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.