Valleys of the Rhine and Rhone. 161 



Mont Blanc, and, after a course more remarkable for rapidity 

 than length, joins the Rhone about a mile below its issue 

 from Lake Leman at Geneva. The course of the Rhone, on 

 issuing from the lake, is through what may be called a deep 

 alluvial trough, on the bottom and sides of which the city of 

 Geneva is built. The Arve, near its junction with the Rhone, 

 flows through a similar trough, one side of which is overhung 

 by the Saleve mountains. When we proceed in our examin- 

 ation of the Arve valley, we find that it is filled from side to 

 side with a deep detrital formation composed of the rocks of 

 the Alps, and of which the alluvial sheet around the junction 

 of the rivers is a continuation. For many miles, this may be 

 traced up the Arve valley, everywhere forming the terraced 

 sides of a deep trough or cut in which the river runs. Sup- 

 posing, indeed, there were no such trough for the river, the 

 valley of the Arve from Bonneville downwards, might be de- 

 scribed as having a smoothly-sloping floor of gravel and other 

 detrital matter ; and it might, on a similar supposition for 

 the Rhone valley, be added, that this alluvial sheet, after 

 passing out from among the mountains, advanced across that 

 valley, so as to form a barrier at the lower end of Lake Le- 

 man. Thus, to abstract the troughs in which the rivers run, 

 is merely to trace backward the course of geological events 

 for a step, for we are warranted by some of the oldest and 

 most settled observations of that science in believing, that 

 these troughs have been cut by the rivers out of a formation 

 which was previously without any such intersections. Lay- 

 ing aside for a brief space farther speculation on the circum- 

 stances attending both the formation and the intersections, 

 I may remark, that the general appearance of the alluvium 

 between the Saleve mountains and the lake, is that of a plain, 

 with very slight inequalities. In reality, however, it rises 

 from about 100 feet above the lake, which is the elevation 

 immediately behind Geneva, to 165 feet, at a point about two 

 miles to the south-eastward, where, for a considerable space, 

 it is perfectly flat ; after which the gentle rise is resumed 

 without interruption for several miles. Within the walls of 

 the Arve valley, the terraces appear to follow this gentle in- 

 clination on both sides of the river pretty uniformly ; but at 



