Alps (possibly a Celtic word meaning ' high;' of. Gaelic alp, ' a high mountain;' or connected with Lat. albus, 'white'), the most extensive system of lofty mountains in Europe, raising their giant masses on a basis of 90,000 sq. m., between 6° 40' and 18° E. long., and extending in some places from the 44th to the 48th parallel of latitude. The Alpine system is bounded on the N. by the hilly ground of Switzerland and the upper plain of the Danube; on the E., by the low plains of Austria; on the S., by the Adriatic Sea, the plains of Lombardy, and the Gulf of Genoa; and on the W., by the plains of Provence and the valley of the Rhone. A string of lakes encircles both the northern and southern bases of these mountains, the former at an elevation of 1200 to 2000 feet; the latter, 600 to 700 feet. The varied natural scenery of France, Italy, Germany, and Austria has a common centre of union in this lofty region. Valleys open out in all directions, sending their melted snows on one side into the North Sea, on another into the Black Sea, and on another into the Mediterranean. The principal basins are those of the Rhine, the Danube, the Po, the Rhone, and the Var.

I. Of the Western Alps the principal ranges are: (1) The Maritime Alps, extending from the middle Durance southwards to the Mediterranean, and rising in the Aiguille de Chambeyron to a height of 11,155 feet. (2) The Cottian Alps, north of these, whose highest summit, Monte Viso, is 12,605 feet. (3) The Dauphine Alps, separated by the valley of the Durance from the Cottian; their highest summit is the Pic des Ecrins, 13,462 feet. (4) The Graian Alps, forming the boundary between Savoy and Piedmont, and attaining in the Grand Paradis, an elevation of 13,300 feet. II. Middle Alps. Central Chain. -(1) The Pennine Alps, between the plains of Lombardy and the valley of the Rhone. Highest summits: Mont Blanc, 15,732 feet; Monte Rosa, 15,151 feet. (2) The Lepontian or Helvetian Alps, from the depression of the Simplon, along the plateau and masses of St Gothard, to the pass of the Splugen. (3) The Rhaetian Alps, between the Inn, the Adda, and the Upper Adige. Northern Chain. - (1) The Bernese Alps, between the Rhone and the Aar. Highest summits: Finsteraarhorn, 14,026 feet; Aletschhorn, 13,803; Jungfrau, 13,671 feet. (2) The Alps of the Four 'Forest Cantons,' the Schwyz Alps, etc. The Southern Chain. - (1) The Ortler Alps, between the Adda and the Adige. (2) The Trientine Alps, between the Adige and the Piave. III. Of the Eastern Alps the principal chains are: (1) The Noric Alps, between the plains of the Drave and the Danube. (2) The Carnian Alps, between the Drave and the Save. (3) The Julian Alps, between the Save and the Adriatic Sea.

No lofty mountains in the world are more easily crossed than the Alps; the Mont Cenis, the Brenner, the St Gothard, and the Simplon (with still longer tunnel bored 1896-1904) railways into Italy from the north now afford special facilities. Other notable passes are the Little St Bernard (7190 feet at the highest point), the Great St Bernard (8120 feet), and the Splugen (q.v.).

The rocks which enter into the composition of the Alps belong to many different geological systems, and occur for the most part as more or less interrupted belts or zones, which extend in the same general direction as the great chain itself - viz. from SW. to NE. The higher and central ranges consist principally of crystalline schists, such as gneiss and mica-schist, with which granite is occasionally associated. These crystalline ArchAean rocks are flanked on either side by an irregular zone of various sedimentary strata, along with beds of limestone, dolomite, etc. The geological structure of the Alps clearly shows that these mountains are 'mountains of upheaval.' The strata of which they are composed must originally have been spread out in approximately horizontal positions, and they have since been folded, flexed, puckered, and fractured. Since their upheaval, the Alps have suffered excessive denudation. Enormous mountain-masses have been gradually removed by the action of ice, running water, etc.

The population of the Alpine regions is estimated at 6,000,000 to 7,000,000, of whom perhaps one half are Teutonic, and the other half of French, Italian (and Romanic), or Slavonic origin, in pretty equal proportions. Six states share the Alps. The western portion is shared by France and Italy. Switzerland claims the Middle Alps almost exclusively for her own. Bavaria has only a small share. Austria has the largest share of the Alps - ill the provinces of Tyrol, Illyria, Styria, and the archduchy. The Alpine mountains are rich in singularly beautiful natural scenery, and attract such crowds of visitors that they have been called ' the playground of Europe.'

See works by Agassiz, the brothers Schlagint-weit, Murchison, Tyndall (1860-73), Bonney (1868), Ball's Guides (3 vols. 1868-70), Umlauft (Eng. trans. 1888), and see also Switzerland.