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, Neuchatel, Berne, and Soleure, rising to the crest of the Jura, and in many points penetrating even beyond its outer range.