RUWENZORI, also known as Runsoro or Kokora, a moun tain range of Central Africa, 65 m. long and with a maximum breadth of 3o m., trending a little east of north, lying just north of the equator between lakes Edward and Albert. The range falls steeply on the west to the central African rif t-valley traversed by the Semliki, the western head-stream of the Nile, while on the east the fall is somewhat more gradual towards the western Uganda uplands. The upper parts are separated by fairly low passes into six groups of snowy summits, lying a little west of the central line, rising in each case above 15,000 ft. and reaching, in the culminating point of the western group (Mount Stanley), about 16,800 f t.
The origin of the range seems connected with that of the rift-valley on the west. Ruwenzori is a fault block of the Archaean floor of the continent, bounded east and west by lines of fracture, and having a general dip from west to east. A further upheaval produced an ellipsoidal anticline, causing the strata to dip out wards at a high angle. Traces of volcanic action are almost non existent. Composed in its outer parts of Archaean gneisses and mica-schists offering no great resistance to denudation, in its centre the range consists of much more refractory rocks (amphi bolites, diorites, diabases, etc.), to which fact, coupled with the existence of vertical fractures, the persistence and separation of the higher summits is probably due. The snow-clad area does not now extend more than ten miles in any direction; the snow-line is 13,450 ft. but there is evidence of a former extension to as low as 4,600 ft.
The upper region is almost entirely enveloped by day in thick cloud, which descends on the east to about 9,00o f t., and lower still on the west. As a result, the climate is excessively humid, the northern slopes having a rainfall of 200 inches a year giving extremely damp conditions on the mountain. The rivers are raging torrents and have cut deep valleys between the outer spurs. From the innermost recesses between Mounts Stanley, Speke and Baker, the main branches of the Mobuku descend to the east, while the four principal streams on the west unite to form the Butagu, the drainage on both sides ultimately finding its way to the Sem liki, either directly or through lakes George and Edward.
The vegetation displays well-marked zones, varying with the altitude; but owing to the lower level to which the cloud descends on the west the limits of the several zones reach a lower level on the west than on the east. They have been defined as follows by Mr. R. B. Woosnam (1907), as follows, the figures in brackets being the upper limit on the east side:—grass (6,500 ft.), forest (8,5oo), bamboos (io,000), tree heaths (12,500) and lobelias and senecios (14,50o), above which is the summit region of snow and bare rock. The boundaries between the zones merely indicate the
levels between which the respective forms are specially character istic. The forest zone is the best marked, but on the west it merges in part with the low-lying forest of the Semliki valley. Mosses, hepaticae and lichens are prevalent in several of the zones, while bogs, vaccinium and other low-growing plants, are common above the forest zone. Helichrysums are abundant in the zone immediately below the snow. The larger mammals are found chiefly on the lower slopes, but bushbuck, pigs, leopards, monkeys, a hyrax and a serval cat occur at higher altitudes. The birds include kites, buzzards, ravens, sun-birds, touracos, a large swift, and various warblers and other small kinds. The upper limit of human settlement, with cultivation of colocasia and beans, has been placed at 6,700 ft.
In modern times the existence of a snowy range in this part of Africa was first made known by Sir Henry Stanley during the Emin Pasha relief expedition of 1887-89. Stanley named the main mass Ruwenzori, and outlying eastern peaks he called Mt. Gordon Bennett, Mt. Lawson, Mt. Edwin Arnold, etc.—the last named lying north-east of Lake George. Subsequently Stanley's own name was given to the chief summit. One of Stanley's officers, Lieut. Stairs, ascended the western slopes to over io,000 ft. in 1889, and partial ascents were afterwards made by Dr. Stuhlmann, Mr. Scott-Elliot, Mr. J. E. S. Moore, Sir Harry Johnston, Mr. Douglas Freshfield, and others. Early in 1906 some of the secon dary ridges above the snow-line were scaled by Messrs. Grauer, Tegart and Maddox, and by Dr. Wollaston and other members of the British Museum expedition, while later in the year the duke of Abruzzi led a well-equipped expedition to the upper parts of the range and ascended all the principal snow-clad peaks. The expedition produced for the first time a detailed map of the upper region, and threw much light on the geology and natural history of the range.
H. M. Stanley, In Darkest Africa (London, 1890) ; G. F. Scott-Elliot, A Naturalist in Mid-Africa (London, 1896) ; J. E. S. Moore, "Tanganyika," etc., Geog. Jnl. (January 1901) ; To the Mountains of the Moon (London, 1901) ; Sir H. H. Johnston, The Uganda Protectorate (London, 5902) ; The Duke of the Abruzzi, in Geog. Jul. (February 5907) ; R. B. Woosnam, ibid. (December 1907) ; F. de Filippi, Ruwenzori (London, 1908), the general account of the Abruzzi expedition, and Il Ruwenzori, Parte scientifica (2 vols., Milan, 1909) ; A. R. F. Wollaston, From Ruwenzori to the Congo (London, 1908) ; R. G. T. Bright, "The Uganda-Congo Boundary," Geog. Jnl. (1909) ; J. W. Gregory, The Rift Valleys and Geology of East Africa (192I).