Page:Encyclopædia Britannica, Ninth Edition, v. 23.djvu/359

GEOGRAPHY.] Tibet is commonly divided into two parts called Great and Little Tibet, the former lying between 102 and 79 divisions. E long? the latter between 79 and 74. Great Tibet is broadly divisible into a western region, in which there is a considerable preponderance of tableland over hill and mountain and of lake basins over river basins, and an eastern region, in which the reverse holds good and the surface of the ground is so greatly corrugated that the natives call it rong-rtsub, " a rough country full of ravines." In Little Tibet the Himalayas converge towards the KuenLun, and the breadth of the plateau meridionally diminishes to less than a fourth of what it attains in Great Tibet. The entire region may be broadly divided into three longi tudinal zones, increasing in elevation from south to north, viz., a southern zone, which contains the centres of the settled and agricultural population; a middle zone, com prising the pasture lands of the Bod-pa nomads; and a northern zone, for the most part abandoned to wild animals, but partly occupied by tribes of Turkic and Mongolian nomads. The southern and middle zones comprise Bodland proper and are divided into four provinces, viz., Nari (Ngari, Ari) on the west, between 74 and 85 E. long.; Kham, otherwise Do-Kham, on the east, between 92 30 and 102; and in the centre, Tsang, adjoining Nari, and U or Us (otherwise Y or Wei), adjoining Kham; the two central provinces are commonly called U-tsang, as one. A considerable belt of the middle zone is known as the Hor country. The middle and northern zones embrace the greater portion of the region known to Bod-pas as the Chang-tang (Byan-tang, Jan-tang) or "Northern Plain," which, however, protrudes southwards and abuts upon the Himalayas from 80 to 85 E. long., thus interposing a nomad population between the settled populations to the east and the west. The northern zone merges on the west into the Pamir tablelands.

The tableland of Tibet attains its maximum elevation, 17,600 feet above sea-level, on the 79th meridian, in the Lingzi-tang plateau of the northern zone; thence there is a gradual fall east, west, and south, the plateau level on the 97th meridian being about 13,500 feet in the northern zone and 10,000 in the southern. Between the 82d and 90th meridians the northern zone is known only from the maps of the lamas survey, which indicate a sur face slightly corrugated with hills and containing numerous lakes, some of great size, but no rivers of importance.

The river basins in this zone apparently commence to the east of the 90th meridian and from them issue the Di-chu (Chinese Kin-sha-kiang), whose headwaters unite at Di-chu Rab-dun, in 94 30 E. long.; the Chiamdo river or Lan-tsan-kiang; the Hoang-ho, in about 96, which flows through the Kiaring and Orin lakes (13,500 feet above the sea and each exceeding 80 miles in circum ference) and passes northwards out of Tibet through the Kuen-Lun; and the Ja-chu or Yalung-kiang, also in about 90 E. long., which flows southwards through eastern Tibet. In the middle zone a system of lakes on the 90th meridian gives birth to the Nag-chu, which becomes the Sok-chu and lower down the Giama-Nu-chu known to the Chinese as the Lu-tse-kiang and, trending southwards, winds round the eastern extremity of the Himalayas. In the lower zone the Indus and the Yaro-tsanpo rise on either side of the 82d meridian and flow in opposite direc tions parallel to the Himalayas, and then, passing through openings in those mountains twenty degrees apart in longi tude, enter India on the extreme east and west. The Lohit Brahmaputra rises behind the eastern Himalayas and flows south-westwards into India. The Giama-Nu-chu, Chiamdo-chu, and Di-chu flow southwards into Burma and Yun nan, through closely contiguous valleys between a system of meridional ranges which project as spurs from the Tibetan plateau. West of 82 a single water-parting between north and south that of the Mus-tagh and Karakoram, some times called the Turkic separates Indo- Tibetan from Turko- Tibetan waters; east of that meridian there are longitudinal water-partings between the basins of the several rivers already mentioned.

The Himalayan Mountains, which constitute so considerable a portion of the southern scarp of Tibet, consist of a succession of longitudinal chains, running in general parallel to each other along the glacis of the plateau. These chains are much higher on their southern than on their northern faces, and are connected in some parts by trans verse ridges, but in other parts are broken and interrupted by fissures and valleys. The principal chain is the one of high peaks covered with perpetual snow which culminates in Mont Everest, 29,000 feet above the sea. This chain may be regarded as the geographical boundary between Tibet and India. In some parts it is the water-parting; but at the several points where its continuity is broken the water-parting recedes to an inner chain on the plateau, and basins are formed between the two chains, the waters of which descend in rivers to the plains of India. The plateau is a region of plains and wide open valleys of little depth; the scarp is a region of mountains and narrow confined valleys of great depth. The narrow valleys of the scarp, being lower, are warmer and more favourably adapted for cultivation than the broad valleys of the plateau.

Higher than these last are the plains of the Chang-tang, which are, for the most part, too high and cold for any but pastoral uses. All such tracts the inhabitants call chdng-tdng, though the word strictly signifies "the Northern Plain "; and all tracts which contain valleys warm enough for cultivation they call rong (signifying a ravine or narrow valley or cleft in a hill), but more par ticularly the lower and warmer valleys which produce crops twice in the year; the word is also commonly em ployed to indicate a warm country. The alluvial beds in the valleys are composed of the debris of the surrounding rocks, laid out in horizontal deposits, which in course of time have become furrowed into gigantic ravines with a succession of narrow terraces in steps on each flank. It is on the existing lower alluvial beds and the remnants of higher beds that cultivation is carried on, in plots which are usually well watered and very fertile. The sharp needle-peaks, which are highest of all and bare of soil, but covered with perpetual snow, are met with most frequently in tracts of rong, and the rounded hills coated with grass to altitudes sometimes exceeding 16,000 feet in tracts of chang-tang. The forest-clad mountain slopes which are occasionally met with occur chiefly in the rong. The general direction of the hill and mountain chains is east and west, but north-west and south-east in western Tibet, north-east and south-west in the province of U, and north and south in eastern Tibet. The peaks rise in many parts to between 20,000 and 25,000 feet in the Mus-tagh range to 28,250 above the sea-level, but rarely to more than 10,000, and often to not more than a few hundred, feet above the general level of the plateaus from which they spring. The principal water-partings in some dis tricts follow the crests of low ridges and gentle undulations which are of barely appreciable elevation above the surface of the ground.

Nári, the western province of Bodland, is divided into Nari. the sub-provinces of Ladak and Balti on the west, between 75 and 79" E. long., now a part of Kashmir; Khorsum,