JURA MOUNTAINS, a range which may be roughly described as the block of mountains rising between the Rhine and the Rhone, and forming the frontier between France and Switzerland. The gorges by which these two rivers force their way to the plains cut off the Jura from the Swabian and Franconian ranges to the north and those of Dauphine to the south. But in very early days, before these gorges had been carved out, there were no openings in the Jura at all, and even now its three chief rivers the Doubs, the Loue and the Ain flow down the western slope, which is both much longer and but half as steep as the eastern. Some geographers extend the name Jura to the Swabian and Fr' anconian ranges between the Danube and the Neckar and the Main; but, though these are similar in point of composition and direction to the range to the south, it is most convenient to limit the name to the mountain ridges lying between France and Switzerland, and this narrower sense will be adopted here.
The Jura has been aptly described as a hugeplateau about 156 m. long and 38 m. broad, hewn into an oblong shape, and raised by internal forces to an average height of from 1950 to 2600 ft. above the surrounding plains. The shock by which it was raised and the vibration caused by the elevation of the great chain of the Alps, produced many transverse gorges or " cluses," while on the plateaus between these subaerial agencies have exercised their ordinary influence.
Geologically the Jura Mountains belong to the Alpine system; and the same forces which crumpled and tore the strata of the one produced the folds and faults in the other. Both chains owe their origin to the mass of crystalline and unyielding rock which forms the central plateau of France, the Vosges and the Black Forest, and which, between the Vosges and the central plateau, lies at no great depth beneath the surface. Against this mass the more yielding strata which lay to the south and west were crushed and folded, and the Alps and the Jura were carved from the ridges which were raised. But the folding decreases in intensity towards the north; the folding in the Alps is much more violent than the folding in the Jura, and in the Jura itself the folding is most marked along its southern flanks.
The Jura is composed chiefly of Jurassic rocks it is from this chain that the Jurassic system derives its name but Triassic, Cretaceous and Tertiary beds take part in its formation. It may be divided into three zones which run parallel to the length of the chain and differ from one another in their structure. The innermost zone, which rises directly from the plain of Switzerland, is the folded Jura (Jura plissc, Kettenjura) , formed of narrow parallel undulations which diminish in intensity towards the French border. This is followed by the Jura plateau (Jura tabulair e, Tafdjura), in which the beds are approximately horizontal but are broken up into blocks by fractures or faults. Finally, along its western face there is a zone of numerous dislocations, and the range descends abruptly to the plain of the Sa6ne. This is the Region du vignoble and is well shown at Arbois.
Owing to the convergence of the faults which bound it, the plateau zone decreases in width towards the south, while towards the north it forms a large proportion of the chain. The folded zone is more constant. Along its inner margin the folds are frequently overthrown, leaning towards France, but elsewhere they are simple anticlinals and synclinals, parallel to the length of the chain, and as a rule there is a remarkable freedom from dislocations of any importance, except towards Neuchatel and Bienne.
The countless blocks of gneiss, granite and other crystalline formations which are found in such numbers on the slopes of the Jura, and go by the name of " erratic blocks " (of which the best known instance the Pierre a Bot is 40 ft. in diameter, and rests on the side of a hill 800 ft. above the Lake of Neuchatel), have been transported thither from the Alps by ancient glaciers, which have left their mark on the Jura range itself in the shape of striations and moraines.
The general direction of the chain is from north-east to southwest, but a careful study reveals the fact that there were in reality two main lines of upheaval, viz. north to south and east to west, the former best seen in the southern part of the range and the latter in the northern; and it was by the union of these two forces that the lines north-east to south-west (seen in the greater part of the chain), and north-west to south-east (seen in the Villebois range at the south-west extremity of the chain), were produced. This is best realized if we take Besancon as a 'centre; to the north the ridges run east and west, to the south, north and south, while to the east the direction is north-east to south-west.
Before considering the topography of the interior of the Jura, it may be convenient to take a brief survey of its outer slopes.
1. The northern face dominates on one side the famous " Troupe " (or Trench) of Belfort, one of the great geographical centres of Europe, whence routes run north down the Rhine to the North Sea, south-east to the Danube basin and Black Sea, and south-west into France, and so to the Mediterranean basin. It is now so strongly fortified that it becomes a question of great strategical importance to prevent its being turned by means of the great central plateau of the Jura, which, as we shall see, is a network of roads and railways. On the other sfde it overhangs the " Troude " of the Black Forest towns on the Rhine (Rheinfelden, Sackingen, Laufenburg and Waldshut), through which the central plain of Switzerland is easily gained. On this north slope two openings offer routes into the interior of the chain the valley of the Doubs belonging to France, and the valley of the Birse belonging to Switzerland. Belfort is the military, Mulhausen the industrial, and Basel the commercial centre of this slope.
