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ASIA General Physiography of the Asiatic Continent. Asia is divided laterally along the parallel of 40° N. lat. by a depression which, commencing on the east of the desert of Gobi, extends westwards through Mongolia to Chinese Turkestan. To the west of Kashgar the central depression is limited by the meridional range of Sarikol and the great elevation of the Pamirs, of which the Sarikol is the eastern face. The level of this depression (once a vast inland sea) between the mountains which enclose the sources of the Hoang-ho and the Sarikol range probably never exceeds 2000 feet above sea, and modem researches tend to prove that in the central portions of the Gobi (about Lob Nor) it may be actually below sea-level. A vast proportion of the continent north of this central line is but a few hundred feet in altitude. Shelving gradually upward from the low flats of Siberia the general continental level rises to a great central water-parting, or divide, which stretches from the Black Sea through the Elburz and the Hindu Kush to the Tian Shan mountains in the Pamir region, and hence to Bering Strait on the extreme northeast. This great divide is not always marked by welldefined ranges facing steeply either to the north or south. There are considerable spaces where the strike, or axis, of the main ranges is transverse to the water-parting, which is then represented by intermediate highlands forming lacustrine regions with an indefinite watershed. Only a part of this great continental divide (including such ranges as the Hindu Kush, Tian Shan, Altai, or Khangai) rises to any great height, a considerable portion of it being below 5000 feet in altitude. South of the divide the level at once drops to the central depression of Gobi, which forms a vast interior, almost waterless, space, where the local drainage is lost in deserts or swamps. South of this enclosed depression is a second great hydrographic barrier which parts it from the low plains of the Amur, of China, Siam, and India, sinking into the shallows of the Yellow Sea and the shoals which enclose the islands of Japan and Formosa, all of them once an integral part of the continent. This second barrier is one of the most mighty upheavals in the world, both by reason of its extent and its altitude. Starting from the Amur river and reaching along the eastern margin of the Gobi desert towards the sources of the Hoang-ho, it merges into the Altyn Tagh and the Kuen Lun, forming the northern face of the vast Tibetan highlands which are bounded on the south by the Himalaya. This great lacustrine plateau averages 15,000 feet above sea-level. The Pamir highlands between the base of the Tian Shan mountains and the eastern buttresses of the Hindu Kush unite these two great divides, enclosing the Gobi depression on the west; and they would again be united on the east but for the transverse valley of the Amur, which parts the Kinghan mountains from the Yablonoi system to the east of Lake Baikal. If we consider the whole continent to be divided into three sections, viz., a northern section with an average altitude of less than 5000 feet above sea, where all the main rivers flow northward to the Mediterranean, the Arctic Sea, or the Caspian ; a central section of depression, where the drainage is lost in swamps or “hamuns,” and of which the average level probably does not approach 2000 feet above sea; and a southern section divided between highly elevated tablelands from 15,000 to 16,000 feet in altitude, and lowlands of the Arabian, Indian, Siamese, and Chinese peninsulas, with an ocean outlet for its drainage, we find that there is only one direct connexion between northern and southern sections which involves no mountain passes, and no formidable barrier of altitudes. That one is afforded by the narrow valley of the Hari Bud to the west of Herat. From the Caspian to Karachi it is pos-
sible to pass without encountering any orographic obstacle greater than the divide which separates the valley of the Hari Rud from the Helmund “ hamun ” basin, which may be represented by an altitude of about 4000 feet above sea-level. This fact possesses great significance in connexion with the development of Asiatic railways. Hydrography.—If we examine the hydrographic basins of the three divisions of Asia thus indicated we find that the northern division, which includes the drainage falling into the Arctic Sea, the Aralo-Caspian depression, or the Mediterranean, embraces an area of about 6,394,500 square miles, as follows :— Sq. miles. 4,367,000 Area of Arctic river basins 1,759,000 ,, Aralo-Caspian basin 268,500 ,, Mediterranean . Total . . . 6,394,500 The southern division is nearly equal in extent— Sq. miles. 3,641,000 Pacific drainage 2,873,000 Indian Ocean Total .
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. 6,514,000
The interior or inland basins, including the lacustrine regions south of the Arctic watershed, the Gobi depression, Tibetan plateau, the Iranian (or Perso-Afghan) uplands, the Syro-Arabian inland basin, and that of Asia Minor, amount to 3,141,500 sq. miles, or about half the extent of the other two. By far the largest Asiatic river basin is that of the Ob, which exceeds 1,000,000 sq. miles in extent. On the east and south the Amur embraces no less than 776,000 sq. miles, the Yang-tse-kiang including 685,000, the Ganges 409,500, and the Indus 370,000 sq. miles. The lakes of Asia are innumerable, and vary in size from an inland sea (such as Lakes Baikal and Balkash) to a highland loch, or the indefinitely extended swamps of Persia. Many of them are at high elevations (Lake Victoria, 13,400 feet, being probably the most elevated), and are undoubted vestiges of an ancient period of glaciation. Such lakes, as a rule, show indications of a gradual decrease in size. Others are relics of an earlier geological period, when land areas recently emerged from the sea were spread at low levels with alternate inundations of salt and fresh water. Of these Lob Nor and the Helmund “ hamuns ” are typical. Such lakes (in common with all the plateau “hamhns” of S.W. Baluchistan and Persia) change their form and extent from season to season, and many of them are impregnated with saline deposits from the underlying strata. The “kavirs,” or salt depressions, of the Persian desert are more frequently widespread deposits of mud and salt than water-covered areas. Geology.—Over a great part of Asia, including the Caspian depression, the Central Asian Khanates, Turkestan, Tibet, China, Siberia, and India, geological research has been closely, and, in many regions, scientifically pursued. The results of such investigations are at present too disconnected and fragmentary to afford material for the construction of a continuous geological history of the formation of the whole continent. They have mainly been directed to those regions whose economic development seems possible, and whose resources of mineral wealth may be expected to enrich the world. The great Caspian depression and its extension to the Aral Sea has been examined by Russian scientists, and the old theory of the former Oxus contribution to the Caspian finally dismissed. Whilst the extent and nature of these beds of an ancient western ocean have been under investigation, the Central Sea to the east of the Pamirs, represented by the Gobi Sands, the Tarim desert, and by the shallow lakes and swamps of Lob Nor, has also received much attention ; but it has not yet been exhaustively explored, and we await the results of Sven Hedin’s expedition to decide the position and extent of its possible survival in the existing lake system. Geological researches in Siberia have proved
