ALTAI (in Mongolian Altain-ula, the "Mountains of Gold"), a term used with various significations. The Altai region, in west Siberia and Mongolia, is similar in character to the Alps, but covers a much greater area. It extends from the river Irtysh and the Dzungarian depression (46°-47°N.) northwards to the Siber ian railway ana to the Sayan mountains. The backbone of the region is the Sailughem mountains (Silyughema or Kolyvan Altai), which stretch north-eastwards from 49°N. and 86°E. towards the west end of the Sayan mountains (5 I ° 6o'N. and 89° E.) . Their mean elevation is 5,00o-5,5oof t. The snow-line runs at 6, 7oof t. on the northern versant and at 7,800ft. on the southern, the rugged peaks standing 3,2ooft. above it. Passes are few and difficult, the chief being Ulan-daban at 9,275ft. (9,445ft. according to Kozlov) and Chapchan-daban, at in the south and north respectively. On the east and south-east this range is flanked by the great plateau of Mongolia, the transition being effected gradually by means of several minor plateaus, such as Ukok (7,800ft.), Chuya (6,000f t.) , Kendykty (8,2o0ft.), Kak (8,27oft.), Suok (8,5ooft.) and Juvlu-kul (7,9oof t.) . This region, which is not accurately known, is studded with large lakes, e.g., Ubsa-nor (2,3 7of t. above sea-level), Kirghiz nor, Durga-nor and Kobdo-nor (3,84oft.), and crossed by moun tain ranges, the principal being the Tannu-ola, roughly parallel with the Sayan mountains as far east as the Kosso-gol (I oo° I o I ° E. ), and the Khan-khu mountains, also stretching west to east.
The Altai proper (the Ek-tagh, Mongolian Altai, Great Altai or Southern Altai) likewise extend in two twin parallel chains eastwards as far as 99°, if not farther. The Ek-tagh, which separates the Kobdo basin (north) from the Irtysh basin (south), is a true border-range, in that it rises in a steep and lofty escarp ment from the Dzungarian depression (1,55o to 3,000f t.) , but descends on the north by a relatively short slope to the plateau (4,000-5,5ooft.) of north-western Mongolia. East of 94° the range is continued by a double series of quite distinct chains. The southern chain bears the names of Karaadzirga and Burkhan ola, and terminates in about 99° ; but the northern range, the principal names of which are Artsi-bogdo and Saikhat, extends probably most of the way to the great northward bend of the Hwang-ho round the desert of Ordos. Whereas the western Ek-tagh Altai rises above the snow-line and is destitute of timber, the eastern double ranges barely touch the snow-line and are clothed with thick forests to an altitude of 6,25oft. The slopes of these chains are inhabited principally by nomad Kirghiz.
The north-western and northern slopes of the Sailughem mountains are extremely steep and very difficult of access. On this side lies the culminating summit of the range, the double headed Byelukha, whose summits reach 14,890 and 14,56oft. respectively, and give rise to several glaciers. Here also are the Kuitun (12,000f t.) and several other lofty peaks. There are numerous spurs, striking in all directions to the lowlands of Tomsk, but their mutual relations are not well known. Such are the Chuya alps (average altitude 9,000ft., with summits from I 1,50o to 12,o0of t., and at least ten glaciers on their northern slope); the Katun alps (mean elevation about io,000ft. and mostly snow-clad) ; the Kholzun range ; the Korgon (6,30o to 7,600ft.), Talitsk and Selitsk ranges; the Tigeretsk alps, and so • on. Several secondary plateaus of lower altitude are also dis tinguished. The River Katun begins in a wild gorge on the south-west slope of Byelukha; then pierces the Katun alps, and enters a wider valley, at an altitude of from 2,000 to 3,5ooft., which it follows until it joins the River Biya, to form the River Ob. The River Charysh has the Korgon and Tigeretsk alps on one side and the Talitsk and Bashalatsk alps on the other, and its valley, like the others, is very fertile. Farther west the valleys of the Uba, the Ulba and the Bukhtarma open south-westwards towards the Irtysh. The lower part of the first, like the lower valley of the Charysh, is thickly populated; in the valley of the Ulba is the Riddersk mine, at the foot of the Ivanovsk peak (6,77oft.). The valley of the Bukhtarma also has its origin at the foot of the Byelukha and the Kuitun peaks, and it falls some 5,000ft. in less than Zoom. to the Bukhtarma fortress (I,13oft.). Its upper parts abound in glaciers, the best known of which is the Berel, which comes down from the Byelukha. On the northern side of the range which separates the upper Bukhtarma from the upper Katun is the Katun glacier, in which the Katun river rises. The middle and lower parts of the Bukhtarma valley have been colonized since the i8th century by runaway Russian peas ants who created there a free republic on Chinese territory ; and after this part of the valley was annexed to Russia, in 1869, it was rapidly colonized. The high valleys farther north, on the same western face of the Sailughem range, are little known, their only visitors being Kirghiz shepherds. Those of Bashkaus, Chulysh man, and Chulcha, all three leading to Lake Teletskoye (length, 48m. ; max. width, 3m. ; altitude, I , 7oof t. ; area, 8 7sq.m. ; max. depth, I,o2oft.; mean depth, 66oft.), are only inhabited by nomad Telenghites or Teleuts. The shores of the lake rise almost sheer to over 6,000ft. and are too wild to accommodate a numerous population. From this lake issues the Biya, which joins the Katun at Biysk. Farther north the Altai highlands are continued in the Kuznetsk district, which has a slightly different geological aspect, but still belongs to the Altai system. But the River Abakan, which rises on the west of the Sayan mountains, belongs to the system of the Yenisei. The Kuznetsk Ala-tau range, on the left bank of the Abakan, runs north-east while a complexus of imperfectly mapped mountains (Chukchut, Salair, Abakan) fills up the country northwards towards the Siberian railway and westwards towards the Ob. The Tom and its numerous tributaries rise on the northern slopes of the Kuznetsk Ala-tau, and their fertile valleys are occupied by a dense Russian population, the centre of which is Kuznetsk, on the Tom.
Geology.—The Altai mountains consist of two distinct ele ments which differ considerably in geological formation. The Mongolian, or Great Altai, consists essentially of Archaean rocks (gneisses, etc.), in which there is no folding of Hercynian or Alpine age, but the strike of the rocks is independent of the direction, determined by fault fractures, of the chains. The region forms a horst. In the Russian Altai we find various Archaean schists with Palaeozoic rocks, predominantly lime stones with Devonian and Carboniferous fossils. They were folded during the Hercynian period, the general trend of the folds being north-north-east. Of the same age as the folding are intrusions of granitic and other igneous bodies with which are associated the famous ore deposits.
Flora.—Theflora of the Altai is rich and very beautiful. Up to a level of i,000ft. on the northern and 2,000f t. on the southern slopes, plant life belongs to the European flora, which extends into Siberia as far as the Yenisei. The steppe flora penetrates into the mountains, ascending some I,Ioo–I,2ooft., and in shel tered valleys even up to 5,5ooft., when it comes into contact with the purely alpine flora. Tree vegetation, which reaches up as high as 6,5oo and 8,15oft., the latter limit on the north and west consists of magnificent forests of birch, poplar, aspen and Coniferae, such as P. cembra, though the fir is not found above 2,5ooft., while the meadows are abundantly clothed with brightly coloured, typical assortments of herbaceous plants. The alpine meadows, which have many species in common with the European Alps, have also a number of their own peculiar Altaian species.
For population, administrative divisions and mining activities, etc., see SIBERIAN AREA.