2. The eastern and western faces offer many striking parallels. The plains through which flow the Aar and the Safine have each been the bed of an ancient lake, traces of which remain in the lakes of Neuchatel, Bienne and Morat. The west face runs mainly north and south like its great river, and for a similar reason the east face runs north-east to south-west. Again, both slopes are pierced by many transverse gorges or " cluses " (due to fracture and not toerosion), by which access is gained to the great central plateau of Pontarlier. though these are seen more plainly on the east face than, on the west ; thus the gorges at the exit from which Lons-le-Saunier, Poligny, Arbois and Salins are built balance those of the Suze, of the Val de Ruz, of the Val de Travcrs, and of the Val d'Orbe, though on the east face there is but one city which commands all these important routes Neuch&tel. This town is thus marked out by nature as a great military and industrial centre, just as is Besancon on the west, which has besides to defend the route from Belfort down the Doubs. These easy means of communicating with the Free County of Burgundy or Franche-Comtd account for the fact that the dialect of Neuchatel is Burgundian, and that it was held generally by Burgundian nobles, though most of the country near it was in the hands of the house of Savoy until gradually annexed by Bern. The Chasseron (5286 ft.) is the central point of the eastern face, commanding the two great railways which join Neuchatel and Pontarlier. This ridge is in a certain sense parallel to the valley of the Loue on the west face, which flows into the Doubs a little tx> the south of D61e, the only important town of the central portion of the Sa6ne basin. The Chasseron is wholly Swiss, as are the lower summits of the Chasseral (5279 ft.), the Mont Suchet (5220 ft.), the Aiguille de Baulmes (5128 ft.), the Dent de Vaulion (4879 ft.), the Weissenstein (4223 ft.), and the Chaumont (3845 ft.), the two last-named points being probably the best-known points in the Jura, as they are accessible by carriage road from Soleure and Neuchatel respectively. South of the Orbe valley the east face becomes a rocky wall which is crowned by all the highest summits, (the first and second Swiss, the rest French) of the chain the Mont Tendre (5512 ft.), the Dole (5505 ft.), the Reculet (5643 ft.), the Crgt de la Neige (5653 ft.) and the Grand Credo (5328 ft.), the uniformity of level being as striking as on the west edge of the Jura, though there the absolute height is far less. The position of the D61e is similar to that of the Chasseron, as along the sides of it run the great roads of the Col de St Cergues (3973 ft.) and the Col de la Faucille (4341 ft.), the latter leading through the Vallde des. Dappes, which was divided in 1862 between France and Switzerland, after many negotiations. The height of these roads shows that they are passages across the chain, rather than through natural depressions.
3. The southern face is supported by two great pillars on the east by the Grand Crddo and on the west by the ridge of Revermont (2529 ft.) above Bourg en Bresse; between these a huge bastion (the district of Bugey) stretches away to the south, forcing the Rhone to make a long ddtour. On the two sides of this bastion the plains in which Amberieu and Culoz stand balance one another, and are the meeting points of the routes which cut through the bastion by means of deep gorges. On the eastern side this great wedge ia steep and rugged, ending in the Grand Colombicr (5033 ft.) above 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 Sa6ne and the Aar, and stretches out to the south so as nearly to join hands with the great mass of the Dauphind Alps. It therefore commands the routes from France into Germany, Switzerland and Italy, and hence its enormous historical importance.
Let us now examine the topography of the interior of the range. This 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. In the northern division it is the east and west line which prevails the Lomont, the Mont Terrible, the defile of the Doubs from St Ursanne to St Hippolyte, and the " Troude " of the Black Forest towns. It thus bars access to the central plateau from the north, and this natural wall does away with the necessity of artificial fortifications. This division falls again into two distinct portions.
(a) The first is the part east of the deep gorge of the Doubs after it turns south at St Hippolyte; it is thus quite cut off on this side, and is naturally Swiss territory. It includes the basin of the river Birse, and the great plateau between the Doubs and the Aar, on which, at an average height of 2600 ft., are situated a number of towns, one of the most striking features of the Jura. These include Le Locle (?..) and La Chaux de Fonds (..), and are mainly occupied with watch-making, an industry which does not require bulky machinery, and is therefore well fitted for a mountain district.
(b) The part west of the "cluse" 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 Montagne, and is given up to cheese-making, curing of hams, saw-mills, etc. But little watch-making is carried on there, Besangon being the chief French centre of this industry, and being 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 agriculture, while along its north edge metalworking and manufacture of hardware are carried on, particularly at Besancon and Audincourt.
