JURA, JURASUS, or, in the Celtic, Jou rag, which sig nifies the government or God, or Jupiter," is a chain of mountains on the south west of Switzerland, which stretches from Mont Vouache, in Savoy, to the canton of Schaff hausen. Its direction is nearly south south-west and north north east, almost parallel to that of the Alps. Its length is from 90 to 100 leagues, and its breadth, in a north-west direction, from 15 to 18 leagues.
The ridge of Jura rises to the height of 3000 or 4000 feet from the plain of Switzerland, with a declivity often very steep, and presents at this elevation throughout the whole of its length an undulated line, above which there rises, in some places, rounded summits to the height of 600, 1000, or even 2000 feet above the rest of the chain. On the side of Franche Compte, the Jura is formed into se veral parallel ramifications, which diminish gradually in height, till they terminate in the plains of Burgundy. The following are the altitudes of the principal summits, as de termined geometrically by Messrs. Pictet and Tralles: The principal passes in the ridge of Jura, are that of Fort Ecluse, where the Rhone runs in a deep channel be tween the fort and the foot of Mont Vouache ; the passage of Esclecs, at a little distance from Orbe, on the road of Pontarlier ; that of the Cluse de Verrieres, in the principa lity of Neuchatel ; that of the Pierre Pertuis, in the Valley of St. lmier ; and the defiles of the Valley of Moutier, of Ballstall, and of Wallenhourg.
As the Ridge of Jura lies below the line of perpetual snow, it contains no glaciers ; but blocks of ice, and columns of snow, are found in some deep caverns ; such as those near St. George's above Rolle, and between the vallies of Travers and Brevine. The pastures on that ridge are drier than those of the higher Alps ; but in some places, parti cularly in the canton of Basle, the meadows are as beautifnl and fertile as those of the central chain. Some of the ramifications of Jura, particularly those in the neighbour hood of St. Claude and Champagnol, produce a great quan tity of box-wood, some of the plants of which rise to the height of 20 feet. The mountains, which extend for four or five leagues round Poligni, are covered with lofty pines, which afford to the ship carpenters of Toulon the tallest masts for their vessels of war. The same forests furnish also the materials of numerous manufactures, which em ploy the inhabitants during the winter, and form a consider able branch of trade. The iron foundcries, the forges, and the salt pits of Salins, Arc, and Senans, obtain here the wood and the charcoal w Inch they require.
The brown bear still inhabits the wildest parts of the western chain of Jura ; and it is not many years ago since it made great ravages among the cattle, and even descend ed into the plains. Wild cats, the flesh of which is eaten
by the inhabitants, are also found in the forests of Jura.
The ridge of Jura is composed of compact limestone, of a greyish or yellowish brown colour, but always less deep than that of the Alps. Sometimes it has a lively yellow colour. The strata alternate with beds of marle and of clay. There is also found gypsum, beds of asphaltum, of the finest marble, sulphuretted springs, and salt springs. Those of Salins, Courbauson, Monunorot, near Loris le Saulnier, Groson, Tormont, and St. Lanthein, near Poligni, all of which belong to France, are among the richest. A great number of beds of oolites are found in Jura.
The stratification of Jura is very singular. The inclina tion of the strata from south to north-west, their vertical position, the vaults which they form, and their junction in the form of the roofs of houses at the summit of the chain, are phenomena highly interesting to the mineralogist. The stretch of the strata is from S. S. W. to N. N. E.
Among the numerous petrifactions found in the calcare ous formation, are 40 species oldie cornu ammonia, 20 other species of univalve marine shells, 8 species of oysters, as many species of bivalve marine shells, and 40 species of corals. The rarest petrifactions are found on Mont Perouse, near Orgcler. Iron is found in such abundance in Jura, that it is capable of supplying all France. The iron mines in Franche Compie, and in the bishopric of Basle, have been wrought with activity ; but Switzerland has not taken advantage of her portion of this treasure. Strata of brown coal occur, which owe their origin to en tire forests which have been burned by the dreadful earth quakes to which Jura has often been exposed.
The innumerable masses of granite and of gneiss, which are scattered up and down on the eastern flank of this chain, even at the height of 2400 feet, form one of the most inte resting facts-in geology. One of these masses, which is found above Neuchatel, and which was measured by Pro fessor Playfair in 1817, is 62 feet long, 32 feet wide, and nearly 17 feet high. As there is neither granite nor gneiss on this ridge, Saussurc and Sir James Hall have supposed, that they have been carried away by some great flood, or debacle, across the lake of Genera from the Savoy Alps ; and it is a remarkable fact, that similar blocks are found in the lake of Geneva opposite to the mouths of the streams which descend from the Savoy hills. See Ehel's /11anuel du Voyageur en Suisse, tom. iii.; Traite sur la Structure de la Terre, ii. p. 90, 147. (for an account of the geology of Jury,) Zurich, 1808 ; Saussu re's Voyages dans les ; and Sir James Hall's paper in the Transactions of the Royal Societe of Edinburgh, vol. vii. p. 142, 143. Ste.