Geologically, the sedimentary rocks of the Jura belong to the Mesozoic age, and were deposited in a sea of variable depth, traces of which survive in the vast salt mines from which Salins and Lons-le Saunier derive their names. The special name of these fossiliferous strata is Oolitic; they are also called Jurassic, from the fact that the Jura is entirely made up of such layers. They include sands, sandstones, marls, clays, and limestones; and the water that deposited these strata must have been highly charged with carbonate of lime, since calcareous rocks abound in the Jura. The action on these rocks of the carbonic acid gas discharged by all animals has been to transform them into bicarbonate of lime, a very soluble body, and hence the work of erosion has been much facilitated. 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 à Bot—is 40 feet in diameter, and rests on the side of a hill 900 feet above the Lake of Neuchâtel), 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 south-west, 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 northeast 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 Besançon 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 “Trouée” (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 side it overhangs the “Trouée” of the Black Forest towns on the Rhine (Rheinfelden, Säckingen, 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 Birs belonging to Switzerland. Belfort is the military, Mühlhausen 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 Saône have each been the bed of an ancient lake, traces of which remain in the lakes of Neuchâtel, 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 to erosion), 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 Vai de Ruz, of the Vai de Travers, and of the Vai d’Orbe, though on the east face there is but one city which commands all these important routes—Neuchâtel. This town is thus marked out by nature as a great military and industrial centre, just as Besançon 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 Comté accounts for the fact that the dialect of Neuchâtel 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 Chasscron (5286 feet) is the central point of the eastern face, commanding the two great railways which join Neuchâtel and Pontarlier. It is in a certain sense parallel to the valley of the Loue on the west face, which flows into the Doubs a little to the south of Dôle, the only important town of the central portion of the Saône basin. South of the Vai d’Orbe the east face becomes a rocky wall crowned by all the highest summits of the chain—the Mont Tendre (5512 feet), the Dôle (5507 feet), the Rcculet (5643 feet), the Crét de la Neige (5653 feet), and the Gram! Credo (5276 feet), 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 Dôle is similar to that of the Chasseron, as along the sides of it run the great roads of the Col de St Cergues (4159 feet) and the Col de la Faucille (4341 feet), the latter leading through the Vallée 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 soιdhcm face is supported by two great pillars—on the east by the Grand Credo and on the west by the ridge of Rcvermont (2529 feet) 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 détour. On the two sides of this bastion the plains in which Amberieu and Culoz stand balance one another, and are ths 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 (5033 feet) 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 Saône and the Aar, and stretches out to the south so as nearly to join hands with the great mass of the Dauphiné 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 Lone, and the Ain.

1. 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 “Trouée” 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 Birs, and the great plateau between the Doubs and the Aar, on which, at an average height of 2600 feet, are situated a number of towns, one of the most striking features of the Jura. These include Locle and La Chaux de Fonds, and are mainly occupied with watchmaking, an industry which does not require bulky machinery, and is therefore well fitted for a mountain district.

(δ) 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 Locle plateau), is called the “Haute Montagne,” and is given up to cheese making, curing of hams, saw mills, &c. But little watchmaking is carried on there, Besançon 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 metal working and manufacture of hardware are carried on, particularly at Besançon 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 Locle, on the north-west to Besançon, on the west to Salins, on the south-west to Dôle 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 Neuchâtel, aud to the west Salins, the meeting place of the routes from the Col de la Faucille, from Besançon, 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 Dôle, 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 “Trouée 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 Ambérieu 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 Valorise 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.

(δ) The Oignon, 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 Vai Romey and the Séran 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).

Thë “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 in its great bend to the south.

The name Jura, which occurs in Caesar and in Strabo, is a form of 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 Leberl>erg, 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, Neuchâtel, Bern, Solothurn, 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, Vai Romey, Bresse, and Bugey (exchanged in 1601 by Savoy for the marquisate of Saluzzo), Franche Comté, or the Free County of Burgundy, an imperial fief till annexed in 1674, the county of Montbéliard (Mümpelgard), acquired in 1793, and the county of Ferrette (French 1648—1871). The northern part of the eastern side was held by the bishop of Basel as a fief of the empire, 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 Neuchâtel and the county of Vallangin, 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.

