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 Wetterhoerner, the Schreckhoerner, 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 Isere, 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.