view of the subject. It is frequently the case, that, when a stretch of time or space lies between us and a matter we have once studied more closely, it presents itself to us as a whole more vividly than when our nearness to it forced all its details upon our observation. In my present position, now that the lapse of many years separates me from my personal investigations of the ancient and modern glaciers, and I look back upon them from another continent, it seems to me that I have, as it were, a bird's-eye view of their whole extent; and I confess that this distant retrospect of the subject has been to me almost as fascinating as were the researches of my earlier years in the same direction. I wish that I could present it to the minds of my readers with something of the attraction it possesses for me. I trust, however, that I have made it plain to them that the great mountain-chain of the Alps has been a central axis from which immense glaciers at one time descended in every direction, not only to its base, beyond which the lowlands extend in flat undulations, but to a greater or less distance over the adjoining plains; while at present they are confined to the higher valleys. So far, then, notwithstanding the extraordinary difference in their dimensions, at the time they reached the Jura and the plain of Northern Italy, when compared with what they are now, they seem directly connected with the Alps, and the mountains appear as their birthplace; so much so that the first attempts at a generalization concerning their origin started from the assumption that they must have been formed between the high ridges from which they seem to flow down. These facts, then the only ones known concerning a greater extension of the glaciers, naturally led to the views advocated by M. de Charpentier. My own theory was also at first, that the upheaval of the Alps must, in some way or other, have been connected with these phenomena. But it soon became evident to me that these views were inadequate to account for the former presence of extensive glaciers in other parts of Europe; and even within the range of the Alps there were insuperable objections to their final admission. If the ancient glaciers had been first formed among the highest mountains, and extended downwards into the plains, the largest and highest moraines ought to be the most distant, and to be formed of the most rounded masses; whereas the actual condition of the detrital accumulations is the reverse, the distant materials being widely spread, and true moraines being found only in valleys connected with great chains of lofty mountains.
Again, all these moraines are within one another,—the most distant from the glacier to which they owe their origin encircling all those which are nearer and nearer to it within the same glacial basin. And as no glacier could reach to its farthest moraine without pushing forward all the intervening loose materials, it is self-evident that the outer moraines were first formed, and those nearer the glacier subsequently, in the order in which they follow one another from the lower valleys to the higher levels at which alone glaciers exist at present. Translating these facts into words, we see that the glaciers to which these ancient moraines owe their origin must have been retreating gradually while the moraines were accumulating. But a glacier while uniformly retreating forms no high walls of loose materials around its edges and at its lower extremity; as it melts away, it only drops the burden of angular rocky fragments which it carries upon its back over the loose fragments above which it moves, and which it grinds to powder, or to sand, or to rounded pebbles, in its progress. It is only where the glacier remains stationary for a longer or shorter period that large terminal moraines can accumulate; and they are generally found in such places in the valleys of the Alps as would naturally determine the lower limit of a glacier for the time being. There is no possibility of escaping the conclusion that the ancient glaciers must have begun that series of oscillations to which the accumulation of the moraines is to be ascribed, at a time when ice-fields already occupied the whole area which they have covered during their greatest extension. After we shall have seen how many centres of dispersion of erratic boulders existed in the northern hemisphere, similar to that of the Alps, we may perhaps be able to form some idea of the manner in which these ice-fields originated and gradually vanished.
Some investigators have been inclined to explain the presence of boulders, moraines, drift, and the like phenomena, by the action of water. But even if we could believe that rivers had brought along with them such masses of rock, and deposited them where they are now found, the regularity in the distribution of the materials disproves any such theory. In the lateral moraines of the Lake of Geneva we have a striking illustration of this apparently systematic division of the loose materials; for the northeastern moraines of that glacial basin contain rocks belonging exclusively to the northern side of the valley of the Rhone, while the moraines on the southern shore of the lake consist of rocks belonging to its southern side. Indeed, rivers, so far from building up moraines, have often partially destroyed them. We find various instances of moraines through which a river runs, having worn for itself a passage, on either side of which the form of the moraine remains unbroken. In the valley of the Rhone there are villages built on such moraines, as, for instance, Viesch, with the river running through their centre.