See E. F. Berlioux, Le Jura, Paris, 1880; Adolphe Joanne, Jura et Alpes Françaises, Paris, 1877; Id., Geographies Départementales (the Doubs, Jura, and Ain volumes); Charles Sauria, Le Jura pittoresque.

JURA, an eastern frontier department of France, formed of the southern portion of the old province of Franche-Comté, owes its name to the offshoots and plateaus of the Jura mountains, which occupy more than half its area. It is bounded N. by Doubs, Haute-Saône, and Côte-d’Or; E. by Doubs, Ain, and Switzerland; S. by Ain; and W. by Saône-et-Loire and Côte d’Or. Lying between 46° 15' and 47° 17' N. lat., and between 5° 15' 39" and 6° 8' 9" E. long., its greatest length from north to south is 143 miles, and its greatest breadth from east to west 83 miles. The department is divided by a not very broad zone of hills into a region of plain in the north and north-west, and a region of mountains in the south-east, increasing in height towards the Swiss frontier. The highest summit is Noir Mont (5085 feet). Jura belongs almost entirely to the basin of the Rhone,—its chief streams being the Oignon, Doubs, and Seille, affluents of the Saône, and the Ain and Valserine, direct tributaries of the Rhone. The Doubs and Ain are navigable. There are numerous lakes; those of Rousses, Châlin, Chambly, and of the abbey of Grandvaux are noteworthy. The climate is, on the whole, cold; the temperature is subject to sudden and violent changes, and among the mountains winter lingers for nearly six months. The plain called the Bresse is rich in fruit trees, and in fields of wheat, rye, maize, and buckwheat; the hill-region grows vines, barley, oats, maize, rape, walnuts, and fruits; the mountains, which exhibit some of the grandest scenery of leaping torrent and silent tarn, are covered with forests or pastures. Jura is one of the most thickly wooded departments of France; a third of its surface is covered with forests, of which that of Chaux, with an area of about 75 square miles, is the largest. The commonest trees are oaks, beeches, hornbeams, aspens, birches, box-trees, and firs. Wolves and foxes are numerous in Jura; wild boars and deer lurk in the forests. The principal minerals are iron, salt, limestone, marble, sandstone, millstone, and clay. Peats are very abundant. Agriculture employs about three-fourths of the inhabitants, though the manufactures extend to wine, cheese (made in the mountain dairies), watches, files, stationery, toys and fancy wooden-ware, machinery, candles, porcelain, basket-work, <fcc.; while some industry is maintained in wool-spinning, silk-weaving, and in brass, pottery, and tanning works. The trade is mainly in wines, cheese, and wooden goods. The first are full-bodied, stout, and rather coarse-flavoured; their chief market is Paris, where they form the basis of the vin ordinaire of the wine-shops. The department of Jura embraces the arrondissements of Lons-le-Saunier, Dole, Poligny, and St Claude, with 32 cantons and 583 communes. Lons-le-Saunier is the chief town. The total area is about 1928 square miles; the population in 1866 was 298,477; in 1876, 288,823.

JURA, an island of the inner Hebrides, on the west coast of Argyllshire, Scotland, the fourth largest of the group, is situated between 55° 52' and 56° 9' N. lat., and 5° 43' and 6° 8' W. long. On the north it is separated from the island of Scarba by the whirlpool of Corryvreckan, on the east from the mainland by Jura Sound, which is 10 miles broad, and on the south and southwest from Islay by Islay Sound. The area is about 160 square miles, the greatest length about 27 miles, and the breadth about 6. A chain of rugged hills, rising into eminences called the Paps of Jura, the highest summit of which is 2500 feet, traverses the whole extent of the island, interrupted only by Tarbert Loch, an arm of the sea, which forms an indentation into the island of nearly 6 miles, and almost cuts it in two. Jura derived its name, meaning “deer island,” from the red deer which abounded on it. On the pasturage a considerable number of black cattle are raised; and some corn and potatoes are cultivated along the eastern shore. Fishing is prosecuted to a small extent. The population, which in 1851 was 1064, was 781 in 1881.