2. The central division is remarkable for being without the deep gorges which are found so frequently in other parts of the range. It consists of the basin of which Pontarlier is the centre, through notches in the rim of which routes converge from every direction ; this is the great characteristic of the middle region of the Jura. Hence its immense strategical and commercial importance. On the north-east roads run to Morteau and Le Locle, on the north-west to Besancon, on the west to Salins, on the south-west to Dole and Lons-le-Saunier, on the east to the Swiss plain. The Pontarlier plateau is nearly horizontal, the slight indentations in it being due to erosion, e.g. by the river Drugeon. The keys to this important plateau are to the east the Fort de Joux, under the walls of which meet the two lines of railway 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 or step, 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, not far from their head, the chief valleys which run down into the South Jura, and thus commands the southern routes as well as those by St Cergues and the Col de la Faucille from the Geneva region, and a branch route along the Orbe river from Jougne. The fort of Les Rousses, near the foot of the Dole, serves as an advanced post to Champagnole, just as the Fort de Joux does to Pontarlier.
The above sketch will serve to show the character of the central Jura as the meeting place of routes from all sides, and the importance to France of its being strongly fortified, lest an enemy approaching from the north-east should try to turn the fortresses of the " Trouee de Belfort." It is in the western part of the central Jura that the north and south lines first appear strongly marked. There are said to be in this district 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 by far the most complicated and entangled part 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 (of which that of the Ain is the chief instance), quite distinct from the natural " cluses " or fissures of those of the Doubs and of 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 north and south line is very clearly seen in the eastern part of this division; the north-east and south-west is entirely wanting, but in the Villebois range south of AmbeVieu we have the principal example of the north-west to south-east line. The plateaus west of the Ain are cut through by the valleys of the Valouse and of the Surand, and like all the lowest terraces on the west slope 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 the manufacture of wooden toys, owing to the large quantity of boxwood in the neighbourhood. Septmoncel is busied with cutting of gems, and Morez with watch and spectacle making. Cut off to the east by the great chain, the industrial prosperity of this valley is of recent origin.
(6) The Oignin, which flows from south to north. It receives the drainage of the lake of Nantua, a town noted for combs and silk weaving, 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 under the walls of the fort of Les Rousses, while by the Val Romey and the Seran Culoz is easily gained.
(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. But of course the strategic importance of these gorges is less than appears at first sight, because they can be turned by following the Rhone Jn its great bend to the south.
The range is mentioned by Caesar (Bell. Gall. 1.2-3,6(1), and 8(i)),Strabo(iv. 3, 4, and 6, n), Pliny (iii. 3 1 ; iv. 105; xvi. 197) and Ptolemy (ii. ix. 5), its name being a word which appears under many forms (e.g. Joux, Jorat, Jorasse, Juriens), and is a synonym for a wood or forest. The German name is Leberberg, Leber being a provincial word for a hill.
Politically the Jura is French (departments of the Doubs, Jura and Ain) and Swiss (parts of the cantons of Geneva, Vaud, Neuchatel, Bern, Soleure and Basel) ; but at its north extremity it takes in a small bit of Alsace (Pfirt or Ferrette) . In the middle ages the southern, western and northern sides were parcelled out into a number of districts, all of which were gradually absorbed by the French crown, viz., Gex, Val Romey, Bresse and Bugey (exchanged in 1601 by Savoy for the marquisate of Saluzzo), Franche-Comte, or the Free County of Burgundy, an imperial fief till annexed in 1674, the county of Montbeliard (Mompelgard) acquired in 1793, and the county of Ferrette (French 1648-1871). The northern part of the eastern side was held till 1792 (part till 1797) by the bishop of Basel as a fief of the empire, and then belonged to France till 1814, but was given to Bern in 1815 (as a recompense for its loss of Vaud), and now forms the Bernese Jura, a French-speaking district. The centre of the eastern slope formed the principality of Neuchatel (q.v.) and the county of Valangin, which were generally held by Burgundian nobles, came by succession to the kings of Prussia in 1707, and were formed into a Swiss canton in 1815, though they did not become free from formal Prussian claims until 1857. The southern part of the eastern slope originally belonged to the house of Savoy, but was conquered bit by bit by Bern, which was forced in 1815 to accept its subject district Vaud as a colleague and equal in the Swiss Confederation. It was Charles the Bold's defeats at Grandson and Morat which led to the annexation by the confederates of these portions of Savoyard territory.
AUTHORITIES. E.F.Berlioux, LeJura (Paris, 1880) ; F. Machacek, Der Schweizer Jura (Gotha, 1905) ; A. Magnin, Les lacs du Jura (Paris, 1895); J. Zimmerli, " Die Sprachgrenze im Jura " (vol. i. of his Die Deutsch-franzosische Sprachgrenze in der Schweiz (Basel, 1891). For the French slope see Joanne's large Itineraire to the Jura, and the smaller volumes relating to the departments of the Ain, Doubs and Jura, in his Geographies departementales. For the Swiss slope see 3 vols. in the series of the Guides Monod (Geneva) ; A. Monnier, La Chaux de Fonds et le Haul-Jura Neuchdtelois; J. Monod, Le Jura Bernois; and E. J. P. de la Harpe, Le Jura Vaudois. (W. A. B. C.)
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)