132 MAN AND THE GLACIAL PERIOD. 



ice of the ancient Rhone Glacier spread to the right and 

 to the left, while its northern boundary was abruptly ter- 

 minated 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 Rhone 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 Isere, past Ohambery, 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 Rhone Glacier spread eastward, being joined in the 

 vicinity of Berne by the confluent ice-stream which de- 

 scended 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.* 



* See map of Rhone Glacier, on p. 58. 



