From its "vomitory," at the head of Lake Geneva, the ice of the ancient Rhône Glacier spread to the right and to the left, while its northern boundary was abruptly terminated by the line of the Jura Mountains. The law of glacial motion was, however, admirably illustrated in the height to which the ice rose upon the flanks of the Jura. At Chasseron, in the direct line of its onward motion, it rose to its highest point, while both to the southwest and to the northeast, along the line of the Juras, the ice-action was limited to constantly decreasing levels. Down the valley of the Rhône the direction of motion was determined by the depression of Lake Geneva, at the lower end of which it received its main tributary from Mont Blanc, which had come down from Chamouni through the valley of the river Arve. From this point it was deflected by a spur of the Jura Mountains more and more southward to the vicinity of Culoz, near the mouth of Lake Bourget. Here the glacier coming down from the western flanks of the Alps, through the upper valley of the Isère, past Chambéry, became predominant, and deflected the motion to the west and north, whither the ice extended to a line passing through Bourg, Lyons, and Vienne, leaving upon one of the eminences on which Lyons is built a boulder several feet in diameter, which is duly preserved and labelled in the public park in that portion of the city. Farther south, glaciers of less extent marked the Alps most of the way to the Mediterranean, but they were not at all comparable in size to those from the central region. To the right of Lake Geneva the movement started by the Rhône Glacier spread eastward, being joined in the vicinity of Berne by the confluent ice-stream which descended from the north flank of the Bernese Oberland, through the valley of the Aar. These united streams filled the whole valley with ice as far down as Soleure.[BL] [Footnote BL: See map of Rhône Glacier, on p. 58.] [Illustration: MAP OF GLACIAL MOVEMENTS IN FRANCE AND SWITZERLAND.] Farther eastward, other ice-streams from the Alps became predominant, one of which, moving down the Reuss, deployed out upon the country lying north of Lucerne and Zug. Still farther down, the ancient glacier which descended the Limmatt spread itself out over the hills and lowlands about Zürich, one of its moraines of retrocession nearly dividing the lake into two portions. Guyot and others have shown that the superficial deposits of this portion of Switzerland are just such as would be distributed by glaciers coming down from the above-mentioned Alpine valleys. Uniting together north of Zürich, these glaciers pushed onward as far as the Rhine below Schaffhausen. In Frickthal the glacial ice was still 1,200 feet thick, and at Kaisterberg between 400 and 500 feet.