3. The southern face is supported by two great pillars—on the east the Grand Credo and on the west the ridge of Revermont (2,529 ft.) above .Bourg en Bresse; between these a huge bastion (the district of Bugey) stretches south, forcing the Rhone to make a long detour. On the two sides of this bastion the plains in which Amberieu and Culoz stand are the meeting points of the routes which cut through the bastion by means of deep gorges. On the eastern side this great wedge is steep and rugged, ending in the Grand Colombier (5,042 ft.), north of Culoz, and it sinks on the western side to the valley of the Ain, the district of Bresse, and the plateau of Dombes. The junction of the Ain and the Surand at Pont d'Ain on the west balances that of the Valserine and the Rhone at Bellegarde on the east.
The Jura thus dominates on the north one of the great highways of Europe, on the east and west divides the valleys of the SaOne and the Aar, and stretches out to the south so as nearly to join hands with the great mass of the Dauphine Alps. It therefore commands the routes from France into Germany, Switzerland and Italy, and hence its enormous historical importance.
The topography of the interior of the range naturally falls into three divisions, each traversed by one of the three great rivers of the Jura—the Doubs, the Loue and the Ain.
I. The northern division is marked by the east and west ridge of the Lomont, and the Mont Terrible; the defile of the Doubs from St. Ursanne to St. Hippolyte, and the "Trouee" of the Black Forest towns. It thus bars access to the central plateau from the north. This division falls again into two distinct portions.
(a) The first is the part east of the deep gorge of the Doubs below St. Hippolyte. It includes the basin of the river Birse, and the plateau between the Doubs and the Aar, on which, at an average height of 2,600 ft., are situated a number of towns, one of the most striking features of the Jura. These include Le Locle (q.v.) and La Chaux de Fonds (q.v.), and are mainly occupied with watch-making, an industry well fitted for a mountain district.
(b) The part west of the "close" of the Doubs: of this, the district east of the river Dessoubre, isolated in the interior of the range (unlike the Le Locle plateau), is called the Haute Mon tagne, and is given up to cheese-making, curing of hams, saw-mills, etc. Besancon is the chief French centre of the watch making industry, and is connected with Geneva by a chain of places similarly occupied, which fringe the west plateau of the Jura. The part west of the Dessoubre, or the Moyenne Montagne, a huge plateau north of the Loue, is more especially devoted to agricul ture, while along its north edge metal-working and manufacture of hardware are carried on, particularly at Besancon and Audincourt.
2. The central division in which no deep gorges are found, consists of the basin of which Pontarlier is the centre, through notches in the rim of which routes converge from every direction; hence its immense strategical and commercial importance. The north-east roads run to Morteau and Le Locle, the north-west to Besancon, the west to Salins, the south-west to Dole and Lons-le Saunier, the east to the Swiss plain. The Pontarlier plateau has only slight indentations in it due to erosion by the river Drugeon.
East of this plateau is the Fort de Joux, under the walls of which meet the two railways from Neuchatel, and to the west Salins, the meeting place of the routes from the Col de la Faucille, from Besancon, and from the French plain.
The Ain rises on the south edge of this plateau, and on a lower shelf which it waters are situated two points of great military importance—Nozeroy and Champagnole. The latter is specially important, since the road leading thence to Geneva traverses one after another' the chief valleys which run down into South Jura, and thus commands the routes from the Geneva region, and a branch route along the Orbe river from Jougne.
There are said to be in the central Jura no less than fifteen ridges running parallel to each other, and it is these which force the Loue to the north, and thereby occasion its very eccentric course. The cultivation of wormwood wherewith to make the tonic "absinthe" has its headquarters at Pontarlier.
3. The southern division is the most complicated of the Jura. The lofty ridge which bounds it to the east forces all its drainage to the west, and the result is a number of valleys of erosion, quite distinct from the "cluses" or fissures of the Doubs and the Loue. Another point of interest is the number of roads which intersect it, despite its extreme irregularity. This is due to the great "cluses" of Nantua and Virieu, which traverse it from east to west. The plateaux west of the Ain are cut through by the valleys of the Valouse and of the Surand, and do not possess any considerable towns. The Ain receives three tributaries from the east : (a) The Bienne, which flows from the fort of Les Rousses by St. Claude, the industrial centre of the south Jura, famous for wooden toys; Septmoncel, a centre for gem cutting, and Morez, a watch and spectacle making centre. The industrial prosperity of this valley is of recent origin.
(b) The Oignin, which receives the drainage of the lake of Nantua, a town noted for combs and silk, and which communicates by the "cluse" of the Lac de Silan with the Valserine valley, and so with the Rhone at Bellegarde, and again with the various routes which meet at Les Rousses, while Culoz is easily gained by the Val Romey and the Seran.
(c) The Albarine, connected with Culoz by the "cluse" of Virieu, and by the Furan flowing south, with Belley, the capital of the district of Bugey (the old name for the south Jura).
The "cluses" of Nantua and Virieu are now both traversed by important railways; and it is even truer than of old that the keys of the south Jura are Lyons and Geneva.
Politically the Jura is French (departments of the Doubs, Jura, Ain and in the north a small portion of Alsace) and Swiss (parts of the cantons of Geneva, Vaud, Neuchatel, Berne, Soleure and Basle).