Rhone

About 12 m. south of Geneva the Rhone enters France. At Bellegarde the Valserine flows in (right), and then the river resumes its southerly direction, from which a great gorge has deflected it for a while. Some way below Bellegarde, between Le Parc and Pyrimont, the RhOne becomes officially "navigable" though as far as Lyons the navigation consists almost entirely of flat-bottomed boats. Above Seyssel the Usses (left) joins the Rhone, while just below that village the Fier (left) flows in from the Lake of Annecy. Below the junction of the Fier the hills sink on either side, the channel of the river widens and it leaves the mountains for the plains. The Geneva-Paris railway follows the river as far as Culoz. The Rhone receives the waters from Lake Bourget by a canal (left). The last of the cluses is at the Pont du Saut or Sault, a little south of Lagnieu. The river now widens but the neighbouring country is much exposed to inun dations.

It receives the Ain (right), which descends from the French slope of the Jura and is navigable for about 6o m., above its junction with the Sake, just below Lyons. The Sake (q.v.) which has received (left) the Doubs, is the real continuation of the lower Rhone, both from a geographical and a commercial point of view, and it is by the means of canals branching off from the course of the Sake that the Rhone communicates with the basins of the Loire, the Seine, the Rhine and the Moselle.

Below Lyons,

the Rhone becomes one of the great historical rivers of France. It was up its valley that various civilizations penetrated from the Mediterranean to Lyons. From Lyons down wards the left bank serves as a great medium of commerce by which central France sends its products to the sea. During this half of its course it flows over an alluvium-filled valley resting on Jurassic and Cretaceous rocks, and it can boast of having on its left bank (the right bank is very poor in this respect) such his torical cities at Vienne, Valence, Avignon, Tarascon and Arles, while it receives (left) the Isere, the DrOme, the Aygues and the Durance rivers, all formed by the union of many streams from the Dauphine Alps.

The Ardeche is the only considerable affluent from the right. Near Arles, about 25 m. from the sea, and by rail m. from Lyons, the river breaks up into two main branches, the Grand Rhone running south-east and the Petit RhOne south-west; they enclose between them the delta of the Camargue, which is culti vated on the banks of the river only, but elsewhere is simply a great alluvial plain, composed of scanty pasturages and of great salt marshes. Changes in sea level have taken place in the RhOne delta in recent times. R. D. Oldham (Nature, vol. cxvi. [1925] pp. 16, 52, ioo), shows that in Pre-Roman times the sea-level was 15 ft. higher than today. A rise was followed by a subsidence which occurred in about the 8th century when the river ended far inland in a shallow land-locked inlet which it proceeded to fill up with alluvium until in the 17th century it had regained the sea-front. Even since that time it has greatly modified its form by changes of channels, etc.

The RhOne river system is dominated by two tectonic features, the Alps and the Central Plateau of France. Below Chalon-sur SaOne, the SaOne-RhOne flows along the eastern side of the central plateau and most of the course is determined by a north to south fault. The remainder of the river system is determined by the structure of the Alps (q.v.). The greater length of the river and of its Alpine affluents is parallel to the trend of the structures, as above Martigny, between the Lake of Geneva and Corbelin, the Arve in the Chamonix valley and parts of the Isere and of the Durance. On the other hand other portions flow radi ally to the trend, as between Martigny and the Lake of Geneva, parts of Isere, the DrOme, the Aygues, the Durance and numerous other tributaries.